Junlian area in the south of Sichuan Basin, as the first commercial production base of coalbed methane in South China, has a gas producing bed in the Upper Permian Leping Formation, it is great to study the characteristics of micropore structure to analyze the characteristics of coalbed methane accumulation. In this paper, a large number of Upper Permian Leping coal samples are selected from coalbed methane evaluation wells for scanning electron microscope observation and liquid nitrogen adsorption experiments. The characteristics of pore development at micro and nano scale have been systematically analyzed from the aspects of pore genetic type, pore structure, pore morphology and methane adsorption performance. The results show that micropores of coal are divided into four genetic types: plant tissue pore, stoma, mineral mold hole and intercrystalline pore. Through quantitative analysis of pore structure parameter, it is concluded that the average BET total pore specific surface area is 2.638 m2/g, and the average BJH total pore volume is 0.003 7 cm3/g, and there is a good positive correlation between total pore specific surface area and total pore volume. The average BJH pore diameter is 5.775~17.842 nm, and the major contribution to the total specific surface area is from pores with an aperture less than 5 nm, while the major contribution to the total pore volume is from pores greater than 10 nm. According to the diameter of pores, the pore types are divided into four categories: micropore (＜5 nm), tiny pore (5~10 nm), mesopore (10~100 nm) and macropore (≥100 nm). Micropores and tiny pores are the main spaces for gas adsorption in high rank coal, and it is further concluded that the boundary value of pore diameter between adsorption pores and free pores of high rank coal is 10 nm. Nitrogen adsorption loops are divided into three types (overlap type, semi-separation and semi-overlap slow drop type, semi-separation and semi-overlap plunge type), and according to the characteristics of the loops, the nanoscale pore morphology is idealized as three typical models, namely open pore, semi-closed pore and inkbottle-shape pore, and all kinds of pores are developed in the high rank coal. Based on the comparison of isothermal adsorption experiments of methane from dry ash free coal samples with different pore morphology, it is found that the adsorption capacity of methane is the highest in inkbottle-shape pores, and the adsorption capacity of semi-closed and open holes is similar but lower than that of inkbottle-shape pores.

Multiple exploration wells including well Mitan 1 have obtained high production natural gas flow in the dolomite of the fourth member of the Ordovician Majiagou Formation(O1m4) in the northeast of Ordos Basin, demonstrating that the O1m4 of the region has good exploration prospects. However, there is still controversy over whether large-scale dolomite reservoirs are developed in the O1m4 in the northeastern basin, and the unclear distribution of dolomite reservoirs restricts the next exploration deployment. Based on comprehensive data such as core, thin sections, field emission scanning electron microscopy and geochemical characteristics, a systematic study is conducted on the characteristics and development controlling factors of the O1m4 dolomite reservoir in the northeast of Ordos Basin. On this basis, the distribution of the O1m4 dolomite reservoir in the northeast of the basin is predicted. The research results indicate that: (1) Tidal flat type dolomite reservoir, mound-shoal type dolomite reservoir and bioturbation type dolomite reservoir are developed in the O1m4 in the northeast of Ordos Basin. The storage space of the three types of dolomite reservoir is mainly intergranular pores with a small number of micro cracks, and the average porosity is 4.77%, 5.12% and 2.52% respectively. (2) The formation of dolomite reservoirs is related to mound-shoal complex, bioturbation and dolomitization. The development of tidal flat type dolomite reservoir is related to dolomitization, which is the key to the formation of intergranular pores in such reservoirs. The development of the mound-shoal type dolomite reservoir is controlled by the mound-shoal complex and dolomitization. The mound-shoal complex is the material basis for reservoir development, and the dolomitization further enhances the compressive capacity of the reservoir, which is conducive to the preservation of intergranular pores. Bioturbation and dolomitization control the development of bioturbation type dolomite reservoir. The burrows formed by bioturbation lay the foundation for reservoir development. Dolomitization forms intergranular pores and is beneficial for pore preservation. (3) The Shenmu-Jingbian area in the northeast of the basin is located on a low uplift belt during the O1m4 period, which is conducive to the development of shoal-mound bodies, biological disturbance and dolomitization. The developed dolomite reservoirs can provide a large-scale storage space for natural gas enrichment.

