Based on a systematic review of the exploration achievements and theoretical technological progress made by China Petroleum&Chemical Corporation (Sinopec) in different fields since the 14^th Five Year Plan, the main challenges, development opportunities,and directions for oil and gas exploration have been proposed. Since the 14^th Five Year Plan, facing challenges such as relatively weak resource foundation and increasingly complex exploration targets, Sinopec has firmly adhered to its main business of oil and gas energy security, focused on expanding resources, increasing reserves, and expanding mining rights, increased efforts to expand and increase oil and gas resources, and achieved multiple strategic breakthroughs and theoretical technological innovations. Developing theoretical understanding of oil and gas accumulation in ultra deep marine fault controlled fractures and caves, and discovered Shunbei Oil Field; Tackle the theoretical and technological system of shale oil exploration in terrestrial fault basins, and promote sustained major breakthroughs in shale oil;Improve the theoretical understanding of “dual enrichment” of marine shale gas, and achieve leapfrog development in multi-layer shale gas exploration in the Sichuan Basin; Tackle the theory of tight detrital rock formation and reservoir formation, and cultivate multiple scale benefit enhanced storage sites; Tackling the mechanism of coalbed methane occurrence and enrichment, achieving strategic breakthroughs in deep coalbed methane; Significant breakthroughs have been achieved in the exploration of new marine areas such as the Beibuwan Basin. In the future, Sinopec will face three major development challenges: the reduction of mining rights, technological innovation in the exploration theory of “two deep and one non”, and the difficulty of efficient exploration. At the same time, it needs to seize four historical development opportunities: national energy security guarantee, China’s shale oil and gas revolution, green and lowcarbon transformation, and digital and intelligent upgrading. Sinopec will focus on five major projects for development, namely, leading the breakthrough in deep and ultra deep exploration in the central and western regions with the “Deep Earth Engineering”, leading the rapid transformation of mature exploration area resources with the “Shale Oil Demonstration Project”, leading the leapfrog development of unconventional natural gas with the “Shale Gas Demonstration Project”, leading the integrated benefit development with the “Tight Oil and Gas Storage Project”, and leading the new discovery of blue ocean strategy with the “Sea Area Breakthrough Project”. Sinopec will make greater contributions to ensuring national energy security and achieving the “dual carbon” goals.

Progress and achievements of shale oil and gas exploration of Sinopec are systematically reviewed, and major measures for highquality exploration are summarized. In addition, the future research directions of shale oil and gas are proposed. In recent years, Sinopec has implemented a series of measures for the high-quality shale oil and gas exploration, covering the full chain of planning, theoretical technology,engineering and management, which are characterized by “planning guidance promoted by top-level design, technological innovation promoted by basic research, economic benefits promoted by technological iteration, and large-scale reserve increase promoted by collaborative work”. As a result, a number of leading demonstration projects have been constructed, including marine shale gas in new strata and new areas in Sichuan Basin and multi-type continental shale oil in the eastern fault basins, which vigorously promotes the high-quality and collaborative development of shale oil and gas exploration in multiple fields. In the future, Sinopec will solidify the foundation of shale oil and gas resources,strengthen confidence in shale oil and gas exploration, continue to deepen and improve the “dual enrichment” theory, pursue the concept of value leading the overall situation, adhere to the six “integrated” operation modes, promote shale oil and gas strategic breakthroughs and discoveries with high quality, and identify positions for increasing reserves and production on a large scale, so as to make greater contributions to ensuring national energy security.

