The low-permeability oil field in complex fault block in the western South China Sea has a large reserve scale, which is a key target area for production capacity replacement in the near future. However, the fault block is characterized by small area, great burial depth of oil reservoir, and complex reservoir characteristics, leading to great challenge in high-efficiency oil field development. In view of the high reservoir heterogeneity, rapid reservoir changes in lateral, and complex main controlling factors for reservoir physical properties, the fine reservoir description technology has been used to accurately predict the distribution of “sweet spot” reservoir, which guides the deployment of development wells; In response to the poor development results by conventional seawater injection due to the strong water sensitivity of low-permeability reservoir, gas injection gravity auxiliary displacement and nanofiltration seawater displacement technology have been researched, and an effective displacement technology series for low-permeability oil fields has been established, improving the injection-production well pattern and enhancing the displacement results; By considering the limited well slot resources on offshore platforms, the technology of high-yield production with few wells has been adopted, and complex well structure has been applied to effectively improve the sweep range of single wells. Meanwhile, supporting technology for the high-efficiency development of low-permeability oil field has been researched and developed, which supports to integrate resources and revitalize internal and surrounding potential, laying a solid technical foundation for production increase of the western oil fields in South China Sea.

In view of the insufficient utilization of residual gas reserves by primary well pattern development in Fuling Shale Gas Field, geology and engineering integrated stereoscopic development technology is the core means to improve gas recovery and achieve accurate utilization of residual gas reserves. As a result, a new high-efficiency shale gas development mode with geology and engineering integration has been established, and shale gas modeling and simulation integrated technology has been innovatively developed to conduct fine research and identify the distribution of residual shale gas; The coupling of geological and engineering double sweet spots enables to determine the gold target window of well drilling trajectory, and the classification standard system of “resource + stress + natural fracture” three-in-one layered benefit combination has been established; Based on the differential distribution pattern of residual gas, the drilling and fracturing optimization design process has been established with “geology-drilling-fracturing-surface collaborative optimization”; By using real-time monitoring, the dynamic adjustment of well drilling trajectory and fracturing construction has been conducted, and integrated data sharing platform and real-time decision system have been constructed. The geology and engineering integrated stereoscopic development technology has guided the development of Jiaoshiba block and increased estimated recovery rate from 12.6% to 23.3%, and up to 39.2% in the stereoscopic development zone. The application of this technology supports to reduce shale gas drilling and production investment, and billion square meter production capacity construction investment and development costs year by year, which effectively guides the recovery enhancement and high-efficiency development of Fuling Shale Gas Field.

There are abundant natural gas resources in Xujiahe Formation in Xinchang-Hexingchang in western Sichuan Basin, with proven reserves of 1700×10⁸ m³ in Sinopec exploration blocks. The reservoir is characterized by “one-deep, two-high, and two-low”, including great burial depth of gas reservoir (4500-5500 m), high formation pressure (pressure coefficient of 1.4-1.7), high fracture pressure (110-165 MPa), ultra-low porosity (average of 3.7%), and ultra-low permeability (average of 0.07 mD), which brings multiple challenges to geological theoretical understanding and high-efficiency gas development, and restricts the progress of exploration and development. Based on the research idea of geology and engineering integrated practice, understanding of tight sandstone gas migration and accumulation has been deepened, and gas accumulation mechanism and enrichment and high-yield production laws have been identified. By starting from the detailed analysis of development mode of geological sweet spots, the formation mechanism of gas reservoir sweet spots has been determined, and a sweet spot geological model has been established. By applying fracture and reservoir fine seismic characterization and quantitative prediction technology, and optimizing drilling and reservoir reconstruction technologies, the geology and engineering integrated collaborative research on key technologies such as geology, geophysics, drilling and completion has been conducted, and the practice of technology and economy integration has been implemented. The successful application of technical sequences supports the large-scale production of the gas field, with a cumulative production capacity of over 10×10⁸ m³, and new addition proven geological reserves of 1300×10⁸ m³ in Hexingchang Gas Field, which further confirms that the integration of geology and engineering is a necessary way for the effective development of low-grade gas reservoirs, promotes the beneficial development of Xujiahe gas reservoir in western Sichuan Basin, and provides reference for the exploration and development of tight and difficult to use reserves, especially deep tight gas.

