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Article

Comprehensive Comparison of Lacustrine Fine-Grained Sedimentary Rock Reservoirs, Organic Matter, and Palaeoenvironment: A Case Study of the Jurassic Ziliujing Formation and Xintiangou Formation in the Sichuan Basin

by
Delu Li
1,2,3,4,
Shiqiang Wu
5,
Qianyang He
2,3,4,*,
Wangpeng Li
5,
Peilong Meng
6,
Haibin Li
2,3,4,
Qiang Sun
2,3,4 and
Xiaochen Zhao
2,3,4
1
State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 102206, China
2
College of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, China
3
Shaanxi Provincial Key Laboratory of Geological Support for Coal Green Exploitation, Xi’an University of Science and Technology, Xi’an 710054, China
4
Geological Research Institute for Coal Green Mining, Xi’an University of Science and Technology, Xi’an 710054, China
5
Petroleum Exploration and Production Research Institute, Sinopec, Beijing 102206, China
6
Research Institute of Exploration and Development, PetroChina Changqing Oilfield Company, Xi’an 710018, China
*
Author to whom correspondence should be addressed.
Minerals 2024, 14(4), 336; https://doi.org/10.3390/min14040336
Submission received: 27 February 2024 / Revised: 22 March 2024 / Accepted: 23 March 2024 / Published: 25 March 2024
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Abstract

:
Lacustrine sedimentary formations potentially contain hydrocarbons. The lacustrine sedimentary rocks of the Ziliujung and Xintiangou Formations have been investigated for their hydrocarbon potential using low-pressure nitrogen adsorption (LP-N2A), low-field nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), total organic carbon (TOC), rock-eval pyrolysis (Rock-Eval), gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), X-ray fluorescence spectrometry (XRF), and inductively coupled plasma mass spectrometry (ICP-MS). The results show that the normalized difference of the pore parameters between the two formations is less than 10%, and the pores are mainly slit-like mesopores with high porosity. Macropores and micropores are often developed in the quartz skeleton, while mesopores often occur among organic matter, clay minerals, carbonate minerals, and pyrite particles. The organic matter abundance of the Ziliujing Formation is relatively high. Additionally, the organic matter types of the two formations are mainly type II and type III, and the sources of the organic matter are plankton and bacteria which have reached the mature gas production stage. The palaeoenvironmental differences between the depositional periods of the two formations lie within 10% of each other. The warm and humid climate promotes the development of quartz minerals to further enhance the proportion of both micropores and macropores, and the clay minerals, carbonate minerals, and pyrite carried in the terrigenous detritus are closely associated with the total organic carbon (TOC), which promotes the development of mesopores to enhance the porosity. The reservoir, organic matter, and palaeoenvironmental characteristics of fine-grained sedimentary rocks in the two formations are similar, and both of them have good potential for development. The above results provide a basic geological theoretical basis for unconventional oil and gas exploration in the northeastern margin of the Sichuan Basin.

1. Introduction

Fine-grained sedimentary rock is composed of silt-grade and clay-grade clastic particles with sizes less than 62.5 μm and a proportion of more than 50% [1,2]. These rocks are rich in oil and gas resources and are regarded as important hydrocarbon source rocks with wide exploration perspectives [3,4]. As one of the largest oil and gas bearing basins in China, the Sichuan Basin has proved unconventional oil and gas reserves, in which the Jurassic stratigraphy is widely developed with terrestrial lacustrine fine-grained sedimentary rocks [5,6]. This area serves as an important research object for the exploration and evaluation of unconventional oil and gas resources [7,8,9].
In past decades, many works in the literature have extensively studied the classification, reservoir characteristics, organic matter characteristics, and palaeoenvironment of fine-grained sedimentary rocks. Their composition mainly includes clay minerals, carbonate minerals, silt, and organic matter, whereas according to the indexes of grain size, they are often classified into three categories: sand grade, silt grade, and mud grade [3]. The pore structure is crucial for controlling the storage and seepage capacity of fluids in the reservoir [10,11,12]. In addition, various techniques have been used by several groups, such as low-pressure nitrogen adsorption–desorption, nuclear magnetic resonance, scanning electron microscopy, mercury compression, and thin-section identification, to explore the reservoir spatial types and pore structure characteristics of fine-grained sedimentary rocks [13,14]. High total organic carbon (TOC) fine-grained sedimentary rocks have relatively high micropore and mesopore proportions and a complex pore structure, which increases both reservoir porosity and permeability and is conducive to oil and gas transport and storage [15]. Also, the mineral composition, thermal maturity, and sealing conditions all affect the pore development and preservation in fine-grained sedimentary rocks [16]. Organic geochemical experiments, such as total organic carbon testing, micro component testing, rock-eval pyrolysis, specular plasma reflectance, and biomarker compound testing, have clarified the abundance, type, and maturity of the organic matter in fine-grained sedimentary rocks in relation to their hydrocarbon potential [17,18,19]. Thermally mature shales contain more residual hydrocarbons [20,21]. Inorganic elements and biomarkers are also often used to reconstruct the palaeoenvironment of fine-grained sedimentary rocks [22,23]. It has been demonstrated that lacustrine fine-grained sedimentary rocks are mainly deposited in a warm and humid palaeoenvironment with high productivity and terrestrial debris input [24,25]. At the same time, the organic matter enrichment model of fine-grained sedimentary rocks has been divided into the “productivity model”, which is affected by palaeoclimate and productivity factors; the “preservation model”, which is affected by redox conditions and palaeosalinity factors; and the “composite model” [26,27,28]. However, the main focuses of the previously reported work on fine-grained sedimentary rocks have been classification, reservoir characterization, the palaeoenvironment, and organic matter enrichment, while a comprehensive analysis of its reservoir, organic matter, and palaeoenvironment is relatively lacking. The components of fine-grained sedimentary rocks help to explore the underlying palaeoenvironmental mechanism promoting organic matter enrichment and mineral development, which further control pore structure.
In this study, the fine-grained sedimentary rocks of the Jurassic lacustrine Ziliujing Formation and Xintiangou Formation in the northeastern part of the Sichuan Basin were analyzed through low-pressure nitrogen adsorption (LP-N2A), low-field nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), total organic carbon (TOC), rock-eval pyrolysis (Rock-Eval), gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), X-ray fluorescence spectroscopy (XRF), and inductively coupled plasma mass spectrometry (ICP-MS) in order to obtain insights regarding the pore structure, organic matter abundance, major and trace elements, and biomarker compounds. The reservoir, organic matter, and palaeoenvironmental characteristics of the two formations were also investigated to reveal the underlying mechanism by which the palaeoenvironment affects the organic matter and mineral structure. This mechanism plays a key role in further controlling the pore structure. A differentiated comparison between the two formations was also carried out to provide a theoretical basis for the exploration of oil and gas resources in lacustrine fine-grained sedimentary rocks and the preference for favourable zones.

2. Geologic Setting

The Sichuan Basin is oil and gas-rich and is located in the western part of the Upper Yangzi Platform [29,30]. During its tectonic evolution, it has gone through several evolutionary stages, such as early Paleozoic craton depression, late Paleozoic craton rift, and Middle Cenozoic foreland depression, forming a diamond-shaped basin pattern with a Northeast–Southwest (NE-SW) direction [31]. In the Middle Triassic, the seawater gradually receded, and the basin transitioned to terrestrial deposition [32,33]. The Indo-Chinese movement led to the successive uplift of the Longmen Mountains and the Dabashan Mountains, and the basin developed into an intralittoral depression dominated by lacustrine deposition in the Jurassic [34]. The Jurassic system of the basin is well developed, with the Lower Jurassic Ziliujing Formation, Middle Jurassic Xintiangou and Shaximiao Formations, and the Upper Jurassic Suining and Penglaizhen Formations developed from the bottom up. The five sampling sites involved in this study are all located in the northeastern part of the Sichuan Basin, which belongs to the high steep fault fold belt in eastern Sichuan. Controlled by large-scale lake-phase intrusion, the strata of both the Ziliujing Formation and the Xintiangou Formation have developed a large number of fine-grained sedimentary rocks, which are deposited as shallow to semi-deep lacustrine deposits (Figure 1) [35].

3. Material and Methodology

3.1. Sample Collection

Five points totalling 46 rock samples from the Ziliujing Formation and Xintiangou Formation in the Sichuan Basin are used in this work, of which the Ziliujing Formation contains 23 rock samples (Figure 1 and Figure 2 and Table 1). The rock samples were taken from the fresh surface of the outcrop and are in the form of irregular blocks. The block samples were subjected to low-field nuclear magnetic resonance and scanning electron microscopy measurements. The remaining samples were ground with an agate mortar and pestle to 100 μm and 200 μm. Then, they were subjected to low-pressure nitrogen adsorption, total organic carbon, rock-eval pyrolysis, gas chromatography, gas chromatography–mass spectrometry, X-ray fluorescence spectroscopy, and inductively coupled plasma mass spectrometry measurements.

