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Article

Characteristics and Origins of the Natural Gas and Implications for Gas-Source Correlation in Deep Formations of the Songliao Basin, NE China

by
Zhengjian Xu
1,2,3,4,5,*,
Biao Peng
2,
Yanjun Feng
5,6,
Luofu Liu
3,4,
Chao Fang
7,
Mingli Shao
8,
Kexin Jia
8,
Kangjun Wu
1 and
Yingying Chen
9
1
School of Petroleum Engineering, Chongqing University of Science and Technology, Chongqing 401331, China
2
Shaanxi Provincial Land Engineering Construction Group Co., Ltd., Xi’an 710000, China
3
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China
4
College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China
5
Energy & Geoscience Institute, University of Utah, Salt Lake City, UT 84108, USA
6
Coal Mining Research branch, China Coal Research Institute, Beijing 100013, China
7
CNPC Engineering Technology R&D Co., Ltd., Beijing 102206, China
8
Research Institute of Petroleum Exploration and Development, Jilin Oilfield Branch, CNPC, Songyuan 138000, China
9
Henan Provincial Information Center of Geology and Minerals, Zhengzhou 450003, China
*
Author to whom correspondence should be addressed.
Energies 2019, 12(24), 4641; https://doi.org/10.3390/en12244641
Submission received: 30 October 2019 / Revised: 26 November 2019 / Accepted: 2 December 2019 / Published: 6 December 2019
(This article belongs to the Section L: Energy Sources)
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Versions Notes

Abstract

:
The Songliao Basin is the most productive petroliferous lacustrine basin in NE China, and numerous large gas fields with large proven reserves occur in its deep formations. However, considerable challenges remain: (1) the origins and genetic types of the natural gases are controversial; (2) the gas-source correlations are poorly studied; and (3) the migration distance is vague. In this study, these problems are addressed by the study of the gas compositions, light hydrocarbons, and stable hydrogen and carbon isotopes. The gases are predominantly of organic and thermogenic origins. The Huoshiling (J3h) and Shahezi (K1sh) gases are mainly mixtures of coal-derived and oil-associated gases and the mixed-sources of primary kerogen degradation and secondary oil cracking, while the Yingcheng (K1yc) gases are mainly coal-derived gases and predominantly derived from primary kerogen degradation. The gases in different sags are derived from the source rocks developed in the same sags where the gases accumulated, characterized by the proximal-source accumulation. Vertically, the gases in the J3h and K1sh are predominantly sourced by the proximal J3h and K1sh mudstones, while the gases in the K1yc are mainly derived from either the J3h or the K1sh source rocks, suggesting the gas migration with short distances.

1. Introduction

Natural gases in sedimentary basins contain hydrocarbons (e.g., methane and its higher homologues), non-hydrocarbons (e.g., CO2, N2, H2, H2S, and Hg), and noble gases (e.g., He and Ar). Generally, hydrocarbon gases are proved to be the result of organic matter conversion by thermal degradation, crude oil and wet gas cracking, and even bacterial action [1,2,3,4,5,6,7,8,9,10]. However, the hydrocarbon gas physical properties, compositions, and stable carbon isotopic distributions in gas reservoirs may change, as a result of the effects of microbial generation, thermal maturation, migration, mixing, leaking, biodegradation, and thermochemical sulfate reduction (TSR) [7,8,11,12,13,14,15,16,17,18,19,20,21]. Combined with stable hydrogen and carbon isotopes, the hydrocarbon gas compositions can be useful parameters to ascertain the gas origins and analyze gas-source correlations. Besides, the non-hydrocarbon gases can be significant markers to analyze the gas origins, genetic types, generation, and migration [4,22,23,24,25,26,27,28,29,30,31,32,33,34,35]. Accordingly, the geochemical characters of gas (hydrocarbon, non-hydrocarbon, and noble gas) compositions and their stable hydrogen and carbon isotopes are the basic parameters to analyze gas origins, mixtures of gases generated at different thermal-evolution stages or from different origins, and gas-source correlations [1,3,16,26,36,37,38,39,40,41,42,43,44,45,46,47,48,49].
In NE China rift basins which developed during the Late Jurassic to Early Cretaceous are widely distributed and have been studied extensively [50,51]. The Songliao Basin (SLB), the largest one, proves to be the most productive petroliferous lacustrine basin in China [52,53,54,55,56,57]. It is commonly accepted that the Upper Cretaceous petroleum systems are very important petroleum-bearing plays in the SLB [58,59,60,61], and numerous studies on these petroleum plays have been carried out [58,59,60,61,62,63]. Based on previous studies [64,65,66], large gas fields occur in the deep formations (the formations underlying the 3rd Member of the Lower Cretaceous Quantou Formation; [67]) with proven reserves of over 200×109 m3 (706.3bcf). The deep gas reservoirs in the Dehui Depression (a sub-tectonic unit located in the uplift area of southeast SLB) possess proven reserves of over 20 × 109 m3 (70.6bcf). The deep formations (mainly including the Jurassic Huoshiling Formation (J3h) (156.0–145.0Ma), the Cretaceous Shahezi (K1sh) (145.0–133.9Ma) and Yingcheng (K1yc) (133.9–125.0Ma) Formations) are predicted be the next main targets for hydrocarbon gases exploration in the Dehui Depression. However, considerable challenges remain. In the deep formations, (1) the gas origins and genetic types are confusing and debatable, (2) the gas-source correlations are poorly studied, and (3) the migration distance for hydrocarbon gas is controversial. During the last decades, some researchers have suggested that the gas origins in the deep formations of SLB are of inorganic and mantle-derived source [68,69,70,71]. However, some previous studies pointed out that the hydrocarbon gases in the deep formations of SLB are of organic origins, mainly derived from the K1sh source rocks [72,73,74,75]. Nevertheless, some scholars held the view that the gases are mainly sourced by the J3h source rocks [76,77]. These debates may constrain the exploration and exploitation of hydrocarbons in the deep formations of SLB, which can be addressed by using the geochemical characters of gas (hydrocarbon and non-hydrocarbon) compositions and their stable hydrogen and carbon isotopes [42,78,79,80,81,82].
In this study, the gases in the deep formations of the Dehui Depression are used for the systematic analyses of the gas density, chemical compositions, stable hydrogen and carbon isotopes, and light hydrocarbons characteristics. The gas origins, genetic types and gas-source correlations have been investigated, which can provide the needed theoretical support for natural gas exploration and target selection in the deep formations of the SLB, and the guidance for the gas exploration in the deep formations of similar geological settings around the world.