Jiyang Depression is a typical continental fault basin in eastern China. A set of thick medium-low maturity shale oil has been identified in the fourth-third member of the Paleogene Shahejie Formation, with resources of more than 100×10⁸ t, which is being evaluated and tested at present, showing broad exploration and development prospects. Based on the characteristics of complex lithofacies, diverse reservoir spaces, high heterogeneity, and large source rock thickness of continental shale oil, seismic data, mud logging, wireline logging, coring, and laboratory test data are combined to conduct “four-property” evaluation of source rock, including favorable lithofacies, reservoir physical properties, oil-bearing property, movability, and fracability. The deployment of appraisal wells and pilot tests of well group enable to develop an evaluation technology with the core of stereoscopic sweet spot evaluation, stereoscopic well network optimization, and stereoscopic horizontal well fracturing, and resource potential and technological adaptability have been determined, which provide important support for optimally selecting production zone and achieving large-scale development and production capacity construction. The stereoscopic evaluation tests have been conducted in Boxing, Niuzhuang, and Minfeng areas, confirming the reliability of sweet spot evaluation standards, rationality of well spacing and layer spacing, and adaptability of fracturing technology, and helping to build the first shale oil pilot test well group of Sinopec with a level of 10×10⁴ t, which effectively support the high-efficiency construction of national shale oil demonstration zone in Jiyang continental fault lake basin.

The Shunbei oil and gas field in the Tarim Basin has a burial depth of 7300 to 9000 m. Fracture-cavity reservoirs develops along high and steep strike-slip fault zones which is formed by the fragmentation of brittle strata. The internal heterogeneity of the fault fracture zones is extremely strong, and the fluid properties vary greatly. Facing this type of ultra-deep and complex fault-controlled fracture-cavity oil and gas reservoirs, efficient well formation faces world-class challenges. The cost of a single well is high, and it is difficult to develop profitably. There is no ready-made experience and technology to learn from. Taking project management as the starting point, Shunbei has established unique "five-for-five improvement" geological engineering integrated management model, and has innovatively formed the seven-element key technologies of "fewer wells and higher production". In recent years, the integration of few wells and high production geological engineering has achieved a qualitative leap, and two hundred-million-ton resource positions in the No.four and No.eight fault zones have been implemented, adding 153 million tons of proven oil and 162 billion cubic meters of natural gas. A total of 20 wells have been deployed in the No.four fault zone, and a production capacity of 1.3 million tons of oil equivalent has been built in two years. Compared with the No.1 fault zone developed in 2016, the success rate of high production wells has increased by 35%, the productivity of single wells has increased by 316%, and the proven reserves discovered by single wells have increased by 55%. Efficient exploration and profitable development have been achieved, and its experience has reference significance for the development of other similar types of reservoirs.

The ultra-deep shale gas reservoir in the Cambrian Qiongzhusi Formation in Deyang-Anyue aulacogen in Sichuan Basin is characterized by old geologic age, large burial depth and high thermal evolution, leading to great difficulty in shale gas exploration and development. However, there is no direct experience to learn from both at home and abroad. In view of this, the idea of geology and engineering integration is applied to preliminarily establish the key technological system of “well deployment-drilling-fracturing-production” for cultivating high-yield wells of Qiongzhusi Formation shale gas: (1) Integrated well deployment. The understanding of “hydrocarbon accumulation controlled by aulacogen” is deepened, the distribution mode of high-quality reservoir is determined, and the technical limits for operating high-yield wells are clarified, supporting the optimization of well deployment. (2) Integrated drilling, logging, and geosteering. Based on the comprehensive evaluation of geological and engineering parameters, the optimum drilling target is selected, the well trajectory is optimized, and the geology and drilling integrated fine management is strengthened, which effectively guarantee the drilling rate of high-quality reservoir. (3) Integrated fracturing and reservoir stimulation. The integrated fracturing model is used to optimize fracturing design, forming fracturing technology of “promoting fracture complexity + expanding fracturing volume + highly fracture supporting + casing deformation prevention”, which effectively achieves the uniform fracture initiation, high-efficiency fracture propagation, full reservoir support and maximum reservoir stimulation volume. (4) Integrated fine management of flowback. The “four-factor” flowback and reservoir stimulation technology is developed, and the fine flowback and production analysis platform is established, which achieve the “double breakthroughs” of reservoir damage reduction and gas well stimulation. By using the above technology system, high-yield gas flow has been obtained in Well Zi 201 for the first time in China in the Cambrian shale reservoir with a depth of greater than 4500 m, and the replication of high-yield production has successfully been achieved in Well Weiye 1H, which support to initially identify a favorable area of nearly 3000 km² with the depth of shallower than 5000 m and gas resources of nearly 2×10¹² m³. The high-yield well cultivation technology and method lay a solid foundation for solving difficulties in large-scale and high-efficiency development of ultra-deep shale gas in the Cambrian Qiongzhusi Formation.

