The ultra-deep carbonate reservoir is characterized by strong spatial heterogeneity, and the interpretation of the internal reservoir structure is limited by the accuracy of seismic data, leading to the difficulty in predicting the distribution of large-scale reservoirs. By taking Shunbei No.4 fault zone of the NE-trending fault system in the central part of Shunbei area as the study object, physical simulation experiment of reservoir formation by the fractured fault structure, fine calibration of well-seismic data, forward modeling, reservoir characterization and reservoir geological modeling are conducted. The study results show that multiple groups of fractured-cavity aggregates composed of cavities and fracture zones were developed near the fault plane. As a result, a structural model of grid reservoir in strike-slip fault is proposed, and the genetic mechanism and main controlling factors of grid reservoir in strike-slip fault are identified. An “integrated multi-grid” structure model of large-scale reservoir in fault zone is constructed, and the technology of spatial positioning of fault-controlled reservoir and the classified well trajectory design of “one well with multi-control, one well with one target and one well with multiple targets” is developed. The application of the study results has guided the well trajectory design in Shunbei No.4 and No.8 fault zones, realized the goal of “high output by drilling few wells” of complex fault-controlled fractured-cavity oil and gas reservoirs, and supported to add a new position with capacity of one million tons, which have certain guidance and reference significance for the exploration of ultra-deep fault-controlled reservoirs in other basins in China.

Shengli Oilfield has abundant low-permeability tight oil resources with various types, dominated by glutenite, turbidite and beachbar sandstone reservoirs, showing complex characteristics and leading to great challenges in improving the speed and efficiency. Therefore, it is urgent to establish a large-scale and beneficial capacity construction mode with the integration of geology and engineering. By innovating working concept, operation mechanism and key technologies, and focusing on the technical bottlenecks and cross integration points of various disciplines, Shengli Oilfield conducted multi-disciplinary collaborative research on the integration of geophysics, geology, oil reservoir and engineering, consolidated the basic comprehensive geological study, strengthened the integration of multiple disciplines, and built an integrated collaborative decision support platform. The pre drilling prediction, while-drilling monitoring and post drilling evaluation were combined to develop geology and engineering integration technology for the whole process of scheme optimization design and implementation, which supported to realize the integration of concept, responsibility, process, operation, technology and platform, and achieve the purpose of improving accuracy, timeliness, and capacity while reducing barrel oil cost. The geology and engineering integration technology enabled to realize the effective utilization of untapped reserves with various oil reservoir types. The dynamic updating of high-precision integrated oil reservoir model and the construction of multi-disciplinary collaborative decision support system are the keys to the sustainable development of geology and engineering integration.

Economic recoverable reserves are the core assets of oil companies. The cumulative proven oil and gas reserves in China at the end of 2005 and 2020 are compared to demonstrate the growth trend of various types of reserves. By applying evaluation indexes such as growth rates of reserves and output, economic recovery factor, economic reserve-production ratio, recovery degree, and oil (gas) recovery rate, the cumulative characteristics of proven developed reserves are systematically analyzed, showing the “four drop and two rise” trend of proven oil and gas reserves, “scissors differential” trend of crude oil reserve-production, and distinctly declined gas reserves life and fatigue increase of gas output, which support to propose the “red line” of reserve-production ratio for national natural gas energy development. The analysis shows that the proven undeveloped oil and gas reserves are characterized by large scale, high proportion, large increment, rapid increase,poor quality, long development life and large reserve assets. Based on the understanding of overall inferior proven reserves in China, it is suggested to emphasize beneficial exploration, control the quality of annually added economic recoverable reserves, accelerate the production of proved undeveloped reserves, and strengthen the dynamic reserve management. In addition, the sequence analysis of proven economic recoverable oil and gas reserves should be strengthened and the research on characteristics should be deepened, which will play an important role in establishing a reserve asset management system with the core of economic recoverable reserves and consolidating the foundation for sustainable development of Chinese oil companies.

