In the early 13^th Five-Year Plan period, petroleum exploration of Sinopec North China Oil & Gas Company in Ordos Basin was faced with challenges in producing natural gas reserves, unclear understanding of oil accumulation law, and uncertain resource replacement fields. In the past five years, by strengthening the integral structure and sedimentary evolution study in the basin, the differential configuration of hydrocarbon accumulation elements was analyzed, understanding of gas differential accumulation in the Upper Paleozoic in the transitional zone at the northern basin margin was innovatively formed, and the exploration and development technology for complex water-bearing gas reservoir in basin margin was developed, which supported to discover Dongsheng Gas Field; Based on the reprocessing and interpretation of 3D seismic data, hydrocarbon accumulation in the Mesozoic tight sandstone fault-fracture body in the transitional zone at the southern basin margin was identified, and new “sweet point” types of the Mesozoic tight oil were evaluated by using “six-determination” description method of fault-fracture body oil reservoir; The fault-fracture controlled karst reservoir in marine carbonate rocks was discovered by largearea 3D seismic data reprocessing, and the reservoir development and hydrocarbon accumulation pattern in large unconformity carbonate karst reservoirs in the Lower Paleozoic was proposed. After identifying and predicting the distribution of carbonate karst reservoirs, favorable zones were selected and evaluated, and carbonate exploration in the Paleozoic in the southern basin was strengthened, which supported to prove two gas replacement fields with reserve of hundred billion cubic meter level. Finally, petroleum exploration results were summarized and geological understanding was formed that the strike-slip fault system is widely developed in the basin and karst reservoirs are controlled by faults. The comprehensive analysis indicates that the karst zones controlled by multi-stage active strike-slip faults below the deep marine carbonate weathering crust and the complex tight clastic reservoir in the peripheral basin are major exploration prospects and fields during the 14th Five-Year Plan period.

Since 2005, the economic recoverable oil and gas reserve, a new category of reserve indicator, has been established in China. The process of the newly increased economic recoverable reserve in China and major oil companies is summarized, and the basic characteristics of the proved new addition oil and gas reserves as well as 38 newly proved large to extra-large scale oil/gas fields or blocks from the 11^th Five-Year Plan to the 13^th Five-Year Plan period in China are discussed. After analyzing the history of the proved new addition economic recoverable oil and gas reserves in China and PetroChina, the distribution and classification characteristics of reserve size, reserve abundance,porosity and permeability of reservoir and burial depth are focused. Then the proved new addition oil and gas reserves in China in the past 15 years are comprehensively evaluated by applying indicators such as finding reserve replacement ratio (FRRR) and technical/economic recovery factor. The study results show that the proved new addition oil and gas reserves have the trend of “three decreases and three increases”, that is, the decrease of FRRR, recovery factor and scale of the integrated oil/gas field, and the increase of tight reservoir, low to ultra-low abundant reserve and burial depth, indicating an overall deteriorating of the new addition oil and gas reserves in China. FRRR is an indicator that has strategic significance for the evaluation of exploration effectiveness. It is suggested to speed up the establishment of economic recoverable reserve classification system and management system adapted to the characteristics of Chinese oil companies to better apply to the petroleum exploration field and further meet the needs of reserve development and production increase.

Given the strong heterogeneity of continental shales in China, small element volumetric method should be adopted for resource assessment of interlayer shale oil and small element volume method for pure shale oil. The fitting relationship curve between S₁ and TOC as well as relationship curve between light hydrocarbon recovery coefficient and R_o are established to obtain the original S₁ content. In addition,four key parameters for the evaluation of pure shale oil resources (S₁, TOC, R_o and shale thickness) and another three for interlayer shale oil resources (cumulative thickness of shale interlayer, porosity and oil saturation) are determined, and the lower limits of these parameters are formulated accordingly. By applying the unified assessment method and standard, typical cases of shale oil resource assessment are studied,including the Cretaceous Qingshankou Formation in the northern Songliao Basin, Triassic Yanchang Formation in Ordos Basin, and Permian Lucaogou Formation in Junggar Basin. The evaluation results show that the geological resources of pure shale oil in the first member of Qingshankou Formation (Qing 1 member) are 52.23×10⁸ t, with light oil (R_o>1.2%) of 11.18×10⁸ t; The total shale oil resources in the third sub member of the seventh member of Yanchang Formation (Chang 7₃ sub member) are 66.80×10⁸ t, among which the interlayer shale oil resources are 27.73×10⁸ t, and the pure shale oil resources are 39.07×10⁸ t; The total shale oil resources in Lucaogou Formation are 15.62×10⁸ t, among which the interlayer shale oil resources are 11.99×10⁸ t, and the pure shale oil resources are 3.63×10⁸ t.

