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The Sichuan Basin
The Sichuan Basin is located at the northwest margin of the Yangzi plate. It is bounded by the squeezing action of the eastward thrust nappe structure of the Tibetan plateau and limits of the perimeter orogenic belt, forming a diamond border with a distinct north– eastward trend. The basin margin is a sedimentary and tectonic basin due to the Longman mountain structural belt, the Qinling orogenic zone and the Songpan–Ganzi fold belt. The Sichuan Basin is an important part of western China’s major oil and gas field.
With the development of exploration technology, having a full understanding of the basic geology and petroleum geological characteristics of the Sichuan Basin. Nowadays, most of the large and middle oil and gas fields and proved reserves in the Sichuan Basin are found in the northern and middle of the basin, with more than 20 gas–bearing layers, 173 gas fields and 13 oilfields proved in the basin (The proven reserves of large oil and gas fields are 300 х108 m3). The results of studies have shown a clear Bouguer gravity height, a relatively small variation in the internal of the Sichuan Basin, and a gradual gravity contour all around the basin periphery. Gravity prospecting plays an important role in the census and exploration stage of oil and natural gas. Therefore, there is an urgent need to study the characteristics of the Bouguer gravity anomaly and oil–gas distribution.
Regional Geological Overview
Since the Phanerozoic eon, based on reservoir filling characteristics and tectonic deformation features, the development and evolutionary stages in the Sichuan Basin are classified as five main stages according to reservoir filling characteristics and tectonic deformation characteristics, which are: the Sinian tectonic evolution stage, the Cambrian– Silurian tectonic evolution stage, the Devonian middle Triassic tectonic evolution stage, the late Triassic Epoch–Early Cretaceous Epoch tectonic evolution stage and the Upper Cretaceous–Cenozoic tectonic evolution stage. The three major tectonic evolution and sedimentary changes in the basin are bounded by the late Triassic epoch, Upper Cretaceous and Eocene.
The surface structural features of the Sichuan basin are subject to geological movements of the structural belt in multiple directions on an edge, showing a complex association of multi–period and multi–combination tectonic frameworks. As shown in Figure 1, the sedimentary depression of the plate, the differential bulge, the fracture and expansion of the basin basement and basin margin within the basin, and the existence of multi–period ramification and splitting between the plates, resulted in the formation and evolutionary development of stacked basins with multiple types. In terms of sedimentary evolution, the Sichuan Basin is a red bed basin that has evolved from a long period as a marine basin.
For a long time, the Sichuan Basin has been in the transitional conversion area of Gondwana–Laurasia. After the formation of the Palestinian period basement, the basin crust was in a phase of intense tectonic activity, suffering from laminated transformation by the Chengjiang movement, Tongwan movement, Caledonian movement, Yunnan movement, Dongwu movement, Indo–china movement, Yanshan movement and Himalayan movement, and the Emeishan basalt finally entered a phase of eruptive activity in the Permian. Sedimentary layers from the Han Dynasty system to the Quaternary were developed in the Sichuan Basin at a thickness of more than 13,000 m. The sedimentary cover is classified as two types, marine and continental, including the Sinian system to Middle Permian marine sedimentary strata, dominated by carbonate rocks, with a formation thickness between 4100 and 7000 m. The Upper Triassic to Cretaceous is a continental deposition layer that is 3500 to 6000 m thick. There are eight regional unconformities between the marine and continental strata, which are: between the Sinian system and the underlying and neo–proterozoic basement rock strata, between the Devonian and the underlying Silurian strata, between the Upper Triassic and the underlying Middle Triassic series strata, between the Jurassic and the underlying Upper Triassic strata, between the Cretaceous and the upper Jurassic underlying formation, between the Paleogene and the underlying Cretaceous formation, between the Neogene and the Paleogene underlying strata, and between the Quaternary and the Neogene underlying strata.