2. Geological Settings

2.1. Tectonics and Structure

The SLB, with an area of 260×103 km2, is an independent half-graben continental basin that was formed during the Late Jurassic-Neogene [56], and featured by a dual-structure of an earlier rift depression and a later thermal depression [56]. It is the most prolific petroliferous lacustrine basin in NE China [83]. The tectonic evolution of the basin was controlled by two active continental margins in the late Mesozoic: (1) the Sikhote-Alin Orogenic Belt to the east, and (2) the Mongol-Okhotsk Belt to the north and northwest [84], which can be divided into four stages: (1) mantle upwelling during the Middle–Late Jurassic, (2) synrift subsidence during the Late Jurassic-Early Cretaceous, (3) postrift thermal subsidence during the Early-Late Cretaceous, and (4) structural inversion during the Cenozoic [56]. According to the tectonic evolution history and structure framework, the SLB can be divided into six first-order structural units: (1) the central depression zone, (2) the southeastern uplift zone, (3) the southwestern uplift zone, (4) the northeastern uplift zone, (5) the northern plunge zone, and (6) the western slope zone (Figure 1).
As a result of synrift extension, the SLB in the synrift stage was characterized by “basin-and-range” fault blocks [56]. The Dehui Depression, located in the uplift zone of southeastern SLB, is NE trending and fault-controlled, with an area of 4053 km2. The tectonic evolution stages of the Dehui Depression are approximately consistent with those of the SLB. Tectonic movements of multi-episodes have resulted in complex internal structures, and the Dehui Depression contains seven sags: the Nong’an sag, the Huajia sag, the Baojia sag, the Nong’annan sag, the Helong sag, the Longwang sag, and the Lanjia sag (Figure 1).

2.2. Stratigraphy and Lithology

As a consequence of mantel upwelling and doming, the Dehui Depression evolved into the Mesozoic rifting and subsidence, including the synrift subsidence and post-rift thermal subsidence. Highlands located in the west and south were the main sediment source areas [86]. The succession deposited during the synrift subsidence includes the Huoshiling (156–145Ma), Shahezi (145–133.9Ma), Yingcheng (133.9–125Ma), and Denglouku (125–116Ma) Formations [56,86] (Figure 2). The Huoshiling-Yingcheng Formations (H-YFs) include clastic floodplain, fluvial, delta, and lacustrine rocks intercalated with pyroclastic and volcanic rocks [56,86], consisting of volcanic, conglomerates, fine sandstones, mudstones, coals and tuff interlayers (Figure 2). The thickness of the H-YFs is generally <1000 m to max 3500 m, mainly 1500–2500 m. Large amounts of tight sandstone and volcanic gases have been discovered in the H-YFs, which are the main targets of unconventional hydrocarbon resources in the Dehui Depression [56,86].

3. Samples and Methods

Firstly, the gases were flushed for 15–20 minutes to remove air contamination, then gas samples were collected directly from the wellheads. Stainless steel cylinders (Φ = 10.0 cm) equipped with two shut-off valves (Pmax = 22.5 MPa) were utilized to contain the gas samples. The inside pressure of the container should be maintained over 5.0 MPa. After the collection, the cylinders were subjected to leakage checks in water. Thirty-six samples from 11 wells in H-YFs were collected for molecular composition analysis. Twenty-seven samples from 11 wells in H-YFs were collected for stable carbon isotope analysis. Two samples from Well DS12 in the J3h and K1sh Formations were analyzed for stable hydrogen isotopes. Eleven mudstone samples from four wells and 23 gas samples from eight wells are collected out for light hydrocarbon analysis.

3.1. Analysis of Molecular Composition

A Trace GC Ultra gas chromatograph (GC) (Thermo Fisher, USA) equipped with flame ionization and thermal conductivity detectors was utilized to ascertain the gas chemical components. The C1–C4 components were isolated utilizing a porous-layer open-tabular capillary column (PLOT, Al2O3 50 m×0.53 mm). The carrier gas was helium (He, flowrate=1 mL/min). At the beginning, the GC oven temperature was 30 °C and kept there for 10 minutes, then raised to 180 °C (rate of 10 °C/min) and held for 20–30 minutes [87,88,89,90,91,92,93].

3.2. Analysis of Stable Carbon and Hydrogen Isotope

A Finnigan Mat Delta S mass spectrometer (Thermo Fisher, USA) interfaced with a HP 5890II chromatograph (HP, USA) can be used to ascertain the stable carbon isotopes. A gas chromatograph (a fused silica capillary column (PLOT Q 30 m×0.32 mm)), with helium as the carrier gas (1 mL/min) was utilized to separate the gas components (C1–C4 and CO2). The gases were converted into CO2 in a combustion interface, then transferred into the mass spectrometer. The GC oven temperature was initially heated from 35 °C to 80 °C (8 °C/min), then heated up to 260 °C (5 °C/min) and held 10 minutes. Gas samples were analyzed in duplicate. The stable carbon isotope values are recorded in the customary “δ” notation in per mil (‰) relative to the Vienna Pee Dee Belemnite (VPDB) standard. The value of ± 0.5‰ should be the reproducibility and analytical precision with respect to the VPDB standard [87,88,89,90,91,92,93]. A Finnigan MAT 253 mass spectrometer with the GC–TC–IRMS method was used to ascertain the stable hydrogen isotope. A chromatographic column (HP-PLOTQ column, 30 m × 0.32 mm × 20 mm) was used to separate the gas components. The accuracy should be ±3‰, and stable hydrogen isotope results are recorded relative to Vienna Standard Mean Ocean Water (VSMOW) [87,88,89,90,91,92,93].

3.3. Analysis of Light Hydrocarbons

A HP5890A gas chromatograph and a PONA capillary column (50 m × 0.25 mm × 0.5 μm) were utilized to analyze the light hydrocarbons. Helium was used as the carrier gas. A container with liquid nitrogen was used to trap the low content of light hydrocarbons. The liquid nitrogen container can be removed after a large volume of gas (15–20 mL) was injected after 20 minutes. Utilizing a FID at 320 °C, the eluted light hydrocarbons were analyzed. At the beginning, the temperature was held at 30 °C for 10 minutes, then heated up to 70 °C (1 °C/min), and then raised to 160 °C (3 °C/min), and finally heated up to 270 °C (5 °C/min) and maintained 20 minutes. An Agilent PONA gas chromatograph was utilized to analyze the light hydrocarbons qualitatively. 53 individual compounds (from isobutane to n-octane) were tested in the experiment. The peak areas of individual compounds on the gas chromatograph were utilized to quantify the light hydrocarbon compounds [87,88,89,90,91,92,93].

4. Results

4.1. Gas Chemical Composition

The gas chemical components in the H-YFs are shown in Table 1 and Figure 3. C1–C5 hydrocarbons the main gases in the natural gas of the Dehui Depression, accounting for 93.23%–99.16% (Avg. = 96.60 %) in volume, while those average values in the J3h, K1sh and K1yc (H-YFs) are 96.49%, 96.84%, and 96.55%, respectively. The non-hydrocarbons (including N2, CO2, H2, and H2S) account for 0–6.75%, with a mean of 3.27%, and the noble gases (He and Ar) account for 0–4.45%, with a mean of 0.13%.
Methane is the main gas among the hydrocarbons, accounting for 74.0%–95.9% (Avg. = 87.4%), and the average methane contents in the J3h, K1sh, and K1yc are 89.2%, 90.0%, and 83.6%, respectively. The contents of C2+ in the J3h, K1sh, and K1yc are 0.8%–21.9% (Avg. = 7.3%), 4.5%–10.4% (Avg. = 6.8%), and 4.8%–19.8% (Avg. = 13.0%), respectively. The dryness coefficients (C1/C1-5) of gaseous hydrocarbons in the J3h, K1sh, and K1yc are 0.78–0.99 (Avg. = 0.93), 0.89–0.95 (Avg. = 0.93), and 0.79–0.95 (Avg. = 0.87), respectively.
The contents of CO2 in the J3h, K1sh, and K1yc are 0–4.77% (Avg. = 1.56%), 0–2.44% (Avg. = 0.90%), and 0.09%–4.46% (Avg. = 0.89%), respectively, and the contents of N2 in the J3h, K1sh, and K1yc are 0–3.20% (Avg. = 1.88%), 0.71%–6.47% (Avg. = 2.28%), and 0.67%–6.47% (Avg. = 2.60%), respectively.
Helium is the predominant noble gas, accounting for 0–4.45% (Avg. = 0.91%), 0.02%–0.04% (Avg. = 0.03%), and 0.02%–0.04% (Avg. = 0.03%), respectively, in the J3h, K1sh, and K1yc of the Dehui Depression.

