Table of Content

10 October 2024, Volume 46 Issue 5

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GEOLOGY EXPLORATION

Application of Fracturing Construction Curve in Fracture Evaluation of Deep Shale Gas Horizontal Wells

YAN Jianping, LAI Siyu, GUO Wei, LIAO Maojie, HUANG Yi

2024, 46(5):  1-18.  DOI: 10.11885/j.issn.1674-5086.2022.10.18.04

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Shale gas horizontal wells usually do not have coring and electrical imaging scales, which makes it difficult to identify fractures. The fracturing operation curve can reflect the fracturing effect and the development of natural fractures before fracturing. Taking the deep shale gas formation of Block Y101 in Luzhou, southern Sichuan as an example, according to the type and characteristics of the fracturing operation curve in the sand-carrying fluid stage, the logging response characteristics of the fracture layer and the matrix layer before the fracturing of the horizontal well are calibrated. The wavelet transform is used to extract the high-frequency weak signal reflecting the fracture information to establish the wavelet comprehensive coefficient (W_I), the crossplot is used to select six parameter indexes sensitive to the fracture response, the analytic hierarchy process and the fuzzy mathematics method are used to construct the fracture evaluation comprehensive coefficient (F_I), and the relationship between different fracturing operation curve types and logging information is further combined to realize the identification and development level evaluation of horizontal well fracture layers. The results show that the fracturing construction curve of the sand-carrying fluid stage has a descending type (I), a descending stable type (II), a stable type (III), and an ascending type (IV). Among them, when the natural gamma high value, the compensated neutron and the density increase significantly, the acoustic time difference increases with the “jagged” cycle jump, the double lateral shows a “positive difference” and W_I≥0.18，F_I≥0.430, the fracturing construction curve is a descending type, and the fracture is well developed (F–A grade); When 0.390≤F_I<0.430, there are both downward type and downward stable type, and the fractures are more developed (F–B grade); when 0.350≤F_I<0.390, it is a descending stable type, and the fractures are generally developed (F–C grade).

Microscopic Occurrence and Production Characteristics of Formation Water in Shaximiao Formation Tight Sandstone Gas Reservoir in Zhongjiang Gas Field

DENG Wenlong, HENG Yong, RAN Xu

2024, 46(5):  19-28.  DOI: 10.11885/j.issn.1674-5086.2024.01.22.03

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The study of the microscopic distribution of formation water can provide reference and basis for the optimization of favorable zone selection and gas well production system. Using thin section, scanning electron microscope, mercury injection, nuclear magnetic resonance, two-phase flow experiment, logging, and production dynamic data, the study of the pore structure, reservoir water distribution state, and production characteristics of the tight sandstone gas reservoir in the Shaximiao Formation of Zhongjiang Gas Field was conducted. The results show that the average median pore throat radius of Class I, II, and III reservoirs in the Shaximiao Formation of Zhongjiang is 0.30, 0.16 and 0.04 μm, respectively. Formation water exists in the form of free water, capillary water, and thin film water in the reservoir. Thin film water is widely distributed, capillary water mainly exists in the throats with a radius less than 0.100 μm, and free water can be seen in reservoir with poor matching relationship between fault and sand body and low structural position. The main source of water production in gas wells is condensate water, capillary water, and thin film water, with the overall characteristics of low water production, low mineralization, low water-gas ratio, and an increase in the latter. The evaluation and development of high water-saturated areas should primarily target I and II reservoirs, and production pressure differentials should be appropriately controlled during production of water-gas wells.

