The China National Petroleum Corporation Limited (CNPC) has preliminarily achieved the large-scale production of unconventional oil and gas. However, considering its abundant resources, the output still has great potential for improvement. The exploration and development progress of unconventional oil and gas of CNPC during the 13^th Five-Year Plan period is summarized, and unconventional oil and gas development trend in the 14^th Five-Year Plan period is discussed. On this basis, the main challenges and key problems are analyzed,and strategies are put forward to promote the high-efficiency development of unconventional oil and gas of CNPC. The results show that: (1) During the 13^th Five-Year Plan period, CNPC has gradually focused on low-grade resources represented by unconventional oil and gas; (2) During the 14^th Five-Year Plan period, the proportion of unconventional oil and gas production will further increase, and production capacity in key areas will grow rapidly; (3) Four aspects of challenges, such as the technology, cost, management and idea, are faced with high-efficiency development of unconventional oil and gas. In view of the above challenges, six key countermeasures are proposed: (1) Properly understand the unconventional resources; (2) Implement the engineering management concept and mode of “one engine with six drives”; (3) Improve management rules and assessment methods; (4) Fully use the big data platform; (5) Effectively promote market-oriented business operation and socialized services; (6) Formulate rational policies for unconventional resource development. The above measures will enable CNPC to promote the high-quality development of its unconventional oil and gas business and contribute to “ensuring the rice bowl of energy firmly in our own hands” by developing the unconventional oil and gas.

Facing the pressure of the increasingly complex exploration and development objects and low oil price, Changqing Oilfield has explored and formed a new development mode of shale oil and tight gas with “horizontal well, multi series, stereoscopic, cluster wells, and factory operation” based on their geological characteristics, which enables to achieve the large-scale, high-efficiency and low-cost development of tight oil and gas resources by integrated geology and engineering. In order to better meet the business needs of integrated comprehensive study, production organization and decision-making, the construction and application of an enterprise-level geology and engineering integrated intelligent decision-making system are explored and studied against the digitization background. The design idea of a complete chain covering “research + analysis + decision making” is proposed, which deeply integrates the new generation of big data, Internet of things and artificial intelligence technology with development mode of tight oil and gas. As a result, the Geology & Engineering Integrated Decision Support System (GEDS) is developed and constructed, including key technologies such as 3D seismic data visualization, display of integrated surface and subsurface, data interface for rapid 3D geological modeling, real-time updating of geological model, etc. It has been applied in shale oil exploration and development demonstration project, realizing remote interaction between indoor and field, real-time monitoring of production process and dynamic optimization of scheme deployment.

The international oil price plummeted in 2014 and continued to operate at a low level. Since 2016, North America energy companies mainly engaged in shale oil and gas development have ushered in the bankruptcies. On June 28, 2020, Chesapeake Energy Company, the leader of shale oil and gas development in the United States, announced bankruptcy protection, attracting great attention of the global energy industry. The industry concerns more about whether shale oil and gas development can be sustainable, and some even regard that shale oil and gas development in North America may be a new Ponzi scheme. By summarizing the rise, development, achievements, social benefits and the reasons for the success of the American shale revolution, the shale oil and gas crisis in North America are analyzed from multiple factors which is caused by low oil prices, and the development paths and results of Chesapeake and EOG, the two typical energy companies mainly engaged in shale oil and gas development in North America are compared. Finally, the basic conditions for the sustainable development of shale oil and gas under the current low oil price environment are summarized, including high-quality oil and gas assets, cost control and profitability, positive cash flow, and investment risk control, so as to provide some enlightenment for the development of unconventional oil and gas in China.