4.2. Stable Hydrogen and Carbon Isotopes

The stable carbon isotope values for gases in the H-YFs of the Dehui Depression are shown in Figure 4 and Table 2. The δ13C1 values in the J3h, K1sh, and K1yc are −42.5‰–−34.3‰ (Avg. = −38.7‰), −37.0‰–−30.2‰ (Avg. = −34.2‰), and −40.3‰–−30.8‰ (Avg. = −33.7‰), respectively, and the δ13C2 values in the J3h, K1sh, and K1yc are −34.9‰–−27.3‰ (Avg. = −30.9‰), −33.7‰–−25.0‰ (Avg. = −28.0‰), and −26.6‰–−24.7‰ (Avg. = −25.2‰), respectively. The δ13C3 values in the J3h, K1sh, and K1yc are −32.9‰–−27.4‰ (Avg. = −29.1‰), −32.8‰–−22.9‰ (Avg. = −26.4‰), and −24.6‰–−22.8‰ (Avg. = −23.9‰), respectively. The values of stable carbon isotope for CO2 range from −20.4‰ to −13.0‰, with a mean of −16.1‰.
The stable hydrogen isotope values of CH4 in the J3h and K1sh are −211‰ and −216‰, respectively, and those of ethane in the two formations are −213‰ and −215‰, respectively (Table 3).

4.3. Light Hydrocarbons of Natural Gas

The chemical components of the light hydrocarbon fraction are shown in Table 4. C5–C7 compounds are the main components, including heptane (n-C7), methylcyclohexane (MCH), and dimethylcyclopentane (DMCP)). For the C7 compounds in the J3h, the relative contents of ∑DMCP is the highest (16.6% to 59.1%, average of 39.3%), and that of n-C7 and MCH is 20.9%–34.0% (Avg. = 28.3%) and 20.0%–55.1% (Avg. = 32.4%), respectively. For the C7 compounds in the K1sh, the relative contents of ∑DMCP is the highest (17.1% to 47.1%, average of 33.6%), and that of n-C7 and MCH is 24.8%–38.6% (Avg. = 29.9%) and 24.9%–57.5% (Avg. = 36.5%), respectively. For the C7 compounds in the K1yc, the relative abundance of MCH is the highest (39.2% to 68.9%, average of 57.2%), and that of n-C7 and ∑DMCP is 18.0%–44.0% (Avg. = 27.5%) and 13.1%–16.8% (Avg. = 15.4%), respectively.
The fingerprints of light hydrocarbons (C5–C7) of the mudstone and natural gas samples, including 11 mudstone samples and six gas samples, have been listed in Table 5, and 15 fingerprint parameters are selected in this study.

5. Discussion

5.1. Gas Origins

The gas origins and the deposition environments of its parent material can be favorably identified utilizing gas chemical compositions and stable hydrogen and carbon isotopes [1,42,78,79,80,81,82,94]. Generally, a gas can be identified as organic or inorganic type. Dai et al. [41] proposed that: a) for the organic origin, the CO2 content is less than 15% and δ13CCO2 value is <−10‰; b) for the inorganic origin, the CO2 content is over 60% and δ13CCO2 value is >−8‰. Moreover, the thermogenic gas is predominantly characterized by δ13C1<δ13C2<δ13C3<δ13C4 (called normal carbon isotopic distribution pattern), while the negative carbon isotopic distribution pattern (δ13C1>δ13C2>δ13C3>δ13C4) generally indicates the inorganic type of natural gas [3,46,95,96]. In the Dehui Depression, the CO2 contents and δ13CCO2 values of the deep natural gas are mainly less than 5% and lower than −10‰, respectively, and the carbon isotopic distribution patterns of the gas hydrocarbons predominantly show the normal patterns, indicating that the origins of the deep natural gas are predominantly organic sources. However, as shown in Table 1 and Figure 5, parts with reversed δ13C series, including δ13C1<δ13C2<δ13C4<δ13C3, δ13C1<δ13C3<δ13C2 and δ13C2<δ13C1<δ13C3, exist in the study area, suggesting that secondary processes may have happened to the gas.
According to the gas parent materials, the oil-associated gas and coal-derived gas should be the two types. The δ13C2 and δ13C3 mainly reflect the inheritance of parent material, which can be utilized to differentiate between coal-derived gas and oil-associated gas [1,97,98,99]. It is favorably effective to use this method for gas derived from a single source, however, it is more complicated to identify the mixed sources of gas [42,94,100,101]. According to a number of analyses in China, Dai et al. [42] pointed out that gases derived from humic and sapropelic kerogens are characterized by the δ13C2 > −27.5‰ and δ13C2 < −29.0‰, respectively, while the gases of mixed origins are featured by δ13C2 values between −27.5‰ and −29.0‰. The cross-plots of δ13C1-δ13C2 show that the J3h gases are mainly oil-associated gas derived from sapropelic kerogens, with a bit of coal-derived gas, and the K1sh gases are mixed-sources of coal-derived and oil-associated gases, while the K1yc gases are predominantly coal-derived gas derived from the humic kerogens (Figure 6). Moreover, according to the δ13C1-δ13C2-δ13C3 cross-plots for the discrimination of coal-derived and oil-associated gases proposed by Dai [3], the results are similar that the gases in the J3h and K1sh are mainly the mixed-sources of coal-derived and oil-associated gases, while the K1yc gases are predominant coal-derived gases (Figure 7).
Besides, the δ2DCH4 value can be an indicator to determine the deposition environment (δ2DCH4 < −190‰ for marine and lacustrine brackish environments and δ2DCH4 > −170‰ for terrigenous fresh water environments [82,102]), while the δ2DC2H6 value can be used to ascertain the parent material types [81,103,104]. The hydrogen isotope distribution of the J3h gas shows a normal pattern, while that the K1sh gas shows a negative pattern, indicating that the gases in the K1sh may be affected by bacterial action or be mixed-sources of coal-derived and oil-associated gases. Moreover, the gases in the deep formations of Dehui Depression are produced by both terrigenous and lacustrine organic matters.
Generally, the relative contents of heptane (n-C7), MCH, and ∑DMCP are useful parameters to analyze the gas origins [88,105,106,107]. Heptane (n-C7) from algae and bacteria is sensitive to thermal maturation. As a result of a high thermodynamic stability, methylcyclohexane (MCH), mainly derived from components of terrestrial higher plants, is a good gas origin indicator, suggesting that a gas with a high MCH content should be the typical humic-type [106]. On the contrary, a gas with a high abundance of dimethylcyclopentane (DMCP), mainly sourced by aquatic microorganisms, is mainly considered to be of sapropelic-type [108]. In China, the ternary chart of n-C7, MCH and ∑DMCP has been broadly utilized to differentiate the coal-derived and oil-associated gases [106,108]. The J3h and K1sh gases are mainly mixed sources of coal-derived and oil-associated gases, while the K1yc gases are predominantly coal-derived gases, as shown in Figure 8.
Consequently, natural gases in the deep formations of Dehui Depression are predominantly of organic origin. The J3h and K1sh gases are predominantly mixed-sources of coal-derived and oil-associated gases and the proportion of oil-associated gas in the J3h is larger, while the K1yc gases are predominantly coal-derived.