Quality Variations and Control Factors of Fan Delta Reservoirs

XU Yunjie, WU Shenghe, ZHANG Ke, XIONG Qicong, YU Jitao

2024, 46(5):  29-41.  DOI: 10.11885/j.issn.1674-5086.2023.06.05.02

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Fan delta is the important reservoir, and its reservoir quality variations strongly influence the distribution of residual oil. It was previously believed that the physical property rhythm and particle size rhythm of sandstone reservoirs were consistent. But it was not clear whether the physical property rhythm and particle size rhythm were consistent for fan delta glutenite reservoirs with coarse grain size. Field survey, unmanned aerial observation and indoor experiments were used to investigate the fan delta of Sangyuan outcrop within Xiguayuan Formation of Lower Cretaceous in Luanping Basin, aiming to analyze the quality variations and control mechanism. The results show that: the small conglomerates and coarse sandstones with moderate sorting and low argillaceous content have the higher original pores and more compaction-resistant, and have the best physical properties; when granularity becomes coarse with worse sorting, and the argillaceous content increases with the granularity finer, the physical properties of the reservoir become worse. In the positive rhythmic distributary channel and the positive rhythm mouth bar, the vertical upward as the medium-fine conglomerate becomes to the medium-fine sandstone, reservoir physical properties from the bottom to the top become better to worse, and as the lateral granularity from the middle to sides becomes finer, the physical properties of the reservoir become worse. The anti-rhythm mouth bar from the bottom to the top becomes from fine sandstone to coarse sandstone and small conglomerate, the physical properties become better, and as the lateral granularity from the middle to sides becomes finer, the physical properties of the reservoir become worse.

Seismic Guided Drilling Based on the Complex Geological Modeling and Its Application

ZHANG Xichen, LIU Xiaobo, CUI Jingbin, CHEN Maoshan, LI Lei

2024, 46(5):  42-51.  DOI: 10.11885/j.issn.1674-5086.2022.11.06.02

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At present, strong structural deformation aggravates the difficulty of well trajectory design and construction, making the predicted depth far from the actual depth. In addition, the existing seismic steering drilling technology is not yet mature. To solve the above problems, in order to efficiently and accurately complete pre drilling geological evaluation, well trajectory design and real-time drilling correction, this paper proposes a seismic steering drilling method and process based on 3D geological modeling, which is divided into three stages. First, complex geological modeling. After setting initial parameters of the model, section modeling and layer modeling, a fine 3D structural model is obtained, and on this basis, a reservoir sensitive attribute model is generated. Second, 3D well trajectory design. According to the characteristics of structure, reservoir and oil and gas reservoir reflected by the attribute model, and in combination with the needs of drilling engineering, the well trajectory is designed and picked up in the 3D attribute model. Third, create the “marker bed inverted triangle layer by layer approach method” to conduct velocity depth interactive correction, correct the velocity volume through the newly drilled marker bed depth, so that the depth domain 3D model gradually approaches the real underground model, and the predicted depth of the target entry point constantly approaches the real depth, timely guide the drilling direction and avoid drilling risks. The technical process has achieved good results in practical application, the error rate of prediction depth is less than 0.2%, and the work efficiency is improved by 5 times.

A New Understanding of Reef and Beach Facies in the Maokou Formation of Southwest Sichuan Basin

YANG Liu, LIANG Hong, WANG Lun, PENG Xin, SI Guoshuai

2024, 46(5):  52-65.  DOI: 10.11885/j.issn.1674-5086.2023.05.15.02

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The gas reservoirs in Maokou Formation of Middle Permian in Sichuan Basin are mostly fracture vuggy limestone reservoirs with limited scale. In recent years, high-energy shoal facies reservoir of Maokou Formation have been drilled successively in wells YB7 and JT1 in northern Sichuan Basin and high-yield industrial gas flow is obtained, which made an important breakthrough in platform margin exploration of oil and gas of Maokou Formation in Sichuan Basin. Based on the basic research on sedimentation, geology and paleogeomorphology, combined with the latest high-quality 3D seismic, time-frequency gravity and magnetic data, it is found that: 1) Maokou Formation in southwest Sichuan Basin develops open platform-rimmed platform margin-depression edge-slope-intra platform depression sedimentation, depression edge reef beach facies distribute in large scale, and the reflection characteristics of “mound like, disordered, intermittent moderate weak amplitude” in the threedimensional seismic sections are obvious; 2) the NE trending basement strike slip faults developed in the southwest Sichuan Basin, mainly formed in the Xingkai rifting movement period, reactivated in the Emei rifting period, resulting in the graben horst pull apart pattern, which is one of the main controlling factors for the formation of the rimmed platform margin of Maokou Formation; 3) the depression edge reef beach facies of Maokou Formation overlapped with the fresh water karst in the Dongwu Period, which has the basis of forming a large-scale and high-quality reservoir. It is located in the high part of the structure in the period of oil and gas accumulation and is the long-term direction area of oil and gas migration and accumulation. The study has a certain guiding significance for expanding the exploration field and increasing reserves and production in southwest Sichuan Basin.