3.2. Test Method

Low-pressure nitrogen adsorption was assessed using a Beijing Jingwei Gaobo Science and Technology Co., Ltd., JW-BK112W specific surface area and pore size analyzer. The pore diameter that can be tested ranges from 1.7–300 nm, and the lower limit of specific surface area is 0.00001 m2/g. The 100-mesh sample was dried in a constant temperature drying oven (120 °C) for 12 h and then degassed in a heating bag to remove impurities after being cooled to room temperature. Finally, it was placed in a test device for determination. The International Union of Pure and Applied Chemistry (IUPAC) classification method was used to divide the pores into micropores (<2 nm), mesopores (2–50 nm), and macropores (>50 nm) [36,37].
A MacroMR12-150H-I-type reservoir nuclear magnetic (NMR) resonance analysis system was used to determine the pore parameters. The resonance frequency was set at 21.67568 MHz, and the magnet temperature control was 32 ± 0.01 °C, with a 0.5 T magnetic field strength and 0.0002–200 μm pore diameter.
The nuclear magnetic resonance (NMR) pore size equation is given in Equation (1):
W = 2 R = 2 T 2   ρ 2   Fs
where W is the pore size, R refers to the radius, and ρ2 denotes the surface relaxation rate (Equation (2)). Moreover, T2 is the transverse relaxation time, and Fs stands for the pore geometry factor, with slit, cylindrical, and spherical pores’ Fs being 1, 2, and 3, respectively (from LP-N2A, it is known that fine-grained sedimentary rocks mainly develop slit pores, and thus Fs = 1).
ρ 2 = V S × T 2 L M
Here, S and V represent the surface area and pore volume, respectively (obtained from LP-N2A results), and T2LM is the logarithmic mean of the T2 distribution (Equation (3)).
T 2 L M = exp ( ∑ ln ( T 2 i ) × φ i ∑ φ i )
T2i is the T2 value corresponding to the ith pore system and φi is the porosity of the ith pore system.
Based on LP-N2A data, combined with the Frenkel Halsey Hill (FHH) equation, the fractal features are often divided at P/P0 = 0.45 by previous authors, and in the range of 0–0.45 (D1), monolayer–multilayer adsorption is produced, reflecting the pore surface complexity. In contrast, from 0.45–1 (D2), gas molecules mainly produce capillary condensation, reflecting the pore structure complexity (Equation (4)) [38,39].
ln ( V ) = ( D − 3 ) ln ( ln ( P 0 / P ) ) + C
Here, V (cm3/g) is the volume of adsorbed N2, P (MPa) denotes the equilibrium pressure, P0 (MPa) states the saturation pressure, D represents the fractal dimension, and C is the characteristic constant.
In nuclear magnetic resonance (NMR), based on the pore size and relaxation time correspondence, three intervals are obtained to classify the pore size in terms of lgT2 size and the fractal dimensions D1, D2, D3, and DNMR corresponding to the micropores (<2 nm), mesopores (2–50 nm), macropores (>50 nm), and full pore sizes, respectively [40].
The low-field nuclear magnetic resonance (NMR) fractal dimension can be estimated by Equation (5):
ln ( V ) = ( 3 − D ) lg ( T 2 ) + ( D − 3 ) lg ( T 2 max )
where V is the cumulative pore volume fraction corresponding to the total pore volume when the lateral relaxation time is less than T2, T2 denotes the lateral relaxation time, T2max signifies the maximum lateral relaxation time, and D refers to the fractal dimension.
A field emission scanning electron microscope (equipment type: JSM-7610F) was used in a high-vacuum (60 Pa) chamber environment with resolutions of 1.0 nm (15 kV), 0.1–30 kV accelerating voltages, 25–1 million times magnifications, and 1 pA–200 nA beam intensities. The working distance was about 4–5 mm and the accelerating voltage was 10–15 kV.
The total organic carbon (TOC) test was measured via the infrared absorption method using a Vario TOC total organic carbon analyzer. The sample was burned in an oxygen flow at 950 °C to oxidize carbon into carbon dioxide. The generated gas was detected by a carbon dioxide infrared detection cell and converted to the relative content of organic carbon. The test method was performed according to GB/T 19145-2003.
A Rock-Eval 6 instrument (RE6) was used to analyze the pyrolysis of powder samples. The sample with a mass of 30 mg was heated to 600 °C in a helium environment to the S1 (volatile hydrocarbon content, mg HC/g rock), S2 (remaining HC generative potential, mg HC/g rock), S3 (carbon dioxide yield, mg CO2/g rock), and Tmax (maximum peak temperature of rock-eval pyrolysis S2, °C).
Gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) analyses were performed on a Shimadzu GC-2010 equipped with a 30 m × 0.25 mm × 0.25 mm HP-5 quartz capillary column and on an Agilent 6890GC/5975i MS equipped with a 60 m × 0.25 mm × 0.25 mm HP-5MS quartz capillary column, respectively. Helium was used as the carrier gas, with a flow rate of 1.0 mL/min.
The major element composition was determined according to the Chinese national standard GB/T 14506.28-2010. The 200-mesh powder sample was dissolved in HClO4 and HF and placed in an open muffle furnace at 950 °C. AA-6800 atomic absorption spectrometry and a UV-2600 ultraviolet–visible spectrophotometer were used to test the main elements through X-ray fluorescence. The trace elements and rare earth element composition was analyzed by placing the powder samples in a microwave oven at 230 °C and dissolving them in a mixture of HNO3, HF, and HClO4 for digestion for 5 h before extraction with aqua regia. The solution samples were determined through inductively coupled plasma mass spectrometry (Agilent-7900), and the analysis uncertainty was within 1% (by the GB/T 14506.30-2010 standard).

4. Results

4.1. Pore Structure Characteristics

The nitrogen adsorption and desorption isotherms of both the Ziliujing Formation and the Xintiangou Formation are of type Ⅳ, indicating that the main pores of the fine-grained sedimentary rocks of the two formations are mesopores, while the obvious H3-type hysteresis loops reflect the slit-like pores associated with the clay–mineral aggregates (Figure 3a,b) [41]. In the pore volume–pore size differential distribution curve, the peak is mainly concentrated in the region of 1–4 nm, suggesting the existence of mesopores, although it also contains some micropores and macropores (Figure 3c,d) [10]. Based on the Barrett–Joyner–Halenda (BJH) model, the specific surface area, total pore volume, average pore size, and average value of the few available pore sizes were calculated for the two stratigraphic sites (Ziliujing Formation (11.34 m2/g, 0.023 cm3/g, 8.41 nm, and 2.46 nm), Xintiangou Formation (13.19 m2/g, 0.026 cm3/g 8.24 nm, and 2.35 nm)), in which the average and most available pore sizes were in the range of 2–50 nm, further verifying that the fine-grained sedimentary rocks in the two formations are dominated by mesopores (Table 1).
The nuclear magnetic resonance (NMR) pore size distribution chart shows a bimodal distribution, indicating a good pore continuity. As can be seen from the nuclear magnetic resonance (NMR) pore size cumulative distribution chart, the slope of the curve steeply increased at mesopores, indicating that the fine-grained sedimentary rock is dominated by mesopores and contains a certain amount of micropores and macropores (Figure 3g,h) [42,43,44].
The average values of micropores, mesopores, and macropores in the Ziliujing Formation are: LP-N2A method (2.76%, 70.54%, 26.70%) and nuclear magnetic resonance (NMR) method (36.71%, 53.91%, 9.28%) (Table 1), respectively. Meanwhile, the average values of micropores, mesopores, and macropores in the Xintiangou Formation are: P-N2A method (3.45%, 73.45%, and 23.10%) (Table 1), and nuclear magnetic resonance (NMR) method (36.75%, 54.97%, and 8.27%) (Table 1), respectively. Both indicators show that the fine-grained sedimentary rocks are predominantly mesopores, followed by macropores and micropores, with a relatively high percentage of micropores and mesopores and a relatively low percentage of macropores in the Xintiangou Formation. Moreover, the nuclear magnetic resonance (NMR) porosity of the Ziliujing Formation is relatively low, ranging from 5.62%–19.41% (average 11.11%) and 6.46%–13.31% (average 13.17%) for the two formations, respectively (Table 1).
The average values of D1 and D2 for nitrogen adsorption in fine-grained sedimentary rocks of the Ziliujing Formation and Xintangou Formation are 2.48 and 2.73, indicating moderate pore surface complexity and high pore complexity (Table 1). Nuclear magnetic resonance D1 is all negative, which is not of practical significance, and at this time, the microporous pore cleavage surface is dominated by adsorption. D2, D3, and DNMR are between 2 and 3, of which D3 has the highest mean value, indicating that the macroporous pore complexity is relatively high. The results of the two methods are consistent, as both indicate that the pore structure is highly complex.

4.2. Organic Matter and Biomarker Compound Characteristics

The total organic carbon (TOC) of fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation is 0.37–1.84 wt% (average 0.84 wt%) and 0.37–0.89 wt% (average 0.56 wt%), respectively (Table 1). The average values of Tmax are 492 °C and 450 °C, respectively, and the average values of S1, S2, S3, and S1 + S2 are as follows: Ziliujing Formation (0.04 mg/g, 0.33 mg/g, 0.27 mg/g, and 0.37 mg/g) and Xintiangou Formation (0.02 mg/g, 0.12 mg/g, 0.18 mg/g, and 0.14 mg/g). In addition, OI varied from 2.65–47.18 mg/g (average 21.68 mg/g) and 10.64–40.69 mg/g (average 25.14 mg/g), respectively, and HI varied from 5.19–54.15 mg/g (average 27.27 mg/g) and 7.09–28.79 mg/g (average 17.11 mg/g), respectively (Table 2).
The n-alkanes and isoprene are distributed in the total ion chromatograms (TIC) of the saturated hydrocarbons, and the n-alkane carbon numbers are mainly distributed between nC12 and nC40 in a pre-single-peak-type distribution, with the main peak carbon numbers of the Ziliujing group ranging from nC17 to nC27 and those of the Xintiangou group ranging from nC20 to nC25 (Figure 4a,b). The carbon preference index (CPI) of the Ziliujing Formation and the Xintiangou Formation ranges from 1.08 to 1.13 (average 1.11) and 1.10 to 1.18 (average 1.14), respectively, and the odd–even predominance (OEP) ranges from 0.97 to 1.45 (average 1.08) and 0.97 to 1.02 (average 0.98), respectively. The ∑nC21−/∑nC22+, (nC21 + nC22)/(nC28 + nC29), Pr/nC17, Ph/nC18, and Pr/Ph of the fine-grained sedimentary rocks in the two formations are: Ziliujing Formation (0.40–1.26 (average 0.91), 0.72–3.94 (average 2.22), 0.09–043 (average 0.22), 0.06–0.55 (average 0.26), and 0.59–1.48 (average 1.06)) and Xintiangou Formation (0.32–1.28 (average 0.82), 0.94–3.72 (average 2.60), 0.05–0.23 (average 0.10), 0.04–0.11 (average 0.07), and 1.08–1.41 (average 1.28)) (Table 3).
The m/z = 217 mass chromatograms showed that the average relative abundance of C27, C28, and C29 rule steranes in the two stratigraphic positions is: Ziliujing Formation (33.83%, 26.18%, 39.98%); Xintiangou Formation (33.13%, 26.47%, 40.41%), with C29 > C27 > C28, characterized by a “V” shape (Figure 4c,d). The distribution of the terpene biomarkers is determined in the ion chromatogram at m/z = 191, with most of the fine-grained sedimentary rocks containing abundant tricyclic terpenes and C24 tetracyclic terpenes (Figure 4e,f). A range of C14–C16 sesquiterpenoids is also present in the m/z = 123 mass spectra (Figure 4g,h).

4.3. Elemental Characteristics and Palaeoenvironmental Parameters

The major elements of the fine-grained sedimentary rocks of the Ziliujing Formation and the Xintiangou Formation are dominated by SiO2, with 63.03–90.14 wt% (average 68.70 wt%) and 65.46–79.60 wt% (average 70.12 wt%), respectively. Al2O3, Fe2O3, and K2O are the second, third, and fourth most abundant major elements, and the average values of the three elements of the Ziliujing Formation are, respectively, 18.12 wt%, 6.38 wt%, and 2.76 wt%, and 16.71 wt%, 6.30 wt%, and 2.25 wt% for the Xintiangou Formation, while the contents of the other major elements are less than 2% (Table 4). The Si content of the fine-grained sedimentary rocks of the Xintiangou Formation is generally higher than that of the Ziliujing Formation, while the Al2O3, Fe2O3, and K2O contents are relatively low. Compared with the upper crustal mean (UCC), the two formations showed a deficit of Na2O, MgO, K2O, CaO, and MnO, while Al2O3, SiO2, TiO2, and Fe2O3 were relatively enriched (Table 4).
The results for trace elements are summarized in Table 5. The enrichment factor (EF) is commonly used to quantitatively describe the relative enrichment or deficit of the trace elements and can be calculated as follows: EF = (Xsample/Alsample)/(XUCC/AlUCC) [45]. Both formations showed an enrichment of V, Cr, Co, Ni, Zn, Zr, Ba, Hf, Th, U, and Y (EF > 1) and a relative deficit of Sr, Mo, and Ta (EF < 1) (Table 5).
The results for rare earth elements are summarized in Table 6. The total rare earth elements (ΣREE) of the Ziliujing and Xintiangou Formations range from 143.21 to 249.96 ppm (average 195.16 ppm) and 172.61 to 303.46 (average 220.11 ppm), respectively, which are significantly higher than that of the North American Shale Complex (NASC) (160.1 ppm) and the Upper Continental Crust (UCC) (146.4 ppm) and are close to the Post-Paleozoic Australian Shale (PAAS) (211.8 ppm). The average δEu and δCe values of both formations are 0.99 vs. 0.85 and 1.00 vs. 0.84, respectively, indicating that Ce shows a strong deficit. The average values of the light and heavy rare earth ratios (ΣLREE/ΣHREE) are 8.99 and 8.13, which are both higher than those of the North American shale (7.50), indicating that the enrichment of light rare earths is significantly higher than that of heavy rare earths (Table 6). The palaeoenvironmental parameters obtained from the combination of elemental geochemistry and biomarker compounds are shown in Table 7.