5.2. Genetic Types of Gas Hydrocarbons

Hydrocarbon gases are predominantly viewed to be from organic matter conversion by kerogen thermal-degradation, oil and gas cracking, and even bacterial action [1,2,3,4,5,6,7,8,9,10]. Generally, the δ13C1 values and dryness coefficients, mainly affected by thermal maturity, can be as the effective indexes of gas thermal maturity [42,94,109]. Bernard et al. [110] proposed using the cross-plots of C1/(C2 + C3)-δ13C1 to distinguish the gas origins of both kerogen type and thermal maturity. As shown in Figure 9a,b, the majority of the gases in the H-YFs belong to the thermogenic gas, and the parent materials of the J3h and K1sh gases are the mixed-sources of kerogen type II (sapropelic-humic) and type III (humic), while those of the K1yc gas are mainly kerogen III (humic).
As the extensively studied before, the stable carbon isotopes of hydrocarbon gases have favorable correlations with the thermal maturity of their source rocks [1,40,78,112]. According to the geological observations and numerous statistics in the lacustrine basins of China, Dai [81] has proposed a semi-logarithmic equation between δ13C1 value and vitrinite reflectance (%Ro):
δ13C1 = 15.80logRo−42.20
δ13C1 = 14.12logRo−34.39
Equation (1) is for oil-associated gas and Equation (2) is for coal-derived gas. According to these two equations, the source rock maturity can be estimated (Table 6). The thermal maturities of the J3h gas range from 0.96 %Ro to 2.73 %Ro with a mean of 1.57 %Ro, and those of the K1sh gas are 0.78–2.49 %Ro with a mean of 1.49 %Ro, while those of the K1yc gas are 0.73–1.77 %Ro with an average of 1.37 %Ro. These indicate that these gases were mainly the products of the mature to over-mature source rocks, predominantly generated by thermal degradation and cracking.
James [113] and Jenden et al. [114] proposed that the values of δ13C3-δ13C2 and δ13C2-δ13C1 reduce with the increasing thermal maturity of gas. As shown in Figure 10a, the gases in the H-YFs predominantly belong to the mature gas class (Figure 10a). As shown in Figure 10b, the J3h gas is mainly located on the trend line of kerogen type II with 0.6–1.2 %Ro, and the K1sh gas is mainly located on the trend lines of kerogen type II and type III with 0.7 %Ro and 0.8 %Ro, respectively, while the K1yc gas is mainly located in the trend line of kerogen type III with 0.7–0.9 %Ro, indicating that all the deep gas hydrocarbons are thermogenic and mature gases.
Prinzhofer and Huc [43] established the cross-plots of ln(C2/C3) vs. ln(C1/C2) to distinguish gases generated from both primary degradation (also called primary cracking) and secondary cracking. The C1/C2 ratios rise gradually in the primary degradation and mainly keep constant in the secondary cracking, while the C2/C3 ratios mainly keep constant in the primary degradation and rise dramatically in the secondary cracking. The gases in the J3h are mainly sourced from kerogen type II and type III and generated by the primary kerogen degradation and secondary oil cracking, and the gases in the K1sh are mainly sourced by kerogen type III and generated by primary kerogen degradation, while the K1yc gases are mainly sourced by kerogen type II and type III and generated by primary kerogen degradation (Figure 11).
Lorant et al. [111] established the cross-plots of C2/C3 vs. δ13C2−δ13C3 to distinguish gases generated by primary degradation and secondary cracking. The gases in the J3h and K1sh mainly plot in the secondary oil cracking area, with a bit in the primary degradation area, while the gases in the K1yc are located in the primary degradation area. Consequently, the gases in the deep formations of Dehui Depression are predominantly thermogenic types. The gases in the J3h and K1sh are mainly generated by primary kerogen degradation and secondary oil cracking, while the gases in the K1yc are mainly produced by primary kerogen degradation.

