Different from foreign countries, the marine carbonate rocks in China are featured by development in small craton block, old geologic age, deep burial depth, and strong transformation, and the theory and technology are faced with problems in the evaluation of oil and gas exploration potential in the intraplatform, intra-carbonate strata, platform margin and old strata in deep formations. By relying on the carbonate reservoir project of national oil and gas special projects during the 11^th and 13^th Five-Year Plan periods and CNPC Key Laboratory of Carbonate Reservoirs, the targeted theoretical and technological researches on carbonate reservoir have been conducted, and innovative understanding has been achieved in four aspects, including: (1) The rifts are generally developed in the intraplatform of small cratons and the geological knowledge of sedimentary differentiation promotes the expansion of exploration field from platform margin to the intraplatform; (2) The discovery of new types of intra-carbonate karst reservoir promotes the expansion of exploration field from the local buried hill to the broad intra-carbonate strata; (3) The deep carbonate reservoir is controlled by sedimentary facies, consolidating the large scale and predictability of reservoir, which understanding promotes the expansion of exploration field from shallow to deep formations; (4) The geological understanding of “ternary” reservoir controlling and distribution of the ancient microbial carbonate rocks promotes the expansion of new exploration fields in the Meso-Neoproterozoic and subsalt Cambrian. The above theoretical progress supports to fill the gap in the field of carbonate reservoir study at home and abroad, and is confirmed by the discovery of large oil and gas fields such as Tazhong, Lungu, Halahatang, Shunbei in Tarim Basin, and Puguang, Yuanba, and Anyue in Sichuan Basin.

The marine carbonate rocks in China are featured by old geologic age, great burial depth, and superimposed transformation by multicycle tectonism-diagenesis, showing strong reservoir heterogeneity and complex genetic process, which lead to great challenges in the study of the main controlling factors of reservoir development and hydrocarbon accumulation. By relying on national special projects during the 11^th, 12^th, 13^th Five-Year Plan periods and CNPC Key Laboratory of Carbonate Reservoirs, the targeted researches on reservoir simulation and geochemical experiment technology have been conducted and achievements been made in three aspects: (1) The multi stage continuous flow device, permeability on-line measurement and visualization device, as well as the improved fluid in situ detection device are used to solve the difficulties in corrosion simulation experiment of ancient and deep carbonate rocks in multicycle superimposed basins in China, providing methods for the evaluation and prediction of buried dissolution vugs and the studies on pore throat patterns and evolution pathway in buried environment; (2) Nine micro-area multi-parameter experiment technology series with the core of laser in situ U-Pb isotope dating of carbonate minerals have been developed, which support to determine the timing, temperature and fluid properties in the process of reservoir genesis;(3) The application of these innovated technologies enables to solve the multi solution and uncertainty problems in reconstructing structuralburial history, diagenesis-porosity evolution history, and hydrocarbon generation and accumulation history, providing an important support for petroleum exploration of carbonate rocks.

The uplift-depression framework of Tarim Craton in Nanhua-Cambrian controlled the temporal and spatial distribution of source rock, reservoir and cap rock assemblages of the subsalt Cambrian, which had an important influence on the selection of favorable exploration zones of the Neoproterozoic-Cambrian. The tectonic paleogeographic evolution of Tarim Craton in Nanhua-Cambrian is comprehensively studied by using field outcrops, new acquired 3D seismic and wells data. Results show that in Nanhua period, active rifts and passive uplifts were formed in extensional setting caused by the breakup of Rodinia supercontinent, with a structural pattern of “two uplifts and four depressions”, including the Central Uplift, Kuqa-Tabei Uplift, Manjiar Depression, Maigaiti Depression, Awati Depression, and Hotan Depression. In Sinian period, affected by the compressional-extensional tectonic settings after the Kuruktag movement, the southern Tarim Uplift was strongly uplifted, the western Tarim Platform was developed, and the Awati Depression and Maigaiti Depression changed into the intra platform sags; The tectonic paleogeography was divided into four units, i.e., southern Tarim Uplift, western Tarim Platform, Manjiar Depression and Hotan Depression. Furthermore, the western Tarim Platform was subdivided into Tabei Bulge, Keping-Gucheng Bulge,Aman Paleo Ridge, Manxi Paleo Ridge, Awati Sag, Manxi Sag, Maigaiti Sag and Wushi Sag. In the Cambrian, controlled by the extensional setting after the Keping movement, the tectonic paleogeography was divided into seven first-order structural units, namely the southern Tarim The uplift-depression framework of Tarim Craton in Nanhua-Cambrian controlled the temporal and spatial distribution of source rock, reservoir and cap rock assemblages of the subsalt Cambrian, which had an important influence on the selection of favorable exploration zones of the Neoproterozoic-Cambrian. The tectonic paleogeographic evolution of Tarim Craton in Nanhua-Cambrian is comprehensively studied by using field outcrops, new acquired 3D seismic and wells data. Results show that in Nanhua period, active rifts and passive uplifts were formed in extensional setting caused by the breakup of Rodinia supercontinent, with a structural pattern of “two uplifts and four depressions”, including the Central Uplift, Kuqa-Tabei Uplift, Manjiar Depression, Maigaiti Depression, Awati Depression, and Hotan Depression. In Sinian period, affected by the compressional-extensional tectonic settings after the Kuruktag movement, the southern Tarim Uplift was strongly uplifted, the western Tarim Platform was developed, and the Awati Depression and Maigaiti Depression changed into the intra platform sags; The tectonic paleogeography was divided into four units, i.e., southern Tarim Uplift, western Tarim Platform, Manjiar Depression and Hotan Depression. Furthermore, the western Tarim Platform was subdivided into Tabei Bulge, Keping-Gucheng Bulge, Aman Paleo Ridge, Manxi Paleo Ridge, Awati Sag, Manxi Sag, Maigaiti Sag and Wushi Sag. In the Cambrian, controlled by the extensionalsetting after the Keping movement, the tectonic paleogeography was divided into seven first-order structural units, namely the southern Tarim

