Origin, Migration, and Characterization of Gas in the Xinglongtai Area, Liaohe Subbasin (Northeast China): Insight from Geochemical Evidence and Basin Modeling
by
,
Sibo Yang
1
,
Meijun Li
1,2,*,
Yanshan Wang
3,
Hong Xiao
1,
Shuangquan Huang
3,
Wujiang Kang
3 and
Fangzheng Wang
4 1
National Key Laboratory of Petroleum Resources and Engineering, College of Geosciences, China University of Petroleum, Beijing 102249, China
2
College of Petroleum, China University of Petroleum-Beijing at Karamay, Karamay 834000, China
3
Research Institute of Petroleum Exploration and Development, Liaohe Oilfield Company, PetroChina, Panjin 124010, China
4
No. 3 Gas Production Plant, Changqing Oilfield Company, PetroChina, Ordos 017000, China
*
Author to whom correspondence should be addressed.
Energies 2023, 16(18), 6429; https://doi.org/10.3390/en16186429
Submission received: 31 July 2023
/
Revised: 16 August 2023
/
Accepted: 1 September 2023
/
Published: 5 September 2023
(This article belongs to the Special Issue Formation and Distribution of Conventional and Unconventional Oil and Gas)
Abstract
:Buried hill zones in the rift basins have a significant impact on the enrichment of natural gas resources, and this is of great significance for exploration and development. This study aims to unravel the origins, migration, and dynamic accumulation process of natural gas in the Xinglongtai structural belt, Liaohe Subbasin. A comprehensive geological and geochemical analysis was performed on source rocks and natural gas samples from various geological structures within the Xinglongtai structural belt. Moreover, basin modeling techniques were employed to trace the genesis and migration of natural gas, offering an in-depth understanding of the dynamic process of accumulation. We identified the Fourth Mbr (Es4) and Third Mbr (Es3) of the Shahejie Fm as the main source rocks in the Qingshui and Chenjia Sags. The Es4, primarily Shallow Lacustrine Mudstones, contributed mainly type II organic matter, while the Es3, consisting of Nearshore Subaqueous Fan and Deep Lacustrine Mudstones, contributed mainly type III and type II organic matter, respectively. Two distinct hydrocarbon accumulation systems were observed, one inside and one outside the buried hills. The system outside the buried hill is governed by a complex fault system within the lacustrine basin, resulting in dual-source directions, dual-source rock types, two migration phases, and late-stage accumulation. In contrast, the system within the buried hill primarily involves reservoirs nested in the basement, exhibiting dual-source directions, dual-source rock types, a single migration phase, and early-stage charging. The understanding of this interplay, alongside dynamic simulation of generation, migration, and accumulation, can provide valuable insights for predicting natural gas distribution and accumulation patterns in terrestrial faulted lacustrine basins. This knowledge can guide more effective exploration and development strategies for natural gas.
1. Introduction
A buried hill refers to the geological structure where ancient topographical highs are buried under younger strata unconformably. In rift basins, intense fault activity can lead to differential subsidence of the basement, forming ancient, buried hill structures [1]. These buried hill zones in rift basins are often highly prolific in oil and gas due to the favorable conditions and spaces they provide for the accumulation of hydrocarbons [2,3].
The Xinglongtai buried hill large-scale oil and gas field in the central and southern parts of the Western Depression, Liaohe Subbasin, located in the Bohai Bay Basin, is a quintessential onshore overburden-type buried hill oil field [4,5,6,7]. It is nestled among two critical sags, which facilitates an abundant supply of oil and gas to this area. Yet, while the predominant belief is that the substantial quantity of humic-type gas generated in the inner Xinglongtai buried hill originates from the Shahejie Formation (Fm) source rocks, it should be noted that these source rocks mainly consist of type II organic matter, which includes contributions from both sapropelic and mixed sapropelic–humic components [7,8,9]. This fact presents a contradiction since humic-type gas is typically associated with humic organic matter [10]. In addition, the hydrocarbon accumulation conditions of gas fields in the inner Xinglongtai buried hill are relatively stringent due to poor reservoir development and strict requirements for hydrocarbon charging and migration [3,4,11,12]. The accumulation of the natural gas reservoir of the Xinglongtai structural belt (inner and outer buried hill) has the characteristics of multiple sources (multiple directions), multi-period hydrocarbon supply, multi-channel conduction, multi-layer system accumulation, multi-genetic trapping, and multi-stage accumulation [6]. However, specific research on the coupling relationship between the various accumulation elements of the Xinglongtai structural belt natural gas field at different periods is lacking. As a result, this poses a challenge for explorers in reasonably estimating the remaining exploration potential.
This study aims to clarify the origins and evolutionary process of natural gas by identifying the changes in the types of organic matter found in the source rocks of the Xinglongtai structural belt hydrocarbon supply sags. Through studying the dynamic mechanisms of natural gas accumulation using geochemical evidence and basin modeling techniques, our objective is to gain a more comprehensive understanding of the accumulation process and evolutionary history of the gas field in the Xinglongtai structural belt. This research will contribute to an understanding of the potential of natural gas resources in this area, providing a scientific basis for future exploration and development of the gas field in the Xinglongtai structural belt. Additionally, it may serve as a reference for studies on other similar gas reservoirs with an inner and outer buried hill.
2. Geological Setting
The Liaohe Subbasin is situated in the northeastern part of the Bohai Bay Basin and is subdivided into three depressions: the Western, Eastern, and Damintun Depressions (Figure 1a,b). Specifically, the Xinglongtai area lies within the middle of the Western Depression (Figure 1b). It constitutes a structural belt extending in the northeast direction and is surrounded by the Qingshui, Chenjia, and Panshan Sags (Figure 1c). The basement rocks of the Xinglongtai area comprise Archean metamorphic and magmatic rocks as well as Mesozoic volcanic eruptive and sedimentary rocks. The Paleogene strata incorporate the Fangshenpao (Ef) and Shahejie (Es) Formations—the latter is further divided into fourth (Es4), third (Es3), and second-first (Es1+2) members—along with the Dongying (Ed) Formation. Conversely, the Neogene strata include the Guantao (Ng) and Minghu zhen (Nm) Formations (Figure 2).
The Western Depression of the Liaohe Subbasin has undergone several significant tectonic phases throughout its formation and evolution. The movements since the Neogene can be further classified into three primary stages: the Eocene rifting phase (58.0–33.9 Ma), the Oligocene transition phase (33.9–23.03 Ma), and the Miocene sag phase (23.0–0 Ma). Each of these stages led to the formation of distinct fault structures (Figure 2) [13].
Figure 2.
Generalized stratigraphy of the Western Depression, Bohai Bay Basin, modified after [14]. Source rocks and major gas reservoirs are marked.
Figure 2.
Generalized stratigraphy of the Western Depression, Bohai Bay Basin, modified after [14]. Source rocks and major gas reservoirs are marked.
During the Eocene rifting phase, the tectonic activity was predominantly characterized by normal faults that had a north-northeast to northeast strike. These faults were widely distributed across the depression, extending downwards into the basement and upwards towards the top or within the Es3 Formation. In the Oligocene transition phase, tectonic activity was primarily typified by normal faults with a north-east-east strike and a near east-west direction. The faults from this phase extended downwards to the Es Formation and upwards to the Ed Formation and its top (Figure 3). Lastly, during the Neogene-Quaternary period, tectonic activity consisted of a mix of north-northeast to northeast faults (including normal faults, reverse faults, and reversed faults), as well as a large number of east-west normal faults. This stage exhibited a shift in fault orientations and activities, indicating a change in the dominant tectonic movements [14,15].
The Western Depression predominantly features four types of sedimentary systems: Fan-delta, Sublacustrine-fan, Lacustrine, and Nearshore Subaqueous Fan sedimentation [9,16]. Within the Xinglongtai structural belt, Es3 primarily consists of Nearshore Subaqueous Fan and Lacustrine sedimentation. The former refers to a sedimentary system composed of gravity flow sediments present in deep water-fan sedimentary systems. In contrast, Es4 and Es2 are mainly characterized by Fan-delta and Lacustrine facies sedimentation [17].
The Qingshui and Chenjia Sags are the primary hydrocarbon-supplying sags to the Xinglongtai structural belt. The primary source rocks in these sags are predominantly characterized by dark mudstone and oil shale in the Es3 and dark mudstone in the upper section of the Es4. These source rocks are composed mainly of a blend of sapropelic and humic organic matter, exhibiting significant heterogeneity. In terms of apparent organic types, the Es4 source rocks are primarily characterized by types II1–I, while Es3 source rocks are predominantly type II1 [17,18,19].
Industrial oil and gas reservoirs identified both inside and outside the buried hills of the Xinglongtai structural belt present differing gas compositions. The gas within the buried hills is thermogenic, encompassing both humic and sapropelic types and primarily originating from Es3 source rocks. However, the gas outside the buried hills shows a more intricate composition, being a blend of primary microbial gases and thermogenic gases [5,6,7,17,20].