A set of source rocks mainly composed of organic-rich shale and intercalated with sandy sediments were developed in the seventh member of the Triassic Yanchang Formation (Chang 7 member) in Ordos Basin. Among them, exploration breakthrough and large-scale beneficial development of intra-source interlayered type shale oil have been achieved. However, there is a lack of study on shale type shale oil, as well as insufficient understanding on the exploration and development prospects. As a result, source rock and reservoir characteristics have been analyzed based on core laboratory tests and well logging interpretation results, and field pilot well development has been tested to evaluate the exploration prospects of shale type shale oil in Chang 7 member in Hujianshan area. The core testing results indicate that intergranular pores, intercrystal pores, and organic matter pores are mainly observed, with common bedding fractures and organic matter shrinkage joints, and free light oil mainly occurs in intergranular pores and bedding fractures; The experimental results of multi solvent continuous stepwise extraction method show that the proportion of free light oil in Chang 7 member shale reaches up to 54.3%. The geochemical experiment results indicate that the average total organic carbon content (TOC) is 14.03% and the average hydrocarbon generation potential is 57.73 mg/g, showing a high-quality source rock; The thermal evolution degree of organic matter is relatively high, with an average R_o of 1.08% and an average T_max of 450℃; The rock pyrolysis movable hydrocarbon content is 4.34 mg/g, indicating a good resource foundation of shale type shale oil. To sum up, Chang 7 member shale in the study area has good organic matter type, high organic content, good fracability, as well as good oil-bearing property indicated by vertical well testing and production results in the basin. By using rock pyrolysis method, the preliminarily estimated movable hydrocarbon resources of shale type shale oil in this area are 4.1×10⁸ t. The comprehensive study shows that the shale type shale oil in the study area has exploration and development prospects by applying horizontal well volume fracturing and reservoir stimulation.

The integrated technology of geological engineering in south Sichuan shale gas not only successfully solved the engineering challenges under complex geological conditions, but also significantly increased the production and EUR per well. This paper summarizes the basic concept, core connotation and technical system of the integration of geological engineering of shale gas in southern Sichuan, and puts forward the cultivation method of high production well suitable for different blocks and different conditions. The results show that: (1) the integrated technical system of geological engineering provides important decision-making basis and guidance for the scheme design and on-site implementation of shale gas wells in the whole life cycle, and effectively solves the bottleneck problems of "pressure channeling" and "casing deformation". The casing deformation and pressure channeling rate in Luzhou block are reduced by 19% and 31%. (2) Continuous iterative updating of geological engineering feature understanding and integrated model can significantly improve the accuracy, reliability, consistency and effectiveness of the design; (3) The implementation of the integrated high-yield well cultivation method of geological engineering can significantly increase the production of a single well, among which the average EUR of wells in Changning block increased to 1.30×10⁸m³, an increase of 26.2%; The average EUR of wells in the western Chongqing block increased to 1.53×10⁸m³, an increase of 36%. This method has been applied to different shale gas blocks in southern Sichuan, and remarkable results have been achieved, which verifies the importance of this method in improving the production and economic benefits of a single well, and can also provide reference for the economies of scale development of unconventional oil and gas reservoirs at home and abroad.