Based on in-depth investigation on the differences in exploration and development, key technologies and operation modes of unconventional oil and gas at home and abroad, and integrated with the current situation of unconventional oil and gas exploration and development in China, some challenges in unconventional oil and gas industry are put forward, including strategic resource replacement,key development technologies, management system and mechanism, as well as digital intelligence and green construction. By referring to experience and enlightenment of “shale revolution” in North America, and focusing on key factors such as resource, technology, management,cost and benefit, five countermeasures and suggestions are proposed to promote the beneficial development of unconventional oil and gas in China: (1) Strategic planning in all domains. Strengthening the top-level design of development strategy, optimizing domestic resource base,and expanding overseas resource market to further consolidate the resource base for the large-scale development of unconventional oil and gas. (2) Full life cycle evaluation. Conducting long-term trial production test of single well to identify the production law, strengthening the evaluation of key pilot wells, conducting modeling and numerical simulation integrated study, and implementing development technological policies, so as to improve single-well production performance and enhance oil and gas field recovery factor. (3) Full-chain technology iteration. With the aim of addressing problems and achieving goals, researching on key core technologies for beneficial development,efficiently promoting the construction of unconventional oil and gas demonstration zones, and integrating feasible and replicable practices to comprehensively promote the beneficial development of unconventional oil and gas resources. (4) Overall planning of resources. Promoting the operation mode of “four integrations, diversified cooperation and market-orientation” to achieve production and efficiency improvement and mutual benefits, and enhance the vitality of unconventional oil and gas development. (5) Whole-process green and intelligent operation.Constructing a large scientific research system, a large operation system and a large environmental protection system to create a new development pattern of the unconventional oil and gas industry. The five countermeasures aim to promote the large- scale and beneficial development of unconventional oil and gas resources in China, ensure the sustainable and high-quality development of domestic oil and gas industry, and fulfill the major responsibility and mission of securing the energy rice bowl.

An exploration breakthrough has been made in the overpressure tight sandstone gas reservoir in the fifth member of the Upper Triassic Xujiahe Formation (Xu 5 member) in Well LG 163, drilled in Yilong–Pingchang area, Sichuan Basin, marking an important field for increasing reserves of continental facies tight oil and gas with a large scale and benefits. Based on the discovery of tight sandstone gas in Well LG 163 and the previous exploration results in Xujiahe Formation, and combined with the experimental and lab test data, a systematic study of reservoir characteristics and gas accumulation and evolution in Xujiahe Formation in Yilong–Pingchang area has been conducted focusing on the hydrocarbon generation center in Xu 5 member. The study results suggest that thick dark shale was developed in Xu 5 member in Yilong–Pingchang area, with an average TOC of greater than 1%, Type Ⅱ₂-Ⅲ organic matter, and high–over maturity, showing a good source rock as a whole. The meandering river delta front facies sandstone reservoir was developed in the southeastern part, with consistent distribution in lateral, porosity range of 1.5%–7.7% and an average of 4.83%, well-developed microfractures, and good reservoir physical properties. The tight sandstone reservoir in the second sub-member (Xu 5₂ sub-member) was wrapped in source rock in Xu 5 member, forming a high-quality hydrocarbon accumulation combination of “sand wrapped by source rock” in vertical. The formation overpressure is generally observed in Xu 5 member, and the pressure coefficient gradually increases from the slope to the center of the lake basin, resulting in tight gas charging and preservation under overpressure conditions. The comprehensive study of source rock conditions and reservoir physical properties indicates that the high-quality source rock in Xu 5 member has an area of 5600 km², the sand enriched zone has an area of 3553 km², and the predicted tight gas resources are 5600×10⁸ m³, showing good exploration prospects, which is expected to be a major replacement field for obtaining largescale gas discoveries.

In response to the challenges of almost all large-sized structural traps being discovered and insufficient resource replacement of production oil fields in Bohai Bay Basin. In the past 20 years, the continuous research has been conducted in exploration fields of the shallow Neogene and deep buried hills by using abundant geological, well drilling, laboratory test and seismic data, forming new geological understanding of hydrocarbon accumulation controlled by “convergence ridge” and “gas generation in lake basin”, respectively. The core of hydrocarbon accumulation controlled by “convergence ridge” includes that: (1) The configuration between “convergence ridge” and fault controlled the differential hydrocarbon enrichment outside source rock; (2) The “dendritic” type large-scale lithologic traps were developed in shallow loose sandstone; (3) The concealed faults controlled by weak tectonic activity enabled to form large-scale “concealed” traps. The main connotation of “gas generation in lake basin” refers to: (1) The late rapid subsidence of Bozhong Sag caused explosive gas generation of Shahejie Formation source rock; (2) The tectonic stress controlled the development of double-layer stereoscopic reservoirs in the Archeozoic granite buried hills; (3) The rapid and high-intensity charging of early oil and late gas and dynamic accumulation occurred under the background of overpressure dynamic sealing. The above understanding has guided the discovery of 18 large and medium-sized high-yield oil and gas fields such as KL10-2 and BZ19-6, which not only facilitates the strategic shift of oil exploration towards hidden oil reservoirs in Bohai Sea area, but also achieves the strategic breakthrough in large gas fields in oil-type basin.