The Middle Permian Maokou Formation is an important stratigraphic series for increasing reserves and production in Sichuan Basin. The preliminary exploration mainly focused on the limestone fissure type reservoirs related to the weathered crust at the top of the Maokou Formation. In recent years, with the breakthrough of a series of high-yield wells in the central Sichuan region, the significant exploration potential in dolomite of the Maokou Member 2 has been demonstrated, including the intraplatform shoal dolomite reservoir of the lower member of Permian Maokou Member 2 in Hechuan - Tongnan area, while the strong reservoir heterogeneity restricts the further exploration. Based on core and thin section observation, physical property experiments and geochemical analysis, the basic characteristics of dolomite reservoir of the lower submember of Maokou Member 2 in Hechuan-Tongnan area are systematically analyzed, and the genesis and formation mechanism of dolomite reservoir are discussed. The results show that the dolomite reservoir of lower submember of Maokou Member 2 consists of pinhole dolomite and vuggy dolomite, and the reservoir space is characterized by intercrystal (dissolved) pore, karst cave and fracture as the main seepage channel. The reservoir type is mainly fracturevuggy reservoir, and secondly fracture-pore reservoir. The average porosity and permeability of pinhole dolomite of the full diameter sample are 2.50% and 0.806×10-3 μm2,and these of vuggy dolomite are 4.32% and 1.047×10-3 μm2. Combined with previous sedimentation and diagenesis research, it is considered that the high energy shoal facies is material base for reservoir development and multi-stage karstification is the key for the formation of high quality reservoir. Penecontemporaneous dolomitization is the key to reservoir space preservation by enhancing the compaction resistance of rocks. The late hydrothermal dolomitization of Maokou Formation related with the Dongwu Movement (Emei taphrogenesis in the upper-Yangtze region) in the late Middle Permian is dominated by cementing and filling early pores, which reduces the reservoir performance of dolomite. This study provides a basis for predicting the distribution zone of high-quality reservoirs in Maokou Formation.

The oil-bearing dolomites exposed in the Long’eni-Angdarco-Dazuoma region have been proven to be a favorable carbonate reservoir in the Qiangtang Basin. Its genetic mechanism is significant for oil and gas exploration in the Qiangtang Basin. In this study, comprehensive analysis of rock thin section identification, carbon and oxygen isotopes, trace and rare earth elements and strontium isotopes are conducted to investigate the genetic mechanisms of the palaeoreservoir dolomites and the formation and evolution process of the dolomites reservoirs. The main findings are as follows: (1) Dolomite types are subdivided into micritic-very fine crystalline residual structure dolomite, fine crystalline subhedral-anhedral dolomite, fine crystalline euhedral dolomite, medium-coarse crystalline subhedral dolomite, cloudy core and clear rim structure crystalline dolomite and saddle dolomite with late filling holes. (2) The petrological and diagenetic fluid geochemical studies indicate that the micritic-very fine crystalline residual structure dolomite is formed by syngenetic microbial dolomitization. The fine crystalline subhedral-anhedral dolomite and medium-coarse crystalline subhedral dolomite are formed via reflux dolomitization, which occurred during the shallow burial stage. The fine crystalline euhedral dolomite is formed by the deep burial dolomitization. The cloudy core and clear rim structure crystalline dolomite is formed by the near-surface mixing-zone dolomitization during the uplift stage. The saddle dolomite is formed by the hydrothermal dolomitization. (3) The genetic mechanism of dolomites in the palaeo-reservoir reveals the evolution process of burial conditions and reservoir space of dolomites. Secondary pores are formed by dolomitization, meteoric freshwater leaching and hydrothermal dissolution, forming a good dolomite scale reservoir, which can be used as one of the target reservoirs for oil and gas exploration. These understandings provide new theoretical references for the study of hydrocarbon accumulation evolution and the prediction of high-quality carbonate reservoirs in the Qiangtang Basin.