5.3. Gas-Source Correlation

Although many features of the Cretaceous petroleum system of the SLB are known, the gas-source correlation in the deep formations are not fully understood. Huang et al. [9], Zhang et al. [72], Chen [77] and Shen and Liang [83] have proposed that the mudstones in J3h, K1sh, and K1yc, with high organic abundance (TOC = ~2.5 wt.%), high thermal maturity (Ro = ~1.5–2.0%) and type II-III kerogens, are the main source rocks for gas in the deep formations of the SLB. The main deficiency in the understanding of the multi-source, multi-reservoir gas system in the deep formations is gas-source correlation. Considering the huge lateral extension of the basin and sets of vertically-developed source rocks and reservoir rocks, the gas-source correlation is challenging. A recent attempt, which tried to determine possible source rocks for the J3h gases using their chemical components and stable carbon isotopes [77], showed that the J3h gas was mainly sourced by the J3h mudstones. However, the sources of the gases in the K1sh and K1yc are still unknown.
Generally, the gas chemical components and stable carbon isotopes are influenced by the parent materials, thermogenic actions, migration, and bacterial actions. As shown in Figure 3 and Figure 4, the C1 contents and dryness coefficients rise with the increasing burial depth, while the C2+ contents reduce with the increasing burial depth, indicating that the gases in the deep formations were predominantly generated by thermogenic actions and accumulated in/approaching the source rocks. Besides, corresponding to the results, the density of gases in the deep formations decrease with the increasing burial depth. The results suggest that the gases in the deep formations should be mainly sourced by the J3h and K1sh mudstones, or just the J3h mudstones.
The relative contents of light hydrocarbon components with similar boiling points can be the fingerprints to ascertain the gas genetic type and access gas-source correlation. The fingerprint trends of the light hydrocarbons in the mudstones of the J3h and K1sh do not display any obvious differences, while those in the K1yc show some differences (Figure 12). In Figure 12a,b, the fingerprint trends of the gases in the middle J3h of Well DS11 and the lower J3h of Well DS12 show high coherence with those of the mudstone samples in the J3h of the Huajia Sag, indicating that the gases accumulated in the low-middle J3h are predominantly sourced by the J3h source rocks, corresponding to the results proposed by Shen and Liang (2015) [77]. In Figure 12c,d, about 70% of the total fingerprint parameters of the gases in the upper J3h of Well DS12 and the K1sh of Well DS15 show similar trends with those of the mudstones in the J3h and K1sh, suggesting that the gases in the K1sh and the upper J3h are mainly produced by the mudstones both in the J3h and K1sh. In Figure 12e,f, less than 50% of the total fingerprint parameters of the gases in the J3h of Well DS19 and the K1yc of Well DS17 show similar trends with those of the mudstones in the deep formations of the Huajia Sag, indicating that the gases in the Baojia and Nong’annan sags are not sourced by the mudstones of the deep formations in the Huajia Sag. Combined with the geological conditions in Dehui Depression and the gas chemical components and density, the gases in the K1yc may be derived from the three sets of source rocks (J3h, K1sh, and K1yc), or one or two of them through the vertical faults shown in Figure 1.
Rooney et al. [44] proposed that if the alkane gas comes from a single source, a linear correlation of carbon number (1/n) vs. δ13Cn exists. The slope changes of regression line can ascertain the gas-mixing between different types at different thermal-maturity stages, and also indicate the bio-genetic gas and methane seepage [44]. In Figure 5d, the trends of 1/n vs. δ13Cn of the J3h alkane gases in the Huajia sag mainly show linear relationships with bits of nonlinear relationships and can be divided into three groups (Groups A, B, and C), indicating the J3h gases may have two types (coal-derived and oil-associated gases) with two sources (maybe both the J3h and the K1sh mudstones). According to the Figure 5e, the trends of 1/n vs. δ13Cn of the alkane gases in the K1sh of the Huajia (Well DS15 and Well N101) and Lanjia (Well DS39-3) sags mainly indicate predominant linear relationships and can be divided into three groups (Groups D, E, and F), and the slopes of the samples in each sag are similar. The Group D is similar with the Group B, and the Group E is similar with the Group A, and the Group F is similar with the Group C. Combined with the gas origins and genic types studied above (Section 5.1 and Section 5.2), these three groups (Group D, E, and F) suggest that the two types gases (coal-derived and oil-associated gases) derived from two sources (two sags) may be mixed. Additionally, in Figure 5f, the trends of 1/n vs. δ13Cn of the alkane gases in the K1yc of the Huajia (Well DS21) and Lanjia (Well DS35, Well H3, and Well H4) sags mainly indicate predominant linear relationships and can be divided into two groups (Group G and H). The Group G is similar with the Group A, and the Group H is similar with the Group C, suggesting that: 1) the two types (oil-associated and coal-derived) of gases may be mixed in the K1yc; 2) the gases were derived from two sources (two sags) with one-type gas; and 3) the gases of two stages (mature or charging) were mixed. According to the study above (Section 5.1), the gases in the K1yc are mainly the coal-derived gases and came from the Baojia sag, so the two-group samples (Group F and G) suggest that the gas samples are mainly controlled by the mixed-sources of two mature or charging stages.
According to the geological and geochemical analyses, as shown in Figure 13 and Figure 14, the gas reservoirs in Well DS17 are mainly distributed in the upper K1yc, and the lithology of the K1yc is predominantly igneous rocks (dacite) in the location of Well DS17. The gas reservoirs in Well DS11 are mainly distributed in the middle of J3h and K1sh, and the reservoir beds are mainly igneous rocks in the K1sh and sandstones in the J3h. The source rocks of both Wells DS17 and DS11 are mainly located in the J3h–K1sh, and the geochemical characters mainly suggest the good to excellent source rock potentials (Figure 13). The gas reservoirs in the J3h of Well DS11 are mainly sourced by the underlying J3h source rocks through the faults, and the gas reservoirs in the K1sh of Well DS11 may be sourced by both underlying J3h and overlying K1sh source rocks through faults and carrier beds, and the gas reservoirs are mainly sourced by the source rocks in the Huajia sag (Figure 14a). The gas reservoirs in the K1yc of Well DS17 are mainly sourced by the underlying J3h and K1sh source rocks through faults and carrier beds, and the gas reservoirs are mainly sourced by the source rocks in the Baojia sags (Figure 14b).
Consequently, the gases in the lower-middle J3h are predominantly derived from the J3h mudstones, and the gases in the K1sh and the upper J3h are mainly the mixed-sources of both the J3h and the K1sh mudstones, while the gases in the K1yc are mainly derived from either the J3h mudstones or the K1sh mudstones, or both the two sets of mudstones. Moreover, the gas accumulations in different sags are mainly controlled by the J3h and K1sh mudstones developed in the sags where the gases accumulated, indicating that the gas migration with a short distance was the main migration type in the deep formations of SLB.

6. Conclusions

Integrated geochemical study suggests the methane contents and stable carbon isotopes and gas dryness coefficients increase with the increasing burial depth in the Dehui Depression, lacustrine SLB. The δ13C series mainly show normal carbon isotopic distribution pattern, with parts of reversal. The gases in the deep formations (generally the H-YFs (156–125Ma)) of the Dehui Depression are predominantly organic and thermogenic. According to the determination charts utilizing gas components and stable carbon isotopes and the gas thermal maturity calculated by equation of δ13C1-Ro%, the gases in the J3h (156–145 Ma) and K1sh (145–133.9 Ma) are mixed-sources of kerogen thermal degradation and oil secondary cracking, while the gases in the K1yc (133.9–125 Ma) are predominantly derived from kerogen thermal degradation.
According to the stable carbon isotopes and fingerprints of light hydrocarbons (C5-7), the gases in the lower-middle J3h are sourced by the J3h mudstones, and the gases in the K1sh and the upper J3h are mainly sourced by the J3h and K1sh mudstones, while those in the K1yc are mainly sourced by either the J3h or the K1sh mudstones. In addition, the gas reservoirs in different sags are mainly sourced by the J3h and K1sh source rocks developed in the sags where the gas reservoirs were found, indicating the proximal-source accumulation. These indicate that the gas migration with a short distance was the main migration type in the deep formations of SLB.

Author Contributions

Z.X. and B.P. contributed equally to this work Y.F. and L.L. provided the funding C.F. made the formal analysis M.S. and K.J. provided the data and samples resources K.W. and Y.C. made the validation.

Funding

This study was jointly supported by the National Natural Science Foundation of China [grant number 41372143], the Research Fund for the Doctoral Program of Higher Education of China [grant number 20130007110002], the National Construction of High-quality University Projects of Graduates from China Scholarship Council (CSC) [NO. 201806440137], the Scientific and Technology Innovation Fund Supported by Coal Mining Research Branch [grant number KJ-2019-TDKCMS-03], and the project of Shaanxi Provincial Land Engineering Construction Group (grand number DJNY2019-23).

Acknowledgments

The authors thank the Research Institute of Petroleum Exploration and Development, Jilin Oilfield Branch, CNPC for providing basic data and the permission to publish the results.