After 60 years of exploration, over 70% of the resources have been discovered in Qianjiang Sag. The exploration degree of conventional sandstone oil reservoirs is high. Saline lacustrine carbonate rocks deposit with a low degree of research and exploration, which is a potentially important area for increasing reserves. In this study, by strengthening the basic research of lithofacies and logging interpretation,the old well data are re-recognized. It is considered that the lacustrine carbonate rocks of Qianjiang Formation are deposited several layers in vertical direction, which cumulative thickness is more than one hundred meters.Four main rock types are identified: granular carbonate,micritic carbonate, mixed granular rock and mixed fine grain rock. The favorable areas of carbonate rocks are zonally distributed. Study shows that shale, micritic carbonate and mixed granular rock are high-quality source rocks of Qianjiang Formation, granular carbonate and granular mixed rock are high-quality reservoirs. The carbonate reservoir of the Qianjiang Formation has the characteristics of ‘lithofacies control reservoir, reservoir physical property control rich’ oil enrichment controlling factors. Researching new insights guides the exploration in lacustrine carbonate reservoirs, significant achievements have been made in Tan Kou and Zhong Shi area, confirming a total resource volume of carbonate reservoir Over 100 million tons, becoming a new area of succession for exploration and reserve enhancement. It is an important guide and reference for deepening the oil exploration of salina lake carbonates in Jianghan Basin, as well as expanding the exploration of new areas in the similar faulted basins in the east.

In the thrust belt of the southern margin of Junggar Basin, the high-yield oil and gas production has successively been obtained in the deep to ultra-deep tight clastic reservoirs in the lower combination, with effective reservoirs and production capacity closely related to formation overpressure intensity. In order to clarify the mechanism of formation overpressure on high-quality reservoir and production capacity, the influence of formation overpressure on reservoir pore structure, permeability, oil and gas saturation, reservoir permeability,and production pressure difference is studied by integrating with previous studies and using geological, logging, drilling, well testing and petrophysical experimental data. In addition, the petrophysical experiments are conducted with the simulated dynamic pore pressure in reservoir formation conditions. The study results show that the highly–extremely over-pressured strata were widely developed in the study area, with intergranular pores retained, overpressure fractures developed, and reservoir “storage pores” and “connection pores” interconnected with each other, forming a high-quality reservoir with double porosity structure of matrix pores and fractures, which was conducive to the formation of high oil and gas saturation. The pore structure of the reservoir was controlled by lithology and overpressure intensity. Formation overpressure had little influence on the absolute reservoir porosity, but had great influence on permeability. When the pore pressure reached a critical value, the permeability increased abnormally, which was conducive to fracture initiation, enhancement of fluid flow capacity,and formation of high-yield oil and gas layers. Therefore, the formation overpressure showed mechanism of “retaining pores, increasing permeability and enhancing saturation”, and the overpressure intensity was the key factor for forming high-quality reservoir and achieving high-yield oil and gas production, as well as the basis for realizing high-yield and steady oil and gas production. The study results indicate that the favorable exploration area of deep to ultra-deep reservoirs in the southern margin of Junggar Basin is the effective traps with formation pressure coefficient of higher than 2.0.