The reservoirs in the Sichuan Basin were mainly developed by sandstones, showing the characteristics of dense development, large fissures, high heterogeneity, and poor reservoir physical properties. The cover is mainly composed of evaporated gypsum rock, which plays a key role in oil and gas sealing. It has a good sealing and preservation effect on the generated oil and gas reservoirs. The Sichuan Basin is rich in high–quality source rocks, with the characteristics of a large number of strata, wide span, mud shale as the primary strata for the development of source rocks, and the development of carbonate source rocks. The source rock has a high degree of thermal evolution and has entered a high maturity stage. Due to the high degree of thermal evolution of some source rocks, crude oil is decomposed into a gas, so the Sichuan Basin has abundant oil and gas resources.
Figure 1. Regional geological map of the Sichuan Basin (modified from Zheng et al.).
Evolution and petroleum systems of Sichuan Super Basin
One of the essential components of a Super Basin is the multiple stacked sets of source rocks and reservoirs. The Sichuan Basin has suitable geological conditions and resource base that meet the definition of a Super Basin. Several petroleum systems are found within the Sichuan Basin, and each system has its unique hydrocarbon accumulation patterns due to the control of tectonic evolution. Only by clarifying the regularity of resource accumulation, can the hydrocarbon potential of the Sichuan Super Basin be fully exploited.
The Sichuan Basin, a tectonically superimposed basin on the base of Yangtze Craton, has undergone three evolutionary stages: the Nanhua rift basin stage, the Sinian–Middle Triassic marine cratonic basin stage, and the Late Triassic–Cretaceous foreland basin stage. Multiple sets of source rocks and reservoir rocks were developed through the evolutionary history of the basin. Vertically, multiple petroleum systems are distributed. Horizontally, hydrocarbon accumulations spread throughout the basin.
Various types of hydrocarbons are endowed in the basin, and conventional and unconventional resources are orderly distributed (Fig. 2). Conventional gas is primarily found in the deep to ultra-deep marine carbonate formations.
Tight sand gas is mainly distributed in the Upper Triassic–Jurassic reservoirs with medium to shallow depth. Shale gas is contained in the Lower Silurian Longmaxi Formation and Lower Cambrian Qiongzhusi Formation, as well as the Sinian Doushantuo Formation, Upper Permian Wujiaping Formation and Lower Jurassic Da'anzhai Formation. Lacustrine tight sand oil and shale oil are found in the Middle–Lower Jurassic in the central- north of Sichuan Basin (Fig. 2).
Figure 2. Vertical distribution of oil and gas reservoirs in the Sichuan Basin. J1z—Zhenzhuchong Formation; T3x1 — the first member of Xujiahe Formaiton; T2l — Leikoupu Formation; T1j1 — the first member of Jialingjiang Formation; T1f1 — the first member of Feixianguan Formation; P2l — Longtan Formation; C — Carboniferous; S — Silurian; O3 — Upper Ordovician; Cambrian2–3 X— Xixiangchi Formation; Cambrian2g—Gaotai Formation; Cambrian1l— Longwangmiao Formation; Cambrian1q—Qiongzhusi Formation; Z2dn3—the third member of Dengying Formation; Z2dn1—the first member of Dengying Formation.
The Nanhua rift basin stage and potential interglacial gas systems
After the unified basement was formed during the Jinning Movement, the Yangtze Craton was influenced by the break-up of the Rodinia Supercontinent, which led to a N–E horst-graben basin structure. In the periphery of the Sichuan Basin, the Chuanxi-Dianzhong rift, the Qiandong-Xiangxi rift, the Xupu-Sanjiang rift, and the Hunan-Guangxi rift were developed. Based on the interpretation of geophysical data, a N–E-oriented intra-continental rift may exist in the interior of the Sichuan Basin (Fig. 3), and two groups of faults (N–E and N–W) were developed, which may be connected to the northern continental margin of the Yangtze craton.
The formation of such intra-continental rift in the Sichuan Basin is related to the pull-apart of the Proto- Tethys Ocean, and it is an extension of the continental margin basin to the interior of the Yangtze Craton.