5. Discussion

5.1. Reservoir Characteristics

5.1.1. Reservoir Characteristics of the Ziliujing Formation

The LP-N2A pore specific surface area (SSA) is positively correlated with the micropore and mesopore proportion and negatively correlated with the macropore proportion (Figure 5a). This result points out that micropores and mesopores per unit volume have more pores compared with macropores, which leads to a relatively large SSA. Since the mesopore proportion is much higher than the sum of the micropore and macropore proportion, it is a decisive factor, resulting in a positive correlation between the total pore volume (TPV) and the mesopore proportion and a negative correlation with the macropore proportion (Figure 5b). In contrast, the average pore diameter (APD) is positively correlated with the macropore proportion and vice versa for the micropore and the mesopore proportions, indicating that the average pore diameter is mainly affected by macropores with larger pore sizes (Figure 5c). The positive correlation between the maximum aperture and the micropores and mesopores further verifies that the pores of the fine-grained sedimentary rocks in the Ziliujing Formation are dominated by mesopores and are concentrated near 2 nm (Figure 5d). It is also worth noting that the correlation between the SSA, TPV, and maximum aperture and pore proportion is consistent, and the three factors are in a companion relationship. This outcome further specifies that the micropores and mesopores with smaller pores play a decisive role as the main part of the fine-grained sedimentary rocks. Furthermore, it can be inferred that the mesopores and micropores located near 2 nm are beneficial in promoting the development of pore specific surface area and pore volume (Figure 5a–d).
The nuclear magnetic resonance (NMR) fractal dimension is positively correlated with the proportion of both micropores and macropores and negatively correlated with the mesopore proportion, indicating that a higher proportion of mesopores increases pore connectivity and further reduces pore complexity (Figure 6a). The porosity is also positively correlated with the mesopore proportion, signifying that it is controlled by the higher proportion of mesopores (Figure 6b). Meanwhile, the porosity is weakly positively correlated with the total organic carbon (TOC) and negatively correlated with the fractal dimension, indicating that the increase in the organic matter content could promote pore development and increase porosity (Figure 6c). The connectivity is also increased accordingly, which leads to the enhancement of the pore homogeneity and, subsequently, the fractal dimension is decreased. The organic matter mainly affects the mesopore development, which is positively correlated with the mesopore proportion, while micropores and macropores in inorganic minerals are mainly located in quartz (SiO2) and mesopores are often located in clay minerals (Al2O3), carbonates (CaO + MgO), feldspars (Na2O + K2O), and pyrite (Fe2O3) (Figure 6d–i). From the SEM images, it can be seen that intergranular pores are often developed in clay minerals, with mesopores dominating, while quartz, as a fine-grained sedimentary rock skeleton, often leads to the formation of intracrystalline pores, with micropores and macropores dominating within it (Figure 5e,f).

5.1.2. Reservoir Characteristics of the Xintiangou Formation

The pore SSA is positively correlated with the micropore and mesopore percentage, which is mainly controlled by the small pores (Figure 7a). Meanwhile, the total pore volume (TPV) and pore percentage are not significantly correlated and are independent factors of each other (Figure 7b). In contrast, the average pore diameter (APD) is positively correlated with the macropore proportion, which is mainly affected by large pores (Figure 7c). The positive correlation between the maximum aperture and mesopores indicates that the pores of the fine-grained sedimentary rocks in the Xintiangou Formation are dominated by mesopores and that the most available pore sizes are concentrated around 2 nm (Figure 7d). It is noteworthy that SSA and APD are inversely correlated with the pore proportion, further indicating that small pores promote surface area development (Figure 7a–d).
The nuclear magnetic resonance (NMR) fractal dimension showed a weak positive correlation with the proportion of both micropores and macropores, indicating that it is controlled by micropores and macropores (Figure 8a). However, the opposite took place for porosity, indicating that it is controlled by mesopores, which had a higher proportion (Figure 8b). Meanwhile, the porosity showed a weak positive correlation with the total organic carbon (TOC) and a negative correlation with the fractal dimension, suggesting that an increase in the organic matter content can promote pore development, which in turn increases connectivity and decreases the fractal dimension (Figure 8c). Organic matter mainly affects mesopore development, while micropores and macropores in inorganic minerals are mainly hosted in quartz (SiO2), and mesopores are often hosted in clay minerals (Al2O3), carbonates (CaO + MgO), and pyrite (Fe2O3) (Figure 8d–i). From the SEM images, it can be seen that intergranular pores are often developed in clay minerals and carbonate minerals with moderate pore sizes and predominantly mesopores, whereas intracrystalline pores, predominantly micropores and macropores, are developed within the quartz skeleton (Figure 7e,f).

5.1.3. Comparison of the Reservoir Characteristics

From the normalized comparison of the pore structure parameters of the two formations, it has been observed that most of the ratios are between 0.9 and 1.1, which is in the range of 10% difference, indicating that the pore characteristics of the two formations are consistent (Figure 9, Table 7). The characteristics of the two formations are as follows: (1) The pores are mainly mesopores with high porosity, and the mesopore proportion and porosity in the Xintiangou Formation are higher; (2) The pores are mainly slit pores associated with clay mineral aggregates, mesopores are mostly developed in the organic matter, intracrystalline pores, mainly macropores and micropores, are often developed within the quartz skeleton of inorganic minerals, and intergranular pores dominated by mesopores often occur between clay minerals, carbonate minerals, and pyrite particles; (3) LP-N2A showed that the pore SSA and maximum aperture are mainly controlled by micropores and mesopores, while APD is mainly affected by macropores, and the correlation between the SSA, TPV, and maximum aperture is consistent with the correlation of pore percentages, which exhibited a concomitant relationship; (4) The nuclear magnetic resonance (NMR) correlation analysis showed that the development of mesopores resulted in a reduction in the fractal dimension and an increase in porosity. At the same time, the organic matter content promoted the increase in porosity, which led to the enhancement of pore connectivity and a reduction in pore complexity. In summary, the reservoir characteristics of the two formations are consistent and had similar development potential.

5.2. Organic Matter Characteristics

5.2.1. Organic Matter Characteristics of the Ziliujing Formation

From the division of hydrocarbon source rock quality shown in the TOC − S1 + S2 and TOC − S2 maps, it can be seen that the organic matter abundance of the fine-grained sedimentary rocks of the Ziliujing Formation is at a good stage and is located in the gas-prone area, which indicates that the hydrocarbon source rock of this formation has matured (Figure 10a,b) [18]. The OI–HI crossplot shows that the organic matter types are mainly type II and type III, with the presence of type I, which is in direct agreement with the results of alkane parameters (Ph/nC18–Ph/nC17 crossplot) (Figure 10c,d), Table 3) [46]. The OEP–CPI and ααααC29strerane20S/(20S + 20R)–C29streraneββ/(ββ + αα) crossplots indicate that the fine-grained sedimentary rocks of the Ziliujing Formation are mature (Figure 10e,f, Table 3) [47,48,49].
The C31 22R hopane/C30 hopane-Pr/Ph diagrams indicate that the organic matter of the fine-grained sedimentary rocks of the Ziliujing Formation mainly originated from lacustrine (Figure 10g). The relative abundance of C27, C28, and C29 rule steranes in the Ziliujing Formation is 30.84–38.10 (average 33.83%), 23.81–31.64 (average 26.18%), and 31.42–45.35 (average 39.98%), respectively, which indicates that the organic matter of the Ziliujing Formation originated from plankton and bacteria (Figure 10h, Table 3) [50,51]. The C29ααα(20R)/C27ααα(20R) sterane–Pr/Ph crossplot indicates that the fine-grained sedimentary rocks of the Ziliujing Formation were formed in a freshwater reducing depositional environment, and the organic matter is mainly derived from algal organisms (Figure 10i, Table 3) [52,53].

5.2.2. Organic Matter Characteristics of the Xintiangou Formation

The TOC–S1 + S2 and TOC–S2 crossplots indicate that the fine-grained sedimentary rocks of the Xintiangou Formation are located in a gas-prone area with fair organic matter abundance, and the hydrocarbon source rocks are mature (Figure 10a,b). The OI–HI (oxygen index–hydrogen index) crossplot points out that the organic matter types are types II and III, which is in agreement with the results of the alkane parameter (Ph/nC18–Ph/nC17 crossplot) (Figure 10c,d, Table 3). From the OEP–CPI (odd–even predominance–carbon preference index) plots and ααααC29strerane20S/(20S + 20R)–C29streraneββ/(ββ + αα) crossplots, it is also evident that the Xintiangou Formation has entered the maturity stage (Figure 10e,f), Table 3).
The C31 22R hopane/C30 hopane–Pr/Ph discrimination diagrams indicate that the source of organic matter in the fine-grained sedimentary rocks of the Xintiangou Formation is mainly lacustrine (Figure 10g). Moreover, the abundance of C27, C28, and C29 rule steranes is 25.44–41.43 (average 33.13%), 23.32–31.08 (average 26.47%), and 28.56–48.81 (average 40.41%), respectively, which indicates that the organic matter originated from plankton and the presence of fungus, algae, and bryophytes (Figure 10h, Table 3). The C29ααα(20R)/C27ααα(20R) sterane–Pr/Ph crossplot indicates that the main source of organic matter is algal organisms, with a small contribution from terrestrial plants, and that the depositional period had a freshwater reductive depositional environment (Figure 10i, Table 3).

5.2.3. Comparison of Organic Matter Characteristics between the Ziliujing Formation and the Xintiangou Formation

It can be seen from the analyses in the previous two chapters that the organic matter characteristics of the fine-grained sedimentary rocks in the two horizons of the Ziliujing Formation and the Xintiangou Formation are consistent as a whole, but there are weak differences, as follows: (1) The organic matter abundances of the fine-grained sedimentary rocks of the Ziliujing Formation and the Xintiangou Formation are consistent with each other, and are in a good stage, but the Ziliujing Formation is higher; (2) The organic matter types of fine-grained sedimentary rocks in both the Ziliujing Formation and the Xintiangou Formation are dominated by type II and type III, but some type I organic matter exists in the Ziliujing Formation, which is consistent with a previous study which found that organic matter in the Ziliujing in the northeastern part of the Sichuan Basin is dominated by types II and III [54]; (3) The fine-grained sedimentary rocks of both the Ziliujing Formation and the Xintiangou Formation have entered the maturity stage, corresponding to specular body reflectance (Ro) values near 0.8; (4). The source of organic matter in the fine-grained sedimentary rocks of the Ziliujing Formation and the Xintiangou Formation is dominated by plankton and bacteria, but a small amount of terrestrial plant matter contributes to the Xintiangou Formation.