Well Ping’an 1, located at the paleo central sag in northeastern Sichuan Basin, achieved a high shale oil production of 100 tons from Lianggaoshan Formation, indicating a major breakthrough of shale oil and gas of Lianggaoshan Formation in Sichuan Basin. Based on the exploration results in Well Ping’an 1, the main controlling factors for shale oil accumulation and exploration orientation of Lianggaoshan Formation in northeastern Sichuan Basin are systematically analyzed. The results show that the shale oil reservoir in Well Ping’an 1 is lacustrine organic rich shale and the rock type is felsic shale. The average porosity is 2.06%, dominated by intergranular pores and intracrystal pores,with micro fractures developed; TOC ranges from 0.64%-1.35%, and Type II organic matter is dominant. R_o is in the range of 1.51%-1.66%.The content of brittle minerals is 50.4%-54.8%. The comprehensive evaluation indicates that the widely distributed semi deep lacustrine shale is rich in organic matter in foreland basin in northeastern Sichuan Basin, which is conducive to shale oil and gas accumulation. Among them, three layers of shale are developed in the Upper Lianggaoshan Formation, with strong hydrocarbon generation capacity and high degree of thermal evolution, which is a set of high-quality source rock as a whole; In addition, it has good preservation conditions, formation overpressure and well-developed pore-fracture system, which enable to serve as an effective reservoir and a high-efficiency production layer. The breakthrough in Well Ping’an1 shows the great exploration potential of the Jurassic lacustrine shale, and plays a positive role in accelerating shale oil exploration in Sichuan Basin.

Turpan-Hami Basin has abundant tight sandstone gas resources. In the early exploration, only small-scale oil and gas reservoirs such as Baka, Wenjisang and Mideng were discovered in positive structural belts in the peripheral Taibei Sag. Based on the comprehensive analysis of source rocks, sedimentary systems, reservoir conditions and source rock–reservoir–cap rock assemblages, the accumulation pattern of tight sandstone oil and gas reservoir is established interior of source rocks in Taibei Sag. The study result shows that two types of high-quality source rocks are developed in Shuixigou Group in Taibei Sag, namely the coal measure source rock of Badaowan Formation, mudstone of Sangonghe Formation and coal measure source rock of the second member of Xishanyao Formation, with high TOC, good organic matter type, mature stage of thermal evolution, and widely developed in the sag; Multiple reservoir–cap rock assemblages are formed in the second and first members of Xishanyao Formation, as well as Sangonghe and Badaowan Formations. The sandstone deposits are widespread in the sag supplied by sufficient sediment sources from five braided river deltas in the west, north and south directions. The source rocks generate large-volume hydrocarbon and serve as the regional cap rocks to form multi-layer “sandwiched” type source rock–reservoir– cap rock assemblage; The sag has the favorable geological conditions for forming large-area tight sandstone gas reservoirs interior of source rocks, such as stable negative structures, good preservation conditions, high formation pressure and high maturity of source rocks. A horizontal well Ji7H was drilled based on the idea of “interior of source rock, marching towards deep sag and drilling horizontal well”, and high yield oil and gas flows of 40.37 m³/d and 51283 m³/d were obtained after fracturing by open flow with 7 mm choke. The tight sandstone condensate gas reservoir interior of source rocks supports to discover a new field of exploration and open up the prelude to the second exploration in Turpan-Hami Basin.

Junggar Basin has abundant shale oil resources and promising exploration potential of the Permian Fengcheng Formation, which is expected to be a major strategic replacement field for increasing oil reserves and production. The exploration history of the Permian shale oil in the Junggar Basin is reviewed and the geological characteristics of alkaline lake type shale oil in Muhu Sag are analyzed by using geological,core lab test, drilling, mud logging, wireline logging and seismic data. Then the geophysical evaluation methods and reservoir stimulation technologies for shale oil “sweet spot” are systematically summarized. Finally, the shale oil exploration orientation of the Permian Fengcheng Formation is put forward. The study results show that: (1) The world’s oldest and the most extensive alkaline lake type high-quality source rocks of Fengcheng Formation are developed in Mahu Sag, with the characteristics of multiple provenances mixed deposition, triple types of reservoir spaces composed of pore, fracture and stylolite, shale oil accumulation controlled by favorable lithofacies and scattered “sweet spots”. Among them, the second member of Fengcheng Formation (Feng 2 member) shows a good exploration prospect. (2) Three key technologies such as the high-resolution seismic prediction of shale oil “sweet spot area”, “three qualities” logging comprehensive evaluation of “sweet spot interval”, and supporting reservoir stimulation technology of engineering “sweet spot” are innovatively developed. As a result, the “sweet spot area” of 1200km² and “sweet spot interval” of 17 layers have been identified. (3) In view of the key issues in exploration, shale oil “sweet spot” of Feng 2 member is still need to be finely characterized, and the geology and engineering integrated technology be deeply researched, so as to realize the overall breakthrough and further large-scale benefit development of shale oil of Fengcheng Formation.