Mechanism of Organic Matter Enrichment in the Wufeng Formation–Longmaxi Formation Shale in the Upper Yangtze Platform

CHEN Lei, DONG Jianhua, HU Yue, JI Yubing, REN Guanbao

2024, 46(5):  66-79.  DOI: 10.11885/j.issn.1674-5086.2022.08.26.02

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The study takes the shale at the bottom of the Wufeng–Longmaxi Formation in the Upper Yangtze Platform as the research object. The organic matter enrichment mechanism of this set of black shale was studied through the test of organic carbon content, major, trace and rare earth elements and other data. The results show that: the shale at the bottom of the Wufeng–Longmaxi Formation in the study area was deposited in a passive continental margin setting with tectonic stability, which was conducive to the enrichment of organic matter; different geological factors exert varying degrees of control over organic matter enrichment, wherein paleoproductivity has shown a non-significant impact on the organic matter enrichment in the bottom shales of the Wufeng–Longmaxi Formation. Conversely, terrestrial input has produced a diluting effect to some extent; during the sedimentation period of the bottom shales in the Wufeng–Longmaxi Formation, the environmental conditions were characterized by dysoxic-anoxic and moderately stagnant settings, which were highly favorable for the accumulation and preservation of organic matter. However, due to a slightly more open water body environment during the deposition period at the base of the Longmaxi Formation compared to that of the Wufeng Formation, there exists a certain degree of difference in the controlling influence of the water body environment on the preservation of organic matter in the two sets of black shales from both formations. The organic matter enrichment in the two sets of shales from the Wufeng Formation and Longmaxi Formation exhibits distinct differences. The organic matter enrichment of the shale of the Wufeng Formation is controlled by productivity-retention environment, and the organic matter enrichment of the shale at the bottom of the Longmaxi Formation is controlled by conservation-open-upwelling ocean current.

Metamorphic Buried Hill Reservoir of Bozhong 19–6 Gas Field: The Characteristics of Hydrothermal Fracture Fillings and Their Geological Significance of Petroleum

ZHOU Yi, GUO Yujie, LUO Yuhang, WANG Yansong, TANG Hongming

2024, 46(5):  80-96.  DOI: 10.11885/j.issn.1674-5086.2023.04.17.05

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The Bozhong 19–6 Gas Field within metamorphic buried hills is a giant one discovered in 2018. The fractures developed in the metamorphic rock buried hill reservoir system are the main seepage channels and storage spaces for oil and gas, and the fracture fillings record the fluid action and evolution process of the reservoir. Therefore, systematic research on fracture fillings is of great significance for oil and gas exploration and development. Based on systematic observation of cores and the casting thin sections from metamorphic buried hill reservoir, we illustrate the geochemical characteristics of the hydrothermal fluid activity and petroleum migration happening to the reservoir and the hydrothermal influence on the reservoir using electron microprobe analysis, LA-ICPMS, cathodoluminescence and fluorometric analysis. The results show that: 1) hydrothermal minerals in fractures include three types of aessemblages which are magnesian siderite+ankerite+quartz, magnesian siderite+quartz, ankerite + quartz. 2) the in-situ geochemical characteristics of magnesian siderite and ankerite indicate the genesis of contemporaneous hydrothermal fluids. 3) hydrocarbons are usually occurred as fixed bitumen hosted in ankerite and inclusions hosted in magnesian siderite. The hydrothermal activity and petroleum migration likely took place at the same time and they were the two contemporaneous geological events. 4) more than the corrosion effect that the hydrothermal fluid took, hydrothermal fluid closing the fractures had damaged the physical property of the reservoir.