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

The compounds and abbreviations of the light hydrocarbons are as follows:
CompoundAbbreviation
IsopentaneiC5
n-PentanenC5
n-HexanenC6
n-HeptanenC7
MethylcyclohexaneMCH
2,2-Dimethylbutane2,2-DMB
2-Methylpentane2-MP
3-Methylpentane2-MP
2,2-Dimethylpentane2,2-DMP
3-Methylhexane3-MH
CyclohexaneCH
MethylcyclopentaneMCP
1,1-Dimethylcyclopentane1,1-DMCP
1,trans3-Dimethylcyclopentane1,t3-DMCP
1,trans2-Dimethylcyclopentane1,t2-DMCP
1,cis3-Dimethylcyclopentane1,c3-DMCP
MCH/(n-Heptane+MCH+∑DMCP)MCH Index
2,3-Dimethylhexane2,3-DMH
3,4-Dimethylhexane3,4-DMH
2-Methylheptane2-MHp
3-Methylheptane3-MHp
4-Methylheptane4-MHp

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Figure 1. Location of the SLB in China (a) (Modified from [85] Ge et al., 2010). Tectonic units of the SLB and the location of Dehui Depression in SLB (b). Tectonic units of the Dehui Depression (c). Geological cross section in the Dehui Depression (d), location of the section is shown in Figure 1c.
Figure 1. Location of the SLB in China (a) (Modified from [85] Ge et al., 2010). Tectonic units of the SLB and the location of Dehui Depression in SLB (b). Tectonic units of the Dehui Depression (c). Geological cross section in the Dehui Depression (d), location of the section is shown in Figure 1c.
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Figure 2. Integrated stratigraphic column in the Dehui Depression, SLB (modified after [56]).
Figure 2. Integrated stratigraphic column in the Dehui Depression, SLB (modified after [56]).
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Figure 3. Relationships between the burial depth, the contents of chemical components and density of the natural gas in the deep formations of the Dehui Depression, SLB. (a) for CH4; (b) for C2+; (c) for dryness coefficient; (d) for CO2; (e) for N2; (f) for density.
Figure 3. Relationships between the burial depth, the contents of chemical components and density of the natural gas in the deep formations of the Dehui Depression, SLB. (a) for CH4; (b) for C2+; (c) for dryness coefficient; (d) for CO2; (e) for N2; (f) for density.
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Figure 4. Relationships between the burial depth and the stable carbon isotopes of the natural gas in the deep formations of the Dehui Depression, SLB. (a) for δ13C1; (b) for δ13C2; (c) for δ13C3.
Figure 4. Relationships between the burial depth and the stable carbon isotopes of the natural gas in the deep formations of the Dehui Depression, SLB. (a) for δ13C1; (b) for δ13C2; (c) for δ13C3.
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Figure 5. Carbon isotope series (a–c) and relationships between carbon number 1/n and δ13Cn (d–f) of natural gases in the deep formations of the Dehui Depression, SLB.
Figure 5. Carbon isotope series (a–c) and relationships between carbon number 1/n and δ13Cn (d–f) of natural gases in the deep formations of the Dehui Depression, SLB.
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Figure 6. δ13C1-δ13C2 cross-plots for the determination of gas origins in the deep formations of the Dehui Depression, SLB.
Figure 6. δ13C1-δ13C2 cross-plots for the determination of gas origins in the deep formations of the Dehui Depression, SLB.
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Figure 7. Cross-plots of δ13C1-δ13C2-δ13C3 indicating the gases origins in the deep formations of the Dehui Depression, SLB.
Figure 7. Cross-plots of δ13C1-δ13C2-δ13C3 indicating the gases origins in the deep formations of the Dehui Depression, SLB.
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Figure 8. Ternary diagram showing C7 light hydrocarbons in natural gas in the deep formations of the Dehui Depression, SLB (modified after [108]).
Figure 8. Ternary diagram showing C7 light hydrocarbons in natural gas in the deep formations of the Dehui Depression, SLB (modified after [108]).
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Figure 9. Cross-plots of gas contents and stable carbon isotopes showing the gases origins in the deep formations of the Dehui Depression, SLB. (a) is the cross-plots of δ13C1 vs. C1/(C2 + C3) (modified after [45,110]) and (b) is the cross-plots of δ13C2−δ13C3 vs. C2/C3 (modified after [111]).
Figure 9. Cross-plots of gas contents and stable carbon isotopes showing the gases origins in the deep formations of the Dehui Depression, SLB. (a) is the cross-plots of δ13C1 vs. C1/(C2 + C3) (modified after [45,110]) and (b) is the cross-plots of δ13C2−δ13C3 vs. C2/C3 (modified after [111]).
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Figure 10. Cross-plots of ethane and propane stable carbon isotopes indicating the thermal-maturity of gases in the deep formations of the Dehui Depression, SLB. (a) is the cross-plots of δ13C2−δ13C1 vs. δ13C3−δ13C2 (modified after [113,114]) and (b) is the cross-plots of δ13C2 vs. δ13C3 (modified after [98]).
Figure 10. Cross-plots of ethane and propane stable carbon isotopes indicating the thermal-maturity of gases in the deep formations of the Dehui Depression, SLB. (a) is the cross-plots of δ13C2−δ13C1 vs. δ13C3−δ13C2 (modified after [113,114]) and (b) is the cross-plots of δ13C2 vs. δ13C3 (modified after [98]).
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Figure 11. Molecular proportions ln(C1/C2) vs. ln(C2/C3) for kerogen- and oil-cracking gases in the deep formations of the Dehui Depression, SLB (modified after Prinzhofer and Huc [43]).
Figure 11. Molecular proportions ln(C1/C2) vs. ln(C2/C3) for kerogen- and oil-cracking gases in the deep formations of the Dehui Depression, SLB (modified after Prinzhofer and Huc [43]).
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Figure 12. The fingerprints trends of the gas and source rocks in the deep formations of the Dehui Depression, SLB, indicating the gas-source correlation. (a) for Well DS11, 2553.00m, gas sample; (b) for Well DS12, 3328.90m, gas sample; (c) for Well DS12, 3067.00m, gas sample; (d) for Well DS15, 2578.00m, gas sample; (e) for Well DS17, 2273.50m, gas sample; (f) for Well DS19, 2295.50m, gas sample.