High-quality lacustrine source rock and extensive sublacustrine fans are developed in deep-lacustrine depositional environment in lower section of the second member of Oligocene Dongying Formation (E3d2l) in southern Bozhong Sag, providing an exploration realm of lithological reservoirs. However, the generally poor porosity and permeability of the deep reservoirs severely hampered the progress for oil and gas exploration and development. Thus, there is an urgent need to elucidate the key factors and the pore evolutionary processes controlling the sandstone reservoir quality of the sublacustrine fans. Based on comprehensive analysis of drilling and logging data, rock grain-size, thin sections, scanning electron microscopy and fluid inclusions, this study has successfully identified the key factors controlling reservoir quality, and established quantitative models of pore evolution. The results show that: The sublacustrine fan reservoir of the E3d2l is characterized by predominantly medium-fine grained lithic feldspathic quartz sandstone with mainly dissolution pores. The favorable sedimentary units such as lobe axis and distributary channels in sublacustrine fan are the basis for the formation of high-quality reservoirs. Persistent compaction and early / late cementation are the main causes of continuous porosity loss. Organic acid dissolution and abnormally high pressure are the key factors for improving reservoir quality. The sublacustrine fan sandstone undergoes four stages during the burial process: rapid compaction in the early diagenesis A phase, rapid compaction and early cementation in the early diagenesis B phase, slow compaction and organic acid dissolution in the middle diagenesis A1 phase, and slow compaction and late cementation in the middle diagenesis A2 phase. During these phases the compaction and early cementation reduce porosity by 13.64% and 8.24% respectively, and organic acid dissolution increases porosity by 9.55%. In particular, the late cementation after the oil and gas accumulation results in a severe porosity decrease of 7.12%. This study will provide a theoretical basis for the oil and gas exploration and development of sublacustrine fan reservoirs in the deep-lacustrine basin of the Bohai Sea.

Huizhou Sag is an important place for crude oil production in the Zhuyi Depression. For a long time, research has been mainly focused on southwestern Huizhou Sag, whereas the study on northern Huizhou Sag is relatively weak and lacks data support, so the northern Huizhou Sag is still in the early stage of exploration. To promote the oil and gas exploration process in northern Huizhou Sag, the characteristics and development controlling factors of reservoirs in Zhuhai Formation and Zhujiang Formation in northern Huizhou Sag were systematically studied by using thin section, grain size analysis, scanning electron microscopy, zircon dating, reservoir properties and other data. The results show that the reservoir sandstone of Zhujiang Formation and Zhuhai Formation in the northern Huizhou Sag is mainly composed of medium to coarse grained quartz sandstone from delta front channels, with high compositional and structural maturity and low argillaceous content. Pores in the sandstone are dominated by primary intergranular pores, locally enriched with dissolution pores and kaolinite micropores. This sandstone has high porosity, and the maximum profitable depth is about 3 800 m. The reservoir quality of Zhujiang Formation and Zhuhai Formation in northern Huizhou Sag is mainly controlled by three factors: high-quality parent rocks, favorable sedimentary facies and constructive diagenetic process. The highquality metamorphic and intrusive parent rocks in the South China block lead to high quartz content in the sandstone, laying the foundation for the development of high-quality reservoirs. The fluvial energy of delta front channels is high, resulting in the deposition of coarse grained sandstone, with low clay content and the best reservoir properties. Dissolution, as constructive diagenesis, can increase porosity, therefore increase reserves.