The pore evolution and storage capacity of oil and gas reservoirs are controlled by various types of diagenetic fluids, which are the key factor for reservoir development. However, the conventional petrographic methods are challenging to identify the types of multiphase diagenetic fluids and their influence on pore transformation in the diagenetic process. The Ordovician diagenetic fluids in Gucheng area are determined by integrating petrographic and geochemical methods, so as to further clarify the control effect of various types of diagenetic fluids on reservoir development. The results show that, there are 10 phases of diagenetic fluids with various types in the process of carbonate reservoir development in the study area, including quasi-contemporaneous atmospheric freshwater, quasi-contemporaneous medium salinity evaporated seawater, shallow buried medium salinity sealed seawater, medium-deep buried organic acid water, medium-deep buried formation brine, phase Ⅰ hydrothermal fluid related to albitization, phase Ⅱ deep brine fluid related to hydrothermal recrystallization, phase Ⅲ magnesium poor hydrothermal fluid related to exogenous fluid, phase Ⅳ silicon rich fluid related to siliceous development, and phase Ⅴ calcium rich fluid related to the late calcite filling. By analyzing the influence of diagenetic fluids in each phase on reservoir development, it is concluded that the quasi-contemporaneous atmospheric freshwater and phase Ⅲ magnesium poor hydrothermal fluid played a constructive role in the development of high-quality reservoirs; The phase Ⅳ silicon rich fluid related to siliceous development had dual reconstruction on reservoir development; The local high-quality reservoirs can be formed by hydrothermal corrosion.

The strategic breakthrough in Well MT 1 indicates promising prospects of the fourth member of Majiagou Formation (Ma 4 Member) in Ordos Basin. However, the lack of understanding on lithofacies paleogeography and reservoir development of Ma 4 Member restricts the further gas exploration and deployment. By integrating geological and geophysical methods, the lithofacies paleogeography restoration of Ma 4 member and its control on reservoir development are analyzed. The study results show that: (1) The paleogeography before the deposition of Ma 4 member had a pattern of “three uplifts and one depression”, i.e., Yimeng Ancient Land, Central Paleo Uplift, Lvliang Uplift, and Intra Platform Depression. Among them, the depression was further divided into two bulges and two sags, namely Yulin-Hengshan Bulge, Shenmu-Mizhi Bulge, Taolimiao Sag and Mizhi Sag. The paleogeographic pattern of alternating uplift and depression and bulge in depression controlled the distribution of favorable reservoir development zone of Ma 4 member; (2) Three fourth-order cycles were developed in the deposition period of Ma 4 member, including the third, second, and first submembers of Ma 4 member (i.e., Ma 4₃, Ma 4₂ and Ma 4₁) from bottom to top. Ma 4₃ submember was dominated by transgression cycle, in which the Central Uplift evolved into a weakly rimmed platform margin and the eastern basin presented a semi-restricted platform, with the main deposits of limestone and dolomitic limestone. Ma 4₂ submember was developed in the early-stage regression. With the accretion of platform marginal beach and the fall of sea level, the barrier effect of platform margin was prominent. The eastern basin was characterized by the restricted platform environment, and thin layers of dolomite and gypsum rocks of mound beach facies were deposited in bulge areas. Ma 4₁ submember was mainly deposited in the middle stage of regression. The barrier effect of the platform margin enhanced, and water depth in the restricted platform in the eastern basin continued to be shallower.The mound beach was dominated in bulge areas, with a larger thickness and wider distribution range of dolomite and gypsum rock; (3) The lithofacies paleogeography controlled the type and distribution of Ma 4 member reservoir, with the grain dolomite, microbial dolomite and porphyritic (limy) dolomite reservoirs developed. Controlled by the grain (mound) beach microfacies, the grain dolomite and microbial dolomite reservoirs were developed at the paleo uplift and bulge area. While the porphyritic (limy) dolomite reservoir was mainly developed in lagoon environments. In conclusion, Yulin-Hengshan and Shenmu-Mizhi bulges are favorable areas for reservoir development and gas exploration practice.