Figure 3. Map of the proto-model of Sichuan Basin and adjacent areas in Nanhua Period.
The Chuanxi–Dianzhong rift is characterized by the filling of thousands of meters thick continental clastic rocks and volcanic rocks, but contains no source rocks. The Nanhua rift system to the east of the Yangtze Craton presents as a horst-graben structure vertically, within which the thickness of glacial-interglacial deposits are up to 1000 m. Therein, the Gucheng Formation and Nantuo Formation are glacial deposits with widely distributed thick moraine conglomerates. The Datangpo Formation containing interglacial deposits appears as the first set of high-quality source rocks in the Yangtze Craton, consisting of 0–100 m thick carbonaceous shale interlaced with manganese- or iron-bearing strata. The analysis of 25 samples from the Songtao and Xiushan outcrop sections reveals the total organic carbon (TOC) of 0.25%–3.76% (avg. 2.23%) and the equivalent vitrine reflectance (Ro) of 2.9%–3.1%. The moraine conglomerates in the Nantuo Formation exhibit moderate reservoir properties, with the porosity of 2.0%–5.5% (avg. 3.5%), which is mainly contributed by feldspar dissolution pores, quartz dissolution pores, and fractures. Studies show that the Datangpo Formation source rocks and the Nantuo Formation reservoir rocks constitute an ideal source-reservoir assemblage, which provides a resource base for the potential hydrocarbon system of the Nanhua interglacial stage.
Such a hydrocarbon system of Nanhua Period has not been confirmed by drilling in the Sichuan Basin. However, according to the global analogy and the rock property in outcrop areas, it should be considered as a backup for exploration. Snowball events occurred globally in the Neoproterozoic. The warm climate in the interglacial period led to the rise of sea level and the development of microbiolites. The black shale rich in algal organic matter in this period is a high-quality source rock globally, which charges the interglacial petroleum system with microbial carbonate reservoirs. Such petroleum system is widely distributed in the northern margin of the Gondwana. As mentioned, the Nanhua Period Chuanzhong Rift in the interior of the Sichuan Basin is connected northward with the Proto-Tethyan Ocean. The Datangpo Formation at the outcrop of Heyu in the Chuanzhong Rift contains shale rich in organic carbon with horizontal beddings. It is speculated that the distribution of such potential source rock can extend to the central Sichuan Basin and provide hydrocarbon source for ultra-deep gas accumulation.
Tectonic Unit
Since the formation of the first sedimentary layer at the bottom of the Sichuan Basin (Sinian Doushantuo Formation), in the process of tectonic evolution and development of the basin, the structure and transformation interact and develop in an episodic manner, forming a unique multi–cycle fold structure in the Sichuan Basin. In order to determine the correlation between the tectonic units of the central and western Sichuan Basin, based on the characteristics reflected by the Bouguer gravity anomaly and the residual gravity anomaly, three regional seismic reflection profiles in the NW-SE direction (L1, L2, L3) were selected for structural interpretation (Figure 4) combined with the results of three seismic reflection profiles in the study area, the tectonic units of Sichuan Basin were delimited comprehensively.
Figure 4. Large seismic profile location map of Sichuan Basin (modified from Li).
L1 was located in the northern part of the basin, the total length is 380 km, and the direction of the seismic profile is from NW to SE. In the eastern part of the basin, there are seven geological structures: Huayingshan structure, Pubaoshan structure, Qilixia structure, Datianchi structure, Huangnitang structure, Dachigan structure, and Fangdoushan structure. The Huacong, Longgang, Shuikouchang, and Shuishen No.1 wells were passed north of the basin. In the west of the basin, through the Hewanchang and Jiulongshan structures (Fig. 5a).
Figure 5. The deep seismic reflection profiles of Sichuan Basin (modified from Li). (a) L1; (b) L2; (c) L3
L2 was located in the central part of the basin with a total length of about 390 km. From northwest to southeast, it passes through the center of the Sichuan Basin, from northwest to Mianyang and from southeast to Chongqing. The section passes through the Jinhua, Longnvsi, and Nvjijing structures in the middle of the basin. In the eastern part of the basin, the Huayingshan structure, Zhongliangshan structure, Longwangdong structure, Tongluoxia structure, Mingyuexia structure, and Fengshengchang structure are passed through the six geological structures (Fig. 5b).