Multi-platform and large-area well deployment is the key to high-efficiency unconventional resource utilization. Due to the geomorphic characteristics of loess tableland, as well as forest edge and water source areas in Qingcheng area in Ordos Basin, well placement for the development of the Triassic Chang 7 member shale oil is restricted. As a result, an innovative fan well pattern is proposed to further maximize the producing reserves of the platform. Based on the geology and engineering integrated method, the influence of various azimuths of fan well pattern on fracture propagation and production capacity is analyzed, and the fracture spacing and fracturing sequence are optimized of fan well pattern. Meanwhile, the practical cases are combined to analyze fracturing characteristics and compare production results of various fan well patterns. The study results show that, compared with conventional horizontal wells (the angle between the horizontal trajectory and the minimum horizontal principal stress is less than 15°), the predicted production capacity of oblique horizontal wells (the angle between the horizontal trajectory and the minimum horizontal principal stress is greater than or equal to 15°) decreases with the increasing deflection angle (the angle between the well placement and the minimum horizontal principal stress). When the deflection angle is greater than 45°, the difference in production capacity is further expanded with the increase of the deflection angle. In addition, the economic evaluation results of various simulation scenarios show that the economic feasibility is the worst when the deflection angle is 90°, and well deployment is not recommended. The predicted production capacity can be improved by increasing fracture spacing and adopting the “outside-in” fracturing sequence of fan well pattern. The fractures in oblique horizontal well first propagate along the vertical wellbore direction with a large microseismic magnitude, but the direction of the maximum horizontal principal stress is still the dominant factor for fracture propagation at a far-field scale. Compared with conventional horizontal well, the oblique horizontal well is characterized by a smaller stimulated reservoir volume, but more complex fractures, and more reconstructed fracture network. In terms of the actual production results, the cumulative production of oblique horizontal wells is lower than that of conventional horizontal wells, but the liquid level is higher and the daily oil production is close at present, indicating a promising development potential.

Pearl River Mouth Basin is a major area for the accumulation of low-permeability oil and gas reservoirs with huge resources in the offshore China. L44 Oilfield in Lufeng Sag is the first integral low-permeability oilfield that have been fractured and developed in the eastern South China Sea. However, problems such as insufficient scale of reservoir reconstruction and unclear understanding of fracture initiation mechanism occur after fracturing. Based on seismic interpretation, logging and geological data, a geology and engineering integrated modeling method for offshore low-permeability oilfield has been established, which enables to more accurately predict fracture propagation. In addition,3D geomechanical modeling has been conducted and geological/engineering double sweet spots have optimally been selected in the study area.The upper limit of reservoir perforation interval applicable for offshore low-permeability oilfield has been proposed in fracturing design, and the new fracturing scheme design and capacity simulation have been conducted for Well C3, showing a basically consistent production level with the expectation after the secondary fracturing. The study results show that: (1) Given a low displacement, when the length of perforation interval increases from 4 m to 16 m, the fracture length in a stage decreases by 30 m on an average, and the cumulative production capacity of a single well decreases by 88% in the first five years; (2) An increase in the length of perforation interval inhibits the scale of reservoir reconstruction. When the perforation interval is more than 6 m, the scope of reservoir reconstruction greatly decreases; When the perforation interval is less than 6 m, the scope of reservoir reconstruction insignificantly decreases; As a result, the optimal length of perforation interval should be no more than 6 m; (3) Given a perforation interval of less than 6 m, the average reservoir reconstruction volume increases by 10.97% when the construction displacement increases by 1 m³/min. A higher construction displacement enables to further increase the reservoir reconstruction volume. The geology and engineering integrated modeling method for offshore low-permeability oil fields provides a new idea for the development plan and fracturing scheme design of low-permeability oilfields in the eastern South China Sea, which is beneficial for improving development benefits of oilfields.