3. Data and Methods
3.1. Database
In this study, we analyzed 204 data points from hydrocarbon source rock samples, including pyrolysis parameters and Total Organic Carbon (TOC). These samples were obtained from sags around the Xinglongtai structural belt (Figure 1). Based on lithofacies classification, the distribution is as follows: 26 Fan-Delta Mudstones from the Western slope (FDM-W), 25 from the eastern slope (FDM-E), 5 Sublacustrine-Fan Mudstones (SFM), 89 Semi-Deep Lake Mudstones (SDLM), 3 Shallow Lake Mudstones (SLM), and 56 Nearshore Subaqueous Fan Mudstones (NSFM) (Table A1). Additionally, we analyzed experimental data from 37 natural gas samples collected at the surface from production wells around the Xinglongtai structural belt in the Western Depression of the Bohai Bay Basin (Figure 1). Of these samples, 25 were from the Ed Fm reservoir, 2 from Es1, 2 from Es3, and 8 from the basement reservoir. The analysis covered molecular compositions and stable carbon isotope ratios of methane to butane (C1 to C5), as well as carbon dioxide (CO2) present in these gas samples (Table A2). The geological data required for basin modeling, including location, formation thickness, fault data, and well logs, are extracted from the 3D seismic survey within the study area. The erosion maps of critical moments are used to determine the erosion thickness at different locations (Table 1). All these data were collected from the Exploration and Development Research Institute of the Liaohe Oilfield.
3.2. Basin Modeling
Basin and Petroleum System Modeling (BPSM) is a crucial discipline in petroleum geology and geophysics. It is extensively employed to forecast and comprehend the occurrence, quantity, and quality of hydrocarbons in subsurface reservoirs [21,22,23,24]. Basin and petroleum system modeling integrate various dynamic processes such as sedimentation, faulting, burial, kerogen maturation kinetics, and multiphase flow. It is an effective tool for analyzing the generation, migration, and accumulation of hydrocarbons [25]. This study selected a representative profile to perform 2D basin modeling using Petromod 2016 software. The specific steps are as follows: (1) Load the extracted stratigraphic and fault data into the model. Age and petroleum system element assignments are shown in Table 2. The study area has experienced three stages of erosion, corresponding to the period after deposition of the Es3, Es1+2, and Ed. The erosion thickness ranges were 0–200 m, 0–50 m, and 0–200 m, respectively. The maximum erosion thickness is observed at the center of the Xinglongtai structural belt. (2) Each stratigraphic unit was divided into 5 to 15 sublayers based on thickness. The lithofacies were defined based on lithology logs, sedimentary facies distribution, and the 3D geological model established in a previous study [26] for the Western Depression, Liaohe Subbasin (Figure 3). (3) The parameters for the source rocks, including TOC and HI, were set based on the average experimental values of different types of source rocks. The source rocks containing type II kerogen and type III kerogen were assigned to kinetic models from the PetroMod catalog (Burnham, 1989 T-II and Burnham, 1989 T-III), respectively. Maturity was calculated using the EASY %Ro model developed by [27]. (4) The boundary conditions, including paleo-water depth (PWD), paleo-heat flow (PHF), and sediment–water interface temperature (SWIT), were determined based on previous literature. The PWDs for different stratigraphic units were assigned based on their sedimentary facies [28]. The PHF data were from [16]. The SWITs were calculated based on the global mean temperature at sea level for the latitude of 41° in Eastern Asia [29]. (5) The types of faults were determined based on their intersection with the stratigraphic units. The sealing capability of different types of faults was assigned based on the main active periods. During active periods, the faults were open and lasted for 1–2 Ma, while at other times, they were closed. (6) The migration model utilizes the Darcy flow and invasion percolation method.
4. Results
4.1. Natural Gas Geochemistry
4.1.1. Molecular and Carbon Isotopic Composition of Different Alkane Gases
We employ the correlation between molecular and carbon isotopic compositions of alkane gases across varying carbon numbers to identify genetic types and post-generation alterations [10,31,32]. In the Xinglongtai area, the natural gas samples exhibit significant differences in their molecular and carbon isotopic compositions within strata. The basement, Es4, Es3, and Es1+2 gas samples display a typical content pattern with C1 ≫ C2 > C3 > iC4 < nC4 and δ13C1 < δ13C2 < δ13C3 > δ13iC4 < δ13nC4 (δ13C3 < δ13nC4), indicating the presence of thermogenic gases without observable post-generation alterations [33] (Figure 4). In contrast, the molecular composition of the Ed gas samples exhibits considerably lower levels of wet gases (C2+) compared to other gas samples and generally follows an atypical content order of C1 ≫ C2 > C3 < iC4 > nC4 (Figure 4a). Furthermore, the Ed gas samples display significantly heavier δ13C3 and δ13nC4 values relative to δ13iC4 and, in some cases, exhibit an abnormal ordering of δ13C3 > δ13nC4 or δ13C3 < δ13nC2, suggesting biodegradation (Figure 4b).
4.1.2. Correlation between C1/(C2 + C3) and δ13C1
The Bernard diagram, which plots the C1/(C2 + C3) − δ13C1 pattern, plays a crucial role in distinguishing microbial gas from thermogenic natural gas derived from different kerogen types. However, due to the heterogeneity of organic sources and secondary processes, variations in chemical and isotopic compositions can introduce uncertainties in genetic classification [10,34,35]. Therefore, it is essential to consider geological evidence, including the structural positioning and connectivity between natural gas reservoirs and sources, and employ multiple parameters or diagrams to make accurate judgments [7,36].
We analyzed natural gas samples from the study area using the C1/(C2 + C3) − δ13C1 correlation diagram developed from [34,35] (Figure 5). Analysis showed that samples from the Shahejie Fm and the basement display a consistently low C1/(C2 + C3) ratio and heavy δ13C1, indicating a thermogenic origin. Upon further classification, three types emerge: gas samples from Es1+2 demonstrate a low C1/(C2 + C3) ratio (<5) and light δ13C1 (<−39‰), suggesting a sapropelic type; gas samples from the basement present a higher C1/(C2 + C3) ratio (>10) and heavy δ13C1 (>−34‰), implying a humic type; and gas samples from Es3 show a high C1/(C2 + C3) ratio (>100) and heavy δ13C1 (−30‰), suggesting a highly mature humic type. As for gas samples from the Ed, they can be further subdivided based on δ13C1 values: samples with δ13C1 > 45‰ display a higher C1/(C2 + C3) ratio (>40), indicating significant biodegradation influence; and samples with δ13C1 < −45‰ show a higher C1/(C2 + C3) ratio and reside in a transitional zone, suggesting a potential thermogenic and biodegraded gas mixture (Figure 5).
4.1.3. Genetic Types of Natural Gas
The carbon isotope composition of natural gas, specifically ethane (δ13C2), can indicate the source rock type—either sapropelic or humic [10,31,37,38,39]. Boundary values, however, remain debated due to varying factors such as the original organic carbon isotope and maturity. Following the approach of [39], we classify δ13C2 values greater than −26‰ as humic-type gas, less than −29‰ as oil-type gas, and between −29‰ and −26‰ as mixed gas. Normally, propane’s carbon isotope (δ13C3) also differentiates gas types, but degradation due to microbial activity inhibits its use in this study [40].
The natural gas samples of Ed exhibit a heavier δ13C3, indicating biodegradation. Some of these gas samples also show a lighter characteristic by δ13C1 < −50‰, possibly due to mixing with biodegraded thermogenic gases, while others are likely secondary microbial gases. The natural gas samples from Es1+2 are characterized by δ13C2 > −28‰, indicating sapropelic-type gases. On the contrary, the natural gas samples from Es3 are characterized by δ13C2 < −28‰, indicating humic-type gases. Samples from the basement are predominantly mixed gases (mixed humic and sapropelic gas), with a minor proportion of humic-type gases (Figure 6).
4.2. Source Rock Types and Assessment
Considering the variations in organic matter sources and preservation conditions, mudstones formed in different depositions can manifest a wide range of geochemical properties. This is particularly evident in lacustrine basins with substantial tectonic evolution and changes in sedimentary systems [41,42]. Within the Shahejie Fm, known for its deltaic–lacustrine and lacustrine–turbidite depositional environments [9,16,43,44,45,46], we have identified six potential source rock types: Sublacustrine-Fan Mudstones (SFM), Fan-Delta Mudstones from the Western slope (FDM-W), Fan-Delta Mudstones from the Eastern slope (FDM-E), Semi-Deep Lake Mudstones (SDLM), Shallow Lake Mudstones (SLM), and Nearshore Subaqueous Fan Mudstones (NSFM).
4.2.1. Organic Matter Richness
The TOC content of SDLM ranges predominantly between 2.45% and 4.30%, averaging 3.4%. Their hydrocarbon generation potential (S1 + S2), plotted against TOC, suggests these are good to excellent source rocks. SLM have the next-highest TOC content, mainly ranging from 0.75% to 1.80%, with an average of 1.35%, and are classified as poor to good source rocks based on hydrocarbon generation potential. The TOC values for all other mudstone types exceed 1%, indicating medium to good hydrocarbon generation potential. Hence, the organic matter abundance in the study area generally meets the lower limit (TOC = 0.5%) for hydrocarbon generation (Figure 7a,b).