5.3. Palaeoenvironmental Restoration and Comparison

5.3.1. Palaeoenvironmental Restoration of the Ziliujing Formation

The Al2O3/(Al2O3 + Fe2O3) ratios of ocean ridges, ocean basins, and land margins are <0.4, 0.4–0.7, and 0.7–0.9, respectively [55]. Additionally, the K2O/Na2O–SiO2 crossplot is often used to discriminate the depositional location [45]. The Al2O3/(Al2O3 + Fe2O3) of fine-grained sedimentary rocks in the Ziliujing Formation is 0.69–0.87 (average 0.74), indicating the location of terrestrial margin deposition, which is consistent with the results of the K2O/Na2O–SiO2 discriminant diagram (Table 7, Figure 11a). The ∑REE–La/Yb crossplot showed that most of the samples fall into the overlap zone of granite and sedimentary rocks, and a small amount falls into the overlap zone of sedimentary rocks and alkaline basalt. This outcome suggests that the source is mainly from the upper crustal feldspathic source area mixed with alkaline basalt (Figure 11b) [56]. The Al2O3 ranges from 5.55–25.22 (average 18.02), which is close to the average of the Post-Palaeogene Australian Shale (18.90), reflecting higher terrigenous detritus (Table 4) [57].
The erosional variability index (CIA = Al2O3/(A12O3 + CaO* + Na2O + K2O) × 100) is commonly used to evaluate the palaeoclimate, with the cold and arid, warm and humid, and hot and humid climates corresponding to 50 < CIA < 70, 70 < CIA < 85, and 85 < CIA < 100, respectively [58].The CIA of fine-grained sedimentary rocks of the Ziliujing Formation is 79.75–92.79 (average 83.94), indicating a warm and humid climate (Table 7). The palaeoproductivity indicator P/Ti is 0.01–0.32 (average 0.11), close to PAAS (0.12), indicating a higher level of palaeoproductivity (Table 7) [27]. The two values of Fe/Ti and (Fe + Mn)/Ti are often used to determine the hydrothermal source and are considered to be affected by hydrothermal fluids when Fe/Ti > 20 or (Fe + Mn)/Ti > 25 ± 5 [55]. All values of the hydrothermal indicators Fe/Ti and (Fe + Mn)/Ti are below 20, specifying no significant hydrothermal input during the depositional period (Table 7).
Oxic, dysoxic, and anoxic Ni/Co correspond to <2.5, 2.5–5, and >5, respectively, and oxic and anoxic δU correspond to <1 and >1, respectively [56]. Also, the Pr/Ph ratio is indicative of the redox conditions, and, usually, high values of Pr/Ph (>3) indicate oxic conditions, while low values (<1) imply anoxic conditions [59]. The average values of redox conditions (Ni/Co, δU) of fine-grained sedimentary rocks in the Ziliujing Formation are 2.70 and 0.87, respectively, and Pr/Ph is 0.59–1.48 (average 1.06), indicating that the bottom water was in an oxic–dysoxic state during the sedimentary period and was mainly dysoxic (Table 3, Table 7). The Sr/Ba ratios have been used to restore palaeosalinity levels, corresponding to >1, 0.5–1, and <0.5 for brackish, semi-saline, and freshwater environments, respectively [26]. The values of Sr/Ba are 0.01–0.45 (average 0.15) and refer to a freshwater state, which is consistent with Pr/Ph–Ts/(Ts + Tm) and C30diahopane/C30hopane–Gammacerane/C30hopance analysis (Table 3, Figure 11c,d) [60]. (La/Yb)N is used as a parameter to evaluate the sedimentation rate. When it is close to 1, it indicates a high sedimentation rate, and vice versa when it is far away from 1 [61]. Stagnant environments can be classified into three classes: strong stagnant environments (Mo/TOC < 4.5), semi-stagnant environments (4.5 < Mo/TOC < 45), and weak stagnant environments (Mo/TOC > 45) [62]. The sedimentation rate indicator (La/Yb)N and stagnant environment indicator Mo/TOC are 0.71–1.73 (average 1.21) and 0.31–3.03 (average 0.85), respectively, indicating a high sedimentation rate and strong stagnant environments during the depositional period (Table 7).
The total organic carbon (TOC) is positively correlated with palaeoclimate (CIA) and palaeoproductivity (P/Ti) indicators, which are strongly positively correlated with redox conditions (Ni/Co, δU) and palaeosalinity (Sr/Ba) indicators (Figure 12a–c). This implies that higher palaeoproductivity provided a certain material basis, warm and humid climatic conditions promoted the growth and reproduction of living organisms, and the anoxic redox conditions of the bottom water and high salinity were conducive to the preservation of organic matter. The combined effect of multiple factors promoted the enrichment of organic matter in fine-grained sedimentary rocks of the Ziliujing Formation. SiO2 is positively correlated with palaeoclimate (CIA), redox conditions (Ni/Co, δU), and palaeosalinity (Sr/Ba), which indicates that the warm and humid climate in conjunction with the reducing and highly saline bottom-water environment are favourable to the development of quartz minerals (Figure 12d–f). The positive correlation between CaO + MgO and palaeoproductivity (P/Ti) and terrestrial detritus (Al2O3) indicates that the carbonate minerals are mainly derived from terrestrial detritus, and biological reproduction and development can also promote their development (Figure 12g–i). According to the literature, clay minerals mainly come from terrigenous detritus. In this work, Al2O3 is accompanied by an increase in the sedimentation rate (La/Yb)N, and the high sedimentation rate shortened the deposition time of clay minerals in the lacustrine and promoted their development and preservation (Figure 12j–l). The clear correlation between Na2O + K2O and the terrigenous detritus (Al2O3) and sedimentation rate (La/Yb)N indicates that feldspar mainly comes from terrigenous detritus, has a certain companion relationship with clay minerals, and is also affected by the high sedimentation rate (Figure 12m–o). Fe2O3 exhibits also some positive correlation with palaeoproductivity (P/Ti), terrigenous detritus (Al2O3), and the sedimentation rate (La/Yb)N, indicating that pyrite mainly originates from palaeontological and land-source detritus, is associated with clay minerals, and is affected by the preservation of the high sedimentation rate (Figure 12p–r). Overall, the correlation between CaO + MgO and Fe2O3 is consistent with the palaeoenvironmental indicators, which indicates that carbonate minerals and pyrite are in an associated relationship, while the correlation between Al2O3 and Na2O + K2O is consistent with the palaeoenvironmental indicators. This result suggests that clay minerals and feldspars are in a certain associated relationship.

5.3.2. Palaeoenvironmental Restoration of the Xintiangou Formation

The Al2O3/(Al2O3 + Fe2O3) of the fine-grained sedimentary rocks of the Xintiangou Formation is 0.59–0.78 (average 0.73), indicating terrestrial margin deposition, which is consistent with the results of the K2O/Na2O–SiO2 discrimination map (Table 7, Figure 11a). The ∑REE–La/Yb crossplot shows that the material source stems from the upper crustal long quartz source region (Figure 11b). Al2O3 is close to that of the average shale in the Post-Palaeogene Australian Shale (18.90), ranging from 11.45–19.21 (average 16.71), which is indicative of a high input of terrigenous detritus in the depositional period (Table 4). The CIA ranges from 74.67–88.81 (average 82.35), demonstrating that the palaeoenvironment was warm and humid during the sedimentary period (Table 7). Moreover, P/Ti is 0.01–0.43 (average 0.15), higher than PAAS (0.12) and slightly lower than UCC (0.17), indicating a higher level of palaeoproductivity (Table 7). Fe/Ti and (Fe + Mn)/Ti are 6.37–13.22 (average 8.77) and 6.51–13.37 (average 8.87), indicating no significant volcanic hydrothermal input during the depositional period (Table 7).
The average redox indexes (Ni/Co and δU) are 2.49 and 0.89, respectively, while the Pr/Ph ratios are 1.08–1.41 (average 1.28), indicating that the bottom water was in an oxic–dysoxic state during the depositional period (Table 3, Table 7). The values of Sr/Ba range from 0.01–0.34 (average 0.15), with all the values being lower than 0.5 (Table 7). The main body was freshwater, which is consistent with the conclusions of the Pr/Ph–Ts/(Ts + Tm) and C30diahopane/C30hopane–Gammacerane/C30hopance discrimination diagrams (Table 3, Figure 11c,d). The sedimentation rate indicator (La/Yb)N and stagnant environment indicator Mo/TOC are 0.97–1.15 (average 1.16) and 0.36–4.18 (average 0.97), respectively, with all samples having (La/Yb)N close to 1 and Mo/TOC below 4.5, suggesting that the sedimentation rate during the depositional period was high and in a strong stagnant environment (Table 7).
The total organic carbon (TOC) is positively correlated with palaeoclimate (CIA) and palaeoproductivity (P/Ti) and strongly positively correlated with redox conditions (Ni/Co, δU) and palaeosalinity (Sr/Ba), which indicates that the higher palaeoproductivity provided a certain material basis, while warm and humid climatic conditions promoted the growth and reproduction of living organisms (Figure 13a–c). In addition, the anoxic redox conditions of the bottom water and high salinity were conducive to the preservation of organic matter, and the combined effect of multiple factors promoted the enrichment of organic matter in fine-grained sedimentary rocks of the Xintiangou Formation. More specifically, SiO2 is positively correlated with palaeoclimate (CIA), redox conditions (Ni/Co, δU), and palaeosalinity (Sr/Ba), which indicates that the warm and humid climate in combination with the reduction in the highly saline bottom-water environment were favourable to the development of quartz minerals (Figure 13d–f). The positive correlation between CaO + MgO and palaeoproductivity (P/Ti) and terrestrial detritus (Al2O3) indicates that the carbonate minerals are mainly derived from terrestrial detritus, and biological reproduction and development can also promote their development (Figure 13g–i). Al2O3 increases with the increase in bottom water reducibility and salinity, and the strong reduction and high-salinity bottom water sedimentary environment are conducive to the preservation of clay minerals (Figure 13j–l). Na2O + K2O also shows some correlation with terrigenous detritus (Al2O3) and palaeosalinity (Sr/Ba), signifying that feldspars are mainly derived from terrigenous detritus and, at the same time, are affected by the environmental rate of high salinity bottom water (Figure 13m–o). Fe2O3 displays some positive correlation with palaeoclimate (CIA), palaeoproductivity (P/Ti), terrigenous detritus (Al2O3), and the degree of stagnation (Mo/TOC), indicating that pyrite is mainly deposited in a warm humid climate of palaeontological origin, with an associative relationship with clay minerals (Figure 13p–r). Pyrite is also subjected to the preservation influence of a strongly stagnant environment. Overall CaO + MgO, Na2O + K2O, and Al2O3 correlate well with palaeoenvironmental indicators, designating an associative relationship with carbonate minerals, feldspars, and clay minerals.