The Cambrian in Ordos Basin has good potential for natural gas exploration. However, due to its low degree of exploration, the lithofacies paleogeographic distribution, hydrocarbon generation potential of source rocks in Cambrian are not clear, and the reservoircap assemblages and accumulation models are not determined. To address these problems, the lithofacies paleogeographic distribution,hydrocarbon generation potential of source rocks, favorable reservoirs distributionand reservoir-cap assemblage types of Cambrian were analyzed by using the newest data of seismic, drilling, outcrop and a large number of analytical tests, and the hydrocarbon accumulation models and natural gas exploration directions from Cambrian were discussed in Ordos Basin. During the Cambrian period, the Ordos Basin developed a paleogeomorphology pattern of three uplifts and three depressions. Controlled by the uplift-depression pattern, Dongpo formation and Xuzhuang formation source rocks are developed in the Fuping-Luochuan deep-water bay in the southern part of the basin, and the thickness of source rocks in the deep-water bay is large. Xuzhuang formation source rock is developed in Shenmu Dong depression, which is located in the northeast of the basin. Controlled by paleo-uplift, platform margin or depression margin, two kinds of favorable reservoirs are developed in Cambrian, including high-energy granular beach of Zhangxia Formation and karst weathering crust of Sanshanzi Formation.There are three types of accumulation assemblages in the Cambrian of Ordos Basin, including self-generation and self-storage, lowergeneration and upper-storage, and upper-generation and lower-storage. Four accumulation models are developed in Ordos Basin, including deep-water bay, depression, platform margin slope and paleo-uplift periphery. Based on the comprehensive analysis of source rocks, favorable reservoirs, reservoir-cap assemblages and accumulation models, it is suggested that the next step is to focus on the high-energy grain beaches and karst weathering crusts around the Fuping-Luochuan deep-water bay in the south of the basin, and the high-energy grain beaches on the edge of the Shenmu Dong depression in the northeast of the basin. At the same time, the natural gas exploration in the favorable areas such as high-energy grain beaches and karst weathering crusts on the east side of Qingyang paleo-uplift and karst weathering crusts on the southeast side of Yimeng paleo-uplift should be strengthened.

The Archean buried hills are the major field for obtaining discoveries in deep formations in Bohai Sea area in recent years. Based on 3D seismic data, mud logging, wireline logging and laboratory test data, hydrocarbon accumulation conditions of the Archaean buried hills in Bohai Sea area are analyzed, and enrichment patterns of key buried hills are summarized. The study results show that the Archean buried hills in Bohai Sea area had unique hydrocarbon accumulation conditions. Jointly controlled by multi-episode compression uplift and fault block tilting during the Indosinian–Himalayan periods, multiple types of buried hill traps were formed in Bohai Sea area. The oil and gas reservoirs were characterized by the upper source rock and lower reservoir type, which were mainly composed of dark mudstone source rocks in the third member of the Cenozoic Shahejie Formation (Sha 3 member) , the first and second members of Shahejie Formation (Sha 1+2 members),and the third member of Dongying Formation (Dong 3 member), as well as the large- and medium-sized buried hill reservoirs around the hydrocarbon-rich sags, showing significant source control effects. Influenced by multi-stage compression, shear, and extensional activities in the Mesozoic–Cenozoic, complex fracture networks were developed in multi-type buried hills, which was the key factor for the formation of large-scale reservoirs after superimposed by later fluid dissolution. The rapid subsidence in Bohai Sea area during the Oligocene–Neogene resulted in overpressure in the thick mudstone in Shahejie–Dongying formations, providing an effective regional cap rock for the Archean buried hills. Based on this understanding, two hydrocarbon enrichment patterns are established, i.e., “overpressure hydrocarbon charging, and gas after oil” pattern below source rock for the exposed type buried hills and “high-intensity hydrocarbon charging in a narrow window, and composite pathway for hydrocarbon migration” pattern beside source rock for the covered types buried hills, respectively. In addition, the key factors for the large-scale hydrocarbon accumulation in the Archean buried hills included the high-intensity hydrocarbon charging and strong reservoir transformation. The Archean buried hills covered by the Mesozoic/Paleozoic in Bozhong Sag is a major exploration field in the future, providing exploration orientation of deep buried hills in Bohai Sea area.