Since 2017, PetroChina has taken the initiative to adapt to the new situation of national oil and gas reform, and effectively strengthened the exploration and development of high-quality mining rights, resource exploration and reserve utilization, so as to contribute to national energy security. Based on the policies of mining rights in different exploration stages, the transfer target was set up, and the transfer principle and transfer scheme were formulated to innovatively implement internal transfer and optimal allocation of mining rights in three rounds, covering 35 blocks with a total area of 117×104km2. As a result, three major breakthroughs, three important discoveries and five major exploration results were made, which supported to effectively produce a number of reserves, establish and improve the internal transfer management mechanism of mining rights, further stimulate the exploration vitality, revitalize mining rights resources, and lay a solid foundation for accelerating resource exploration, alleviating the unbalanced development between the eastern and western regions, helping some enterprises turn around losses, and achieving sustainable and high-quality development. The study results show that internal transfer and optimal allocation of mining rights is one of the effective ways to obtain rapid exploration breakthrough, accelerate resource exploration and hold high-quality mining rights. The successful experience and enlightenment can be replicated and popularized in four aspects: First, a scientific and effective management system is an important guarantee for internal transfer of mining rights; Second, positive transformation of exploration ideas is the key to achieve rapid breakthrough; Third, the rational allocation of resources is an effective way to relieve the difficulties of resource replacement in the mature oilfields and turn around the deficit; Fourth, implementing the reform of “oil company model” is an effective means for high-efficiency exploration and profitable development of allocated blocks.

A major breakthrough has been obtained in the high-energy platform marginal beach in the second member of the Ordovician Yingshan Formation in Well Fudong 1 drilled in the transitional zone of Awati Sag-Manjiar Sag in Tarim Basin, which is of great significance to the understanding of hydrocarbon accumulation in the inner carbonate rocks. Based on the in-depth studies on hydrocarbon accumulation conditions, reservoir properties and hydrocarbon sources in Well Fudong 1, the hydrocarbon accumulation assemblage in the eastern Fuman Oilfield is identified, which is composed of source rock of the deep Cambrian Yuertus Formation, reservoir of the high-energy platform marginal beach body, and cap rock of the overlying tight carbonate rocks, as well as a new complex hydrocarbon accumulation pattern is established, namely “hydrocarbon supply by the Cambrian, reservoir and oil source connection by secondary network faults, vertical hydrocarbon transport, and reservoir of fault-controlled high-energy beach body”. The success of Well Fudong 1 confirms that the high-energy platform marginal beach reconstructed by the secondary network faults has the capacities of reservoir development and hydrocarbon accumulation, breaking through the exploration forbidden zone in ultra-deep high-energy beach carbonate rocks with a depth of greater than 8000 m, and expanding the understanding on hydrocarbon accumulation pattern in fault-controlled carbonate reservoir. In addition, it is a successful practice of exploration idea of “high-energy platform marginal beach body + secondary network fault oil and gas reservoir”, which supports to open a new situation of exploration in Lunnan-Fuman platform marginal zone and lead the exploration deployment of ultra-deep complex marine carbonate rocks in Tarim Basin.

At present, large-scale discoveries in Central Sichuan paleo-uplift are mainly concentrated in the deep Sinian-Cambrian system of high-energy beach facies, while the exploration of the Permian is ignored by considering that it was generally developed in low-energy environment of intraplatform slope facies. In order to further identify the enrichment law of gas reservoirs in the Middle Permian in Central Sichuan Basin, the lithofacies paleogeography, reservoir genesis, reservoir development pattern and gas reservoir characteristics are analyzed by means of core description, thin section analysis, U-Pb dating and ancient landform restoration (impression method), and the second member of Maokou Formation (hereinafter referred to as Mao 2 member) is re understood at the basin level. The study results show that: (1) Three NW trending paleo high zones were developed in Sichuan Basin during the deposition period of Mao 2 member, namely, the southern zone, the middle zone and the northern zone. Central Sichuan Basin was located in the central-southern part of the southern paleo high zone and largescale beach body was developed; (2) The paleo high zones controlled the distribution of beach body, karstification in the penecontemporaneous period and dolomitization of Mao 2 member. On this basis, the reservoir development pattern is constructed, which indicates that high-quality dolomite reservoirs were widely developed in Mao 2 member in Central Sichuan Basin; (3) The seismic prediction technology of thin bedded dolomite of Mao 2 member is innovatively established, which shows that the distribution of high-quality reservoirs and the enrichment and high yield of gas reservoir in Mao 2 member were controlled by the paleo high zone. As a result, breakthroughs were obtained in the new exploration field guided by new geological understanding, achieving high gas flows of more than one million cubic meters during the test of five wells (including Well TS4), and marking a major breakthrough in gas exploration of Mao 2 member in Sichuan Basin, with the submitted proven gas reserves of exceeding 100 billion cubic meters. Now, the gas reservoir in Mao 2 member in Central Sichuan Basin is a major resource base for increasing proven reserves during the 14th Five-Year Plan period.