The re-examination of core and well drilling data showed that the large-area beach facies thin layered dolomite was developed in the Middle Permian Qixia Formation in Weiyuan-Gaoshiti area in Sichuan Basin, and commercial gas flows were obtained from the dolomite reservoir in several wells. Therefore, it is of great significance to clarify the genesis and distribution law of dolomite for gas exploration of Qixia Formation in the near future. The petrology and distribution characteristics of dolomite are studied by using core, wireline logging and mud logging data. The results indicate that the thin layered dolomite is divided into two types of porphyritic dolomite and laminated dolomite in terms of the macroscopic occurrence, with fine-meso crystalline dominated of dolomite grains, and distinct phantoms of the residual bioclastic grains. The main protolith is sparry bioclastic limestone with microbial bond stucco fabric. Significantly controlled by the sedimentary cycle, the dolomite has a thin single layer thickness of 1-4 m, and cumulative thickness of 3-16 m, showing the characteristics of multi-stage superposition in vertical and mainly developed in the middle-upper part of the sedimentary cycle. The geochemical experiment results show that the dolomitization fluids of Qixia Formation were dominated by penecontemporaneous seawater, and only part of the vuggy dolomite was transformed by deep hydrothermal fluids to a certain extent. By analyzing the coupling relationship between the paleogeographic pattern of uplift and depression during the deposition period and the distribution of wells encountering the thin-layered dolomite, it is found that the thin-layered dolomite was generally developed in the slope break between uplift and depression in the platform, and new understanding is proposed that the superimposing and migrating microbial mound beach bodies and the restricted seawater environment promoted the infiltration reflux dolomitization. The multi-stage superimposed microbial mound beach bodies in the platform laid a good material foundation for the development of dolomite reservoirs. In addition, the penecontemporaneous karstification was conducive to the improvement of porosity and permeability of mound beach body and provided a dominant pathway for the migration of dolomitization fluids. The results confirm that the thin layered dolomite in the platform has a large-area discontinuous zonal distribution pattern in the circum subsag, which provides an important theoretical support for expanding the exploration field of the intra platform dolomite reservoir of Qixia Formation.

The Triassic Leikoupo Formation is an important strategic preparation field for gas exploration in Sichuan Basin. In recent years,Pengzhou Gas Field has been proved in the western Sichuan Basin, gas flow has been achieved in Well Xingtan 1 in the southwestern basin,and unconventional gas reservoir has been discovered in Well Chongtan 1 in the central basin, showing good exploration prospects of Leikoupo Formation. By integrating well and seismic data, the comprehensive study on reservoir and hydrocarbon accumulation characteristics is conducted and new understanding is obtained in three aspects: (1) There are two exploration fields of conventional and unconventional gas reservoirs of Leikoupo Formation in Sichuan Basin; (2) The Indosinian paleo uplift controlled the development and migration of “double beach zones” (Longmenshan barrier mound beach zone in the Western Sichuan and lagoon marginal beach zone in the Central Sichuan Basin),in which the large-scale reservoirs were developed. The area close to the hydrocarbon source center is a favorable zone for conventional gas exploration; (3) The integrated source rock and reservoir assemblage is widely developed in lagoon facies marl in the third member of Leikoupo Formation (Lei 3 member) in the Central Sichuan Basin, forming a tight gas reservoir system sealed by gypsum rocks at the roof and floor. It is inferred that the continuously distributed tight gas reservoirs occur in Lei 3 member in the Central Sichuan Basin, which is a new field for unconventional gas exploration.

