With the continuous expansion of oil and gas exploration into ultra-deep and ancient strata in the three major marine cratonic basins, challenges such as unclear favorable exploration zones have emerged. Therefore it is imperative to deepen research on depositional models for critical geological periods. Based on the summary of the NeoproterozoicPaleozoic tectonic-sedimentary differential evolution characteristics of the three major basins, this paper analyzes the controlling effects of tectonic differentiation on sedimentary evolution. It is pointed out that the three ancient marine cratonic basins exhibit a tectonic differentiation pattern of "rift-depression-uplift", driving carbonate platforms undergoing an evolutionary cycle of "isolated platform-ramp-rimmed platform", and the formation and evolution of rifts control the sedimentary differentiation of platforms and the similarity of the vertical sourced-reservoer-cap assemblages. Four new models of carbonate sedimentation were established: "multi-type platform margins" and "double shoals" ramp models, carbonate-gypsum/salt symbiotic system model, fault terrace platform margin model of Dengying Formation in Sichuan Basin, and continuously expanding platform margin sedimentary model of Cambrian in Tarim Basin. The "multitype platform margins" and "double shoals" ramp model reveal that the continental margin and rift margin, depression margin, paleo-uplift of inner ramp and lagoon periphery are favorable mound-shoal development areas. The carbonategypsum/salt symbiotic system model reveals that the margin of the paleo-uplift during transgression period is a favorable shoal development area. The fault terrace platform margin sedimentary model indicates that multiple syndepositional fault systems control the formation of step-like platform margins of the 2nd member of Dengying Formation in Sichuan Basin, with thick mound-shoal complexes developed on high fault blocks. The continuous extension platform margin sedimentary model reveals that the Cambrian platform margin belt of Lunnan-Gucheng area in Tarim Basin has undergone the evolution of mud-rich ramp→low-angle progradational ramp/weakly rimmed platform→vertically aggrading platform→laterally prograding rimmed platform. The new understanding of carbonate sedimentary models confirms that the mound-shoal belts around the paleo-rift of the three ancient marine craton basins are still important areas for increasing oil and gas reserves and ensuring resource succession. In addition, new fields such as gravity flow deposits in slope facies and marlstones in evaporative lagoon facies are worthy of exploration. The establishment of the new models of carbonate sedimentation strongly supports the deployment of oil and gas exploration, and also provides a new direction and ideas for future exploration.

The Cambrian in Ordos Basin has the potential for natural gas exploration. To clarify the distribution pattern of favorable sedimentary facies zones and reservoirs，by comprehensively analysing core, outcrop and seismic data，two types of sequence boundaries, unconformities and lithological transition surfaces are have been identified in the Cambrian of the Ordos Basin.The Cambrian strata can be divided into two 2nd-order sequences (SS1, SS2) and eight 3rd-order sequences (SQ1-SQ8), each 3rd-order sequence consists of a TST and a HST, lacking a LST. The unconformity surfaces of the bottom and top of the Cambrian system serve as the bottom and top boundaries of SS1 and SS2. The lithological transition surface is the 3rd-order sequence boundary. Eight lithofacies palaeogeoguaphic maps were systematically compiled to analyze the lithofacies paleogeographic distribution characteristics under 3rd-order sequence stratigraphic framework of Cambrian in Ordos Basin. The Cambrian in the Ordos Basin has gone through two sedimentary stages. SQ1- SQ4 is the stage of transgression, developing carbonate ramp sedimentary system. SQ5-SQ8 is the stage of regression, developing shallow water carbonate platform sedimentary system. Controlled by the evolution of sequence lithofacies paleogeography, the Cambrian reservoirs in Ordos Basin are mainly distributed longitudinally in SQ6-SQ8, and the good reservoirs of Cambrian in Ordos Basin include three types: dolomitizational oolitic shoal reservoir, supergene karst reservoir and fault-dissolution reservoir. Due to the control of the platform margin and high-level system tract, as well as the distribution and faulting of ancient uplifts, the oolitic shoal reservoir is mainly distributed in the western and southern platform margin of the basin, the supergene karst reservoir is distributed in the periphery of the palaeouplift, and the faultdissolution reservoir is isolated in the basin.