Constrained by geological conditions such as rapid facies change, thin thickness, and great burial depth of shale formation in the Permian Wujiaping Formation in Sichuan Basin, no major breakthrough has been made in unconventional gas exploration. In 2020, a risk exploration well HY-1HF was drilled and commercial gas flow of 8.9×104m3/d was obtained during well test, showing good exploration potential of shale gas in the Permian Wujiaping Formation in Hongxing area of eastern Sichuan Basin. In order to identify the main controlling factors for the enrichment and high yield of the Permian shale gas and its exploration implications, well drilling, logging and geochemical experiment data are analyzed. The study results indicate that deposits of deep-water shelf facies were generally developed in the second member of Wujiaping Formation (Wu 2 member), as well as high-quality organic-rich shale, with the characteristics of “four high and one thin”, namely, high TOC, high porosity, high gas content, high carbonate content and thin shale reservoir thickness (<20 m). Hongxing area is located in the tectonically stable zone, with good preservation conditions; In addition, the reservoir is conducive to fracture treatment owning to its rock mechanical features of low Young’s modulus and Poisson’s ratio. On the whole, it is a high-quality deep marine formation for shale gas exploration in combination with the excellent sealing conditions of roof and floor. The evaluation results conclude that Longjuba, Jiannan and Sanxing blocks are favorable exploration zones in Hongxing area of eastern Sichuan Basin.

Yingen-Ejinaqi Basin is one of the large basins with low degree of exploration in China. The multiple processing and interpretation results of deep seismic data led to unclear understanding of the current basin structure and restricted the understanding on the direction of petroleum exploration in the basin. The analysis of the drilled wells, reprocessing and interpretation of seismic data, and study on basin tectonic deformation enable to clarify the stratigraphic age, determine the current structural features of deep formations and basin type, and propose the direction of petroleum exploration in the basin. The results show that: (1) There is a distinct unconformity between the Mesozoic and Pre-Mesozoic in Yingen-Ejinaqi Basin, which is characterized by continuous seismic event with strong energy; (2) The previously regarded Carboniferous-Permian system below the unconformity with horizontal continuous seismic reflection is actually multi wave imaging since that the Carboniferous-Permian system could not be horizontally distributed below the Mesozoic; (3) It is a Mesozoic rift basin above the unconformity surface, and each layer of the Cretaceous shows clear reflection features in the main basin part; (4) The Pre-Mesozoic (mainly Carboniferous-Permian system) below the unconformity is characterized by a series of thrust structures and complex folds, discontinuous seismic imaging, and low signal-to-noise ratio. On the whole, Yingen-Ejinaqi Basin was a Mesozoic rift basin developed on the fold basement of Hercynian orogenic belt, and strong fold deformation and thrust tectonism occurred before the Mesozoic. The oil and gas discoveries are mainly obtained in the Cretaceous, which is the main formation for the petroleum exploration. The analysis method combining geology and seismic is helpful to correctly understand the complex basin or complex areas in the basin.

In order to identify the genesis and distribution of crude oil in Fukang Sag and its peripheral bulges in Junggar Basin, the latest geochemical data of source rocks and crude oil as well as petroleum exploration data are used to evaluate the geochemical characteristics of various source rocks, which enable to divide the genesis of crude oil into four types, clarify the genetic relationship between crude oil and source rocks,and determine the spatial distribution of crude oil with different genesis types. The study results show that type Ⅰ crude oil was mainly generated by source rocks of the Middle Permian Lucaogou Formation and distributed in Shanan, Beisantai, and Santai oilfields and deep formation of the Permian-Triassic in Fukang Sag; Type Ⅱ crude oil was generated by source rocks of the Lower Jurassic Badaowan Formation, and distributed in Shabei Oilfield, Fubei and Fudong slopes and the Jurassic in the sag; Type Ⅲ crude oil was the mixture generated by the Permian and Jurassic source rocks and distributed in the Jurassic in Cainan Oilfield and west Cainan block, as well as the western slope of Beisantai Bulge; Type Ⅳ crude oil was generated by source rocks of B member of the Carboniferous Songkaersu Formation, and mainly distributed in Fukang Sag and the adjacent bulges.The oil and gas generated by the Permian source rocks in Fukang Sag mostly accumulated in high-quality reservoirs and seal assemblage of the Permian and Lower Triassic, showing great exploration potential.