The vertically differential hydrocarbon enrichment in Pinghu slope in Xihu Sag was significantly controlled by faults. But there is a poor correlation between the timing of fault activities and the period of hydrocarbon accumulation, that is, faults were inactive (hereinafter referred to as “static faults”) in hydrocarbon accumulation periods. As a result, a clear understanding on the characteristics and main controlling factors for vertical hydrocarbon migration along static faults enables to provide a theoretical basis for petroleum exploration in Xihu Sag or similar areas. The comprehensive wireline logging, mud logging, seismic data, and core testing data such as homogenization temperature and salinity of inclusions, and rock pyrolysis are used to analyze the hydrocarbon supply formations and periods of hydrocarbon accumulation, and determine characteristics and main controlling factors for vertical hydrocarbon migration along statistic faults. The study results show that hydrocarbon was supplied by the good-superior mature source rocks in Pinghu Formation and Baoshi Formation, and vertically enriched in the middle-upper parts of Pinghu Formation, showing characteristics of lower source rock and upper reservoir. Two stages of hydrocarbon charging occurred during the deposition periods of Yuquan-Liulang Formation and Santan Formation-present. While faults were mainly active during the deposition period of Baoshi-Longjing Formation, which had poor matching relationship with hydrocarbon accumulation period, and hydrocarbon migrated vertically along static faults in the late stage. The influencing factors for the vertical hydrocarbon migration along static faults include the width of fault zone, source rock pressure, and displacement pressure in the fault zone. In the study area, the width of fault zone ranges in 138-288 m, which has a positive correlation with the distance of vertical hydrocarbon migration. The source rock pressure experienced a complex evolution process, with a slightly lower pressure in the hydrocarbon accumulation period than the present, but still weakly overpressure or overpressure. The higher the pressure coefficient at present and during the hydrocarbon accumulation periods, the longer distance of vertical hydrocarbon migration. The displacement pressure in the fault zone ranges in 0.2-3.5 MPa, and it shows a negative correlation with the distance of vertical hydrocarbon migration. Based on the relationship between three influencing factors and the distance of vertical hydrocarbon migration, a quantitative evaluation formula for the vertical transport capacity of faults is developed, and the evaluation results indicate a distinctly positive correlation with the maximum hydrocarbon migration distance, according to which the favorable exploration targets in Pinghu slope are determined, including Pinghu Formation and the lower member of Huagang Formation near F2 and F5 faults.

The shale oil reservoir in the seventh member of the Triassic Yanchang Formation (Chang 7 member) in Longdong area in Ordos Basin is mainly composed of alternating deposits of deep lacustrine shale and gravity flow sand bodies, with complex and variable reservoir distribution both vertically and laterally, and thin single sand body. In addition, influenced by natural fractures, there are a number of challenges in scientific fracturing engineering and production operation in the area. Some engineering problems such as pressure channeling and sand plugging, as well as cost reduction and production increase, are important research topics at present. The work and understanding on the characterization of natural fractures in the area in the past two years are summarized, and the latest concepts and strategies in fracturing reconstruction are introduced. On the basis of comprehensive geological study, 3D fine geological, oil reservoir, and geomechanical models have been established, and rational fracturing design, construction, post fracturing analysis, and computer simulation have been conducted to better understand the interaction between natural fractures and hydraulic fractures and the propagation law of hydraulic fractures, achieving the customized fracturing design and construction optimization. After field application, the amounts of proppant and fracturing fluid have been reduced by about 20% and 10%, respectively, given the similar oil production between the construction well and adjacent wells on the same platform. The workflow with integration of geology and engineering enables the implementation of “one well, one strategy” and “one section, one method”. In the long run, it will be the fundamental technical guarantee for achieving the best EUR of single well and well platform for continental shale oil in Ordos Basin.