In Jiyang Depression, the organic rich and carbonate rich shale of semi deep-deep lake facies is developed of the Cenozoic salinized continental fault rift basin, and the shale oil is featured by medium-low and medium-high maturity, with high abundance and great resource potential, which is different from that in North American marine basins and other continental basins in China. Looking back to the shale oil exploration history for 50 years in Jiyang Depression, it can be divided into three stages, i.e., accidental discovery, active exploration and innovation breakthrough. At present, strategic achievements of multiple series and multiple types shale oil have been made in medium-maturity carbonate-rich lamina matrix type and high-maturity carbonate-rich lamina-thin layer matrix type shale in the upper part of the fourth member of Shahejie Formation in Dongying Sag and the lower part of the third member of Shahejie Formation in Zhanhua Sag, as well as major progress in low-maturity carbonate-rich lamina matrix type shale. More than 10 years’ study and exploration practice have enabled to establish the lithofacies division scheme of shale in Jiyang Depression, obtain the innovative understanding of reservoir performance, oil bearing, oil mobility and fracability of organic shale, establish a geological evaluation system including 20 parameters with the core of “four properties”,develop the supporting geological, engineering and geophysical prediction, drilling engineering and fracturing technologies, and form the integrated operation and management mode adapted to geological characteristics of Jiyang Depression, which has effectively guided shale oil exploration practice in Jiyang Depression.

The geological conditions of Fuling marine shale gas in Sichuan Basin are different from that in North America. Therefore, the development mode of large-scale, high-density and continuous well drilling applied in North America is not applicable to Fuling shale gas field. In view of the difficulties of fine characterization of the remaining resources after the primary well pattern development of the lower gas layer, low production rate of remaining resources and imperfect technology to improve the ultimate technically recoverable reserves (EUR) of old wells, the idea of geology and engineering integration is proposed suitable for stereoscopic development of Fuling marine shale gas. During the implementation of shale gas development, the multi-disciplinary knowledge such as remaining gas distribution, drilling and completion,fracturing and production has systematically been summarized, and a set of geology and engineering integrated technology series been formed, including geology modeling and numerical simulation integrated reserve production evaluation technology, integrated stereoscopic development and well adjustment optimization technology, integrated drilling and completion supporting engineering technology, which has effectively guided the high-efficiency stereoscopic exploration and development of Fuling marine shale gas.

The shale oil reservoir in Jimsar Sag in Junggar Basin is a typical onshore unconventional shale oil reservoir with complex reservoir lithology, large differences in burial depth laterally, many interlayers vertically, thin oil layers, strong heterogeneity, high crude oil viscosity,and great difficulty in development. Major progress has been made during four stages of exploration, i.e., discovery, pilot test, breakthrough in utilization, and large-scale construction of production capacity. However, the reachability of design capacity is low, and the contradiction between cost and output of single well is prominent, showing that the low benefit is the main issue restricting shale oil development in Jimsar Sag. Since 2021, Xinjiang Oilfield Company has explored benefit shale oil development focusing on two aspects of management and technology. With regard to the main control factors for single-well production such as distribution of sweet spot shale, drilling rate of highquality reservoirs, and reservoir stimulation intensity, technical measures have been adopted, including reservoir fine characterization, shale oil mobility evaluation by NMR logging, improving the precise of borehole trajectory regulation, and increasing reservoir stimulation intensity, so as to form a mature management and technical system by integrating with market-oriented independent operation. The practice shows that the single well cost reduced by 53.4%, single well EUR increased by about 50%, and profits could be achieved at oil price US$45/bbl, which promoted the benefit development of shale oil in Jimsar Sag.