Tarim Basin has large scale marine oil and gas reserves. However, it is still uncertain whether the Lower Cambrian source rocks which have high TOC content but thin thickness are sufficient for the current huge reserves. On the other hand, there is a lack of understanding on the development of the Precambrian source rocks and their contribution to hydrocarbon accumulation. In order to comprehensively evaluate the potential of marine oil and gas resources in Tarim Basin, the carbon isotope curve, sedimentary filling and seismic reflection characteristics are used to establish the stratigraphic correlation framework of Nanhua-Cambrian between Tarim Basin and the world, identify the potential source rocks of the Nanhua Triaiken Formation, Sinian Yukengou Formation and Shuiquan Formation, and define the development section, thickness and TOC of the Cambrian source rocks. Furthermore, an innovated technology of TOC normalized evaluation of source rocks is established, which enables to more accurately reflect the organic carbon abundance of source rocks. The hydrocarbon generation evaluation of source rocks indicates that oil and gas resources of the Cambrian source rocks are about 7500×10⁸ t oil equivalent, which contribute the most to marine oil and gas resources in Tarim Basin.

Gucheng area is a major field for petroleum exploration. In recent years, discoveries have been obtained in multiple wells with dolomite developed in the central and western parts of Gucheng area. However, the unclear distribution law of gas reservoirs restricts the exploration deployment in the near future. Based on the analysis of regional stress field, 3D continuous seismic data acquired in recent years are used to finely interpret the faults guided by 3D characterization results such as structural guidance filtering and extraction and analysis of seismic attributes of the most positive curvature. By combining with the simulation experiment, the control effect of strike slip faults on dolomite gas reservoirs in Gucheng area is analyzed. The study result shows that five groups of strike slip faults in NEE, NE, NNE, NNW and NW directions were developed in Gucheng area during the Early Caledonian, Middle Caledonian, Middle Caledonian-Early Hercynian,Indosinian and Yanshanian-Himalayan. Among them, fault groups of NE and NNE trending have intensive activities and large number, with an included angle of about 40°, forming a stereoscopic network fault system in space. Due to the differences in lithologies, lithofacies, and karstification conditions, two types of gas reservoirs are developed in the dolomite deposition area in the central and western parts and the limestone deposition area in the eastern part in Gucheng area, namely the quasi layered lithologic gas reservoir controlled by structural settings and “vertical plate” gas reservoir in fault karst with unique spatial style, which require different exploration strategies such as characterization technologies and well type, laying foundation for the benefit exploration in Gucheng area.

In recent years, in addition to the western and southern Sichuan Basin, dolomite reservoirs of the Middle Permian Qixia Formation-Maokou Formation have been penetrated in multiple wells in Tongnan-Hechuan block in the central Sichuan Basin and high production has been achieved, showing promising exploration potential in the central Sichuan Basin. However, there is little understanding on Qixia Formation-Maokou Formation in the central Sichuan Basin from previous study, and great disputes appear on the genesis and distribution of dolomite reservoirs. The latest petroleum exploration results and a large number of basic data are analyzed to identify the stratigraphic distribution, sedimentary and reservoir characteristics, especially the main controlling factors of the high-quality dolomite reservoir. The results show that: (1) Qixia Formation-Maokou Formation in Tongnan-Hechuan block is divided into two third-order sequences and six fourth-order sequences, and the high-quality dolomite reservoir is developed in the highstand system tract. (2) The sedimentary facies of Qixia Formation-Maokou Formation in Tongnan-Hechuan block was conducive to the deposition of granular beach, with a large number of bioclastic beach developed. The dolomite reservoir was mainly developed in high-energy beach facies zone. (3) The single layer of dolomite reservoir of Qixia Formation is thin and vertically superimposed, while that of Maokou Formation is greater and continuous in lateral. The reservoir space is dominated by primary pores and quasi syngenetic dissolution pores. The development of dolomite reservoir is mainly controlled by highenergy granular beach, sequence related karstification and early dolomitization. (4) The dolomite reservoir of Qixia Formation is mainly distributed in the circum subsag and the western part of Tongnan-Hechuan block is a favorable exploration zone. The dolomite reservoir of Maokou Formation is mainly developed in the edge slope of micro paleogeomorphologic high area and the northeast side of Well Heshen 4 is the most favorable exploration zone.