5.3.3. Comparison of Palaeoenvironments between the Ziliujing Formation and the Xintiangou Formation

Comparing the average values of the palaeoenvironmental parameters of the fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation, it can be seen that the ratio of the average values of almost all parameters is between 0.9 and 1.1 (Table 7, Figure 14). This indicates that the palaeoenvironment of the Ziliujing Formation and the Xintiangou Formation in the sedimentary period was consistent as a whole. The depositional location was the continental margin, the rock source was the long quartz source area of the upper crust, the depositional period belonged to the warm and humid climate, the productivity was high, and there was no obvious hydrothermal phenomenon of volcanoes. The depositional water was in an oxic–dysoxic state and was freshwater, and the depositional rate was high in an environment of strong stagnation.
The enrichment of organic matter in the two formations was affected by palaeoclimate (CIA), palaeoproductivity (P/Ti), and redox conditions (Ni/Co, δU). There are weak differences in the palaeosalinity (Sr/Ba) and stagnant environment (Mo/TOC). A higher palaeoproductivity provides a certain material basis. The existence of warm and humid climatic conditions can promote biological growth and reproduction. The anoxic and reducing conditions of the bottom water were conducive to the preservation of organic matter. Under the combined action of multiple factors, organic matter enrichment is promoted. As can be ascertained from the literature, organic matter mainly promotes the development of mesopores. Thus, it can be deduced that the changes in palaeoclimate, palaeoproductivity, and redox conditions control the enrichment of organic matter, further promoting the development of mesopores and improving the porosity of fine-grained sedimentary rocks.
The development of quartz minerals (SiO2) in the two formations is positively correlated with the palaeoclimate, and there are differences in preservation factors such as the redox, palaeosalinity, and deposition rate. Carbonate minerals (CaO + MgO) are positively correlated with palaeoproductivity and terrigenous detritus, and there are differences in palaeosalinity. Carbonate minerals are mainly derived from terrigenous detritus, and biological reproduction and development can also promote carbonate development. Clay minerals (Al2O3) are mainly derived from terrigenous detritus. The high deposition rate of the Ziliujing Formation shortens the deposition time of clay minerals in the lake and promotes their development and preservation. In contrast, the strong reduction and high salinity bottom water sedimentary environment of the Xintiangou Formation was conducive to the preservation of clay minerals. Feldspar (Na2O + K2O) is affected by the input of terrigenous detritus, and the artesian well group is also affected by the deposition rate, while the palaeosalinity affects the Xintiangou group. Pyrite (Fe2O3) is positively correlated with palaeoproductivity and terrigenous detritus, and there are differences in the deposition rate, palaeoclimate, and stagnant environment. On the whole, the mineral composition of the two formations is consistent with the palaeoenvironment. Among them, clay minerals and feldspar have a similar correlation, and the two are associated with each other, mainly due to terrigenous detritus. At the same time, carbonate and pyrite have an associated relationship, which is consistent with the palaeoenvironment. They are derived from terrigenous detritus, and biological reproduction and development can also promote their development. The development of quartz is different from that of other minerals. The intracrystalline pores dominated by macropores and micropores are often developed in the quartz skeleton, while the intergranular pores dominated by mesopores are often found between clay minerals, carbonate minerals, and pyrite particles. By combining these pieces of information, it can be inferred that the warm and humid climate conditions promoted the development of quartz minerals, which increased the proportion of micropores and macropores. At the same time, the clay minerals, carbonate minerals, and pyrite carried in terrigenous detritus and the carbonate minerals and pyrite controlled by paleoaquatic organisms are associated with TOC and further control the development of mesopores and porosity.
The ratios of the reservoir, organic matter, and palaeoenvironment parameters of fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation are all around 1, indicating that the two layers have similar development potential. The palaeoenvironment further controls the pore structure by affecting the enrichment of organic matter and the mineral development of fine-grained sedimentary rocks.

6. Conclusions

The two formations have similar potential for hydrocarbon development. The following conclusions can be drawn:
  • The fine-grained sedimentary rocks of the Ziliujing Formation and the Xintiangou Formation are dominated by mesopores, mainly developing slit pores, with high porosity and a complex pore structure. In addition, macropores and micropores are often present as intracrystalline pores within the quartz skeleton. Mesopores occur mainly in the development of both formations’ intergranular pores between the organic matter, clay minerals, carbonate minerals, and pyrite particles. The surface area and the maximum pore diameter are mainly controlled by the micromediaturized pores, and the organic matter promotes the increase in the porosity of the fine-grained sedimentary rocks, especially the mesopores. This enhances the connectivity of the pore space and reduces the complexity of the pore spaces.
  • The fine-grained sedimentary rocks of the Ziliujing Formation and the Xintiangou Formation have good hydrocarbon potential, indicated by the high abundance of organic matter. The organic matter was sourced from plankton and bacteria. Organic matter types were dominated by types II and III, while type I organic matter exists in the Ziliujing Formation. Both formations have entered the mature stage.
  • The palaeoenvironment of the fine-grained sedimentary rocks in the two formations of the Ziliujing Formation and the Xintiangou Formation was highly consistent during the sedimentary period. The ratio of the average values of the parameters is close to 1, and the upper and lower values are not more than 0.1. The enrichment of organic matter in the two formations was controlled by the palaeoclimate, productivity, and redox index. A warm and humid climate can promote the development of quartz minerals to further increase the proportion of micropores and macropores. At the same time, clay minerals, carbonate minerals, and pyrite carried in terrigenous debris are associated with total organic carbon (TOC), which can promote the development of mesopores and further increase porosity.
  • The reservoir structure, organic matter, and palaeoenvironment characteristics of the fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation are highly similar, meaning they can be used as potential horizons for oil and gas exploration.

Author Contributions

Data curation, H.L.; Formal analysis, P.M. and X.Z.; Investigation, Q.S.; Methodology, S.W.; Project administration, D.L.; Software, W.L.; Writing original draft, Q.H. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Natural Science Basic Research Program of Shaanxi Province (No. 2020JQ-744), Opening fund of State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development (No. 33550000-22-ZC0613-0297), and National Natural Science Foundation of China (No. 4210021463).