OIL AND GAS ENGINEERING

Research on Productivity Characteristics and Correction of Productivity Equations of Gas Wells in Fractured Gas Reservoirs

LI Xiaoping, LI Yumin, SHAO Jianbo, DUAN Huating, ZHU Songbai

2024, 46(5):  97-105.  DOI: 10.11885/j.issn.1674-5086.2022.07.26.04

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Fractured gas reservoirs are characterized by abundant reserves and high gas well productivity. The binomial productivity equation of conventional theory has bad applicability in fractured gas reservoirs, and the turbulence flow coefficient obtained by theoretical model is far less than the measured results. Taking Keshen Gas Field as an example, we summarize natural gas production characteristics in fractured natural gas reservoirs based on geological cognition, test data, percolation theory and numerical simulation. The analysis results show that intersection of wellbore and natural fractures is the main production well section, and the accumulation of gas in natural fractures increases the turbulence effect during production, resulting in obvious highspeed nonDarcy effect, and the theoretical binomial productivity equation cannot accurately evaluate its productivity. Secondly, the binomial productivity equation correction method for fractured gas reservoirs is established by regressing the relationship between the theory of Keshen Gas Field and the actual nonDarcy flow coefficient. The reliability of the productivity model is verified by the measured data. The case analysis shows that most of the energy consumed in the production process of Keshen gas well is turbulent effect, so it is necessary to control production for reducing pressure loss in fractured gas reservoir. Finally, the calculation value of production is tested with the singlepoint productivity formula. The computed result shows that the gas well productivity calculated under the condition of low production pressure difference is much higher than the actual results, and the reasonable test production pressure difference should be between 4% and 10% of the formation pressure.

Water-yielding Laws and Patterns of Volcanic Condensate Gas Reservoir in Kalameili

GUO Qiaozhen, LI Daoqing, QIU Peng, YAN Liheng, LUO Jianxin

2024, 46(5):  106-114.  DOI: 10.11885/j.issn.1674-5086.2021.04.10.01

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Kelameili volcanic condensate gas reservoir is rich in resources, but due to the variable lithofacies, developed fracture and active edge and bottom water, the gas wells generally produce water in the process of development. Accurate identification of water invasion laws, water production characteristics and water production patterns of gas wells has important reference value for the development of new gas reservoirs and the adjustment of old gas reservoirs. Based on the comprehensive analysis of the geological and development data of typical gas reservoirs in Kelameili, we find that the conventional method suitable for water invasion identification of fractured water-producing gas reservoirs has some limitations, and the combination of numerical simulation technology is more beneficial to recognize the water production laws. The curves of water invasion and water production of gas reservoir show that the main source of water production are edge and bottom water, which seriously affect the gas well productivity. According to the results of numerical simulation, the water production modes of gas wells are divided into five categories. The actual water production curves of 98 gas wells in typical gas reservoirs in the study area are qualitatively divided into five categories by statistical analysis. The results of simulation curves are basically consistent with the actual production curves. The results of water production mode division based on numerical simulation are highly reliable, which can provide reference for the deployment and real-time control of gas wells in volcanic condensate gas reservoirs.

Shale-liquid Interaction and Its Effect on In-situ Stress

LI Gao, LI Ze, HU Song, LI Minghao, LI Zhuoyang

2024, 46(5):  115-123.  DOI: 10.11885/j.issn.1674-5086.2022.06.29.01

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During drilling and completion in shale formation, shale-liquid interaction between working fluid and shale is inevitable. In order to study the mechanism of shale-liquid interaction and its effect on in-situ stress distribution, laboratory experiments of shale-liquid interaction were carried out on Longmaxi Formation shale in southern Sichuan, and the mechanism and results of the shale-liquid interaction were clarified. On this basis, the influence of shale-liquid interaction on in-situ stress distribution was studied. The results show that the shale-liquid interaction can cause shale damage, and then the micro-fracture occurs, which leads to the shale swelling. The stress distribution can be affected during shale-liquid interaction, and the more complex the fracture network, the more obvious the influence of shale-liquid interaction on stress. Due to the shale-liquid interaction, the distribution of in-situ stress changes significantly during hydraulic fracturing, and the casing stress increases with the shale-liquid interaction time.