L3 is located in the southern part of the basin, about 400 km long, from northwest to southeast through the western basin Gaojiachang structure, Baimamiao structure, and Xiongpo anticline. In the south of the basin, L3 passed through the Longquanshan structure, Weiyuan structure, Luoguanshan structure, Gufoshan structure, Longdongping structure, and Liziba structure of the six geological structures Ziyang No.5 well and Zishen No.2 well (Figure 5c).
Combined with the results of gravity anomalies and seismic reflection data, the tectonic units of the central and western Sichuan Basin are divided into five blocks, which are the central Sichuan uplift area, the western Sichuan depression area, the eastern Sichuan high and steep area, the southern Sichuan low and steep area and the northern Sichuan low and gentle area, as shown in Figure 6. As can be seen from the figure, it is roughly equivalent to the previous division results, which are reflected in the central region as the uplift area, the western region as the depression area, the northern region as the low–slow area and the southern region as the high–steep area.
Figure 6. Delineation of tectonic elements of the central and western Sichuan Basin.
The central Sichuan uplift area is located east of the Longquan mountain fault zone and west of the Huayingshan fault. It is the most stable central uplift in it, and has maintained highly position since the Sinian period. There are relatively wide and gentle fold structures in the shallow layer of this area, and the number of fractures is small.
The deeper the fracture is, the smaller and weaker it is. Previous research has shown that this area presents the characteristics of high resistance, a high–velocity layer and high–density paleostratum. It corresponds to the high–gravity anomaly value and seismic profile L2 protrusion characteristics in this area. It is in a multi–directional extrusion tectonic environment, and the fold–thrust structure around the basin is strongly deformed.
It is a foreland depression formed in the western Sichuan Basin since the Late Triassic. There are three sets of main structures, which are characterized by nearly east–west trending, nearly north-south trending and northeast–trending, with east–west tilt zoning, north–south trending segmentation and north–south vertical stratification.
There is an obvious gravity gradient belt in the Bouguer gravity anomaly map, and it is shown as a high gravity value in the residual gravity anomaly map. The buried depth of the basement is more than 8 km, the structure is generally in the northeast direction, the fold amplitude is large, the fault is developed, and there is continuous subsidence after the Indosinian movement. The high and steep area of eastern Sichuan is located southeast of the Huayingshan fault zone. The east boundary is the Xuefeng uplift, dominated by metamorphic basement strata. The northern boundary is the northwestward–southeastward trending South Dabashan arc orogenic belt. In this region, the Bouguer gravity anomaly is high, and several isolated small high–value Bouguer gravity anomaly traps are developed, most of which are shown as low gravity values in the residual gravity anomaly map. The basement lithology of shallow strata is non-magnetic or weakly magnetic, and the buried depth of the basement is 6–10 km. The gravity anomaly zone in this area strikes nearly east–west, and the eastern part of Chongqing shows a negative gravity anomaly, which is generally manifested as an arc–shaped structural belt that protrudes slightly to the northwest, interspersed with a series of intricate anticlines, synclines and faults alternately arranged.
The low-steep area of southern Sichuan is located south of the Huayingshan fault. It can be seen from the residual gravity anomaly diagram that there are alternating distribution characteristics of high gravity and low gravity, and the region is generally shown to have a low gravity anomaly, with a basement depth of 3–5 km. It is the highest uplift and shallowest buried area of sedimentary cover in the Sichuan Basin. The tectonic belt is more complex, the crustal tectonic movement is more intense, the fold deformation in the region is severe, and multiple secondary fault zones have developed, which have experienced multi–period complex crustal movement. In addition, the oil and gas in southern Sichuan are not affected by structural traps, most of which exist in structural styles.