Figure 12. The fingerprints trends of the gas and source rocks in the deep formations of the Dehui Depression, SLB, indicating the gas-source correlation. (a) for Well DS11, 2553.00m, gas sample; (b) for Well DS12, 3328.90m, gas sample; (c) for Well DS12, 3067.00m, gas sample; (d) for Well DS15, 2578.00m, gas sample; (e) for Well DS17, 2273.50m, gas sample; (f) for Well DS19, 2295.50m, gas sample.
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Figure 13. Comprehensive geochemical columns of the deep formations in the Dehui Depression, SLB. ((a) is for Well DS 17 and (b) is for Well DS 11.) (The data in the columns are provided by the Research Institute of Petroleum Exploration and Development, Jilin Oilfield Branch, CNPC, which are unpublished.).
Figure 13. Comprehensive geochemical columns of the deep formations in the Dehui Depression, SLB. ((a) is for Well DS 17 and (b) is for Well DS 11.) (The data in the columns are provided by the Research Institute of Petroleum Exploration and Development, Jilin Oilfield Branch, CNPC, which are unpublished.).
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Figure 14. Sketch profiles for the gas source and migration in the deep formations of the Dehui Depression, SLB. ((a) is for the profile crossing Well DS 11 and (b) is for the profile crossing Well DS 17.) (The seismic profiles are provided by the Research Institute of Petroleum Exploration and Development, Jilin Oilfield Branch, CNPC, which are unpublished.).
Figure 14. Sketch profiles for the gas source and migration in the deep formations of the Dehui Depression, SLB. ((a) is for the profile crossing Well DS 11 and (b) is for the profile crossing Well DS 17.) (The seismic profiles are provided by the Research Institute of Petroleum Exploration and Development, Jilin Oilfield Branch, CNPC, which are unpublished.).
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Table
Table 1. Chemical components and density of the natural gas in the H-YFs of the Dehui Depression, SLB.
Table 1. Chemical components and density of the natural gas in the H-YFs of the Dehui Depression, SLB.
WellLayerDepth (m)Density (kg/m3)Dryness CoefficientRelative Contents of the Natural gas (%)
CH4C2H6C3H8iC4H10nC4H10iC5H12nC5H12N2CO2H2H2SHeAr
DS11Huoshiling2551.50/0.8883.90.931.220.491.360.956.69////4.45/
DS11Huoshiling2553.000.640.9388.74.171.250.210.230.530.523.121.26////
DS11Huoshiling2556.000.620.9390.54.781.150.200.190.090.061.691.31////
DS11Huoshiling2560.000.620.9490.74.521.030.180.180.090.071.991.29////
DS11Huoshiling2562.000.630.9489.74.191.110.230.250.170.262.861.28////
DS12Huoshiling3067.00/0.9491.74.061.060.190.220.110.410.811.390.01/0.02/
DS12Huoshiling3328.50/0.9492.13.760.980.180.200.110.350.851.410.01/0.02/
DS12Huoshiling3328.90/0.9995.90.700.05///0.021.302.04//0.02/
DS2Huoshiling3030.550.670.9892.81.750.270.020.02//0.374.77////
N101Huoshiling2520.100.590.9693.53.440.74////1.840.46////
N101Huoshiling3044.000.610.9490.24.401.450.150.20//2.800.77////
N103Huoshiling2335.000.720.7876.114.415.452.02///1.290.77////
N103Huoshiling3011.000.690.9186.78.29/////3.201.86////
DS19Huoshiling2295.50/0.8985.66.642.280.330.470.150.512.341.660.01/0.04/
DS11Shahezi2368.50/0.8985.76.652.270.330.470.150.512.251.580.01/0.04/
DS11Shahezi2368.50/0.9592.53.450.690.200.130.080.212.490.140.08/0.03/
DS11Shahezi2369.50/0.9594.03.900.720.210.130.080.120.71/0.10/0.02/
DS11Shahezi2370.50/0.8985.66.642.280.330.470.150.512.341.660.01/0.04/
DS15Shahezi2578.00/0.9291.26.041.330.150.06//1.140.050.01/0.02/
DS15Shahezi2578.00/0.9291.26.041.320.140.06//1.130.050.01/0.02/
N101Shahezi2354.40/0.9487.23.390.680.200.130.091.546.470.200.08/0.03/
N101Shahezi2354.500.620.9590.73.331.300.320.28//1.612.44////
N101Shahezi2354.900.600.9591.93.261.08/0.16//2.371.20////
DS12Yingcheng2662.380.710.8379.09.584.490.820.920.270.323.770.81////
DS12Yingcheng2664.750.700.8380.19.754.280.750.890.240.273.230.52////
DS17Yingcheng2249.00/0.9487.23.390.680.200.130.091.546.470.200.08/0.03/
DS17Yingcheng2249.00/0.9592.53.450.690.200.130.080.212.490.140.08/0.03/
DS17Yingcheng2273.50/0.9594.23.690.720.210.130.080.120.71/0.10/0.02/
DS2Yingcheng2368.500.710.9085.36.071.980.440.550.190.300.674.46////
H12Yingcheng2163.500.730.7974.012.154.771.241.050.260.326.030.16////
H3Yingcheng1971.500.710.8480.77.554.391.231.040.410.522.192.01////
H3Yingcheng1971.700.700.8582.37.644.101.180.990.390.491.881.02////
H3Yingcheng1971.700.690.8583.67.674.151.191.000.390.480.920.62////
H5Yingcheng1665.200.690.8582.68.063.710.950.900.350.482.680.31////
H5Yingcheng1665.200.670.8684.48.093.390.820.860.320.441.570.09////
H5Yingcheng1897.000.720.8280.78.695.051.471.260.540.781.200.30////
Table
Table 2. Stable carbon isotopes of the natural gas in the H-YFs of the Dehui Depression, SLB.
Table 2. Stable carbon isotopes of the natural gas in the H-YFs of the Dehui Depression, SLB.
Sample no.WellLayerDepth (m)δ13CO2 (‰)δ13CH4 (‰)δ13C2H6 (‰)δ13C3H8 (‰)δ13iC4H10 (‰)δ13nC4H10 (‰)
1DS11Huoshiling2553.00/−34.3−27.3−28.3//
2DS12Huoshiling3328.90/−37.3−34.8−33.0//
3DS12Huoshiling3328.50/−35.3−34.9−32.9//
4N103Huoshiling2336.00/−38.0−29.9−28.4//
5N103Huoshiling2337.20/−42.4−30.1−28.2−26.9−25.4
6N103Huoshiling2335.50/−42.5−30.2−28.1//
7N103Huoshiling2335.00/−40.4−30.5−27.9//
8N103Huoshiling2335.20/−40.3−30.3−27.9−26.8/
9N103Huoshiling2336.20/−37.8−29.8−27.4−26.3−26.3
10DS15Shahezi2578.50/−32.5−25.4−23.5//
11DS15Shahezi2578.00/−32.5−25.3−23.5//
12DS39-3Shahezi2232.40/−35.9−25.0−22.9//
13DS39-3Shahezi2232.00/−35.9−25.2−22.9//
14N101Shahezi2354.90/−37.0////
15N101Shahezi2354.50/−35.9−33.7−32.8//
16N101Shahezi2354.40/−36.9−33.7−32.8−31.7/
17N101Shahezi2022.46/−33.7////
18N101Shahezi2021.46/−30.2////
19N104Shahezi1935.50/−31.4////
20DS21Yingcheng1756.50/−30.8−24.7−24.6//
21DS21Yingcheng1756.00/−30.9−24.8−24.6//
22DS35Yingcheng1450.00−13.0−36.4−26.6−23.9//
23H3Yingcheng1971.50/−34.5−25.3−22.8//
24H3Yingcheng1971.70−20.4−34.6−25.3−22.8−23.1/