The basic geophysical exploration management is a major content in geophysical prospecting technology management, a key factor for scientific management, scientific decision-making and cost reduction, as well as an important guarantee for comprehensively promoting quality, accelerating speed and increasing efficiency. Associated with the continuous deepening of exploration and development in various oil fields, professional database systems are required to manage and apply the massive basic geophysical data. The basin level geophysical exploration basic database system developed by BGP, taking the data standard of PetroChina Petroleum Exploration and Production Data Model (EPDM) and applying the same micro-service architecture as that of PetroChina Dream Cloud, enables to achieve the cross regional data sharing and application through the intranet of PetroChina. Till now, initial results have been achieved in the establishment of the professional database systems, such as survey and SPS database, surface data result database, static correction database, high resolution satellite image database, velocity database and document management database, which are highly recognized by Yumen Oilfield. This system not only supports to promote the digital transformation, but also provides scientific basis for the exploration deployment decision of Yumen Oilfield.

High gas flow of 10.⁴×10⁴m³/d has been obtained in the first shale gas exploration well Puluye 1 in Puguang area, marking a major breakthrough in shale gas exploration of the Middle Jurassic Qianfoya Formation in the northeastern Sichuan Basin. By using lab test data such as shale gas content, geochemical, petromineralogical, and reservoir characteristics, accumulation conditions and enrichment rule of shale gas in Well Puluye 1 are analyzed. The study results show that: (1) The laminated felsic clay rock of semi-deep lake facies was continuously developed in No. 3 thin layer of the first member of Qianfoya Formation in Well Puluye 1, with the average desorption gas content of 0.58 m³/t, total gas content of 1.58 m³/t, average TOC of 1.13%, Type Ⅱ₁-Ⅱ₂ organic matter, average R_o of 2.03%, and average porosity of 3.8%,which is a sweet spot interval for shale gas exploration; (2) The high-quality shale of semi-deep lake-deep lake is the basis for shale gas enrichment; (3) The key factors for the enrichment and high production of shale gas include high intensity of hydrocarbon supply by the highover mature shale, good fluidity of gas cracked by crude oil, and high reservoir space and methane adsorption capacity of the organic pores;(4) The intensively developed High-angle fractures, bedding micro fractures and cleavage fissures support to increase the reservoir space and permeability of shale, which are important conditions for high shale gas production of Qianfoya Formation in Well Puluye 1. The above results enrich the understanding of oil and gas reservoir types, reservoir space characteristics, enrichment and high production rules of the high-over mature shale in the Jurassic Qianfoya Formation in the northeastern Sichuan Basin, which has important guiding significance for shale oil and gas exploration in the study area.

Continental shale oil has grown to be one of the major replacement fields for petroleum exploration in China. The laminar structure,a unique fabric feature of shale, significantly influences the evaluation of source rock quality, reservoir quality and engineering quality, which has attracted increasing attention for study. By taking typical organic-rich shales in saline and fresh-brackish lake basins in the central-western China as study objects, the characteristics of laminar structure are analyzed and their influence on the selection of sweet spot is discussed. The results show that: (1) The laminar structure varies in different types of lake basins, which is affected by the salinity of lake basin. The carbonate laminar is mainly developed in saline lake basin, but less in fresh-brackish lake basin; (2) The laminar structure has strong heterogeneity of sub-millimeter level. There are differences in TOC and pore structure among different laminae, and the quality of the same type of laminae varies greatly in various basins; (3) The laminar structure determines the characteristics of microscopic shale oil migration and accumulation as well as the enrichment mode of “in-situ source rock and reservoir”, and affects the retained hydrocarbon content, fluid mobility and fracturing engineering. The fine evaluation of laminar structure of continental shale and identification of the favorable lithofacies zone for high-quality shale development are the critical issues for petroleum exploration from outside to inside the source rock, which are the basis for the discovery of economic and effective resources inside the source rock and have great significance for the selection of shale oil “sweet spot area” and “sweet spot interval”.

Reservoir of the Lower Cretaceous Shahezi Formation in Xujiaweizi Fault Depression in the northern Songliao Basin is characterized by close provenance, rapid facies change, strong heterogeneity and superimposed source rock and reservoir, which has geological conditions for the accumulation of tight gas reservoir. The study results show that reservoir of Shahezi Formation is tight with low textural maturity. The lower limit of pore throat for fluid flow is 20 nm and the upper limit of pore throat is 0.4 μm of the tight reservoir. NMR and high pressure mercury injection experiments on core samples of Shahezi Formation indicate that the reservoir physical properties were greatly affected by sediment grain size. Firstly, the reservoir types are classified according to different lithologies such as tight sandstone and glutenite. Then the sweet spot evaluation method of “subdivision after classification” is innovatively researched for tight reservoirs in fault basin based on the comprehensive factors such as porosity, reservoir thickness, and shale content affecting on single well production. As a result, 31 sweet spot areas are divided in the entire area and totally 230 sweet spot bodies are identified. Among them, Anda area in the northern Xujiaweizi Fault Depression is an optimal sweet spot area, with sweet spot bodies of the underwater distributary channel, sheet sandstone and channel mouth bar microfacies of delta front facies are well developed, which provides guidance for the exploration deployment in this area.