Along the piedmont fault fold belt, the low, gentle area of North Sichuan extends north to the Micangshan orogenic belt and the Dabashan orogenic belt. In this area, the high and low Bouguer gravity are interphase. It can be seen that there is an obvious gravity anomaly zone in the residual gravity anomaly map, which is the high gravity anomaly value, due to different structural stresses, local structural units such as thrust nappe structural belts, back thrust anticline structural belts and low fold belts are formed, and the buried depth of bedrock is more than 8–10 km. The development of local structural folds in this area is not obvious. After the Caledonian movement, faults developed and continued to subside, forming a geological depression.
Compared with the previous division of tectonic units in the Sichuan Basin, there are three differences in the division of tectonic units in this paper, namely, central Sichuan, southern Sichuan, and northern Sichuan. The divided difference between central and southern Sichuan is mainly based on the Huayingshan fault zone and the residual gravity anomaly map. Most residual gravity anomaly maps in the central Sichuan area show positive anomalies, while the divided southern Sichuan area obviously has negative anomalies. This is because the basin’s southern part is affected by multi–stage structures and is compounded with the surrounding structures, reflecting the relatively shallow burial depth of the high-density basement in the surrounding area.
Oil-Gas Distribution
The Sichuan Dasin is a more typical superimposed western China basin and the largest petroliferous basin. It has formed many oil and gas fields (Fig.7). The predecessors have also conducted a lot of research on the distribution of oil and gas fields in the Sichuan Basin and obtained a series of important understandings.
Figure 7. Residual anomaly and distribution features of the research area’s major oil and gas fields. (I: Leshan–Longnvsi paleo–uplift; II: Luzhou paleo–uplift; III: Kaijiang paleo–uplift).
Current distribution characteristics of big and middle–sized oil and gas fields in the Sichuan Basin reflect the spatial distribution characteristics of residual oil and gas fields during the uplift and denudation of Mesozoic and Cenozoic basins and the adjustment and transformation. At present, Micangshan Mountain and Daba Mountain in the north of the basin have a total of 21 gas fields (including 10 large gas fields and 11 medium–sized gas fields). The number of large oil and gas fields in the central basin is small.
Types of large and medium gas fields are mainly associated with paleo uplift and tilted zone of paleo uplift. It can be seen that the paleo uplift is very important in the oil and gas cumulation process. Three paleo–uplifts were formed during the evolutionary development of the Upper Yangtze Craton in the Sichuan Basin: Leshan–Longnvsi paleo–uplift, Luzhou paleo–uplift and Kaijiang paleo–uplift. Each paleo–uplift evolved and developed in different periods, distributed in different regions of the Sichuan Basin, and had different evolution stages.
Leshan–Longnvsi ancient paleo uplift developed in the western margin of the basin, and continued until the Permian sedimentary evolution. It is speculated that the formation is related to the strong collision and extrusion of the Yangtze plate and the North China plate along the Mianlue suture zone. The Longmen mountain fault zone is the boundary of positive and negative Bouguer gravity anomalies between the Sichuan Basin and Songpan–Ganzi block. There is an obvious Bouguer gravity anomaly zone in the western margin of the Leshan–Longnvsi ancient paleo uplift, and the residual gravity anomalies are interdistributed with high gravity and low gravity, of which the high gravity value area occupies a large part. The abnormal values on both sides decreased sharply, and the abnormal values decreased from 16x10-5 m/s2 to -8x10-5 m/s2, which was consistent with the topographic characteristics of the western margin of the Sichuan Basin.
Multiple gas fields found in the western Sichuan area are mainly located in the ancient uplift zone, which is mostly the residual high gravity zone and the transition zone between high gravity and low gravity zones, in which the detachment layer is not developed, the ground faults are few, the sedimentary cover is thin, and the fold is gently developed.