The Jurassic lacustrine shale in Sichuan Basin has multiple producing layers and abundant shale oil and gas resources, which is expected to become a major replacement field for “increasing reserve and production” in China. By taking the Jurassic continental shale in Fuxing area as the study object, the geological characteristics of high-quality continental shale reservoirs are summarized, the understanding of continental shale oil and gas accumulation is updated, and three key exploration and development technologies applicable for continental shale oil and gas are proposed. The results show that: (1) During the Early-Middle Jurassic, three sets of high-quality semi-deep lacustrine shale reservoirs were developed in Fuxing area in Sichuan Basin, including the Dongyuemiao member and Da’anzhai member of Ziliujing Formation, and the second member of Lianggaoshan Formation, with the overall characteristics of medium TOC, medium porosity and high clay content; (2) The development and distribution of continental shale reservoir are controlled by sedimentary facies zone, and hydrocarbon enrichment and accumulation is determined by sedimentary environment and preservation conditions. The natural fracture development affects the high yield zone while the thermal evolution degree determines the types of shale oil and gas reservoir; (3) Three key technologies, such as high resolution “sweet spot” prediction technology, high-efficiency geosteering drilling technology of horizontal well and volume fracturing technology for low-brittleness shale reservoir, are applicable to continental shale gas exploration and development. To sum up, the Jurassic continental shale in Fuxing area has promising resource potential, and it has good exploration and development prospects by applying the existing technologies.

Panzhuang CBM Field has the highest CBM production in China. Multi set coal seams are developed, with superior geological conditions such as shallow burial depth, large thickness, high gas content, and high permeability, as well as abundant CBM resources. In the process of CBM development, a series of technical difficulties occurred, such as poor production result of the main No. 3 coal seam, rapid decline, and no breakthrough in development of No. 15 coal seam. In view of these problems, geological characteristics of each coal seam are studied in detail, geological evaluation technology of thick and thin coal interbeds is researched, CBM exploration and development technologies for thick and thin coal interbeds and desulfurization are researched, and cooperative work platform is established with geology and engineering integration. This study is based on the early geological and engineering knowledge, and makes full use of the existing seismic data, coalfield boreholes, and CBM wells data. The repeated engineering tests and comparison of different well types enable to develop four series of CBM exploration and development technology for thick and thin coal interbeds, including comprehensive geological evaluation,development of single lateral horizontal well for thick coal seam, desulfurization development of No. 15 coal seam, and commingle production of multi-layer thin coal seams, and establish the optimal stereoscopic CBM development mode, which realize the low-cost and high-efficiency production of low-grade and difficult-to-utilize resources.

The development of continental shale oil in China faces the bottleneck of low production of single well, rapid decline and low ultimate recovery. Therefore, the CO₂ enhanced oil recovery (EOR) technology is necessary to be researched in advance. The development process of CO₂ EOR technology in North America is systematically analyzed, and the applicability and prospects of this technology are discussed by combining with the conditions of domestic continental shale oil resources. The result shows that the shale oil plays in China are characterized by a significant variation on crude oil viscosity, formation pressure coefficient and mineral compositions, which have distinctly different challenges for benefit development and largely different CO₂ EOR mechanisms. As a result, a targeted application index of CO₂ EOR technology is required for various shale oil plays, as well as a technical adaptability evaluation criterion. Meanwhile, efforts should be intensified in all links of field application of CO₂ EOR technology, and clear national financial support should be sought actively. Considering the technology prospects and resource conditions, it is proposed to build a pilot demonstration area for CO₂ EOR application in Jimsar shale oil block in Junggar Basin and establish an integrated technology and policy supporting system, so as to effectively promote the development of CO₂ EOR technology, ensure the domestic energy security and support to achieve the strategic goal of carbon neturality.

With regard to the casing deformation in shale gas development wells in Changning-Weiyuan national demonstration area in Sichuan Basin, an integrated prevention and control technology is proposed. By using the fluid channel-fault activation model and combining with mechanics condition of fault slip and quantitative risk assessment (QRA), the section with casing deformation risk is predicted; The law of interaction between fault slip and casing is analyzed to prevent casing deformation by method of “overcoming hardness with softness”;The microseismic characteristics are analyzed in wells with casing deformation, and the microseismic signals are monitored in real time during fracturing, so as to early warn the casing deformation; Based on fluid channel and fracturing model, casing deformation is controlled by optimizing fracturing parameters and technology of multi-cluster perforation + temporary plugging. To sum up, an integrated casing deformation prevention and control strategy is formed, including pre-drilling prediction, pre-fracturing prevention, early warning and control in fracturing, which provides a basis for solving the problem of casing deformation in shale gas development wells.