4.2.2. Kerogen Type
The source rock samples from the study area encompass a variety of organic matter types. Contributions from sapropelic, mixed sapropelic–humic, and humic organic matter are evident and correlate with source rock types. SDLM primarily contain type I-II1 organic matter. FDM developed on the Western slope (FDM-W) and SFM mainly possess type II1-II2 organic matter. SLM are of type II2 organic matter, while the FDM on the Eastern slope (FDM-E) and NSFM primarily contain type III organic matter (Figure 7c). According to box plots in Figure 7b–d, the average values of TOC and HI for different types of source rocks have been calculated (Table 2). The results are used as input parameters in basin modeling.
4.3. Modeling of Gas Generation, Migration, and Accumulation
4.3.1. Hydrocarbon Generation History
We selected a representative profile for 2D basin modeling to reconstruct the dynamic history of hydrocarbon generation in the study area. The Transformation Ratio (TR), typically corresponding to the maturity of the source rocks, is commonly used to denote the timing of hydrocarbon generation and expulsion [48]. Based on the hydrocarbon generation process proposed by [48], the results reveal the following: (1) At 40 Ma, only Es41 and lower Es33 source rocks in the central Qingshui Sag entered the oil generation window (Ro > 0.5%) (Figure 8a,b). Meanwhile, the source rocks in the Chenjia Sag had not reached the mature stage due to their relatively shallow burial depth. (2) By 38 Ma, Es41 and part of Es33 in the Qingshui Sag had entered the gas generation stage (Ro > 1.3%) due to deep burial. The upper part of Es33 to the lower part of Es32 was in peak oil generation, with a TR of 40–60%. A small segment of Es41 in the western slope entered the oil generation stage, with a maximum TR exceeding 50% (Figure 8c,d). In the Chenjia Sag, the source rocks of Es41, Es33, and the bottom of Es32 entered the oil window, with TR ranging from 20% to 50%. (3) At 30 Ma, the Es41, Es33, and part of the Es32 in the central Qingshui Sag entered the main gas generation stage (Ro > 1.3%), with a significant strata thickness reaching the dry gas generation stage (Ro > 2.0%). By contrast, only the Es41 source rocks reached the gas window in the Chenjia Sag. During this stage, except for the western slope belt at the basin margin, all formations of the Shahejie Fm in the study area had entered the oil window, with the maximum TR reaching 100% (Figure 8e,f). Due to the diverse types of organic matter present in the source rocks, the TR of these rocks at the same depth may vary. (4) During 30–0 Ma, the Liaohe Subbasin became relatively stable, and hydrocarbon generation almost ceased (Figure 8g,h).
By assessing the volume changes in natural gas generated by source rocks from each unit along the AA’ cross-section over geological time, we can divide the entire process into a single hydrocarbon generation phase from 40 Ma to 34 Ma. Both Es41 and Es33 commenced gas generation concurrently. Es32 had the longest gas generation period, attributable to its maximum shale thickness, whereas Es33 had the latest onset of gas generation (Figure 9).
4.3.2. Gas Migration and Accumulation History
As demonstrated in Figure 10, simulation results of natural gas migration and accumulation suggest reservoirs are found both within (basement) and outside (Es1+2, Es3, and Ed) the buried hill of the Xinglongtai structural belt. This distribution aligns well with the actual exploration results of natural gas reservoirs. The simulation successfully predicted the existing natural gas reservoirs extracted from wells MN603, MT1, M256, and X256-2.
The history of natural gas migration and accumulation in the study area can be summarized as follows: (1) Beginning at 40 Ma, natural gas generated in the Qingshui Sag began to migrate upward, while the Chenjia Sag showed a relatively lower production of natural gas (Figure 10a). By 38 Ma, in situ structural natural gas reservoirs began to form within Es3 in both sags, attributed to the absence of fault conduction during this period. Meanwhile, the natural gas generated from Es4 underwent lateral migration and accumulation in the cracks inside the Xinglongtai buried hill (Figure 10b). (2) Around 34 Ma, concurrent with the Ed deposition period, most faults became active. These primarily included the syndepositional faults between the Qingshui Sag and the Xinglongtai structural belt, as well as other faults intersecting the Es3 and Ed. At this time, these faults served as conduits, directing the natural gas produced within the central sags towards the sand bodies present in Es1+2–Es3 of the Xinglongtai structural belt (Figure 10b,c). (3) After 30 Ma, as the basin deepened, fault displacement increased, and the formation of fault mud drapes contributed to the occurrence of natural gas reservoirs along these faults (Figure 10c,d).
4.3.3. Contribution of Source Rocks in the Filling of Reservoirs
Furthermore, according to the migration simulation results of Profile AA’, we calculated the contribution ratios of gas source rocks to various representative gas reservoirs over time. The in situ and basement natural gas reservoirs, once established in the early stages, did not undergo any secondary transformations. The Es3 natural gas reservoirs located within the Qingshui and Chenjia Sags were primarily contributed by the Nearshore Subaqueous Fan Mudstones (NSFM—Type III organic matter) of their respective Es3 layers. Meanwhile, the anticlinal natural gas reservoirs within the Xinglongtai structural belt received a mixture of contributions from the Shallow Lake Mudstones (SLM—Type II organic matter) from the Es4 layer of the Qingshui Sag and the NSFM from the Es3 layer of the Chenjia Sag (Figure 11). Reservoirs outside the Xinglongtai buried hill, which formed later, received their Es1+2 natural gas primarily from the Semi-Deep Lake Mudstones (SDLM—Type I organic matter) of the Es3 layer from the Qingshui Sag. The Es3 natural gas was primarily contributed by the NSFM from the Es3 layers in both sags (Figure 11b,c).
5. Discussion
5.1. Source of Thermogenic Gas
Oil and gas generation from sapropelic organic matter are intertwined, with oil generation taking precedence during the mature stage. Conversely, humic organic matter primarily generates a minimal amount of light oil in the mature stage, while gas generation is the dominant process throughout the entire maturation cycle [18,48]. According to the findings in Section 4.2, there is a distinct correlation between the type of organic matter in source rocks and the categorization of those rocks. NSFM and FDM-E are mainly contributed by Type III organic matter, which generates humic-type gas throughout the maturity process. In contrast, the remaining mudstone types (FDM-W, SLM, and SDLM) primarily consist of Type I-II organic matter, which largely produces sapropelic-type gas at the high maturity stage.
Given the poor connectivity of reservoir fractures inside the buried hill, it is not conducive to the migration of natural gas within it. As a result, the source rock of the natural gas is in direct contact with the buried hill [6]. Based on the distribution of different types of source rocks in the profile (Figure 3), those in direct contact with the Xinglongtai buried hill are SLM in Es4 and NSFM in Es3, which generate sapropelic-type gas and humic-type gas, respectively. Therefore, the humic-type gas found inside the Xinglongtai buried hill is contributed by the NSFM in Es3, and the mixed gas (a combination of sapropelic-type gas and humic-type gas) is contributed by both the SLM in Es4 and the NSFM in Es3. These findings are in line with the results of the source–reservoir–accumulation simulation for gas origin comparison (Figure 11).
The SDLM and SLM in the Es32 of the Qingshui Sag have entered the gas-generating stage (Ro > 2.0%), thereby generating sapropelic-type gas. This indicates that these source rocks may serve as the primary contributors to the sapropelic-type gas found in the Es1+2 of the Xinglongtai structural belt. Meanwhile, the humic-type gas in Es3 originates from the NSFM within the Es3.
5.2. Petroleum System
We have delineated the important elements of the petroleum systems both inside and outside the Xinglongtai structural belt (Figure 12). The main source rocks external to Xinglongtai are the Es4 and Es3 shales, with the reservoir rocks being the Es3, Es1+2, and Ed sandstones and the cap rock being the Ed shale. The generation of natural gas spanned from the middle Eocene to the early Oligocene period. The migration of natural gas is jointly dictated by hydrocarbon generation and the associated fracture systems. Importantly, faults activated during the Oligocene period restructured the deep natural gas reservoirs that were formed earlier, leading to secondary migration and accumulation of natural gas. As such, the crucial period for the system outside Xinglongtai transpired during the Oligocene period. Within the confines of Xinglongtai, the principal source rocks are also the Es4 and Es3 shales, with the natural gas stored in the basal fractures and the cap rock being the Es shale. The generation of natural gas likewise occurred from the middle Eocene to the early Oligocene period. The migration of natural gas is co-governed by hydrocarbon generation and fractures in rocks below the unconformity. Consequently, the critical moment for the system within Xinglongtai occurred in the mid-Eocene period.
5.3. Implications for Natural Gas Accumulation
This study categorizes the Xinglongtai area into two distinct hydrocarbon accumulation systems: the inner and outer Xinglongtai buried hill systems.