Effective prediction of petroleum exploration risks is of great significance for optimizing exploration deployment and improving drilling success rate and economic benefits. Based on the analysis of the progress of risk prediction technology, a new prediction method of petroleum exploration risks is proposed based on Bayesian network. The transformation process from petroleum geological problems to probability prediction model is discussed, and the algorithm and prediction steps of average one-dependence estimators (AODE) training model are constructed. The quantitative evaluation of geological conditions of hydrocarbon accumulation in the Jurassic Sangonghe Formation in the hinterland of Junggar Basin is conducted, four main geological parameters of hydrocarbon supply, reservoir, trap, cap rock and preservation are determined, and a data set composed of parameters from 203 exploration wells is established. The results of five-fold cross validation show that: (1) The discrimination accuracy of the training set of four Bayesian networks (Naive Bayesian classifier, tree-augmented Bayesian classifier, AODE and k-dependence Bayesian classifier) is greater than 85%, indicating that the classification of parameters in the training set is effective; (2) The discrimination accuracy of the test set is greater than 82%, indicating a high success rate of prediction. AODE has the best prediction results, with an accuracy of 85.22%, therefore, it is used to predict the risk of petroleum exploration in the study area. The prediction results of AODE model not only agreed well with the exploration results within the reserve area, but also supported to predict favorable areas of three types of oil and gas resources outside the reserve area.

By considering the basic geological conditions and reservoir characteristics of typical continental shale oil reservoirs in China,such as complex lithology, diversified macro-structure types, and complex pore structure and oil bearing properties, the targeted processing of new logging technologies, including electric imaging, 2D NMR, three-component induction and array acoustic waves, are conducted to finely describe the macro- and micro-structural characteristics of shale oil reservoir, and a new method fusing micro-structure and macro-structure (referred to as “double-structure sweet spot evaluation method”) is proposed to evaluate shale oil sweet spots. The main technical connotation includes: (1) Based on image edge detection method, the processing technology of electric imaging logging and optimal selection of processing parameters are researched to evaluate the formation macro-structure. In addition, the adaptability of three macro-structural evaluation methods,namely, the electric imaging logging edge detection method, three-component induction logging electric anisotropy method, and array acoustic logging stiffness coefficient method, is systematically analyzed from three aspects of measurement principle, detection volume and wellbore environment applicability, and the optimal application method is proposed. (2) Based on the systematic comparative analysis of macrostructural shale characteristics in typical blocks, and calibrated with the fine description of core samples, the macro-structural classification standards are established by using the above three logging evaluation methods. (3) Combined with the micro-structural characteristics of reservoir physical properties, oil-bearing properties and brittleness, a favorable optimization method for shale oil sweet interval is proposed based on the macro-structural characteristics. The study results show that the main sweet intervals in the first member of Qingshankou Formation (Qing 1 member) in Gulong area in Songliao Basin, the third sub member of the seventh member of Yanchang Formation (Chang 73 sub member) in Ordos Basin, and the upper part of the Paleogene Lower Ganchaigou Formation (E32) in Yingxiongling area in Qaidam Basin are developed in laminated clay shale, thin interbedded siliceous shale, and thin interbedded lime-dolomitic shale, respectively.

In China, lacustrine carbonate rocks are widely distributed and show great prospects for petroleum exploration. The high-content terrigenous debris and diversified lithofacies lead to great difficulty in identifying lithofacies and severely restrict the exploration expansion and efficient development in this field, which is typically represented by the upper part of the Paleogene Lower Ganchaigou Formation (E₃²) in Yingxi area in Qaidam Basin with a burial depth of greater than 4000 m. Therefore, a large number of core data, thin section and experimental analysis data in Yingxi area are studied in detail, and lithofacies and logging response characteristics of lacustrine carbonate rocks are systematically analyzed to establish the lithofacies identification method and chart. The study results show that five types of lithofacies are identified in E₃² in Yingxi area, including granular lime-dolostone, micrite lime-dolostone, laminated lime-dolostone, argillaceous gypsum and lime-dolomitic mudstone. The analysis of logging response characteristics indicates that GR, matrix density and bulk density are sensitive parameters for lithofacies identification, and rock fabric factor ( RFF ) technology is proposed for the first time. The calculated RFF and element logging data are integrated to establish the lithofacies identification chart, which is applied to 48 wells in the study area. The average coincidence rate of lithofacies interpretation reaches up to 80.2% in 12 coring wells, showing good application results. RFF technology supports to improve the lithofacies identification accuracy of lacustrine carbonate rocks, and is of great significance to determine the reservoir distribution law and guide the petroleum exploration and development in practice.