Data Availability Statement

The data presented in this study are available in the article.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Sample collection location map. (a) Global satellite map (based on Google earth); (b) Tectonic regional division map of the Sichuan Basin; (c) Local amplification diagram of the sampling position.
Figure 1. Sample collection location map. (a) Global satellite map (based on Google earth); (b) Tectonic regional division map of the Sichuan Basin; (c) Local amplification diagram of the sampling position.
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Figure 2. Fine-grained sedimentary rock sampling photos of Ziliujing Formation and Xintiangou Formation. (a) Fine-grained sedimentary rocks of the Ziliujing Formation in profile P1; (b) Boundary between the Ziliujing Formation and the Xintiangou Formation in profile P3; (c) Fine-grained sedimentary rocks of the Xintiangou Formation in profile P4; (d) Boundary between the Ziliujing Formation and the Xintiangou Formation in profile P4. The red dotted line in the picture is the boundary between the two formations.
Figure 2. Fine-grained sedimentary rock sampling photos of Ziliujing Formation and Xintiangou Formation. (a) Fine-grained sedimentary rocks of the Ziliujing Formation in profile P1; (b) Boundary between the Ziliujing Formation and the Xintiangou Formation in profile P3; (c) Fine-grained sedimentary rocks of the Xintiangou Formation in profile P4; (d) Boundary between the Ziliujing Formation and the Xintiangou Formation in profile P4. The red dotted line in the picture is the boundary between the two formations.
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Figure 3. (a,b) Nitrogen adsorption desorption curves; (c,d) pore volume–pore size differential distribution curve of LP-N2A; (e,f) nuclear magnetic resonance (NMR) pore size distribution chart; (g,h) nuclear magnetic resonance (NMR) pore size cumulative distribution chart.
Figure 3. (a,b) Nitrogen adsorption desorption curves; (c,d) pore volume–pore size differential distribution curve of LP-N2A; (e,f) nuclear magnetic resonance (NMR) pore size distribution chart; (g,h) nuclear magnetic resonance (NMR) pore size cumulative distribution chart.
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Figure 4. Typical samples (Z-06, X-08) of biomarker compounds: (a,b) total ion chromatogram (TIC); (c–h) m/z = 217, 191, 123 mass chromatograms.
Figure 4. Typical samples (Z-06, X-08) of biomarker compounds: (a,b) total ion chromatogram (TIC); (c–h) m/z = 217, 191, 123 mass chromatograms.
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Figure 5. Correlation diagram of pore parameters and scanning electron microscope photos of fine-grained sedimentary rocks in the Ziliujing Formation. (a–d) LP-N2A pore structure correlation plots; (e,f) SEM images of the pore structure of fine-grained sedimentary rocks of the Ziliujing Formation. The falling point corresponds to the color of the longitudinal axis.
Figure 5. Correlation diagram of pore parameters and scanning electron microscope photos of fine-grained sedimentary rocks in the Ziliujing Formation. (a–d) LP-N2A pore structure correlation plots; (e,f) SEM images of the pore structure of fine-grained sedimentary rocks of the Ziliujing Formation. The falling point corresponds to the color of the longitudinal axis.
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Figure 6. Correlation analysis diagram of pore development of fine-grained sedimentary rocks in the Ziliujing Formation using the nuclear magnetic resonance method. (a) Correlation analysis of the fractal dimension and pore proportion; (b) correlation analysis of the porosity and pore proportion; (c) correlation analysis of the porosity with organic matter and fractal dimension; (d–i) correlation analysis of the organic matter (TOC), quartz (SiO2), clay minerals (Al2O3), carbonate minerals (CaO + MgO), feldspar (Na2O + K2O), pyrite (Fe2O3), and pore proportion. The falling point corresponds to the color of the longitudinal axis.
Figure 6. Correlation analysis diagram of pore development of fine-grained sedimentary rocks in the Ziliujing Formation using the nuclear magnetic resonance method. (a) Correlation analysis of the fractal dimension and pore proportion; (b) correlation analysis of the porosity and pore proportion; (c) correlation analysis of the porosity with organic matter and fractal dimension; (d–i) correlation analysis of the organic matter (TOC), quartz (SiO2), clay minerals (Al2O3), carbonate minerals (CaO + MgO), feldspar (Na2O + K2O), pyrite (Fe2O3), and pore proportion. The falling point corresponds to the color of the longitudinal axis.
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Figure 7. Correlation diagram of pore parameters and scanning electron microscope photos of fine-grained sedimentary rocks in the Xintiangou Formation. (a–d) LP-N2A pore structure correlation plots; (e,f) SEM images of the pore structure of fine-grained sedimentary rocks of the Xintiangou Formation. The falling point corresponds to the color of the longitudinal axis.
Figure 7. Correlation diagram of pore parameters and scanning electron microscope photos of fine-grained sedimentary rocks in the Xintiangou Formation. (a–d) LP-N2A pore structure correlation plots; (e,f) SEM images of the pore structure of fine-grained sedimentary rocks of the Xintiangou Formation. The falling point corresponds to the color of the longitudinal axis.
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Figure 8. Correlation analysis diagram of the pore development of fine-grained sedimentary rocks in the Xintiangou Formation using the nuclear magnetic resonance method. (a) Correlation analysis of the fractal dimension and pore proportion; (b) correlation analysis of the porosity and pore proportion; (c) correlation analysis of the porosity with organic matter and fractal dimension; (d–i) correlation analysis of the organic matter (TOC), quartz (SiO2), clay minerals (Al2O3), carbonate minerals (CaO + MgO), feldspar (Na2O + K2O), pyrite (Fe2O3), and pore proportion. The falling point corresponds to the color of the longitudinal axis.
Figure 8. Correlation analysis diagram of the pore development of fine-grained sedimentary rocks in the Xintiangou Formation using the nuclear magnetic resonance method. (a) Correlation analysis of the fractal dimension and pore proportion; (b) correlation analysis of the porosity and pore proportion; (c) correlation analysis of the porosity with organic matter and fractal dimension; (d–i) correlation analysis of the organic matter (TOC), quartz (SiO2), clay minerals (Al2O3), carbonate minerals (CaO + MgO), feldspar (Na2O + K2O), pyrite (Fe2O3), and pore proportion. The falling point corresponds to the color of the longitudinal axis.
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Figure 9. The normalized distribution map of pore structure parameters of fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation. The normalized value is the ratio of the average value of each parameter.
Figure 9. The normalized distribution map of pore structure parameters of fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation. The normalized value is the ratio of the average value of each parameter.
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Figure 10. Organic matter characteristics of fine-grained sedimentary rocks in Ziliujing Formation. (a,b) Identification map of the hydrocarbon generation potential of organic matter; (c,d) organic matter type identification diagram; (e,f) organic matter maturity regional division map; (g–i) biological source identification diagram.
Figure 10. Organic matter characteristics of fine-grained sedimentary rocks in Ziliujing Formation. (a,b) Identification map of the hydrocarbon generation potential of organic matter; (c,d) organic matter type identification diagram; (e,f) organic matter maturity regional division map; (g–i) biological source identification diagram.
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Figure 11. The sedimentary environment identification diagram of fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation. (a) Deposition position identification diagram; (b) sediment source identification diagram; (c,d) identification diagram of redox conditions of sedimentary water.
Figure 11. The sedimentary environment identification diagram of fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation. (a) Deposition position identification diagram; (b) sediment source identification diagram; (c,d) identification diagram of redox conditions of sedimentary water.
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Figure 12. The correlation analysis diagram of organic matter (TOC), quartz (SiO2), clay minerals (Al2O3), carbonate minerals (CaO + MgO), feldspar (Na2O + K2O), pyrite (Fe2O3), and palaeoenvironmental parameters of fine-grained sedimentary rocks in the Ziliujing Formation. The falling point corresponds to the color of the longitudinal axis.
Figure 12. The correlation analysis diagram of organic matter (TOC), quartz (SiO2), clay minerals (Al2O3), carbonate minerals (CaO + MgO), feldspar (Na2O + K2O), pyrite (Fe2O3), and palaeoenvironmental parameters of fine-grained sedimentary rocks in the Ziliujing Formation. The falling point corresponds to the color of the longitudinal axis.
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Figure 13. The correlation analysis diagram of (a–c) organic matter (TOC), (d–f) quartz (SiO2), (g–i) carbonate minerals (CaO + MgO), (j–l) clay minerals (Al2O3), (m–o) feldspar (Na2O + K2O), (p–r) pyrite (Fe2O3), and palaeoenvironmental parameters of fine-grained sedimentary rocks in the Xintiangou Formation. The falling point corresponds to the color of the longitudinal axis.
Figure 13. The correlation analysis diagram of (a–c) organic matter (TOC), (d–f) quartz (SiO2), (g–i) carbonate minerals (CaO + MgO), (j–l) clay minerals (Al2O3), (m–o) feldspar (Na2O + K2O), (p–r) pyrite (Fe2O3), and palaeoenvironmental parameters of fine-grained sedimentary rocks in the Xintiangou Formation. The falling point corresponds to the color of the longitudinal axis.
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Figure 14. The normalized distribution map of paleoenvironmental parameters of fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation. The normalized value is the ratio of the average value of each parameter.
Figure 14. The normalized distribution map of paleoenvironmental parameters of fine-grained sedimentary rocks in the Ziliujing Formation and the Xintiangou Formation. The normalized value is the ratio of the average value of each parameter.
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Table 1. Pore structure parameters and organic matter summary table of fine-grained sedimentary rock samples in Ziliujing Formation and Xintiangou Formation.