The inner Xinglongtai buried hill system receives contributions from two source directions, namely the Qingshui and Chenjia Sags. The Nearshore Subaqueous Fan Mudstones (predominantly composed of humus organic matter) and Semi-Deep Lake Mudstones (mainly constituting sapropelic organic matter) within the Es3 sag generate humic-type gas and oil-type gas, respectively, under thermal influence. These gases accumulate in the Es3 and Es1+2 layers. As the burial depth decreases to less than 2000 m, the system enters a transitional stage between thermal and biological influences, with the thermogenic natural gas either biodegraded or further mixed with primary biogas. The primary migration and accumulation routes are dictated by faults, with long-distance vertical migration being the most prevalent. Due to two instances of fault activity, the system underwent two migration phases, with the present natural gas reservoir formed after the Oligocene fault activity and preserved until now (Figure 13a,c).
The outer Xinglongtai buried hill system also draws from two source directions in the Qingshui and Chenjia Sags. However, the sources are the Nearshore Subaqueous Fan Mudstones of Es3 and the Shallow Lake Mudstones of Es4 (primarily contributed by sapropelic organic matter) from the Qingshui and Chenjia Sags, which generate coal-type gas and sapropelic-type gas, respectively, under thermal influence. The natural fractures are the principal transmission system [2], and the fractures in the basement constitute the reservoir, so the system experienced only a single phase of migration and accumulation during the Eocene period. Sapropelic-type gas and coal-type gas mingle within the unconformity surface and reservoir to form mixed natural gas reservoirs (Figure 13b,c).
5.4. Significance
Terrestrial lacustrine basins typically exhibit a relatively enclosed structural environment, leading to hydrocarbons often accumulating within or near hydrocarbon-generating sags. Given this context, the distribution and properties of source rocks play a significant role in determining the distribution and characteristics of oil and gas.
The presence of diverse fault systems within faulted lacustrine basins can result in a heterogeneous distribution of source rocks. This, in turn, adds complexity to the distribution of natural gas reservoirs, which often manifest as more abundant accumulations near the hydrocarbon-generating sags. As a result, natural gas reservoirs in the Xinglongtai structural belt are generally richer and deeper. Additionally, the geochemical attributes of the source rocks, such as organic matter type, abundance, and maturity, also exhibit heterogeneity in these faulted lacustrine basins. Variations in organic matter type and maturity influence the genesis type of natural gas that source rocks generate, and the organic matter’s abundance impacts the hydrocarbon-generating capability of the source rocks. This leads to multiple genesis types of natural gas coexisting within the same terrestrial lacustrine basin. Moreover, complex fault systems play a pivotal role in natural gas transmission within these basins. The distribution of these faults, coupled with their multiple periods of activity, can spur natural gas migration or diffusion and can potentially disrupt early gas reservoirs. This promotes further mixing of different genesis types of natural gas during migration and diffusion processes.
Consequently, by elucidating the heterogeneity of source rocks—their distribution, organic matter type, abundance, and maturity—and their relationship with the distribution and genesis type of natural gas, along with analyzing the dynamic processes of generation, migration, and accumulation, we can enhance our understanding and prediction of natural gas distribution and storage patterns in terrestrial faulted lacustrine basins. This insight could guide and inform decision-making processes for natural gas exploration and development.
6. Conclusions
In conclusions, our study provides insightful revelations on the complex systems governing the generation, migration, and accumulation of natural gas in terrestrial faulted lacustrine basins. These findings can be drawn as follows:
- Within the peripheries of the Xinglongtai structural belt, in the Qingshui and Chenjia Sags, the primary hydrocarbon source beds are the Es4 and Es3 of the Shahejie Fm; Es4 is characterized by Shallow Lake Mudstones (SLM) and dominated by type II organic matter, while Es3 mainly comprises Nearshore Subaqueous Fan Mudstones (NSFM) and Semi-Deep Lake Mudstones (SDLM), primarily contributed by type III and type I organic matter, respectively. These factors play a critical role in determining the genesis type of natural gas and the hydrocarbon-generating capacity of the source rocks.
- The distribution of varied source rocks has a direct bearing on the type of gas discovered within different layers and positions. Inside the Xinglongtai structural belt, the natural gas comprises humic-type and mixed-type gas (a blend of sapropelic and humic-type gases) originating from Es3 NSFM and Es4 SLM. Outside the Xinglongtai structural belt, the natural gas encompasses sapropelic-type gas, humic-type gas, and secondary biodegraded gas. The humic gas derives from Es3 Nearshore Subaqueous Fan Mudstones, whereas the sapropelic gas stems from Es3 SDLM.
- The Xinglongtai structural belt hosts two distinct hydrocarbon accumulation systems, one outside and one inside the buried hill. For the system outside the buried hill, the migration and accumulation of natural gas are guided by a complex fault system within the lacustrine basin. Two separate periods of fault activity not only encouraged the vertical migration and diffusion of natural gas but also disrupted early gas reservoirs, leading to a later-stage consolidation of the natural gas. This system exhibits dual-source directions, dual-source rock types, two migration phases, and late-stage accumulation. Contrastingly, within the buried hill system, the reservoirs nested in the basement are primarily steered by hydrocarbon generation. The further mixing of various genesis types of natural gas within the unconformities and fractures culminates in early-stage accumulation. This system presents dual- source directions, dual-source rock types, a single migration phase, and early-stage accumulation.
Author Contributions