The Sinian Dengying Formation reveals a great resource potential in the central part of Sichuan Basin. Describing the microbialite depositional fabrics at multi-scale is beneficial for clarifying their distribution. Based on outcrop, core, and thin section data, this study characterizes the fabrics of microbialites at mesoscopic, microscopic, and macroscopic scales. Two types of microbialites, stromatolites and thrombolites, are identified in the Sinian Dengying Formation in Sichuan Basin. In addition, non-skeletal grains such as intraclasts, oncoids, ooids, and peloids have also been observed in the Dengying Formation. Based on these petrological characteristics, eleven lithofacies and three sedimentary cycles have been identified, which correspond to three depositional environments, including supratidalintertidal, shallow subtidal, and lagoon environments. In the supratidal-intertidal environment, the multi-stage microbial biostrome build-ups are observed with the frequently occurrence of the fenestral and teepee structures. The shallow subtidal environment exhibits lens-shaped microbial bioherm build-ups and grain-dominated intraclastic packstone/ grainstone. The lagoon cycle is dominated by medium to thick-bedded dolo-mudstone in the lower part. A depositional model for the microbialite of Dengying Formation in Sichuan Basin is established, in which high-quality microbial reservoir are predominantly developed in the lower supratidal-intertidal environment and the upper shallow subtidal environment.

Abundant oil and gas discoveries have been made in the platform edge oolitic shoals of the Lower Triassic Feixianguan Formation in Sichuan Basin. In order to further promote the research and exploration of the inner platform oolitic shoal, based on drilling, logging, and three-dimension seismic data, the sequence characteristics, sequence evolution and oolitic shoal distribution pattern of the Feixianguan Formation in Pengxi-Yanting area, northwestern Sichuan Basin are studied. The results show that: (1) The Feixianguan Formation can be generally divided into three thirdorder sequences (SQ1, SQ2, SQ3), with typical rock electrical characteristics and seismic response of each sequence boundary. SB1, SB2, and SB3 are all lithological discontinuity surfaces, corresponding to reflection peaks; SB4 is the lithological conversion surface, corresponding to the reflection trough. The four interfaces exhibit abrupt changes in logging responses such as natural gamma and interval transit time. (2) During the deposition period of SQ1 in the study aera, the terrain slope was relatively steep, with a high-angle S-shaped progradational reflection structure. Mainly controlled by the sea-level fluctuation cycle of high-frequency sequences, a high-frequency restricted oolitic shoal sedimentary pattern was developed, in which the deposition scale of a single-stage shoal body was small, and the shoal bodies migrated rapidly in the horizontal direction towards northwest. (3) During the deposition period of the SQ2, the platform depression was basically filled, the overall terrain slope was relatively gentle, and the sequence had a low-angle progradational reflection structure. Controlled by the sea-level fluctuation cycle of third-order sequences, a stable and widely distributed oolitic shoal sedimentary pattern was developed, and the single-stage shoal body had a relatively large thickness and a stable planar distribution. (4) The SQ3 sequence had a continuous parallel reflection structure, and restricted-evaporative platform facies was developed, characterized by interbedded mudstone and dolomite gypsum with uniform thickness. This study could provide a geological basis for the fine exploration and efficient development of oolitic shoal reservoirs within the platform of the Feixianguan Formation in northwestern Sichuan Basin.