Table 1. Pore structure parameters and organic matter summary table of fine-grained sedimentary rock samples in Ziliujing Formation and Xintiangou Formation.
FormationsSample IDNitrogen AdsorptionNuclear Magnetic Resonance
123456789101112131415161718
Ziliujing FormationZ-011.975.2422.878.760.0188.42.582.562.7834.8755.89.337.142.61−0.682.792.990.49
Z-021.3866.9131.718.920.0198.342.382.542.7433.5457.928.546.192.61−0.692.752.990.5
Z-033.3670.9625.6813.110.0288.572.312.452.6941.6242.613.495.622.59−0.132.842.980.41
Z-040.6563.5335.827.880.02412.432.642.422.5831.2454.0314.738.12.57−0.32.722.980.41
Z-051.4667.1231.4314.70.0287.542.32.352.6936.3156.497.27.212.58−0.322.762.990.53
Z-061.6176.9621.434.450.0097.794.022.462.745.8439.4814.687.492.530.612.842.971.84
Z-072.8973.6523.4611.290.0238.012.842.522.7935.7956.597.626.72.57−0.262.752.991.29
Z-083.9674.2921.7413.930.0277.692.592.452.8237.5751.9210.5110.112.510.142.792.981.24
Z-093.7873.7722.4515.380.0297.612.552.432.7631.2265.083.7113.692.54−0.262.72.990.77
Z-101.4283.5415.0512.140.039.772.62.52.7331.3558.5710.0812.032.57−0.442.722.990.93
Z-111.4268.5929.999.220.0219.042.032.512.6443.7642.3713.878.532.57−0.022.842.981.13
Z-125.3871.8822.7514.070.0216.052.222.412.7950.9938.7710.248.682.580.022.872.981.07
Z-134.175.9519.9515.820.0287.062.892.412.7435.6757.616.7314.112.55−0.222.752.990.93
Z-14471.1324.8614.350.0277.592.552.412.7154.9625.9519.0812.222.550.862.92.960.53
Z-154.6777.2718.0612.440.0227.042.562.472.859.1723.7217.1114.852.520.422.932.970.37
Z-162.5572.4624.9912.970.0257.752.22.522.7738.2651.610.1412.952.54−0.032.792.980.37
Z-173.8273.3122.8714.880.0287.492.182.432.7134.862.862.3414.332.510.272.6930.72
Z-183.8275.9120.2713.430.0267.682.592.432.7624.8372.462.7217.512.46−0.352.6431.68
Z-190.6757.4941.846.980.01911.022.272.542.7626.7564.918.349.682.56−0.52.662.990.56
Z-200.4541.9857.574.430.01513.972.022.632.5418.1576.485.368.52.52−0.312.492.991.38
Z-213.8269.7226.4613.20.0278.31.942.482.7326.9768.74.3319.222.49−0.052.652.990.64
Z-224.4858.3537.178.280.0188.792.272.632.7526.2466.647.1219.412.470.042.662.991.01
Z-231.8182.4915.7110.130.0145.5822.542.8244.4849.456.0711.22.5602.822.990.53
Avg.2.7670.5426.711.340.0238.412.462.482.7336.7153.919.2811.112.55−0.12.752.980.84
Xintiangou FormationX-011.4885.2613.2611.470.0279.282.632.52.6736.7353.299.989.162.58−0.282.772.990.57
X-022.868.7928.4112.660.0329.982.292.462.7230.2459.7310.0310.292.59−0.632.712.990.66
X-033.6376.8219.5525.330.0517.982.552.352.6835.4558.066.4923.312.440.122.732.990.57
X-044.7884.7910.4312.650.0237.122.62.472.7252.632.2615.1315.312.530.472.872.980.36
X-052.9567.5729.499.790.0239.592.612.472.6339.4748.0112.5114.862.59−0.162.792.980.37
X-061.4865.4933.0213.490.0277.892.32.462.7333.659.916.4815.822.56−0.232.722.990.37
X-073.773.4822.8213.770.0267.592.612.412.7147.7740.6211.6112.492.59−0.042.852.980.38
X-084.5875.4419.9817.390.0327.412.612.42.7941.5750.517.9217.812.520.162.792.990.59
X-091.979.7118.3911.690.0196.552.612.52.7644.2148.17.6911.822.59−0.292.832.990.46
X-104.2775.9419.7912.350.0227.052.282.522.7342.2450.037.74132.58−0.242.812.990.89
X-116.6360.8332.549.40.0187.611.962.592.8231.1164.344.5510.872.57−0.522.72.990.56
X-123.6972.9823.3414.890.0318.382.22.462.7731.8660.487.6613.272.55−0.332.722.990.57
X-133.7769.7126.5314.360.038.342.292.482.6632.0160.027.9712.952.58−0.582.732.990.54
X-141.1254.6544.238.640.0167.382.312.592.7734.6858.856.4715.672.54−0.132.742.990.83
X-151.6776.621.7313.510.0247.152.272.472.7134.4159.935.6512.582.55−0.282.742.990.81
X-160.8477.5421.613.640.01618.12.012.82.5712.3479.777.899.952.5−0.792.42.990.44
X-176.8364.3228.858.980.0146.111.972.622.7945.8545.978.1811.872.58−0.172.842.990.56
X-181.3484.0814.5815.860.0317.822.622.422.734.2859.046.6915.082.54−0.222.732.990.57
X-194.4974.6520.8614.410.0267.312.562.52.7432.1163.324.5711.732.57−0.532.722.990.7
X-204.6383.2912.0818.420.0326.941.962.382.7335.4358.486.0913.352.57−0.482.772.990.45
X-212.5254.0543.4414.610.04211.532.532.472.6618.3575.65612.862.59−1.152.562.990.72
X-225.1185.918.9811.60.0186.062.272.442.8154.4631.7213.836.462.580.132.92.980.46
X-235.1477.3617.514.470.0236.261.972.372.8544.5746.349.0812.412.490.62.82.990.39
Avg.3.4573.4523.113.190.0268.242.352.482.7336.7554.978.2713.172.56−0.242.752.990.56
Note: 1: Micropore proportion (%); 2: mesopore proportion (%); 3: macropore proportion (%); 4: SSA (m2/g); 5:TPV (cm3/g); 6: APD (nm); 7: maximum aperture (nm); 8: D1; 9: D2; 10: micropore proportion (%); 11: mesopore proportion (%); 12: macropore proportion (%); 13: porosity (%); 14: DNMR; 15: D1; 16: D2; 17: D3; 18: total organic carbon (wt%).
Table 2. Results of the rock-eval pyrolysis of fine-grained sedimentary rocks (Tmax: maximum peak temperature of rock-eval pyrolysis S2, °C; S1: volatile hydrocarbon content, mg HC/g rock; S2: remaining HC generative potential, mg HC/g rock.; S3: carbon dioxide yield, mg CO2/g rock; S1 + S2: potential of generating hydrocarbon, mg HC/g rock; HI: hydrogen index = S2 × 100/TOC;. OI: oxygen index = S3 × 100/TOC).
Table 2. Results of the rock-eval pyrolysis of fine-grained sedimentary rocks (Tmax: maximum peak temperature of rock-eval pyrolysis S2, °C; S1: volatile hydrocarbon content, mg HC/g rock; S2: remaining HC generative potential, mg HC/g rock.; S3: carbon dioxide yield, mg CO2/g rock; S1 + S2: potential of generating hydrocarbon, mg HC/g rock; HI: hydrogen index = S2 × 100/TOC;. OI: oxygen index = S3 × 100/TOC).
FormationsSample IDTmaxS1S2S3S1 + S2OIHI
Ziliujing FormationZ-065300.030.560.830.5945.1130.43
Z-075200.030.180.610.2147.1813.92
Z-085300.040.170.060.214.8313.68
Z-095890.010.040.170.0522.085.19
Z-104550.030.250.180.2819.3526.88
Z-114540.060.580.030.642.6551.24
Z-124520.080.580.10.669.3454.15
Z-134490.030.180.340.2136.6419.4
Z-204510.040.420.110.467.9930.5
Avg.4920.040.330.270.3721.6827.27
Xintiangou FormationX-024450.020.190.230.2134.8528.79
X-104590.030.240.150.2716.8927.03
X-114390.010.040.060.0510.647.09
X-134500.020.050.170.0731.729.33
X-144510.010.110.280.1233.9413.33
X-154470.010.20.330.2140.6924.66
X-194510.010.060.110.0715.748.58
X-204600.020.040.070.0615.568.89
X-214480.020.190.190.2126.2826.28
Avg.4500.020.120.180.1425.1417.11
Table 3. Summary of n-alkanes, isoprenoids, and biomarker parameters of fine-grained sedimentary rock samples.
Table 3. Summary of n-alkanes, isoprenoids, and biomarker parameters of fine-grained sedimentary rock samples.
FormationsSample ID123456789101112131415161718
Ziliujing FormationZ-061.091.450.91.140.430.550.77nC170.480.360.1731.8528.7939.361.240.540.170.08
Z-081.0810.40.720.380.520.59nC270.560.40.1736.9531.6431.420.850.490.140.08
Z-131.120.990.811.920.120.11.19nC230.590.480.3338.120.9840.921.070.80.243.66
Z-181.1311.193.350.10.061.48nC210.550.30.2330.8423.8145.351.470.790.190.77
Z-211.110.971.263.940.090.071.26nC190.580.450.2431.4425.6942.881.360.660.090.76
Avg.1.111.080.912.220.220.261.06 0.550.40.2333.8326.1839.981.20.660.171.07
Xintiangou FormationX-081.150.971.283.720.070.051.37nC210.540.530.3140.3525.4534.20.850.710.52.88
X-101.11.020.923.440.230.111.35nC200.60.50.2625.4431.0843.481.710.370.070.36
X-141.140.980.741.930.050.041.08nC230.60.330.2429.6221.5748.811.650.70.10.48
X-161.180.970.822.410.10.071.4nC230.60.370.230.623.3246.081.510.610.210.37
X-201.160.970.843.170.060.041.41nC230.580.450.241.433028.560.690.660.170.5
X-231.10.980.320.940.10.11.08nC250.520.550.2931.3127.3841.31.320.750.171.71
Avg.1.140.980.822.60.10.071.28 0.570.450.2533.1326.4740.411.290.630.21.05
Note: 1: CPI (carbon preference index = [(C25 + C27 + C29 + C31 + C33)/(C24 + C26 + C28 + C30 + C32) + (C25 + C27 + C29 + C31 + C33)/(C26 + C28 + C30 + C32 + C34)]/2); 2: OEP (odd–even predominance = (C23 + 6 × C25 + C27)/(4 × C24 + 4 × C26)); 3: ∑nC21−/∑nC22+ (C21− represents carbon numbers less than C21; C22+ represents carbon numbers greater than C22); 4: (nC21 + nC22)/(nC28 + nC29); 5: Pr/nC17; 6: Ph/nC18; 7: Pr/Ph (pristine to phytane ratio); 8: Cmax; 9: αααC29strerane20S/(20S + 20R); 10: C29streraneββ/(ββ + αα); 11: C31 22R-hopane/C30-hopane; 12: C27; 13: C28; 14: C29; 15: C29ααα(20R)/C27ααα(20R); 16: Ts/(Ts + Tm); 17: Gammacerane/C30 hopance; 18: C30 diahopane/C30 hopane.
Table 4. Major elemental characteristics of fine-grained sedimentary rock samples (wt%).
Table 4. Major elemental characteristics of fine-grained sedimentary rock samples (wt%).
FormationsSample ID12345678910
Ziliujing FormationZ-010.381.7517.7267.700.072.790.820.830.067.89
Z-020.652.3318.6765.330.083.230.670.800.098.15
Z-030.481.1017.0272.840.002.480.190.860.054.98
Z-040.691.9020.8463.440.014.100.160.850.077.94
Z-050.801.9020.2165.900.063.780.180.820.056.31
Z-060.100.165.5590.140.020.260.141.390.042.19
Z-070.692.0719.2063.790.183.490.321.250.188.82
Z-080.581.5725.2263.030.004.580.111.080.033.80
Z-090.722.1118.2766.980.172.980.371.290.107.01
Z-101.411.8019.0867.020.182.570.580.960.056.35
Z-111.192.3720.6164.350.192.281.120.850.086.98
Z-120.492.3319.5568.180.221.890.850.770.065.65
Z-130.491.5412.4576.550.362.200.650.830.044.88
Z-140.571.4017.1070.470.122.040.390.930.146.84
Z-150.251.1017.4272.730.052.100.300.780.055.23
Z-160.301.7820.3966.240.072.760.380.780.027.29
Z-170.541.9622.7263.990.092.960.510.880.046.32
Z-180.441.9420.1364.830.063.760.411.070.037.34
Z-190.831.3614.7672.760.301.830.460.710.086.92
Z-200.852.0016.1769.430.201.991.790.730.136.72
Z-210.771.7116.5468.960.183.410.620.940.066.81
Z-220.421.7118.6466.790.203.461.170.930.056.63
Z-230.652.0218.5268.630.192.660.540.940.065.78
Avg.0.621.7318.1268.700.132.760.550.920.076.38
Xintiangou FormationX-011.381.7916.4870.990.131.571.130.700.055.79
X-020.741.2715.2773.890.191.190.520.700.036.21
X-030.451.5820.5267.040.142.520.220.760.036.75
X-041.500.9514.7474.350.062.830.870.590.054.08
X-051.531.7013.3576.230.141.481.090.650.083.76
X-061.442.0519.7265.490.193.610.990.990.105.41
X-071.061.7915.9271.790.152.650.770.690.085.09
X-080.701.6418.4169.200.212.410.680.850.045.86
X-091.281.8718.8868.030.152.920.810.780.045.23
X-101.212.0419.0067.590.212.160.510.930.076.29
X-110.982.0117.1168.790.212.091.240.880.076.62
X-120.602.1819.2167.090.131.570.680.900.077.57
X-130.891.8818.4867.060.102.410.811.000.067.32
X-140.591.8518.6667.180.202.650.940.990.066.87
X-150.421.4111.4575.420.411.270.600.820.098.12
X-160.270.7712.1779.600.001.780.260.720.034.40
X-171.472.1217.3566.450.182.491.000.960.107.88
X-181.511.4717.6068.540.211.800.660.990.077.15
X-191.382.2117.8565.760.272.751.311.030.097.37
X-201.592.2017.5067.000.163.240.760.950.076.53
X-211.901.9116.2365.460.502.561.020.840.099.48
X-220.701.1913.4075.100.071.880.500.810.076.29
X-230.471.5214.9874.720.131.990.540.790.064.80
Avg.1.051.7116.7170.120.182.250.780.840.076.30
UCC3.272.4815.4066.000.152.803.590.640.105.04
Note: 1: Na2O; 2: MgO; 3: Al2O3; 4: SiO2; 5: P2O5; 6: K2O; 7: CaO; 8: TiO2; 9: MnO; 10: Fe2O3.
Table 5. Trace element characteristics of fine-grained sedimentary rock samples (ppm).
Table 5. Trace element characteristics of fine-grained sedimentary rock samples (ppm).