S.Y.: provided ideas, wrote, reviewed, and edited the manuscript; M.L. and H.X.: revised the manuscript; S.H., Y.W. and W.K.: collected data and materials; F.W.: analyzed data. All authors have read and agreed to the published version of the manuscript.
Funding
This work was funded by the National Natural Science Foundation of China (Grant No. 42173054) and the Natural Science Foundation of Sichuan Province (No. 2022NSFSC0182).
Data Availability Statement
Data will be made available on request.
Acknowledgments
This work was partly supported by the CNPC Liaohe Oilfield Exploration and Development Company for data support and for making an academic license available for the use of PetroMod.
Conflicts of Interest
The authors declare no conflict of interest.
Appendix A
Table A1.
Hydrogen index (HI), pyrolysis parameters of all mudstone samples.
| Sample ID | Depth (m) | Strata | Mudstone Types | TOC (%) | Pyrolysis Data | ||
|---|---|---|---|---|---|---|---|
| S1 (mg/g) | S2 (mg/g) | Tmax (°C) | |||||
| SG1-1 | 3239 | Es3 | FDM-W | 1.99 | 0.71 | 6.34 | 437 |
| SG1-2 | 3372 | Es3 | FDM-W | 1.87 | 0.84 | 5.49 | 439 |
| SG1-3 | 3518 | Es3 | FDM-W | 2.21 | 0.7 | 7.33 | 440 |
| SG1-4 | 3537 | Es3 | FDM-W | 2.40 | 0.78 | 7.95 | 442 |
| SG1-5 | 3752 | Es3 | FDM-W | 1.72 | 1.12 | 4.02 | 441 |
| SG1-6 | 3819 | Es3 | FDM-W | 1.64 | 0.78 | 3.48 | 439 |
| SG1-7 | 2906 | Es3 | FDM-W | 2.02 | 0.35 | 7.12 | 432 |
| SG1-8 | 3464 | Es3 | FDM-W | 1.8 | 0.33 | 5.99 | 437 |
| SG1-9 | 3516 | Es3 | FDM-W | 2.22 | 0.48 | 7.4 | 443 |
| SG1-10 | 3518 | Es3 | FDM-W | 2.01 | 0.52 | 7.21 | 441 |
| SG1-11 | 3520 | Es3 | FDM-W | 1.86 | 0.27 | 5.5 | 437 |
| SG1-12 | 3534 | Es3 | FDM-W | 2.38 | 0.42 | 8.74 | 438 |
| SG1-13 | 3536 | Es3 | FDM-W | 2.11 | 0.5 | 7.42 | 440 |
| SG1-14 | 3538 | Es3 | FDM-W | 2.48 | 0.74 | 8.6 | 440 |
| SG1-15 | 3620 | Es3 | FDM-W | 1.82 | 0.68 | 5.65 | 442 |
| SG1-16 | 3622 | Es3 | FDM-W | 1.87 | 0.83 | 5.9 | 439 |
| SG1-17 | 3680 | Es3 | FDM-W | 1.63 | 0.55 | 4.67 | 442 |
| SG1-18 | 3686 | Es3 | FDM-W | 1.99 | 0.56 | 5.44 | 441 |
| SG1-19 | 3692 | Es3 | FDM-W | 1.63 | 0.59 | 4.32 | 439 |
| SG1-20 | 3696 | Es3 | FDM-W | 1.72 | 0.44 | 4.59 | 443 |
| SG1-21 | 3704 | Es3 | FDM-W | 1.71 | 0.41 | 4.61 | 445 |
| SG1-22 | 3710 | Es3 | FDM-W | 1.75 | 0.64 | 4.92 | 442 |
| SG1-23 | 3712 | Es3 | FDM-W | 1.71 | 0.44 | 4.19 | 441 |
| SG1-24 | 3722 | Es3 | FDM-W | 1.91 | 0.58 | 5.27 | 443 |
| SG1-25 | 3728 | Es3 | FDM-W | 1.77 | 0.3 | 4.58 | 442 |
| SG1-26 | 3732 | Es3 | FDM-W | 1.63 | 0.47 | 3.92 | 441 |
| SG1-27 | 4280 | Es4 | FDM-E | 0.79 | 0.07 | 1 | 442 |
| SG1-28 | 4282 | Es4 | FDM-E | 0.67 | 0.03 | 0.72 | 444 |
| SG1-29 | 4284 | Es4 | FDM-E | 0.77 | 0.04 | 0.84 | 444 |
| SG1-30 | 4286 | Es4 | FDM-E | 0.69 | 0.06 | 0.81 | 440 |
| SG1-31 | 4288 | Es4 | FDM-E | 0.91 | 0.13 | 0.88 | 447 |
| SG1-32 | 4290 | Es4 | FDM-E | 1.97 | 0.06 | 6.79 | 430 |
| SG1-33 | 4292 | Es4 | FDM-E | 1.81 | 0.36 | 2 | 444 |
| SG1-34 | 4292 | Es4 | FDM-E | 1.66 | 0.36 | 2 | 444 |
| SG1-35 | 4294 | Es4 | FDM-E | 1.8 | 0.21 | 1.58 | 438 |
| SG1-36 | 4296 | Es4 | FDM-E | 1.38 | 0.4 | 1.8 | 438 |
| SG1-37 | 4298 | Es4 | FDM-E | 1.15 | 0.17 | 1.42 | 435 |
| SG1-38 | 4300 | Es4 | FDM-E | 0.82 | 0.08 | 1.14 | 436 |
| SG1-39 | 4300 | Es4 | FDM-E | 0.82 | 0.52 | 1.86 | 431 |
| SG1-40 | 4302 | Es4 | FDM-E | 1.02 | 0.12 | 1.02 | 438 |
| SG1-41 | 4304 | Es4 | FDM-E | 1.77 | 0.29 | 1.53 | 437 |
| SG1-42 | 4306 | Es4 | FDM-E | 1.64 | 0.31 | 1.82 | 437 |
| SG1-43 | 4308 | Es4 | FDM-E | 1.74 | 0.36 | 1.65 | 444 |
| SG1-44 | 4310 | Es4 | FDM-E | 1.59 | 0.3 | 1.56 | 442 |
| SG1-45 | 4312 | Es4 | FDM-E | 1.55 | 0.41 | 1.66 | 433 |
| SG1-46 | 4314 | Es4 | FDM-E | 1.69 | 0.25 | 1.41 | 444 |
| SG1-47 | 4316 | Es4 | FDM-E | 1.59 | 0.32 | 1.39 | 441 |
| SG1-48 | 4318 | Es4 | FDM-E | 1.44 | 0.24 | 1.36 | 438 |
| SG1-49 | 4320 | Es4 | FDM-E | 1.47 | 0.16 | 1.22 | 445 |
| SG1-50 | 4322 | Es4 | FDM-E | 1.46 | 0.24 | 1.34 | 437 |
| SG1-51 | 4328 | Es4 | FDM-E | 1.48 | 0.19 | 2.04 | 440 |
| S213-1 | 3440 | Es3 | SDLM | 1.2 | 0.23 | 4.9 | 440 |
| S213-2 | 3442 | Es3 | SDLM | 1.77 | 0.15 | 5.1 | 437 |
| S213-3 | 3450 | Es3 | SDLM | 1.39 | 0.2 | 3.66 | 439 |
| S213-4 | 3458 | Es3 | SDLM | 1.99 | 0.24 | 6.07 | 440 |
| S213-5 | 3464 | Es3 | SDLM | 1.86 | 0.22 | 5.92 | 438 |
| S213-6 | 3472 | Es3 | SDLM | 1.75 | 0.26 | 4.9 | 441 |
| S213-7 | 3486 | Es3 | SDLM | 1.64 | 0.2 | 5.5 | 438 |
| S213-8 | 3488 | Es3 | SDLM | 2.14 | 0.26 | 6.51 | 440 |
| S213-9 | 3496 | Es3 | SDLM | 1.92 | 0.3 | 5.39 | 446 |
| S213-10 | 3504 | Es3 | SDLM | 1.89 | 0.75 | 5.31 | 436 |
| S213-11 | 3524 | Es3 | SDLM | 1.77 | 0.25 | 6.23 | 441 |
| S213-12 | 3526 | Es3 | SDLM | 2.9 | 0.19 | 6.14 | 440 |
| S213-13 | 3554 | Es3 | SDLM | 1.72 | 0.23 | 5.92 | 437 |
| S213-14 | 3558 | Es3 | SDLM | 2.26 | 0.45 | 6.81 | 438 |
| S213-15 | 3568 | Es3 | SDLM | 1.89 | 0.71 | 5.55 | 442 |
| S213-16 | 3574 | Es3 | SDLM | 1.74 | 0.35 | 4.78 | 438 |
| S213-17 | 3582 | Es3 | SDLM | 2 | 0.56 | 6.28 | 439 |
| Q233-1 | 3451 | Es3 | SFM | 2.09 | 0.35 | 6.37 | 434 |
| Q233-2 | 3352.25 | Es3 | SFM | 2.27 | 0.28 | 6.5 | 439 |
| Q233-3 | 3352.75 | Es3 | SFM | 2.27 | 0.41 | 7.19 | 438 |
| Q233-4 | 3353.25 | Es3 | SFM | 2.33 | 0.37 | 7.47 | 436 |
| Q233-5 | 3353.75 | Es3 | SFM | 2.19 | 0.32 | 7.06 | 435 |
| D306-1 | 3373 | Es3 | SLM | 0.77 | 0.16 | 0.97 | 443 |
| D306-2 | 3413 | Es3 | SLM | 1.45 | 1 | 5.77 | 404 |
| D306-3 | 3414 | Es3 | SLM | 1.8 | 0.07 | 3.74 | 441 |
| SG168-1 | 2913 | Es3 | SDLM | 3.56 | 1.37 | 17.45 | 433 |
| SG168-2 | 2919 | Es4 | SDLM | 3.37 | 0.81 | 17.95 | 438 |
| SG168-3 | 2925 | Es4 | SDLM | 5.38 | 3.45 | 27.9 | 436 |
| SG168-4 | 2931 | Es4 | SDLM | 4.46 | 1.88 | 24.46 | 434 |
| SG168-5 | 2937 | Es4 | SDLM | 5.36 | 3.08 | 28.1 | 434 |
| SG168-6 | 2955 | Es4 | SDLM | 4.93 | 2.38 | 30.06 | 443 |
| SG168-7 | 2961 | Es4 | SDLM | 4.61 | 2.35 | 28.79 | 441 |
| SG168-8 | 2967 | Es4 | SDLM | 4.62 | 2.44 | 28.62 | 441 |
| SG168-9 | 2973 | Es4 | SDLM | 6.11 | 4.18 | 42.04 | 441 |
| SG168-10 | 2979 | Es4 | SDLM | 4.46 | 4.07 | 27.3 | 438 |
| SG168-11 | 2985 | Es4 | SDLM | 3.5 | 3.6 | 23.28 | 438 |
| SG168-12 | 2991 | Es4 | SDLM | 4.31 | 5.8 | 31.66 | 436 |
| SG168-13 | 2997 | Es4 | SDLM | 4 | 3.88 | 29.58 | 435 |
| SG168-14 | 3003 | Es4 | SDLM | 3.92 | 2.68 | 27.84 | 439 |
| SG168-15 | 3009 | Es4 | SDLM | 3.18 | 1.76 | 22.94 | 441 |
| SG168-16 | 3015 | Es4 | SDLM | 2.44 | 2.01 | 17.82 | 438 |
| SG168-17 | 3021 | Es4 | SDLM | 3.02 | 2.48 | 22 | 438 |
| SG168-18 | 3027 | Es4 | SDLM | 2.96 | 1.85 | 14.24 | 435 |
| SG168-19 | 3033 | Es4 | SDLM | 3.62 | 2.67 | 22.04 | 439 |