The Ordovician Wulalike Formation in the northwestern margin of Ordos Basin is an important field for shale gas exploration in Northern China. However, the geological conditions and gas enrichment characteristics have not been fully recognized. By using basic data such as core, lab test, logging and seismic data, key wells including Li 105 and Zhongping 1 and regional geological data are analyzed to study the enrichment conditions and accumulation patterns of shale gas in Wulalike Formation. The study results show that the favorable source rock,reservoir and cap rock combination was controlled slope facies zones. The deep water slope facies siliceous shale, calcareous siliceous mixed shale and clayey siliceous mixed shale were developed in the lower section, forming the main source rock and reservoir. The shallow water slope facies clayey shale, calcareous mudstone or marl were deposited in the upper section, forming good cap rocks. The geochemical index indicates a medium-good source rock, with mainly self-generated oil cracking gas, and good gas source conditions. The reservoir is generally characterized by high brittleness, with an average brittleness of 51.6%. The reservoir space is dominated by matrix pore and bedding fracture system, with an average total porosity of 4.7%, and an average fracture porosity of up to 1.8% (accounting for more than 38%). The roof generally has good sealing capacity, with clayey shale cap rocks in the middle and south regions, and marl cap rock in the north region. Shale gas is dominated by free gas, accounting for more than 64%. The comprehensive analysis shows that shale gas enrichment in Wulalike Formation was controlled by the consistent distribution of highly brittle shale in the lower section, gas source conditions, tectonic background and fracture development degree, and the favorable cap rock in the upper section. The fractures were mainly developed from the middle stage of Early Cretaceous to the present, which was consistent with the peak of gas generation. There are two main modes of shale gas accumulation. A fractured type shale gas reservoir controlled by the structure was dominant in the south region, and mainly accumulated in fault nose and fault anticline sealed by counter-inclined faults. While a continuous mixed shale gas reservoir was developed in the north region and dominated by a large area of continuous accumulation. In summary, Wulalike Formation has good exploration prospects, and the south and north sections are favorable areas for shale gas exploration.

The oil and gas resources in the Amu Darya Right Bank are abundant. Recently, a large-scale carbonate “ fault-fracture “ gas reservoir was discovered in the eastern region, demonstrating the excellent natural gas accumulation conditions of the carbonate rocks in this area. This study integrates seismic, core, thin section, and drilling log data to investigate the gas accumulation and enrichment patterns in the Upper Jurassic carbonate “ fault-fracture reservoir.” The study suggests that in the research area, under three different levels of faults—controlling faults, transformed faults, and micro-faults—and three types of depositional environments—shoal, mud mound, and intershoal environments—the interaction with associated corrosive fluids has led to the formation of fault-fracture with varying reservoir and permeability characteristics. These fault-fracture reservoirs include six types: shoal body-controlling fault, shoal body-intershoal-controlling fault, shoal body + transformed fault, shoal body + micro-fault, intershoal body + transformed fault, and intershoal body + micro-fault. These six types represent a new type of gas reservoir in the eastern part of the Amu Darya Right Bank. Based on the development geological parameters of several already producing “ fault-fracture “ gas reservoirs, these reservoirs can be further classified into three categories: Type I—large-scale fault-fissure bodies with strong fractures and strong corrosion near controlling faults (structural belts); Type II—local fault-fracture bodies with moderate fractures and moderate corrosion near transformed faults; and Type III—fracture-pore or fracture-type gas reservoirs with weak fractures and no corrosion in micro-faults. Among these, Type I reservoirs, with their significant advantages in reserve scale and stable high production, are the main target for further exploration potential in the region.

There are multiple petroliferous basins in Central and Western African Rift System (CWARS), with abundant oil and gas resources.Based on the study of the control of CWARS basins orientation and regional stress field direction on basin formation, relationship between tectonic evolution of CWARS and source rock development, as well as the sedimentary filling and hydrocarbon accumulation patterns of rift basins in different directions, the author presents the latest study progress of basin formation, hydrocarbon generation and hydrocarbon accumulation in CWARS. In addition, hydrocarbon accumulation patterns in various types of basins and exploration practice in typical basins are analyzed, which clarify the high-efficiency exploration practices and future exploration fields and orientations in CWARS. The study results show that, controlled by basin orientation and direction of regional stress field, multi-stage superimposed and single-stage rift basins were developed in CWARS. Among them, multi-stage rift processes occurred in NW–SE trending basins in the Early Cretaceous, Late Cretaceous,and Paleogene, forming the main hydrocarbon accumulation pattern of “lower source rock and upper reservoir, and hydrocarbon accumulation above source rock”. While a single-stage rift process experienced in the NE–SW trending basins in the Early Cretaceous, forming hydrocarbon accumulation patterns of “integrated source rock and reservoir, and hydrocarbon accumulation inside source rock” in the Lower Cretaceous and “upper source rock and lower reservoir, and hydrocarbon accumulation below source rock” in the Lower Cretaceous and buried hill.The diverse tectonic settings and geological evolution processes determined that terrigenous marine source rock was developed in the Upper Cretaceous in Western African Rift System and continental facies source rock was developed in the Lower Cretaceous in Central African Rift System. The thick, high-quality and mature source rocks provided a material basis for hydrocarbon enrichment in CWARS. The exploration practice in Melut Basin indicates that the key to achieving the high-efficiency exploration of overseas oil and gas projects relies on the rapid identification of oil-rich sags and the subsequent deployment of connected 3D seismic data. The major fields and orientations for the future exploration in CWARS include intra-source rock hydrocarbon accumulation combination in NW-SE trending multi-stage superimposed rift basins such as Termit and Melut, intra-source rock lithological oil reservoirs in NE-SW trending single-stage rift basins such as Bongor and Doseo, as well as traps outside source rock in oil-rich sags.