25H4Yingcheng1508.70−14.9−31.1−24.8−24.2//
26H4Yingcheng1508.50/−31.0−24.9−24.1//
27N102Yingcheng1785.00/−40.3////
Table
Table 3. Stable hydrogen isotopes of the natural gas in the H-YFs of the Dehui Depression, SLB.
Table 3. Stable hydrogen isotopes of the natural gas in the H-YFs of the Dehui Depression, SLB.
WellLayerDepth (m)δD ‰(VSMOW)
C1C2C3iC4nC4
DS12Shahezi3067.00−211−213−219//
DS12Huoshiling3328.90−216−215−192//
Table
Table 4. Relative contents of light hydrocarbons (C5-7) in the natural gases of the deep formations in the Dehui Depression, SLB.
Table 4. Relative contents of light hydrocarbons (C5-7) in the natural gases of the deep formations in the Dehui Depression, SLB.
WellLayerDepth (m)Relative Contents of Light Hydrocarbons (C5–7) (%)
n-C7∑DMCPMCH
DS16Huoshiling2290.0020.959.120.0
DS16Huoshiling2291.0024.155.020.8
DS16Huoshiling3060.0032.047.120.8
DS16Huoshiling3080.0028.348.023.7
DS16Huoshiling3065.0027.049.323.7
DS12Huoshiling3335.0030.244.924.9
DS12Huoshiling3067.0026.948.125.0
DS12Huoshiling3340.0030.243.126.7
DS12Huoshiling3328.9034.034.131.9
DS19Huoshiling2295.5025.529.145.4
DS11Huoshiling2556.0031.716.651.7
DS11Huoshiling2553.0029.718.651.7
DS11Huoshiling2562.0027.617.355.1
DS2Shahezi2844.5028.047.124.9
DS2Shahezi2845.5029.044.127.0
DS12Shahezi2393.0029.842.627.6
DS12Shahezi2396.0033.736.729.6
DS12Shahezi2400.0038.628.832.6
DS15Shahezi2578.0024.819.156.1
DS15Shahezi2578.0025.517.157.4
DS17Yingcheng2273.5044.016.839.2
DS13Yingcheng1656.5020.416.163.5
DS13Yingcheng1658.5018.013.168.9
Table
Table 5. Fingerprint parameters of light hydrocarbons (C5–7) in the natural gases of the deep formations in the Dehui Depression, SLB.
Table 5. Fingerprint parameters of light hydrocarbons (C5–7) in the natural gases of the deep formations in the Dehui Depression, SLB.
Sample number1234567891011abcdef
Sample typeRockRockRockRockRockRockRockRockRockRockRockGasGasGasGasGasGas
WellDS12DS2DS2DS12DS12DS11DS12DS12DS12DS16DS16DS11DS12DS12DS15DS17DS19
LocationHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaHuajiaBaojiaNong’annan
LayerK1ycK1shK1shK1shK1shJ3hJ3hJ3hJ3hJ3hJ3hJ3hJ3hJ3hK1shK1ycJ3h
Depth (m)1972.002453.702459.052329.382337.002640.502867.503264.503381.002593.002664.002553.003328.903067.002578.002273.502295.50
iC5/nC52.111.101.220.680.701.281.141.061.241.571.181.541.121.984.123.171.43
MCH/nC72.621.241.901.531.601.941.931.052.052.271.831.611.960.873.102.221.76
2,2-DMB/2-MP0.130.140.200.060.060.090.110.140.121.300.130.140.250.400.541.670.25
2,2-DMB/3-MP0.230.250.320.110.100.140.190.220.200.530.200.180.390.640.852.490.43
2-MP/3-MP1.761.721.651.711.681.621.711.591.650.411.601.341.581.611.591.491.75
2-MP/nC60.770.660.770.410.410.490.580.320.640.240.540.490.681.031.501.920.89
2-MP/3-MH2.001.381.661.941.761.821.871.041.500.271.081.671.942.742.833.203.18
nC6/CH0.621.891.322.191.961.051.452.021.200.991.351.401.063.791.142.222.28
MCP/MCH0.200.280.300.290.260.290.300.230.230.140.190.540.520.660.320.110.51
1,t3-DMCP/1,t2-DMCP0.550.670.670.670.740.670.680.620.640.420.470.660.750.620.420.333.30
MCH Index0.630.490.570.530.540.580.570.460.580.590.560.520.550.390.640.570.45
nC6/(MCP+2,2-DMP)1.142.111.672.832.681.451.722.791.621.231.731.621.392.621.131.821.91
3-MH/(1,1-DMCP+1,c3-DMCP)1.303.953.062.091.861.491.902.641.892.122.262.232.174.872.474.950.72
2,3-DMH/2-MHp0.330.150.000.120.140.170.220.090.200.380.300.310.270.320.400.760.34
(4-MHp+3,4-DMH)/3-MHp0.660.430.380.210.200.310.400.440.390.620.650.390.700.320.401.000.49
Table
Table 6. Thermal-maturity of the natural gas calculated by the formula δ13C1-Ro in the Dehui Depression, SLB.
Table 6. Thermal-maturity of the natural gas calculated by the formula δ13C1-Ro in the Dehui Depression, SLB.
Sample no.WellLayerDepth (m)δ13CH4 (‰)δ13C2H6 (‰)δ13C3H8 (‰)Gas TypeRo (%)
1DS11Huoshiling2553.00−34.3−27.3−28.3Coal-derived1.01
2DS12Huoshiling3328.90−37.3−34.8−33.0Oil-associated2.04
3DS12Huoshiling3328.50−35.3−34.9−32.9Oil-associated2.73
4N103Huoshiling2336.00−38.0−29.9−28.4Oil-associated1.85
5N103Huoshiling2337.20−42.4−30.1−28.2Oil-associated0.97
6N103Huoshiling2335.50−42.5−30.2−28.1Oil-associated0.96
7N103Huoshiling2335.00−40.4−30.5−27.9Oil-associated1.30
8N103Huoshiling2335.20−40.3−30.3−27.9Oil-associated1.32
9N103Huoshiling2336.20−37.8−29.8−27.4Oil-associated1.90
10DS15Shahezi2578.00−32.5−25.4−23.5Coal-derived1.35
11DS15Shahezi2578.00−32.5−25.3−23.5Coal-derived1.35
12DS39-3Shahezi2232.40−35.9−25.0−22.9Coal-derived0.78
13DS39-3Shahezi2232.00−35.9−25.2−22.9Coal-derived0.78
15N101Shahezi2354.50−35.9−33.7−32.8Oil-associated2.49
16N101Shahezi2354.40−36.9−33.7−32.8Oil-associated2.17
20DS21Yingcheng1756.00−30.8−24.7−24.6Coal-derived1.77
21DS21Yingcheng1756.00−30.9−24.8−24.6Coal-derived1.74
22DS35Yingcheng1450.00−36.4−26.6−23.9Coal-derived0.73
23H3Yingcheng1971.50−34.5−25.3−22.8Coal-derived0.98
24H3Yingcheng1971.70−34.6−25.3−22.8Coal-derived0.97
25H4Yingcheng1508.70−31.1−24.8−24.2Coal-derived1.70
26H4Yingcheng1508.50−31.0−24.9−24.1Coal-derived1.71

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Xu, Z.; Peng, B.; Feng, Y.; Liu, L.; Fang, C.; Shao, M.; Jia, K.; Wu, K.; Chen, Y. Characteristics and Origins of the Natural Gas and Implications for Gas-Source Correlation in Deep Formations of the Songliao Basin, NE China. Energies 2019, 12, 4641. https://doi.org/10.3390/en12244641

AMA Style

Xu Z, Peng B, Feng Y, Liu L, Fang C, Shao M, Jia K, Wu K, Chen Y. Characteristics and Origins of the Natural Gas and Implications for Gas-Source Correlation in Deep Formations of the Songliao Basin, NE China. Energies. 2019; 12(24):4641. https://doi.org/10.3390/en12244641

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Xu, Zhengjian, Biao Peng, Yanjun Feng, Luofu Liu, Chao Fang, Mingli Shao, Kexin Jia, Kangjun Wu, and Yingying Chen. 2019. "Characteristics and Origins of the Natural Gas and Implications for Gas-Source Correlation in Deep Formations of the Songliao Basin, NE China" Energies 12, no. 24: 4641. https://doi.org/10.3390/en12244641

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