In order to clarify the conditions for the formation of tight gas reservoirs in complex structural deformation zones and implement the next exploration areas, a systematic study is conducted on the hydrocarbon source rocks, sedimentary systems, tight sandstone reservoirs, and trap conditions of the Xujiahe Formation in Da'an exploration area of Sichuan Basin. The results show that: (1)The Xujiahe Formation in the Da'an exploration area has developed a shallow water delta sedimentary system, and the multi-stage sand bodies of the delta plain braided distributary channels in the 4th and 6th members are stacked and connected. Due to compaction and cementation, the reservoirs were generally dense, and later dissolution and fractures effectively improved the physical properties of the reservoirs. (2)The 3th and 5th members are the main source rock layers in the study area. The source rocks are thick, wide distribution in area, and have high organic matter content, mainly consisting of type Ⅲ and type Ⅱ2 kerogen. Currently, they are in the mature to high mature stage, laying a resource foundation for the formation of tight gas reservoirs in Da'an exploration area. (3)The tight sandstone reservoirs of the 4th and 6th members are interbedded with the source rocks of the 3th and 5th members in an uneven thickness in the vertical direction, forming a lower source-upper reservoir combination, which is conducive to the formation of structural gas reservoirs. The main source rock layers of the 3th and 5th members are developed with "mudstone wrapping sandstone" type meandering river channel sand bodies and tight sandstone reservoirs, forming a self generating and self storing combination, which is conducive to the formation of lens-shaped lithological gas reservoirs. The main part of Danfengchang anticline belt and the north, middle, and south wings of Linjiang syncline, as well as the east wing of Yunjin syncline are proposed as the key replacement areas of structural gas reservoir of the 4th and 6th members in Da'an exploration area. Of the Danfengchang anticline, the north of Laisu syncline, and the central part of Linjiang depression, the 3th and 5th members are integrated with source and reservoir, which is conducive to the formation of a "mudstone wrapping sandstone" type structural-lithological gas reservoir and is a potential exploration area for tight gas reservoirs in the next step.

Paleogeomorphology plays an important controlling role in the spatial distribution characteristics of sedimentation. Based on the structural restoration of 16 typical north-south geological profiles by using balanced crosssection techniques, the pre-Cretaceous paleogeomorphology in Kuqa Depression has been reconstructed, and its control effect on sedimentation has been analyzed. Firstly, based on the calculation of the shortening amount of the balanced profile, the northern boundary of the pre-Cretaceous sedimentary basin in Kuqa Depression is calculated. Then, based on the restored thickness data of the Cretaceous stratum, the pre-Cretaceous paleogeomorphology of Kuqa Depression is mapped. Finally, a paleogeological map of the Kuqa Depression at the end of the Jurassic is compiled based on the restored balanced profile, and the controlling effect of paleogeomorphology on sedimentation is analyzed. The results show that: (1) The north-south geological profile of the Kuqa Depression has a structural shortening amount ranging from 3.74 to 26.02 km since the Early Cretaceous, with a structural shortening rate ranging from 3.76% to 24.74%. The structural deformation is mainly concentrated in the mountainous areas of the southern Tianshan Mountains. Based on the calculation according to the angle between the geological profile and the normal to the structural strike, the current basin boundary has shifted southwards by a minimum of 3.70 km and a maximum of 25.19 km compared to the pre-Cretaceous boundary. (2) The pre-Cretaceous paleogeomorphology is characterized by alternating uplift and depression, which can be divided into Wensu uplift, Baicheng low uplift, central subsidence area, Yangxia slope, and Yangdong low uplift from west to east. The uneven structural compression stress on the north and south sides of the Kuqa Depression, as well as the lithological differences in the internal sedimentary strata, led to the occurrence of east-west zoning characteristics of paleogeomorphology. (3) Paleogeomorphology controls the development of two sets of sedimentary systems in the Early Cretaceous Yageliemu Formation in Kuqa Depression. The northern sedimentary system develops fan delta on the east and west sides of the depression, and braided river delta in the middle of the depression. In the northern sedimentary system, the Kelasu structural belt is the favorable development area of structural hydrocarbon reservoirs, and the Yiqikelike structural belt and Yangxia sag are the favorable development areas of stratigraphic-lithologic hydrocarbon reservoirs. The southern sedimentary system develops mainly small near-source fan deltas, and stratigraphic lithologic reservoirs.