| SG168-20 | 3039 | Es4 | SDLM | 3.8 | 1.88 | 24.2 | 439 |
| SG168-21 | 3045 | Es4 | SDLM | 3.71 | 2.09 | 20.94 | 440 |
| SG168-22 | 3051 | Es4 | SDLM | 3.56 | 1.38 | 19.62 | 439 |
| SG168-23 | 3057 | Es4 | SDLM | 1.55 | 1.19 | 7.37 | 434 |
| SG168-24 | 3063 | Es4 | SDLM | 1.65 | 0.55 | 6.65 | 438 |
| SG168-25 | 3069 | Es4 | SDLM | 2.98 | 1.52 | 16.8 | 436 |
| SG168-26 | 3075 | Es4 | SDLM | 1.1 | 0.27 | 3.86 | 435 |
| SG168-27 | 3081 | Es4 | SDLM | 1.07 | 0.36 | 3.22 | 434 |
| SG168-28 | 3087 | Es4 | SDLM | 2.82 | 1.83 | 14.89 | 439 |
| SG168-29 | 3093 | Es4 | SDLM | 2.25 | 1.2 | 11.38 | 436 |
| SG168-30 | 3099 | Es4 | SDLM | 1.75 | 0.41 | 6.55 | 435 |
| SG168-31 | 3105 | Es4 | SDLM | 1.5 | 0.61 | 7.97 | 434 |
| SG168-32 | 3111 | Es4 | SDLM | 1.76 | 0.51 | 8.18 | 443 |
| SG168-33 | 3117 | Es4 | SDLM | 2.31 | 0.65 | 13.64 | 440 |
| SG168-34 | 3123 | Es4 | SDLM | 2.61 | 0.98 | 13.72 | 440 |
| SG168-35 | 3129 | Es4 | SDLM | 2.22 | 0.87 | 10.27 | 438 |
| SG168-36 | 3135 | Es4 | SDLM | 1.53 | 0.46 | 6.49 | 438 |
| SG168-37 | 3141 | Es4 | SDLM | 2.09 | 0.71 | 9.99 | 439 |
| SG168-38 | 3147 | Es4 | SDLM | 2.51 | 0.79 | 9.21 | 438 |
| SG168-39 | 3153 | Es4 | SDLM | 2.14 | 0.43 | 7.83 | 436 |
| SG168-40 | 3159 | Es4 | SDLM | 3.22 | 0.87 | 12.99 | 440 |
| SG168-41 | 3165 | Es4 | SDLM | 3.91 | 1.68 | 18.6 | 440 |
| SG168-42 | 3171 | Es4 | SDLM | 3.15 | 1.08 | 14.3 | 443 |
| SG168-43 | 3177 | Es4 | SDLM | 4.08 | 1.48 | 17.72 | 442 |
| SG168-44 | 3183 | Es4 | SDLM | 3.34 | 1.42 | 13.43 | 442 |
| SG168-45 | 3189 | Es4 | SDLM | 4.16 | 2.77 | 20.69 | 440 |
| SG168-46 | 3195 | Es4 | SDLM | 4.05 | 2.6 | 19.85 | 441 |
| SG168-47 | 3201 | Es4 | SDLM | 5.13 | 3.35 | 25.52 | 441 |
| SG168-48 | 3207 | Es4 | SDLM | 5.05 | 1.87 | 28.1 | 444 |
| SG168-49 | 3213 | Es4 | SDLM | 4.94 | 1.87 | 25.17 | 441 |
| SG168-50 | 3219 | Es4 | SDLM | 4.73 | 1.02 | 29.57 | 439 |
| SG168-51 | 3225 | Es4 | SDLM | 2.88 | 1.39 | 14.8 | 442 |
| SG168-52 | 3231 | Es4 | SDLM | 3.91 | 0.97 | 20.04 | 442 |
| SG168-53 | 3237 | Es4 | SDLM | 3.78 | 1.43 | 28.87 | 442 |
| SG168-54 | 3243 | Es4 | SDLM | 4.75 | 1.47 | 27.6 | 441 |
| SG168-55 | 3249 | Es4 | SDLM | 3.59 | 1.05 | 20.38 | 440 |
| MS1-1 | 3160 | Es3 | SDLM | 1.68 | 0.103 | 4.77 | 436 |
| MS1-2 | 3182 | Es3 | SDLM | 1.82 | 0.35 | 4.77 | 439 |
| MS1-3 | 3202 | Es3 | SDLM | 1.85 | 0.26 | 6.49 | 437 |
| MS1-4 | 3222 | Es3 | SDLM | 2.61 | 0.54 | 5.87 | 439 |
| MS1-5 | 3238 | Es3 | SDLM | 1.78 | 0.42 | 5.59 | 440 |
| MS1-6 | 3262 | Es3 | SDLM | 1.66 | 0.35 | 5.56 | 439 |
| MS1-7 | 3281 | Es3 | SDLM | 2.15 | 0.44 | 9.87 | 440 |
| MS1-8 | 3299 | Es3 | SDLM | 1.81 | 0.38 | 6.05 | 440 |
| MS1-9 | 3319 | Es3 | SDLM | 1.93 | 0.31 | 7.16 | 441 |
| MS1-10 | 3340 | Es3 | SDLM | 1.94 | 0.46 | 5.65 | 438 |
| MS1-11 | 3360 | Es3 | SDLM | 2.13 | 0.46 | 4.51 | 438 |
| MS1-12 | 3382 | Es3 | SDLM | 2.17 | 0.98 | 8.03 | 441 |
| MS1-13 | 3399 | Es3 | SDLM | 3.01 | 1.06 | 6.65 | 440 |
| MS1-14 | 3410 | Es3 | SDLM | 2.26 | 0.34 | 5.45 | 440 |
| MS1-15 | 3450 | Es3 | SDLM | 2.47 | 0.33 | 6.92 | 442 |
| MS1-16 | 3470 | Es3 | SDLM | 2.21 | 0.51 | 8.09 | 439 |
| MS1-17 | 3477 | Es3 | SDLM | 2.01 | 0.29 | 4.24 | 442 |
| MS1-18 | 3596 | Es3 | NSFM | 2.09 | 0.41 | 3.33 | 444 |
| MS1-19 | 3621 | Es3 | NSFM | 1.71 | 0.49 | 3.46 | 446 |
| MS1-20 | 3670 | Es3 | NSFM | 2.34 | 0.63 | 3.03 | 448 |
| MS1-21 | 3702 | Es3 | NSFM | 1.64 | 0.43 | 1.89 | 448 |
| MS1-22 | 3720 | Es3 | NSFM | 1.91 | 0.34 | 3.59 | 447 |
| MS1-23 | 3755 | Es3 | NSFM | 1.81 | 0.56 | 2.23 | 446 |
| MS1-24 | 3740 | Es3 | NSFM | 1.72 | 0.48 | 2.74 | 447 |
| MS1-25 | 3826 | Es3 | NSFM | 1.63 | 0.51 | 1.47 | 448 |
| MS1-26 | 3872 | Es3 | NSFM | 1.93 | 0.56 | 2.11 | 450 |
| MS1-27 | 3901 | Es3 | NSFM | 1.57 | 0.72 | 1.86 | 449 |
| MS1-28 | 3925 | Es3 | NSFM | 2.16 | 0.65 | 1.99 | 442 |
| MS1-29 | 3948 | Es3 | NSFM | 1.66 | 0.92 | 2.61 | 438 |
| MS1-30 | 3970 | Es3 | NSFM | 2.45 | 0.81 | 1.42 | 450 |
| MS1-31 | 4011 | Es3 | NSFM | 1.73 | 1.06 | 2.02 | 442 |
| MS1-32 | 4025 | Es3 | NSFM | 1.78 | 0.84 | 2.02 | 446 |
| MS1-33 | 4070 | Es3 | NSFM | 1.61 | 0.78 | 1.88 | 445 |
| MS1-34 | 4090 | Es3 | NSFM | 1.68 | 0.84 | 1.56 | 442 |
| MS1-35 | 4121 | Es3 | NSFM | 2.27 | 0.58 | 1.17 | 445 |
| MS1-36 | 4141 | Es3 | NSFM | 1.64 | 1.97 | 2.68 | 435 |
| MS1-37 | 4202 | Es3 | NSFM | 1.94 | 0.66 | 1.56 | 437 |
| MS1-38 | 4221 | Es3 | NSFM | 1.57 | 2.36 | 2.48 | 439 |
| MS1-39 | 4260 | Es3 | NSFM | 1.72 | 0.71 | 1.27 | 437 |
| MS1-40 | 4256 | Es3 | NSFM | 1.67 | 0.69 | 0.94 | 436 |
| MS1-41 | 4286 | Es3 | NSFM | 1.97 | 0.98 | 1.58 | 440 |
| MS1-42 | 4340 | Es3 | NSFM | 1.73 | 0.92 | 1.33 | 438 |
| MS1-43 | 4420 | Es3 | NSFM | 1.72 | 1.52 | 1.31 | 441 |
| MS1-44 | 4461 | Es3 | NSFM | 1.68 | 0.65 | 0.95 | 434 |
| MS1-45 | 4485 | Es3 | NSFM | 1.67 | 0.64 | 0.96 | 450 |
| MS1-46 | 4499 | Es3 | NSFM | 1.53 | 0.84 | 0.95 | 436 |
| MS1-47 | 4526 | Es3 | NSFM | 1.69 | 1.41 | 2.22 | 446 |
| MS1-48 | 4545 | Es3 | NSFM | 1.81 | 0.68 | 0.87 | 440 |
| MS1-49 | 4580 | Es3 | NSFM | 1.73 | 1.35 | 1.62 | 442 |
| MS1-50 | 4600 | Es3 | NSFM | 1.75 | 0.39 | 1.35 | 437 |
| MS1-51 | 4620 | Es3 | NSFM | 1.82 | 0.31 | 0.74 | 437 |
| MS1-52 | 4641 | Es3 | NSFM | 1.77 | 0.83 | 1.27 | 443 |
| MS1-53 | 4652 | Es3 | NSFM | 2.18 | 0.66 | 0.65 | 448 |
| MT1-1 | 4226 | Es3 | NSFM | 1.45 | 0.735 | 2.175 | 395 |
| MT1-2 | 4302 | Es3 | NSFM | 1.9 | 0.833 | 2.527 | 400 |
| MT1-3 | 4320 | Es3 | NSFM | 1.36 | 0.6164 | 2.0536 | 399 |
| MT1-4 | 4344 | Es3 | NSFM | 1.78 | 0.5958 | 2.4742 | 400 |
| MT1-5 | 4378 | Es3 | NSFM | 2.1 | 0.85 | 2.73 | 399 |
| MT1-6 | 4392 | Es3 | NSFM | 1.97 | 0.9984 | 2.5216 | 398 |
| MT1-7 | 4422 | Es3 | NSFM | 1.93 | 0.6989 | 2.4511 | 399 |
| MT1-8 | 4500 | Es3 | NSFM | 1.72 | 0.654 | 1.806 | 392 |
| MT1-9 | 4518 | Es3 | NSFM | 1.4 | 0.338 | 1.302 | 392 |
| MT1-10 | 4544 | Es3 | NSFM | 2.11 | 0.7037 | 2.8063 | 432 |
| MT1-11 | 4694 | Es3 | NSFM | 1.85 | 0.384 | 1.776 | 395 |
| MT1-12 | 4720 | Es3 | NSFM | 1.77 | 0.2708 | 1.6992 | 393 |
| MT1-13 | 4736 | Es3 | NSFM | 1.76 | 0.3456 | 1.6544 | 388 |
| MT1-14 | 4798 | Es3 | NSFM | 1.97 | 0.4879 | 1.8321 | 395 |
| MT1-15 | 4844 | Es3 | NSFM | 2.07 | 0.5542 | 1.9458 | 392 |
| MT1-16 | 5104.4 | Es3 | NSFM | 1.29 | 0.0091 | 0.2709 | 554 |
| MT1-17 | 5105.5 | Es3 | NSFM | 1.11 | 0.0147 | 0.2553 | 568 |
| MT1-18 | 5107 | Es3 | NSFM | 1.2 | 0.016 | 0.324 | 550 |
| MT1-19 | 5734 | Es3 | NSFM | 1.31 | 0.24 | 0.47 | 379 |
| MT1-20 | 5782 | Es3 | NSFM | 1.046 | 0.26 | 0.51 | 376 |
Table A2.