Faults played an important role in controlling oil accumulation in Yanchi area in the northwestern Ordos Basin. Based on the analysis of the regional geological data and combined with 2D and 3D seismic interpretation results, characteristics of the Mesozoic faults and their relationship with oil reservoir are studied by using technologies such as electron spin resonance (ESR) dating, calcite U-Pb isotope dating,equilibrium section restoration, and tectonophysical simulation. The results show that three stages of faults were developed in Yanchi area. The NW trending fault system in the Indosinian had a small scale and was mainly developed in the Triassic Yanchang Formation; The nearly NS trending fault system in the Yanshanian had the largest scale, with large fault throw and complex lateral and vertical distribution patterns; The NEE trending fault system in the Himalayan had a relatively large scale, late development period, and strike slip feature to a certain extent.The three stages of faults were formed by the regional stress of NW, nearly E-W and NE-SW directions respectively, and the nearly S-N faults were closely related to the activities of the major faults in the western basin margin. The NW trending fault system in the Indosinian connected source rock to reservoir, which delivered good configuration between migration and sealing, showing the most favorable conditions for the accumulation of oil and gas reservoirs. In addition, faults supported to improve the reservoir physical properties to some extent. When the oil well is close to the fault, oil accumulates will be easily accumulated in high permeability reservoirs in the high structural parts and high-yield production will be achieved.

Shale gas shows have been observed from the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in several wells in Xichang Basin. The drilling results indicate that gas content of Wufeng Formation-first member of Longmaxi Formation (Long 1 member) is relatively good, showing promising potential for shale gas exploration and development. By comprehensively applying core observation and thin section data, and integrating with logging interpretation, the high-quality shale is classified and the stratigraphic sequence,sedimentary facies and depositional pattern are studied, so as to primarily evaluate shale gas potential of Long 1 member in Xichang Basin.The study results show that: (1) The high-quality shale of Wufeng-Longmaxi Formation is composed of five thin layers ① - ⑤ ; (2) The highquality shale is divided into two third order sequences. Deposits of bioclastic beach microfacies of tidal flat facies and siliceous mud shelf microfacies of deep-water shelf facies were developed in SQ1, while SQ2 was composed of lime mud shelf and limy sandy mud shelf deposits of deep-water shelf facies; (3) The development of high-quality shale was controlled by the deep-water shelf environment during the deposition period of Wufeng-first sub member of the first member of Longmaxi Formation (Long 1₁ sub member), which had high organic carbon content,high silica content and rich graptolite; (4) The shale gas accumulation in high-quality shale of Wufeng-Longmaxi Formation is affected by three key factors, i.e., development degree of fault zone, burial depth of high-quality shale and distance between the high-quality shale to fault zone.

Keshen 10 gas reservoir, developed in Kelasu structural belt in Tarim Basin, is an ultra-deep tight sandstone gas reservoir, which shows complex drilling conditions, low natural production capacity and great challenge in increasing well production. In order to improve the benefits of gas exploration and development, geomechanic analysis such as the current in-situ stress field and fracture activity is conducted on the basis of geological study, which enables to determine the distribution law of the current in-situ stress field and fracture activity of Keshen 10 gas reservoir, and identify great variation in permeability of fractures with different directions. Then the fracturing results are analyzed of various well trajectories with different well types and deviations, and the geology and engineering integrated working method is proposed to guide the optimization of well trajectory design. The results show that: (1) Different from the medium-shallow gas reservoirs, well production capacity is distinctly affected by the current in-situ stress and its induced fracture activity of the ultra-deep gas reservoir, and it is indicated that low current in-situ stress and active fractures are conducive to the high production of gas wells; (2) The current in-situ stress, fracture characteristics, wellbore stability and the propagation of fracture network vary greatly in various parts of the ultra-deep reservoir, therefore,the highly deviated wells have more advantages in drilling safety, drilling rate of the low in-situ stress areas and high angle fractures, as well as better fracturing results than wertical wells, and the practice shows that the high-yield production can be obtained by a favorable wellbore trajectory when effectively dealing with the strong heterogeneity of the ultra-deep tight sandstone gas reservoir; (3) The current in-situ stress field modeling based fracture activity analysis, wellbore stability prediction and fracture network simulation are the key technologies in geology and engineering integrated fracturing engineering, which are conducive to the optimization of wellbore trajectory and optimal selection of fracturing method and intervals; (4) The geology and engineering integrated working method supports to build a bridge between geological study and engineering construction, which plays a positive role in well stimulation of ultra-deep gas reservoir and improving the benefits of ultra-deep oil and gas exploration and development.