Reasonable prediction of fracture parameters and brittleness index plays an indicative role in the hydraulic fracturing process in the exploration and development of shale oil reservoirs and lays the foundation for the comprehensive evaluation of sweet spots in a study area. Starting from the anisotropy theory, based on the linear sliding theory, scattering theory and Born approximation theory, this paper derives the anisotropic reflection coefficient equation of HTI media containing the brittleness index of Young's modulus to Poisson's ratio, Poisson's ratio, density, quasifracture normal weakness and quasi-fracture tangential weakness. And under the Bayesian framework, the expectation maximization algorithm introduces the conditional expectation value of the implicit variable into the random simulation of the model parameters at each iteration to solve the problem that the likelihood function can not take extreme values when the posterior distribution function of the model parameters is implicit or nonlinear. Compared with the traditional method of obtaining the maximum a posteriori probability solution, the introduction of the expectation maximization algorithm can obtain more stable model parameter inversion results, and finally realize the direct prestack seismic inversion of the brittleness index and fracture parameters of shale oil reservoirs. Model testing and actual data application verify the accuracy and applicability of the inversion method proposed in this paper.

In order to study the effect of well pattern infilling on enhancing gas recovery of carbonate gas reservoirs, taking the T2l11 gas reservoir of Moxi gas field in Sichuan Basin as an example, a set of large-scale 18-meter physical simulation experimental device and method are established. The experimental model have a permeability of 0.56×10-3 μm2 and single well exploitation and well infilling (Well 1 and Well 2 are deployed at 14.1 m (78.3%) and 4.6 m (25.6%) from the initial well, respectively) exploitation have been simulated based on the model. The experiment measure gas production and pressure throughout the entire life cycle, revealing the reserve utilization laws under different water saturation conditions of the gas reservoir. The study compares and analyzes the effects of batch and simultaneous infilling methods, as well as the timing of two infilling methods at the end of stable production and under abandoned conditions, on improving the recovery efficiency of the gas reservoir. The experimental results show that: (1) For single well exploitation, gas recovery is significantly affected by water saturation, showing a significantly decrease with increasing water saturation. The recovery is 14.6% to 64.7% under the condition of water saturation of 20%-50%; compared with single well deployment, the rate of recovery can increase to 85.9%-92.7% after two wells are infilled, and the effect of infilling is significant. (2) Infilling wells enhancing gas recovery have two functions: one is to improve the production range of reserves in the undeveloped area, and the other is to improve the pressure drop efficiency in the developed area. The production of gas reservoir reserves is closely related to the water saturation and the distance from the gas well. The well pattern infilling can be deployed according to the production of reserves, and the undeveloped area and the developed (insufficient) area of reserves are preferred. (3) The enhancement of recovery rate through the deployment of infilling wells initially increases and then decreases as the number of well increases. Therefore, it is recommended to optimize the number of infilling wells in developed areas based on the characteristics of the remaining reserves in the gas reservoir, avoiding excessive infilling. Further analysis from the perspectives of enhanced gas recovery range and exploitation efficiency shows that adopting a centralized deployment of infilling wells and simultaneous infilling at the end of stable production period is more beneficial for extending stable production period, improving recovery, and shortening production cycle. The research results can guide the deployment of well pattern infilling in gas reservoir to enhance gas recovery.

Desorption characteristics reflect shale gas enrichment and its preservation conditions indirectly. Marine shale gas desorption types and their genesis in southern China have been divided and evaluated by thermal variation desorption test and gas constitution test. There are four marine shale gas desorption types. The atmospheric temperature desorption shale gas desorbed greatly under atmospheric temperature, the desorbed gas was mainly methane. Its main causes are ascribed to a good gas generation material base and preservation conditions, as well as well-developed fracture system. The reservoir temperature desorption shale gas desorbed greatly under reservoir temperature, the desorbed gas was also mainly methane. Its cause is ascribed to the absence of pressure sealing conditions formed mainly by weak caprock sealing and lateral dissipation. The high temperature desorption shale gas desorbed greatly under a high temperature above 90 ℃, the desorbed gas had relatively high O2 and N2 contents. Its causes are ascribed to shallow burial condition and destroyed preservation condition. High temperature-low content desorption shale gas desorbed a little gas under a high temperature above 90 ℃, the desorbed gas had little hydrocarbon. Its causes are ascribed to long time deep burial history and destroyed preservation condition. The atmospheric temperature desorption shale gas had better exploration and development condition, however, the reservoir temperature desorption shale gas maybe lack of economical development conditions at present. The other two types of shale gas are not worth further exploration.