Molecular and carbon isotopic composition of all natural gas samples.
| Sample ID | Strata | Compimemts (%) | δ13C (‰, VPDB) | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| N2 | CO2 | CH4 | C2H6 | C3H8 | iC4H10 | nC4H10 | δ13CC02 | δ13C1 | δ13C2 | δ13C3 | δiC4 | δnC4 | ||
| X1 | Ed | / | / | 97.64 | 1.04 | 0 | 0.25 | 0.1 | / | −44.0 | / | / | / | / |
| X2 | Ed | 0.12 | 0.16 | 98.64 | 0.74 | 0.02 | 0.31 | 0 | / | −42.4 | −22.1 | −7.0 | / | / |
| X3 | Ed | 0.09 | 0.34 | 98.42 | 0.75 | 0.04 | 0.29 | 0.01 | −12.3 | −43.3 | −22.5 | −14.5 | −26.9 | −19.4 |
| X4 | Ed | 0.15 | 0 | 98.3 | 1.37 | 0.02 | 0.13 | 0 | / | −44.4 | −25.8 | −9.6 | −26.9 | / |
| X5 | Ed | 0.1 | 0 | 98.18 | 1.3 | 0.07 | 0.25 | 0.02 | / | −43.2 | −25.1 | −13.5 | −28.0 | / |
| X6 | Ed | 0.06 | 0.18 | 98.39 | 0.97 | 0.05 | 0.19 | 0.01 | −18.3 | −43.8 | −25.5 | −18.7 | −25.2 | −21.0 |
| X7 | Ed | 0.01 | 0 | 97.01 | 2.17 | 0.13 | 0.44 | 0.02 | −20.4 | −44.2 | −26.2 | −15.0 | −28.0 | −19.8 |
| X8 | Ed | 0.11 | 0 | 97.56 | 1.7 | 0.09 | 0.34 | 0.02 | / | −43.7 | −26.1 | −14.6 | −28.0 | / |
| X9 | Ed | 0.11 | 0 | 97.37 | 1.85 | 0.12 | 0.35 | 0.03 | −20.6 | −43.8 | −26.1 | −14.8 | −27.9 | −19.6 |
| X10 | Ed | 0.1 | 0.32 | 96.48 | 1.94 | 0.34 | 0.36 | 0.08 | −18.7 | −42.7 | −25.6 | −19.9 | −27.4 | −20.8 |
| X11 | Ed | / | / | 98.24 | 0.71 | 0 | 0.09 | 0 | / | −44.9 | / | / | / | / |
| X12 | Ed | 0.1 | 0 | 97.54 | 1.84 | 0.09 | 0.34 | 0.01 | −21.1 | −43.6 | −26.0 | −12.8 | −28.1 | |
| X13 | Ed | 0.09 | 0.15 | 97.01 | 2.03 | 0.12 | 0.35 | 0.03 | / | −43.7 | −26.1 | −15.0 | −28.2 | −20.4 |
| X14 | Ed | 0.15 | 0 | 97.78 | 1.72 | 0.03 | 0.3 | 0 | / | −44.2 | −26.1 | −8.8 | −27.8 | / |
| X15 | Ed | 0.17 | 0 | 97.05 | 2.16 | 0.3 | 0.19 | 0.05 | / | −44.4 | −26.6 | −22.0 | −27.1 | −20.6 |
| X16 | Ed | 0.05 | 0.33 | 96.53 | 2.29 | 0.13 | 0.39 | 0.02 | / | −42.8 | −26.1 | −13.2 | −28.9 | −17.4 |
| X17 | Ed | 0.11 | 0 | 97.64 | 1.85 | 0.06 | 0.32 | 0 | −21.3 | −44.1 | −25.9 | −10.0 | −28.2 | / |
| X18 | Ed | 0.26 | 0 | 99.52 | 0.18 | 0.02 | 0.02 | 0.01 | −18.4 | −51.3 | −25.5 | / | / | / |
| X19 | Ed | 0.22 | 0 | 97.89 | 1.56 | 0.14 | 0.09 | 0.04 | / | −52.1 | −31.8 | / | / | / |
| X20 | Ed | 0.31 | 0 | 99.46 | 0.22 | 0 | 0.01 | −20.8 | −50.6 | −27.7 | / | / | / | |
| X21 | Ed | 0.23 | 0 | 97.72 | 1.75 | 0.08 | 0.1 | 0.03 | / | −52.4 | −31.4 | −19.8 | −27.3 | −21.3 |
| X22 | Ed | 0.24 | 0 | 97.56 | 1.73 | 0.13 | 0.22 | 0.03 | / | −51.0 | −29.1 | −18.2 | −28.0 | −22.5 |
| X23 | Ed | 0.37 | 0 | 99.5 | 0.13 | −20.3 | −51.9 | −34.8 | / | / | / | |||
| X24 | Ed | 0.21 | 0 | 97.4 | 1.74 | 0.28 | 0.16 | 0.09 | / | −51.0 | −30.7 | −21.3 | −28.0 | −24.0 |
| X25 | Ed | 0.25 | 0.76 | 84.75 | 7.89 | 4.34 | 0.52 | 0.95 | −3.1 | −45.7 | −30.4 | −27.8 | −26.7 | |
| X26 | Es1 | 0.13 | 1.5 | 82.46 | 8.81 | 4.59 | 0.58 | 1.09 | −4.2 | −45.4 | −31.1 | −28.0 | −26.8 | |
| X27 | Es1 | 2.44 | 19.65 | 77.44 | 0.31 | 0.05 | 0.01 | 0.00 | −0.7 | −28.6 | −18.9 | −18.6 | / | / |
| X28 | Es3 | 1.19 | 20.37 | 78.24 | 0.11 | 0.01 | 0.00 | 0.00 | −2.4 | −28.7 | −17.5 | / | / | / |
| X29 | Es3 | 2 | 0.16 | 91.77 | 4.8 | 0.7 | 0.12 | 0.26 | −6.0 | −31.0 | −24.8 | −23.8 | −23.9 | |
| X30 | Ar | 2.12 | 0.28 | 85.21 | 5.08 | 2.8 | 1.01 | 1.29 | −6.8 | −31.9 | −26.2 | −25.7 | −25.7 | |
| X31 | Ar | 1.7 | 0.1 | 90.1 | 4.4 | 1.9 | 0.6 | 0.8 | − | −36.37 | −25.30 | −24.30 | ||
| X32 | Ar | 0.83 | 0.45 | 85.7 | 7.14 | 3.16 | 0.84 | 1.04 | −2.7 | −37.2 | −27.0 | −25.9 | −25.6 | |
| X33 | Ar | 30.16 | 0.073 | 63.39 | 4.63 | 0.7 | 0.12 | 0.28 | − | −36.3 | −26.6 | −24.5 | −24.0 | |
| X34 | Ar | 31.17 | 0.15 | 62.65 | 4.76 | 0.56 | 0.061 | 0.14 | − | −37.2 | −27.2 | −24.7 | −23.1 | |
| X35 | Ar | 0.8 | 0.46 | 83.49 | 9 | 3.57 | 0.77 | 0.85 | −11.8 | −36.6 | −27.4 | −25.6 | −25.7 | |
| X36 | Ar | 1.31 | 0.19 | 85.51 | 7.37 | 3.31 | 0.77 | 0.9 | − | −36.8 | −27.6 | −25.8 | −24.8 | |
| X37 | Ar | / | / | 97.64 | 1.04 | 0 | 0.25 | 0.1 | / | −44.0 | / | / | / | / |
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Figure 1.