Major breakthroughs have been achieved in the exploration of dolomite reservoir of the Middle Permian Qixia Formation in Sichuan Basin, which has become the focus for petroleum exploration and geological study. However, there are several problems such as thin reservoir thickness, strong heterogeneity, unclear reservoir distribution rule and main controlling factors for hydrocarbon accumulation. The core interval of 200 m is taken from seven typical outcrop sections and 10 wells in northwest Sichuan Basin, and core and thin section observations, as well as geochemical tests are conducted, including micro-area carbon and oxygen stable isotopes, micro-area rare earth elements, carbonate mineral laser in-situ U-Pb dating, cluster isotope temperature, and inclusion homogenization temperature, so as to constrain the diagenesis and hydrocarbon accumulation history of Qixia Formation dolomite reservoir. The following understanding is concluded in three aspects:(1) There are three types of dolomites of Qixia Formation in northwest Sichuan Basin, i.e., blocky dolomite, porphyritic dolomite and calcareous porphyritic dolomite, and six types of textural components are identified in various dolomites, namely, the limestone surrounding rock, anhedral crystal dolomite, euhedral crystal dolomite, fine crystal dolomite cement, saddle dolomite and bulk crystal calcite; (2) The anhedral and euhedral crystal dolomites were the products of dolomitization in the quasi-contemporaneous-shallow burying period (before the precipitation of fine crystal dolomite cement) superimposed by the recrystallization (dolomite accretion girdle, accompanied by the precipitation of saddle dolomite and bulk crystal calcite) in medium burial depth (2-3km) in the Indosinian period. Among them, the anhedral dolomite was generated by the metasomatism of grain beach limestone, and the reservoir space of blocky dolomite, composed of the anhedral dolomite, was dominated by dissolution pores; While the euhedral crystal dolomite was originated from the dolomitization of fine limestone filled in the meteoric karst system, and the reservoir space of porphyritic dolomite, composed of the anhedral and euhedral crystal dolomites,was dominated by intercrystalline pores of euhedral crystal dolomite. The reservoir space of both was essentially formed by the karstification of atmospheric fresh water in the early epigenetic period. Therefore, the paleomorphologic high areas are favorable exploration zones for dolomite reservoir; (3) The main hydrocarbon accumulation event of Qixia Formation in northwest Sichuan Basin occurred in the Indosinian period, represented by the cementation age of bulk crystal calcite (229 Ma±16 Ma and 229.3 Ma±3.4 Ma) with rich hydrocarbon inclusions,and experienced differential hydrocarbon accumulation in the Yanshanian- Himalayan, during which oil and gas reservoirs were destroyed in the thrust nappe zone, and gas reservoirs were re-formed in the thrust concealment zone and foreland sag zone. The understanding not only has important guiding significance for the exploration of dolomite reservoir of Qixia Formation in Sichuan Basin, but also supports to open up a new way for the study of reservoir development and hydrocarbon accumulation.

The dolomite reservoir in the 3^rd member of the Ordovician Yingshan Formation (Ying 3 member) in Gucheng area in Tarim Basin experienced multiple stages of transformation by diagenetic fluids during its evolution process, showing strong reservoir heterogeneity. There are great disputes about the dolomitization pathway and pore evolution process of dolomites with different occurrence. Accurately determining the key diagenesis period is very crucial to identify the relative sequence of diagenesis and its coupling relationship with reservoir pores in the evolution process of Ying 3 member dolomite reservoir. Based on techniques such as laser in-situ U-Pb isotope dating and element area scanning, the systematic laser in situ U-Pb dating is conducted on rock components of four core samples, including the matrix of host rocks (powder crystal dolomite, medium-fine crystal dolomite), medium-coarse crystal dolomite on the wall of vugs, and guest mineral in vugs (calcite and dolomitized vadose siltstone). The study results show that the high energy beach carbonates of Ying 3 member were primarily deposited at a geologic age of approximately 475.35 Ma in Gucheng area in Tarim Basin, laying a material basis for the development of reservoir. The reservoir pore evolution experienced two stages of dolomiti zation and one stage of calcite filling. The first stage of dolomitization occurred at 470.1 Ma, causing dolomitization of the fine-medium crystal dolomite in host rocks and the local vadose siltstones. The second stage of dolomitization was approximately at 452.1 Ma, leading to the further enlargement and coarsening of dolomite crystals of host rocks and the formation of medium-coarse crystal dolomite on the wall of vugs. The filling of calcite fluid was no later than 448 Ma, which damaged the local reservoir space. The main reservoir space of dolomite was inherited from the pre-existing pore space and adjusted by fault-hydrothermal transformation, rather than the traditional understanding that the pores were formed by the tectonic-hydrothermal corrosion. The above understanding provides basis for the study of pore genesis and prediction of effective dolomite reservoir in deep formation in Tarim Basin.