Description of Fluid Flow Characteristics for Fracture-cave Carbonate Reservoirs

ZHENG Songqing, WANG Qiang, ZHANG Shiliang, YUAN Feiyu

2024, 46(5):  124-131.  DOI: 10.11885/j.issn.1674-5086.2022.04.22.02

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Many scholars believe that the seepage theory can not describe the fluid flow in fracture-vuggy carbonate reservoirs in Tarim Basin which have complex flow and are different in pore scale and pipe flow theory can solve the problem. In order to clarify this problem, the relationship between pipe flow and seepage is studied from three aspects: the concept of pipe flow and seepage, single-phase flow characteristics and mathematical characterization methods, oil-water two-phase flow characteristics and mathematical characterization methods. On this basis, the feasibility of using pipe flow equation to describe fluid flow in fracture-vuggy reservoirs is analyzed, and the characterization methods of fluid flow in fracture-vuggy reservoirs are discussed. The results show that, the seepage can be regarded as small-scale complex pipeline flow; In case of single-phase flow, there are two flow patterns in pipe flow: laminar flow and turbulent flow, and there are also two flow patterns in seepage flow: laminar flow and turbulent flow. The equations describing pipe flow and seepage flow are unified, while the equations describing turbulent flow are inconsistent, but both consider the influence of inertial force. In two-phase flow, there are many flow patterns in pipe flow. The seepage flow is small in scale and simple in flow pattern. Different characterization models are established for pipe flow according to flow patterns, and relative permeability curve is used to solve the two phase flow problem in seepage flow. It shows that there is no“conflict” between pipe flow and seepage flow. Seepage flow is small-scale complex pipe flow, but due to different disciplines and different research objects, different characterization methods are used for fluid flow. Restricted by the accuracy of reservoir description and the scope of research, the existing pipe flow description methods are not suitable for describing fluid flow in fracture-vuggy reservoirs. The characterization of fluid flow in fracture-vuggy reservoirs should be solved within the framework of seepage mechanics, with reference to the description method of pipe flow.

Architecture Construction Scheme of Intelligent Comprehensive Energy Supply Station Based on Digital Twin

XU Hai, HE Wei, GU Jinjian, DING Bo, ZHU Baikang

2024, 46(5):  132-142.  DOI: 10.11885/j.issn.1674-5086.2022.10.10.01

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Under the goals of“carbon neutrality and carbon peaking”, traditional energy supply stations are unable to meet the growing demand for diversified customer services due to their single energy structure. Research is conducted on a new business model and new mode of energy supply services that integrates the supply functions of electricity, hydrogen, natural gas and clean oil products. The study combines the business function requirements of integrated energy supply stations and adopts the framework of building a digital twin of a smart energy supply station, with user-centric, multi-dimensional indicator-driven and whole life cycle management as the three general concept technologies of the construction scheme. Analyse are done of the overall system architecture of a smart integrated energy supply station through technical principles, construction ideas, twin frameworks, business functions and technical applications. The business framework designed on the basis of three levels of employees, station masters and headquarters is explained, and the technical framework is designed on the five scenarios of security, infrastructure, marketing, service and management, so as to provide users with diversified energy supply services and to effectively promote the digitalization and cleanliness of the oil and gas industry transformation and development. It provides a reference idea for the future development of digitalization and informatization of intelligent integrated energy supply stations in the new energy industry.

PETROLEUM MACHINERY AND OILFIELD CHEMISTRY

Research Progress, Challenges and Countermeasures in Chemical Water Plugging of Gas Wells