The formation of the Luzhou paleo–uplift located at the southern end of the Huaying mountain structural belt in southern Sichuan has a certain influence on the tectonic framework of southern Sichuan. The Bouguer gravity anomaly in the Luzhou paleo–uplift region has a high value anomaly trap, the gravity value in the high value anomaly closure area is about -70x10-5 m/s2, and the residual gravity anomaly is distributed between high gravity and low gravity. The Indosinian orogenic movement of surrounding blocks controls the Luzhou paleo–uplift’s formation, evolution and development. It is a front uplift zone formed during the migration from east to west and the Xuefengshan orogenic belt extrusion on the Yangtze block’s southeastern margin. It was developed in the
Indo–Chinese epoch, and its nucleus is located in Luzhou, extending in a north–easterly direction. The residual gravity anomaly in the southern Sichuan area is gradually increased to the north–east. The Bouguer gravity anomaly in the southeastern margin of the Sichuan Basin is characterized by a north east–south west zonal distribution. It overlaps with the low–value area of the annular negative anomaly with the small scattered distribution.
The low–value area may reflect the influence of the evolution of the nearly north–south structural belt in southern Sichuan. The residual gravity anomaly values in the study area are generally between -13x10-5 m/s2 and 12 x10-5 m/s2, and continue to extend to the southeast. The residual gravity anomaly increases to 12 x10-5 m/s2. It continues
to increase to the southeast, reflecting a significant change in the crustal structure or the degree of crustal tectonic uplift and deformation. The oil and gas fields in this area are mainly distributed in the Luzhou palaeo uplift and are located in the area of high residual gravity anomaly.
The Kaijiang paleo–uplift and the Luzhou paleo–uplift located in northeastern Sichuan are located in the same uplift belt, with similar evolution characteristics. They are NE–trending erosional paleo–uplifts formed in the Indosinian movement at the end of the Middle Triassic. Bouguer gravity in this region presents a band of high–value anomalies
with a small variation range. The residual gravity anomalies are intermingled with high gravity and low gravity, with a maximum value of 2.0 x10-5 m/s2 and a minimum value of -8.0 x10-5 m/s2. Some small trap anomalies are growing from the Kaijiang paleo–uplift area. The analysis is related to this area’s exposure and distribution of structural arc belts and deep strata. The explored oil and gas fields in this area are mainly distributed in the
transition area between the residual high gravity anomaly area and the low gravity area.
The Bouguer gravity value in the central and western Sichuan Basin shows a stable regional high–value anomaly. The gravity anomaly changes gently, and the amplitude is low, caused by basement uplift of the whole basin. In the basin, the high and low residual gravity anomalies are distributed in alternate phases, corresponding to the distribution of oil and gas fields. There are obvious gravity gradient zones in the western and northern margins of the basin, and the Longmenshan fault zone and Micangshan uplift are developed.
The oil and gas fields in these two areas are more widely distributed. In the eastern region of the basin, there is contour distortion in the residual gravity anomaly, which is due to the development of more fault zones, more secondary tension faults, interlayer fracture due to extrusion of the Huayingshan fault zone, good conditions for oil and gas generation and preservation, and the distribution of oil and gas fields in this region. In the south, there are many low–gravity anomaly traps that do not correspond to the distribution of oil and gas fields. This is due to the strong fold deformation in this area. The basin is generally characterized by high–density rigid block, stable internal structure, developed source rock and high gas formation rate. Due to the entire basement uplift and the strong deformation of metamorphic rocks and magmatic rocks, the Sichuan Basin has an obvious double–layer structure; that is, the underlying basement tectonic layer and the overlying tectonic layer composed of sedimentary rocks, and the basement structure and caprock structure and their configuration relationship determine the oil and gas distribution to a certain extent. Since the Late Paleozoic, the Sichuan Basin’s sedimentary environment has always been relatively stable, all of which are Cenozoic sediments, so the residual gravity anomalies show low–value anomalies. Because sediments provide basic conditions for the development of source rocks, there are many oil and gas fields in the basin, mainly located in the highly steep areas of eastern Sichuan, western Sichuan depression and central Sichuan uplift.