Chang 7 member oil reservoir is a major production layer in Jiyuan Oilfield in Ordos Basin, which is characterized by deep burial depth, complex oil-water contact and strong reservoir heterogeneity, so the technology of geology and engineering integration is a necessary method to improve the result of water injection development. Guided by the integration of geology and engineering, rock mechanic parameters are corrected in calculation model established by lab test results, and rock mechanic parameters and in-situ stress of single well are calculated by core and logging data, mechanic parameter and in-situ stress field models of the block are built by random modeling method,and the distribution direction of hydraulic fractures is characterized according to the in-situ stress distribution. The development well pattern is optimally designed based on permeability and in-situ stress distribution. The numerical simulation technology is used to optimize well pattern and development countermeasures, and the model is established and continuously updated with the goal of EOR, forming an integrated technology of in-situ stress analysis, geological modeling, oil reservoir engineering design, and numerical simulation. The research shows that the flat management structure and multidisciplinary cooperation enable to efficiently develop oil reservoir. The integration of fine geological description and dynamic analysis supports to continuously update the geological model and establish a model closer to the real geological condition. The random modeling method constructed in-situ stress field model by using rock mechanic data of core samples, logging data and fracturing engineering data shows good agreement with dynamic performance, which provides a basis for dynamic analysis, well pattern optimization and deployment. The dynamic well pattern optimization and development technology countermeasures effectively guided the development of Chang 7 member oil reservoir in An 83 well block. During the refracturing process, the engineering parameters were optimally designed, with the half length of fracture of 120 m, the width of fracture of 30 m, conductivity of the main fracture of 15 D·cm, and that of the secondary fracture of 1 D·cm. Good results were achieved from the five optimized wells after construction, with oil production increase multiple significantly higher than that of the adjacent well, and production capacity increase by 30.46% of the adjacent well. 

Songliao Basin has abundant hard-to-recover reserves. The economic and effective utilization of this type of resources is a realistic way to improve the degree of energy self-sufficiency in China. The key indicators such as drilling cycle and horizontal section length of tight oil wells in Songliao Basin are much worse than those in North America, Sichuan and Chongqing region, and the intensive well construction mode has not been formed yet, which show a great potential of drilling speed and efficiency improvement. The geology and engineering integrated study is conducted to increase the drilling rate of reservoir; The intensive drilling and completion technology of multi well types such as large platform well group and long horizontal well is developed to significantly increase the drilling speed; The high-performance water-based drilling fluid technology for shale oil and supporting technology for thin-layer heavy oil development are researched to reduce the complexity in drilling operations; The integrated application of advanced and applicable technologies such as near bit geo-steering system and one trip drilling technology enables to greatly improve the drilling efficiency and single well production, as well as continuously reduce the drilling cycle and operation cost of hard-to-recover reserves in Songliao Basin. The improvement of supporting drilling and completion technology will provide strong support for the high-efficiency production of hard-to-recover reserves in Songliao Basin.

Sadi oil reservoir, an ultra-low to super-low permeability limestone oil reservoir in Halfaya Oilfield, has barely been developed due to the poor reservoir property. Based on mature experience, pilot Well S5H1 has been deployed to test the feasibility of developing this type of oil reservoir by multi-stage hydraulic fracturing in horizontal well, and the evaluation technology of double sweet spots (geological and engineering) has been researched. The combination of rock type classification and the comprehensive understanding of geological genesis facies and petrophysical facies enables to establish the evaluation technology for geological sweet spot, so as to optimally select the favorable area with the best reservoir property. While the brittleness index, Poisson’s ratio, Young’s modulus, minimum horizontal principal stress and fault toughness are comprehensively analyzed to identify the reservoir fracability in various zones, so as to determine the engineering sweet spot. The close integration of geological and engineering sweet spots supports to evaluate the oil reservoir in different levels and select the favorable exploration area, which ensures the successful implementation of the pilot well. The initial production and cumulative production in the first year from Well S5H1 were 4 and 2.3 times of those in vertical well after fracturing, which laid a foundation for the overall development of Sadi oil reservoir and provided a reference for the benefit utilization of the same type of reservoirs in the Middle East.