The gas reservoirs were mainly accumulated in lower member of the Neogene Minghuazhen Formation (lower Minghuazhen member) in Shijiutou bulge, Bozhong Sag, Bohai Bay Basin. However, the exploration results were unsatisfactory due to the consequent faults in the slope zone in the lower part of the bulge and the fact of “hydrocarbon passing through without retention” in Guantao Formation transport layer. Based on the previous study, and combined with abundant seismic, well drilling and geochemical data, the hydrocarbon migration path in the eastern Shijiutuo bulge has been analyzed in detail, clarifying the migration mechanism in the slope zone of the bulge.The study results indicate that Shinan No.1 Fault, a boundary fault on the south side of the bulge, had a greater opening coefficient in Guantao Formation than in Dongying and Minghuazhen formations. The hydrocarbon filling degree in traps in Guantao Formation in the bulge slope zone in the upper fault plate was much higher than the steep slope zone in the lower fault plate, controlling the upward hydrocarbon migration from sag area to bulge zone and the lateral diversion in Guantao Formation, with the advantageous diversion direction of the bulge zone. The heterogeneous transport layer in Guantao Formation and slope gradient controlled the oil accumulation in the slope zone, and the microscopic bed plane “lithologic traps” were formed by sandstones with different physical properties. On this basis, when the slope angle of convergent ridge in Guantao Formation was less than 1°, a large amount of reservoir space was formed for oil accumulation. Affected by tectonic activity of consequent faults in the late stage, oil and gas in Guantao Formation in the slope zone migrated to the lower Minghuazhen member sand reservoir and accumulated on a large scale. The above new migration pattern of “hydrocarbon convergence in gentle slope–transit by fault” has broken through the traditional understanding that hydrocarbon “passing through without retention” in the transport layer in the consequent slope zone, and successfully discovered Qinhuangdao 27-3 Oilfield in the lower Minghuazhen member in the slope zone in the eastern Shijiutuo bulge with reserve level of 100 million tons, providing a reference for the subsequent exploration outside source rock in the slope background in Bohai Bay Basin.

At present, China’s petroleum companies are fully promoting the exploration and application of unconventional oil and gas development. The particularity of unconventional oil and gas development makes its economic evaluation different from that of conventional oil and gas economic evaluation.Therefore, based on the analysis of the characteristics of unconventional oil and gas development, the individual demand for economic evaluation of unconventional oil and gas development is sorted out, and the tasks and principles of economic evaluation of unconventional oil and gas development are put forward.First, the economic evaluation of unconventional oil and gas development should adhere to the whole life cycle optimization concept and highlight the integrated management and evaluation.Second,it is necessary to establish an integrated optimization linkage model and promote program optimization through the backforcing mechanism.Then,three kinds of economic evaluation methods of unconventional oil and gas development are put forward, which are quick economic evaluation model and chart, whole life cycle linkage and benchmarking analysis, and risk analysis.In the optimization of unconventional project scheme and integrated optimization design of geological engineering,it is suggested to build a rapid evaluation model and map evaluation method.It is recommended to adopt the methods of linkage and benchmarking analysis in the preparation of the whole life cycle development scheme of unconventional projects.For non-conventional projects with high risk and uncertainty (such as projects in the exploration phase),a risk analysis method is required.In addition,for these three kinds of economic evaluation methods, the improvement and upgrading direction are proposed respectively.