The Paleogene gypsum-salt rock is extensively developed in the main part of Kuqa Depression, with a maximum thickness of up to 4000m. There are diverse deposition patters of the base salt rock but a lack of the unified marker bed. Moreover, influenced by the vertical shear stress and orogenic compression during the uplift of the south Tien Shan Mountains, the gypsum-salt rock experienced intensive plastic creeps, and the complex lithologic association brought difficulties in accurately discriminating the base salt rock. Based on the undercompaction theory, the differences between inter-salt mudstone and base-salt mudstone are summarized. Then the sedimentary pattern of multiple salt lakes is characterized and the zonal sedimentary sequences are identified of the subsalt sequence by using drilling data from 120 wells, as well as the subsalt sedimentary sequence, lithologic association of basal sandstone and residual thickness of the Cretaceous;The cuttings, mud logging and wireline logging data enable to determine the lithologic associations at the base salt layer and establish a lithologic association plate for different zones; The differences between inter-salt mudstone and base-salt mudstone are compared and an on-site identification standard is set up based on the lithology, mineral composition, element composition, wireline logging and seismic facies characteristics; A series of quantitative indexes for discriminating the base salt mudstone are precisely established in various zones by using sedimentary sequences, drilling, mud logging, wireline longing and element geochemistry data; Finally, the micro-drilling time, XRF logging, and pilot well data are applied to develop an applicable discrimination method and field operation scheme by integrated geology and engineering. The technology ensures the safe and rapid completion of 31 exploration wells, which provides solid technical supports for building the largest production base of ultra-deep natural gas with a production capacity of 30 billion cubic meters.

The reservoir of Chang 7 member shale oil in Longdong area is mainly composed of interbedding layers of deep lacustrine shale and gravity-flow sandstone, which is characterized by strongly heterogeneous reservoir distribution vertically and laterally and thin single sand layer, with natural fractures developed. In view of the technical challenges in shale oil development, such as well location placement, high-efficiency well drilling and customized well stimulation, a complete set of geology and engineering integrated solution is proposed.Firstly, by applying the comprehensive geological study results, 3D fine geological and geomechanical modeling and reservoir simulation are performed, and then well location selection, well-factory platform design, well drilling and geosteering schemes optimization are implemented to ensure that the well trajectory is reasonable and applicable, reservoir penetration rate is improved while well drilling and completion time is reduced; The combined geomechanical model and reservoir simulation enable the rational fracturing design and operation; In the flowback and production stage, a pertinent scheme is designed by considering the geological, oil reservoir, geomechanical and well completion conditions for fracturing operation to achieve the maximized single well production as well as a long-term cumulative production of the well block.

Faced with the challenges in stimulation of ultra-deep fractured gas reservoir, the key stimulation technology system with geology and engineering integration is researched and developed by taking geomechanics as a link, and a multi-dimensional ultra-deep reservoir stimulation workflow is formed including well location selection, well type and well trajectory optimization, and fine design of stimulation scheme. The results show that the ultra-deep reservoir is characterized by high temperature, high pressure, high in-situ stress, well developed fractures and strong heterogeneity. Different from the stimulation mechanism for medium-shallow reservoir, activation of natural fractures is the key in stimulation of ultra-deep fractured gas reservoirs. The geology-engineering integrated stimulation technology enables to increase production more precisely and more effectively, reduce difficulties in field engineering, and avoid risks in conventional fracturing operations.The technology has been applied for more than 150 wells in Kelasu structural belt in Kuqa Depression, with open gas flow increased by 3-5 times, which supports realize the efficient development of ultra-deep fractured sandstone gas reservoir, and build a large gas field with production capacity of 150×10⁸m³.