In summary, it was found that the main distribution of large and medium–sized oil and gas fields discovered in the Sichuan Basin nowadays is controlled and influenced by basin basement structure, sedimentary cover and peripheral faults. Comparing the distribution of oil and gas fields with the distribution of residual gravity anomalies in the
basin and paleo–uplifts distribution map (Figure 7), most of the oil and gas fields in the central and western Sichuan Basin correspond to high gravity areas, but there is a close correlation between low gravity and oil and gas fields near Dazhou, which is caused by the existence of high–quality reef beach reservoirs, deep and large faults, and reservoir cracking of large-scale paleo–uplift.
Exploration history and remaining oil/gas distribution in the Sichuan Basin
The oil and gas exploration in the Sichuan Basin began in the 1940s and has gone through four stages (Fig. 8). In the first stage (1953–1977): structural trap exploration, middle and shallow structural traps were mainly explored, the cumulative proved gas reserves were 1511x108 m3, and the gas production exceeded 50 x108 m3 in 1977. In the second stage (1978–2004): large- and mediumsized gas reservoir exploration, the Carboniferous in eastern Sichuan Basin and the Feixianguan Formation in northeastern Sichuan Basin were mainly explored, the cumulative proved gas reserves were 6250x108 m3, and the gas production exceeded 100 x108 m3 in 2004. In the third stage (2005–2010): lithologic reservoir exploration, the sandstone gas reservoirs of the Xujiahe Formation and the reef-beach gas reservoirs of Longgang in central Sichuan Basin were mainly explored, the cumulative proved gas reserves were 6153 x108 m3, and the gas production exceeded 150x108 m3 in 2009.
Figure 8. Exploration history, proved reserves, and annual gas production in the Sichuan Basin
In the fourth stage (2012 to present): gas province exploration, the conventional gas in the Sinian–Cambrian carbonate reservoirs, shale gas in southern Sichuan Basin and tight sand gas in Jurassic were mainly explored, the cumulative proved gas reserves were 20 541 x108 m3, and the gas production exceeded 300 x108 m3 in 2021. In terms of exploration discoveries, reserves and production, the Sichuan Basin is now in the golden period with rapidly growing reserves and production, which is benefited from the integrated development mode of the natural gas industry formed over a long period. This mode is a unique economic development strategy and management mode adapting to the development characteristics and environment of the regional natural gas industry.
Based on the oil and gas resource evaluation of the Sichuan Basin in 2019, the distribution of remaining recoverable oil and gas resources was analyzed (Fig. 9).
Figure 9. Remaining recoverable gas distribution in the Sichuan Basin
Regarding formations, the remaining recoverable resources are mainly distributed in Permian, Cambrian, Sinian, Middle–Lower Triassic, and Upper Triassic (excluding shale gas), where 17%–30% of the resources are proven. Regarding resource types, the remaining recoverable shale gas is the largest in quantity, accounting for 56.3%, followed by marine carbonate conventional gas (38.2%) and tight sand gas (5.5%). Regarding burial depth, 54% of the remaining recoverable resources are buried in the middle–shallow reservoirs (2000–4500 m), 35% in the deep reservoirs (4500–6000 m), and 7% in the ultra-deep reservoirs (6000–8000 m). Regarding horizontal distribution, the central Sichuan uplift zone contains the remaining resources as high as 3.65x1012 m3, with a volume abundance of 0.9x108 m3/km2, followed by the high and steep structural belt in eastern Sichuan Basin with the remaining resources of 1.75x1012 m3 and a volume abundance of 0.36 x108 m3/km2.
Data source: Features of Gravity Anomalies and Oil-Gas Distribution Rules
in Central and Western Sichuan Basin, China. Xiaoyu Huang, Qing Chen, Hao Chen, Jie Zhu and Gege Li. 2023
Exploring the potential of oil and gas resources in Sichuan Basin with Super Basin Thinking. Wang Zecheng, Shipeng Huang, Yizuo Shi. 2022
Следующий Бассейн: Old Crow