FormationsSample IDVCrCoNiZnSrZrMoBaHfTaThUY
Ziliujing FormationZ-01139.9688.5421.1445.68132.5299.70326.000.30746.269.041.1914.333.7129.32
Z-02133.9879.1520.1044.41115.85103.33330.780.19858.529.241.2515.123.1620.82
Z-03118.1475.1812.2027.4094.0490.60346.620.26601.5110.001.2514.253.3017.41
Z-04153.8896.7719.1445.71126.37122.76336.290.13835.409.631.2115.323.0022.78
Z-05157.39107.3516.4445.73133.63123.23365.940.27888.1110.381.2316.444.8428.66
Z-0678.0545.211.395.3015.3852.95489.631.78117.5613.471.2410.545.1724.67
Z-07152.0594.7220.3541.17116.4286.67318.401.17752.319.581.289.783.0238.22
Z-08192.18119.635.7932.2170.24166.36425.540.75875.6511.551.6016.764.8922.96
Z-09145.45110.7823.4550.01116.0758.62357.180.81516.9110.651.319.742.8641.41
Z-10116.8698.3613.3137.16107.50119.53403.931.67548.8810.491.3015.194.4239.66
Z-11108.3781.8216.2141.24109.92120.06390.860.73505.819.801.3614.503.9940.58
Z-1293.6364.0215.2932.4785.0599.94337.780.70447.298.671.0312.713.4733.65
Z-13101.1762.9612.3236.5188.4782.19339.880.91614.718.901.1510.593.0228.99
Z-14115.6173.4912.6030.1079.8987.47274.151.61693.997.210.8710.772.9527.68
Z-15114.6668.4911.8331.5683.4589.59288.100.22655.947.860.9713.382.6325.33
Z-16138.3383.2615.9446.50121.99101.73302.070.24817.307.900.9214.312.6827.80
Z-17143.4497.2815.1839.39112.15123.45321.291.02676.048.401.0315.313.6432.85
Z-18168.33133.7217.1461.21151.6194.71349.190.80792.739.461.3416.583.8428.66
Z-19105.2580.0317.3334.98117.1693.76283.330.32480.428.330.9413.753.2737.15
Z-20130.3294.0816.7839.38117.05114.94293.661.24588.237.990.9313.943.6428.66
Z-21111.5254.6713.3335.5792.5185.91268.370.52561.558.011.4313.723.1622.48
Z-22142.6492.4215.8845.57118.31100.04307.330.51736.848.481.6414.223.3125.62
Z-23126.4583.2817.4742.01101.5697.92316.680.35653.659.221.5115.493.5724.92
Avg.129.9086.3115.2438.75104.66100.67337.960.72650.689.311.2213.773.5429.14
EF Avg.3.594.052.443.102.370.473.210.951.892.900.962.182.282.28
Xintiangou FormationX-0191.7088.3415.0733.44101.41140.88434.610.29409.2810.841.1013.063.4535.31
X-02103.2489.1015.7451.56115.72113.65345.200.53706.709.051.1212.302.7339.56
X-03146.92103.6912.7540.40117.5878.63434.100.70527.4811.131.2617.654.6239.44
X-0453.5843.7510.7320.6253.88153.82241.860.17598.626.410.6810.072.0427.56
X-0579.3659.2412.0025.2666.26135.02287.080.13695.697.330.9311.122.2828.23
X-06118.5893.6417.4139.1499.37136.64394.590.25789.419.851.0413.857.8039.64
X-0783.2473.2915.0832.8483.69131.25337.980.19744.438.610.9312.932.4733.86
X-08112.7795.0912.7335.6697.8092.63392.181.02564.3110.071.2415.473.8743.12
X-09108.3483.9414.3936.0194.97138.41386.920.33630.719.811.2013.983.0137.88
X-10109.8587.5517.6040.07101.01153.65401.880.82575.1410.181.2614.203.9843.35
X-1185.4158.2011.9932.3389.3796.38316.350.62505.889.271.0513.024.0830.90
X-12110.9779.1613.2143.49108.1696.63381.140.33594.5510.481.2014.114.1234.49
X-13108.3180.0212.4130.46105.43102.03399.520.43530.8310.771.1615.265.2834.62
X-14113.4585.8317.8939.94116.41103.31383.740.63518.2110.581.2016.324.3640.21
X-1597.7264.7721.7335.3494.8690.84328.403.39479.969.201.1610.582.9446.44
X-1678.4150.158.1726.9972.7045.05279.630.27354.838.190.8412.113.1621.58
X-17123.49109.9719.3646.48125.00126.75450.000.37741.6011.991.3216.523.7849.55
X-18111.0698.0414.4040.15115.00127.80451.100.69625.6512.091.6716.044.7048.15
X-19119.91105.4316.5746.53115.06132.72482.130.79646.0912.391.8717.344.9651.55
X-20111.7886.4517.9938.36118.07136.41570.600.21792.8714.221.4216.246.2745.00
X-21100.0679.6817.9139.17122.42135.62374.051.26762.7410.191.0914.373.5357.46
X-22106.5074.5616.6433.8992.1068.85361.420.22507.8210.661.1913.683.6527.51
X-23108.9969.0714.1236.1896.2484.84315.860.23924.208.841.1814.683.4322.52
Avg.103.6480.8215.0436.71100.11113.99380.450.60618.5610.091.1814.133.9438.17
EF Avg.3.034.022.683.232.470.573.510.761.993.060.942.312.433.05
UCC60.0035.0010.0020.0071.00350.00190.001.50550.005.802.2010.702.8022.00
Table 6. Rare earth element characteristics of fine-grained sedimentary rock samples (ppm).
Table 6. Rare earth element characteristics of fine-grained sedimentary rock samples (ppm).
FormationsSample IDLaCePrNdSmEuGdTbDyHoErTmYbLu
Ziliujing FormationZ-0146.3583.139.8337.236.81.45.110.8551.053.010.533.420.56
Z-0245.3579.579.133.265.130.983.540.573.480.772.460.483.050.49
Z-0345.3479.779.1634.016.0113.770.512.830.642.130.382.680.45
Z-0445.6685.1410.0438.986.31.093.580.573.690.862.820.483.320.53
Z-0551.4891.1411.0143.087.81.645.370.844.871.033.840.553.870.59
Z-0630.8260.416.4523.854.240.693.510.543.660.92.960.583.940.69
Z-0737.9570.878.7734.917.411.726.151.096.681.394.040.634.410.69
Z-0843.774.318.6731.984.941.063.850.573.640.82.870.563.650.58
Z-0935.3965.88.0131.776.41.415.591.058.571.484.270.74.840.76
Z-1053.0193.811.2343.737.771.496.831.086.331.434.010.674.690.7
Z-1145.583.89.9139.087.651.426.691.16.671.393.690.623.990.62
Z-1242.1377.228.9134.486.511.285.590.965.611.193.280.553.660.58
Z-1333.865.587.3828.815.621.274.970.835.071.072.90.473.250.47
Z-1440.8474.568.9935.426.481.325.610.855.011.052.850.493.250.48
Z-1544.9680.419.536.666.441.295.060.744.370.892.450.433.020.47
Z-1646.9682.759.7137.316.261.325.220.84.931.012.820.53.530.54
Z-1748.0583.1410.1739.577.021.395.890.885.171.133.090.523.710.58
Z-1843.8675.269.8838.136.361.315.430.844.961.133.20.563.50.62
Z-1957.6593.0912.8950.599.191.938.011.196.531.293.280.543.230.54
Z-2044.0384.461039.737.281.636.250.975.431.112.950.483.170.55
Z-2135.7464.997.9730.885.451.144.750.774.410.962.60.463.040.49
Z-2236.7466.758.0730.95.71.35.180.824.651.012.710.493.040.53
Z-2346.7583.1610.0638.516.461.35.380.824.550.992.90.573.490.58
Avg.43.5778.229.3836.216.491.325.270.845.051.073.090.533.550.57
Xintiangou FormationX-0142.8481.319.5737.687.031.376.230.996.041.273.350.63.90.58
X-0243.874.8710.2140.517.791.596.871.136.651.353.610.63.930.57
X-0365.0190.6812.443.126.391.165.290.895.821.353.940.724.950.73
X-0435.2876.197.5629.25.261.244.730.774.610.972.780.443.120.47
X-0539.374.118.6532.935.871.245.060.824.881.022.70.493.130.48
X-0648.7386.7710.4640.027.251.66.581.066.411.363.650.614.060.61
X-0744.9476.989.3435.166.21.365.640.95.471.23.380.553.510.55
X-0850.5984.2411.1942.678.071.657.161.187.141.54.220.684.470.67
X-0946.8885.4610.2839.257.261.526.411.036.131.293.580.574.010.6
X-1046.3784.3410.6341.648.021.737.171.177.091.513.960.644.620.66
X-1143.5680.289.533.926.441.556.261.026.051.143.170.533.430.56
X-1244.0980.379.6734.866.321.526.11.056.531.233.470.583.810.59
X-1346.2284.029.9334.25.951.45.70.966.151.193.560.613.870.62
X-1451.4793.0511.0440.147.781.747.351.227.61.413.930.624.240.7
X-1542.1379.269.538.68.3927.431.357.911.524.090.63.760.56
X-1640.0380.169.0733.995.791.114.410.673.830.942.860.483.380.5
X-1760.09102.4313.2251.719.081.918.321.337.971.74.520.794.730.84
X-1856.5494.9812.8550.118.961.837.871.277.641.694.510.784.750.78
X-1959.08103.9813.2151.159.21.948.271.348.091.784.790.850.81
X-2050.3492.0311.0241.717.471.676.71.117.031.564.380.754.90.76
X-2156.41119.2814.561.0611.682.3210.621.7510.662.25.740.925.450.86
X-2250.9497.2911.6645.47.761.526.070.95.061.093.040.573.380.55
X-2346.3580.259.5635.416.081.214.670.713.960.932.650.472.970.56
Avg.48.387.0610.6540.637.391.576.561.076.471.363.730.634.060.63
Note: ∑REE = LREE + HREE; LREE = La + Ce + Pr + Nd + Sm + Eu; HREE = Gd + Tb + Dy + Ho + Er + Tm + Yb + Lu; L/H = LREE/HREE; δEu = EuN/(SmN × GdN)0.5; δCe = CeN/(LaN × PrN)0.5.
Table 7. The normalized summary table of each parameter of fine-grained sedimentary rock samples of Ziliujing Formation and Xintiangou Formation. It is normalized to the ratio of the average values of the parameters in the two formations.
Table 7. The normalized summary table of each parameter of fine-grained sedimentary rock samples of Ziliujing Formation and Xintiangou Formation. It is normalized to the ratio of the average values of the parameters in the two formations.
ParametersZiliujingXintiangouNormalizationParametersZiliujingXintiangouNormalization
10.45–5.38 (2.76)0.84–6.83 (3.45)1.24162.49–2.93 (2.75)2.40–2.90 (2.75)1
241.98–83.54 (70.54)54.05–85.91 (73.45)1.04172.96–3.00 (2.98)2.98–2.99 (2.99)1
315.05–57.57 (26.70)8.98–44.23 (23.10)0.87180.68–0.87 (0.74)0.59–0.78 (0.73)0.99
44.43–15.82 (11.34)3.64–25.33 (13.19)1.16195.55–25.22 (18.12)11.45–19.21 (16.71)0.92
50.009–0.030 (0.023)0.014–0.051 (0.026)1.142079.75–92.79 (83.94)74.67–88.81 (82.53)0.98
65.58–13.97 (8.41)6.06–18.10 (8.24)0.95210.01–0.32 (0.11)0.01–0.43 (0.15)1.36
71.94–4.02 (2.46)1.96–2.63 (2.35)0.96222.02–5.57 (2.70)1.63–3.31 (2.49)0.92
82.35–2.63 (2.48)2.35–2.80 (2.48)1230.72–0.19 (0.87)0.73–1.26 (0.89)1.02
92.54–2.82 (2.73)2.57–2.85 (2.73)1240.59–1.48 (1.06)1.08–1.41 (1.28)1.21
1018.15–59.17 (36.71)12.34–54.46 (36.75)1250.01–0.45 (0.15)0.01–0.34 (0.15)1
1123.72–76.48 (53.91)31.72–79.77 (54.97)1.02260.49–0.80 (0.66)0.37–0.75 (0.63)0.95
122.34–19.08 (9.28)4.55–15.13 (8.27)0.89270.08–3.66 (1.07)0.36–2.88 (1.05)0.98
135.62–19.41 (11.11)6.46–23.31 (13.17)1.19280.09–0.24 (0.17)0.07–0.50 (0.20)1.18
142.46–2.61 (2.55)2.44–2.59 (2.56)1290.71–1.73 (1.21)0.97–1.15 (1.16)0.96
15−0.69–0.86 (−0.10)−1.15–0.60 (−0.24)2.51300.31–3.03 (0.85)0.36–4.18 (0.97)1.14
Note: Pore parameters of the low pressure nitrogen adsorption method (1: micropore proportion (%); 2: mesopore proportion (%); 3: macropore proportion (%); 4: SSA (m2/g); 5: TPV (cm3/g); 6: APD (nm); 7: maximum aperture (nm); 8: D1; 9: D2); nuclear magnetic resonance method pore parameters (10: micropore proportion (%); 11: mesopore proportion (%); 12: macropore proportion (%); 13: porosity (%); 14: DNMR; 15: D1; 16: D2; 17: D3); 18: Al2O3/(Al2O3 + TFe2O3); 19: Al2O3; 20: CIA; 21: P/Ti; 22: Ni/Co; 23: δU; 24: Pr/Ph; 25: Sr/Ba; 26: Ts/(Ts + Tm); 27: C30 diahopane/C30 hopane; 28: Gammacerane/C30 hopance; 29: (La/Yb)N; 30: Mo/TOC.
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Li, D.; Wu, S.; He, Q.; Li, W.; Meng, P.; Li, H.; Sun, Q.; Zhao, X. Comprehensive Comparison of Lacustrine Fine-Grained Sedimentary Rock Reservoirs, Organic Matter, and Palaeoenvironment: A Case Study of the Jurassic Ziliujing Formation and Xintiangou Formation in the Sichuan Basin. Minerals 2024, 14, 336. https://doi.org/10.3390/min14040336

AMA Style

Li D, Wu S, He Q, Li W, Meng P, Li H, Sun Q, Zhao X. Comprehensive Comparison of Lacustrine Fine-Grained Sedimentary Rock Reservoirs, Organic Matter, and Palaeoenvironment: A Case Study of the Jurassic Ziliujing Formation and Xintiangou Formation in the Sichuan Basin. Minerals. 2024; 14(4):336. https://doi.org/10.3390/min14040336

Chicago/Turabian Style

Li, Delu, Shiqiang Wu, Qianyang He, Wangpeng Li, Peilong Meng, Haibin Li, Qiang Sun, and Xiaochen Zhao. 2024. "Comprehensive Comparison of Lacustrine Fine-Grained Sedimentary Rock Reservoirs, Organic Matter, and Palaeoenvironment: A Case Study of the Jurassic Ziliujing Formation and Xintiangou Formation in the Sichuan Basin" Minerals 14, no. 4: 336. https://doi.org/10.3390/min14040336

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