JIA Hu, HE Wei, ZHANG Yufei, LI Pengwu

2024, 46(5):  143-160.  DOI: 10.11885/j.issn.1674-5086.2022.10.26.01

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At present, more than 80% of the developed gas fields in China produce water, which seriously affects the productivity of gas wells. Chemical water plugging is an important means to enhance gas recovery of water producing gas reservoir. This paper summarizes the chemical water plugging materials commonly used in gas wells at home and abroad, and discusses the mechanism and adaptability of water plugging. The results show that the polymer and polymer gel achieve disproportionate gas-water permeability reduction (DPR) through resistance effect, inertia effect and lubrication effect. The polymer plugging agent is suitable for medium and high porosity and permeability reservoirs, and its environmental adaptability is improved by pretreatment fluid + modified polymer. Polymer gel is suitable for high temperature, high salinity and fractured water producing gas reservoir. The relative permeability modifier realizes DPR through wettability change, which is suitable for low permeability, dense and high water producing gas reservoirs, but not suitable for fractured gas reservoirs. Functional fluids (functional nanofluids, microemulsion systems, etc.) are designed for specific reservoir conditions (such as condensate gas reservoirs) to achieve DPR through wettability changes; foam gel achieves DPR by Jiamin effect and shunting effect, which is suitable for strong heterogeneity and fractured gas reservoirs. At the same time, this paper analyzes the challenges faced by gas well water control, and further puts forward six gas well water control strategies and research directions, such as adopting different ideas according to the source of water, developing new materials for separating membrane water control, transforming reservoir environment with pretreatment fluid, and integrating moderate water production and water control. The research results of this paper can provide guidance for gas well water plugging practice.

Heat Extraction Characteristics of Medium to Deep Horizontally Connected Geothermal Wells

ZHANG Jie, WANG Guiyang, WANG Pengtao, WANG Shuyuan

2024, 46(5):  161-169.  DOI: 10.11885/j.issn.1674-5086.2022.06.17.01

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Efficient heat extraction technology of geothermal well is the key to efficient and sustainable development. A numerical simulation model for horizontally connected geothermal wells has been established. The outlet fluid temperature and heat transfer under continuous and intermittent heat exchange conditions were calculated. Effects of injection temperature, injection flow rate and horizontal section length on the heat transfer performance of the geothermal system and the temperature recovery ability of rock strata were analyzed. The results show that the water temperature at the outlet of the geothermal well decreases with the increasing of injection flow, but heat extraction capacity of the whole system increases. When the injection temperature is high, the outlet water temperature can be effectively increased, but the heat exchange capacity of the system decreases greatly. With the increasing of horizontal section length, the outlet water temperature and heat exchange capacity gradually increase, and the heat transfer performance of geothermal well improves. Rock temperature recovery ability increases with the increasing of injection flow rate and injection temperature. Taking into account factors such as drilling cost and pump power consumption, the heat transfer performance of geothermal well can be effectively improved by appropriately increasing the injection flow, lowering the injection temperature and increasing the horizontal section length. Although increasing the injection temperature can improve the temperature recovery ability of rock formation, it is not conducive to improving the system heat production efficiency.

DISCUSSIONS AND ARGUMENTS

May Downward Flow of Oil and Gas Occur? A Discussion with Mr. Wang Yongshi

LI Chuanliang, LIU Donghua

2024, 46(5):  170-182.  DOI: 10.11885/j.issn.1674-5086.2024.05.08.01

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In response to whether downward flow of oil and gas occurs in petroleum geology, based on the relevant theories of flow mechanics in porous media, the migration and accumulation mechanism of oil and gas and the formation mechanism of formation overpressure were deeply studied through theoretical analysis. The main understandings were obtained as follows: firstly, migration is different from flow, flow requires differential pressure drive, migration does not require differential pressure drive, and oil and gas migration is a discrete flow or droplet flow under buoyancy; secondly, oil and gas can migrate upwards, and downward flow of oil and gas will not occur due to the lack of driving force; thirdly, the laboratory experiments did not simulate underground conditions, with a large pressure difference and a high flow velocity, indicating oil and gas flow rather than oil and gas migration; fourthly, the mudstone formation is an open formation and there is no overpressure and formation water can balance formation pressure through flow; fifthly, oil and gas are separated and surrounded by formation water, and overpressure can occur and the overpressure is balanced by capillary pressure; sixthly, there is no upper source-lower reservoir model, and the source rock may not necessarily be located directly below the oil and gas reservoir. Lateral upward migration can also achieve the formation of oil and gas reservoirs.