(a,b) show the location of the Xinglongtai area, Western Depression, Liaohe Subbasin. (c) Structural division of the Xinglongtai area.
Figure 1.
(a,b) show the location of the Xinglongtai area, Western Depression, Liaohe Subbasin. (c) Structural division of the Xinglongtai area.
Figure 3.
Two-dimensional lithofacies models for three representative profiles. The locations are illustrated in Figure 1b. SFM = Sublacustrine-Fan Mudstones; FDM-W = Fan-Delta Mudstones from the Western slope; FDM-E = Fan-Delta Mudstones from the Eastern slope; SDLM = Semi-Deep Lake Mudstones; SLM = Shallow Lake Mudstones; NSFM = Nearshore Subaqueous Fan Mudstones; Mixed lithology of N + Q = Sandstone (95%) + Conglomerate (5%).
Figure 3.
Two-dimensional lithofacies models for three representative profiles. The locations are illustrated in Figure 1b. SFM = Sublacustrine-Fan Mudstones; FDM-W = Fan-Delta Mudstones from the Western slope; FDM-E = Fan-Delta Mudstones from the Eastern slope; SDLM = Semi-Deep Lake Mudstones; SLM = Shallow Lake Mudstones; NSFM = Nearshore Subaqueous Fan Mudstones; Mixed lithology of N + Q = Sandstone (95%) + Conglomerate (5%).
Figure 4.
(a) Diagrams of Cn/C1–5 ratio and (b) carbon isotope series of natural gas samples from the Xinglongtai area, Liaohe Subbasin, Bohai Bay Basin.
Figure 4.
(a) Diagrams of Cn/C1–5 ratio and (b) carbon isotope series of natural gas samples from the Xinglongtai area, Liaohe Subbasin, Bohai Bay Basin.
Figure 5.
Genetic diagram of C1/(C2 + C3) versus δ13C1 for natural gas samples from the Xinglongtai area, Liaohe Subbasin, Bohai Bay Basin. The diagram is modified from [34,35].
Figure 6.
(a) Cross plot of δ13C1 versus δ13C2 and (b) δ13C2 versus δ13C3 for natural gas samples from the Xinglongtai area, Liaohe Subbasin, Bohai Bay Basin.
Figure 6.
(a) Cross plot of δ13C1 versus δ13C2 and (b) δ13C2 versus δ13C3 for natural gas samples from the Xinglongtai area, Liaohe Subbasin, Bohai Bay Basin.
Figure 7.
(a) Cross-plot of TOC versus (S1 + S2) [47]. (b) Box plot of mudstone types and TOC contents. (c) Cross-plot of HI versus Tmax of mudstones. (d) Box plot of mudstone types and HI contents.
Figure 7.
(a) Cross-plot of TOC versus (S1 + S2) [47]. (b) Box plot of mudstone types and TOC contents. (c) Cross-plot of HI versus Tmax of mudstones. (d) Box plot of mudstone types and HI contents.
Figure 8.
Evolution of the maturity and the transformation ratio with age in Profile AA’ at 40 Ma (a,b), 38 Ma (c,d), 30 Ma (e,f), and 0 Ma (g,h).
Figure 8.
Evolution of the maturity and the transformation ratio with age in Profile AA’ at 40 Ma (a,b), 38 Ma (c,d), 30 Ma (e,f), and 0 Ma (g,h).
Figure 9.
Diagrams showing the gas generation with time in Profile AA’.
Figure 10.
Simulation results of hydrocarbon migration and accumulation in Profile CC’ at 40 Ma (a), 38 Ma (b), 30 Ma (c), and 0 Ma (d). Under the background of overpressure.
Figure 10.
Simulation results of hydrocarbon migration and accumulation in Profile CC’ at 40 Ma (a), 38 Ma (b), 30 Ma (c), and 0 Ma (d). Under the background of overpressure.
Figure 11.
Simulation results of hydrocarbon accumulation and proportional contribution of source rocks in each stratum in Profile CC’ at 38 Ma (a), 30 Ma (b), and 0 Ma (c).
Figure 11.
Simulation results of hydrocarbon accumulation and proportional contribution of source rocks in each stratum in Profile CC’ at 38 Ma (a), 30 Ma (b), and 0 Ma (c).
Figure 12.
Events chart showing the petroleum system elements in the Xinglongtai structural belt.
Figure 13.
(a) Genetic types of gas samples in the outer Xinglongtai buried hill; (b) genetic types of gas samples in the inner Xinglongtai buried hill; (c) origin and accumulation of natural gases in the Xinglongtai structural belt, Western Depression.
Figure 13.
(a) Genetic types of gas samples in the outer Xinglongtai buried hill; (b) genetic types of gas samples in the inner Xinglongtai buried hill; (c) origin and accumulation of natural gases in the Xinglongtai structural belt, Western Depression.
Table 1.
Summary of all layers modeled using the PetroMod 2016 software.
| Age at the Top (Ma) | Layer Name | PSE | Event Type |
|---|---|---|---|
| 0.0 | N + Q | Overburden Rock | Deposition |
| 24.6 | / | / | Erosion (after Ed) |
| 26.6 | Ed | Reservoir Rock | Deposition |
| 36.0 | / | / | Erosion (after Es1+2) |
| 36.5 | Es1+2 | Reservoir Rock | Deposition |
| 38.0 | / | / | Erosion (after Es3) |
| 38.3 | Es31 | Rock Source | Deposition |
| 39.0 | Es32 | Source Rock | Deposition |
| 41.5 | Es33 | Source Rock | Deposition |
| 43.0 | Es41 | Source Rock | Deposition |
| / | Basement | Reservoir Rock | Deposition |
Note. Es31: The upper Submember of the Mbr 3 of the Shahejie Formation. Es32:The middle Submember of the Mbr 3 of the Shahejie Formation. Es33: The lower Submember of the Mbr 3 of the Shahejie Formation. Es41: The upper Submember of the Mbr 4 of the Shahejie Formation.
Table 2.
Summary of input parameters for Eocene source rocks. The kerogen types were classified following [30], and the hydrocarbon generation kinetic models were proposed by [27].
| Formation | TOC | HI | Kerogen Type | Kinetic Model |
|---|---|---|---|---|
| (%) | (mg HC/g Rock) | |||
| SFM | 2.2 | 305 | Type II | (Burnham, 1989 T-II) |
| FDM-W | 1.9 | 290 | Type II | (Burnham, 1989 T-II) |
| FDM-E | 1.5 | 100 | Type III | (Burnham, 1989 T-III) |
| SDLM | 2.2 | 490 | Type I | (Burnham, 1989 T-I) |
| SLM | 1.4 | 200 | Type II | (Burnham, 1989 T-II) |
| NSFM | 1.6 | 75 | Type III | (Burnham, 1989 T-III) |
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Yang, S.; Li, M.; Wang, Y.; Xiao, H.; Huang, S.; Kang, W.; Wang, F. Origin, Migration, and Characterization of Gas in the Xinglongtai Area, Liaohe Subbasin (Northeast China): Insight from Geochemical Evidence and Basin Modeling. Energies 2023, 16, 6429. https://doi.org/10.3390/en16186429
AMA Style
Yang S, Li M, Wang Y, Xiao H, Huang S, Kang W, Wang F. Origin, Migration, and Characterization of Gas in the Xinglongtai Area, Liaohe Subbasin (Northeast China): Insight from Geochemical Evidence and Basin Modeling. Energies. 2023; 16(18):6429. https://doi.org/10.3390/en16186429
Chicago/Turabian StyleYang, Sibo, Meijun Li, Yanshan Wang, Hong Xiao, Shuangquan Huang, Wujiang Kang, and Fangzheng Wang. 2023. "Origin, Migration, and Characterization of Gas in the Xinglongtai Area, Liaohe Subbasin (Northeast China): Insight from Geochemical Evidence and Basin Modeling" Energies 16, no. 18: 6429. https://doi.org/10.3390/en16186429
APA StyleYang, S., Li, M., Wang, Y., Xiao, H., Huang, S., Kang, W., & Wang, F. (2023). Origin, Migration, and Characterization of Gas in the Xinglongtai Area, Liaohe Subbasin (Northeast China): Insight from Geochemical Evidence and Basin Modeling. Energies, 16(18), 6429. https://doi.org/10.3390/en16186429
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