The development practice of deep shale gas in southern Sichuan Basin indicates that fracture-driven interactions (FDIs) dominated by negative impact severely affect the high-efficiency and beneficial development, which poses a great challenge to the long-term beneficial development of deep shale gas. By taking Luzhou block in southern Sichuan Basin as an example, the reservoir stress field inversion and natural fracture identification have been conducted to determine the combination characteristics of in-situ stress and natural fractures, as well as their influence on hydraulic fracture propagation, so as to avoid the occurrence of FDIs between deep shale gas horizontal wells. On this basis, the micro-seismic monitoring results in fracturing process of wells with FDI have been compared for verification, and the distribution characteristics of volume fracture network pattern have been analyzed to identify the intrinsic mechanism of FDIs between horizontal wells. Furthermore, based on the UFM model, a multi-well fracture propagation model has been established, focusing on the analysis of competing propagation law of multi-cluster fractures, so as to provide theoretical basis for avoiding FDIs between horizontal wells. The study results show that in the bulge area, the strata have dual characteristics of relatively low horizontal in-situ stress and well-developed stripe shaped natural fractures, and the induced hydraulic fractures are prone to propagation in this area, which are the key geological factors for FDIs between horizontal wells in the southern Sichuan Basin; In addition, due to the competing propagation of multi-cluster fractures, large-scale stripe shaped natural fractures have significant induction and capture effects on hydraulic fractures, which will cause excessive propagation of a certain cluster or side fractures, leading to fracture connection and FDIs between horizontal wells.

Ordos Basin has abundant natural gas resources in Taiyuan Formation limestone reservoir, which is a major replacement field for gas exploration and development in Changqing Oilfield Company. However, no gas production breakthrough has been made before by using various acid fracturing technologies due to the factors such as tight limestone, thin reservoir thickness, and fast acid-rock reaction rate. As a result, after changing idea of well stimulation technology, study on fracture propagation mechanism, research and development of support technologies of fracturing fluids and key materials, and fine characterization of volume fracturing mode have been strengthened, developing an integrated horizontal well composite fracture network sand fracturing technology with “multiple stages, less clusters, dense fractures, and composite acid-sand fracturing”. Based on the physical simulation experiments on large outcrop, and combined with geological characteristics and rock mechanic properties, the reservoir characteristics of high brittleness, low difference between the two horizontal principal stresses and well-developed natural fractures are determined, and the volume fracturing technology enables to obtain complex fracture network. By applying the double technological advantages of “deep acid fracturing + large-scale sand fracturing”, a high-conductivity fracture flow pathway with “hydraulic fracture network + acid corrosion fracture” has been constructed, which supports to significantly increase fracture volume together with densely cutting fracturing in horizontal well. In view of the limestone characteristics of high Young’s modulus, high fracture pressure, high fracture propagation pressure and low fracture width, the anti-pressure level of casing pipe has been improved and differential design of sand placement for fractures has been conducted, forming a continuous sand adding mode with multi-scale small size proppants, which solves the problem of difficult sand fracturing of reservoir with high Young’s modulus. Based on the three-level damage evaluation of matrix, wall surface and fracture, a low damage variable viscosity slick water system has been developed to propagate fractures, form fracture network and achieve sand carrying in high modulus reservoirs. This fracturing technology has been applied in four wells, obtaining an average gas rate of 59.7×10⁴ m³/d in single well, which is 5-20 times higher than that by acid fracturing in vertical well, indicating a significant increase in production. At present, the horizontal well composite fracture network sand fracturing technology has been used as the main reservoir stimulation technology for Taiyuan Formation limestone in Changqing Oilfield, which provides strong technical support for the exploration breakthrough and effective development of this type of gas reservoirs.

The oil and gas resource abundance is one of the key parameters in resource assessment, and the determination of this parameter is of great significance. The statistical analysis of the abundance of oil and natural gas resources in key basins in China is conducted, which indicates that the conventional oil and gas resources in the major proliferous basins is dominated by medium-low abundance. The resource abundance in most blocks is ultra-low to low, and it is high in only a few dominant blocks. On this basis, the geological factors affecting the abundance of oil and gas resources are determined, including three main controlling factors of hydrocarbon generation intensity, trap area coefficient, and regional unconformities. By using the three main controlling factors, prediction model of conventional oil and gas resource amount is established for foreland basin, cratonic basin and rift basin. Subsequently, the model is applied to six sags in the three types of basins, and relatively consistent results of the calculated resource amount are obtained with those in the fourth round oil and gas resource assessment, indicating advantages of simple operation, reliable results and easy application of this prediction method, which can be used to preliminarily predict the amount of conventional oil and gas resources in areas with less abundant data and low degree of exploration.