The forming environment of volcanic rocks is complex, and the lithology of volcanic rocks in a certain area may be mainly composed of two or three types, which leads to serious imbalance of core data of different lithology. The existing lithology identification methods are not effective in dealing with unbalanced samples among classes. To solve these problems, a volcanic rock lithology identification method based on ADASYN-GS-XGBOOST hybrid model is proposed. The unbalanced samples are processed by ADASYN oversampling algorithm to obtain a new sample set, and then XGBOOST is used as the base classifier to classify the samples. The ADASYN-GS-XGBOOST hybrid lithology identification model is established by using Grid Search to optimize the parameters of the model. The results of the hybrid model training are compared with those of K nearest neighbor, naive Bayes, random forest, XGBOOST and SMOTE-GS-XGBOOST algorithms. The results show that the model based on ADASYN-GS-XGBOOST algorithm has the best identification effect. This method overcomes the problem that existing lithology identification methods can not effectively solve the problem of unbalanced samples, and greatly improves the accuracy of lithology identification of volcanic rocks.

Nuclear magnetic resonance (NMR) and nuclear magnetic resonance cryoporometry (NMRC) experiments are carried out to quantitatively characterize the pore structure of shale gas reservoirs of Longmaxi Formation in southeast Sichuan Basin. The results show that: (1) Four types of pore are developed in the shale of the study area: organic matter pores, intra-granular pores, intergranular pores and micro-fractures. The pore size distribution of the shale is widely distributed, and the pore size is mainly between 1 and 100 nm. The reservoir space is dominated by mesopores, accounting for 76.2%, followed by macropores, accounting for 21.9%, and micropores contribute the least, accounting for only 2.0%. (2) The pore size distribution characteristics revealed by NMRC are more accurate, especially for the pore characterization in the range of 2-100 nm, which is more advantageous for the pore characterization of shale reservoirs with strong heterogeneity. (3) NMR characterization of reservoir pore size distribution is affected by many factors. The development of shale lamellation and the properties of saturated fluid will affect the NMR experiment, and then affect the characterization results of pore size distribution. The characterization of pore size distribution by NMRC method is affected by the KGT value of probe liquid and the size of the sample. It is necessary to calibrate the KGT value of probe liquid reasonably and select a suitable sample size to obtain reliable characterization results. The research results have reference and guiding significance for pore structure characterization of shale reservoir.

The fine interpretation of time-frequency domain is based on high-resolution time-frequency analysis algorithms. Reviewed the evolution of time-frequency analysis algorithms including S-Transform (ST), Generalized STransform (GST), Synchrosqueezing S-Transform (SST), High-order Synchrosqueezing S-Transform (HSST), Synchrosqueezing Generalized S-Transform (SGST), Multi-channel Synchrosqueezing Generalized S-Transform (MSGST), it is claimed that MSGST has high vertical and horizontal resolution. To meet the requirements of highprecision exploration and development, a High-order Multi-channel Synchrosqueezing Generalized S-Transform (HMSGST) is proposed to focus on time-frequency resolution and improves the accuracy of reservoir prediction. By comparing the calculation results of six time-frequency algorithms with theoretical signals and theoretical noise signals, it is verified that HMSGST has high time-frequency resolution and better characterization ability for complex signals, but when the signal-to-noise ratio of the signal is below 70 dB, the time-frequency noise resistance of HMSGST begins to deteriorate, and the time-frequency spectrum of the effective signal is disturbed, making it difficult to accurately characterize the time-frequency characteristics of the signal. Taking the marine sandstone in a certain 3D survey as an example, based on HMSGST, time slices are extracted along the main oil and gas reservoirs (T2 layer) in the timefrequency domain. Due to the corresponding relationship between frequency and geological information, high seismic frequency is often more advantageous to the identification of thin reservoir. Attribute analysis such as frequency attenuation gradient and frequency coherence are carried out to enhance the ability of hydrocarbon detection and recognition of short axis river channels and secondary faults. Furthermore, RGB multi-attribute fusion including the former and curvature attribute is carried out with fine carving for geological details, especially in the time slice of T2 layer based on medium-high frequency coherence. For seismic data from different survey and geological condition, parameter analysis of HMSGST is required, and suitable parameters are a prerequisite for achieving more accurate calculation results.

In view of the multi-stage construction and reconstruction of complex structure of Bayanhushuu fault depression in the western fault depression of Hailaer Basin, there are not only various fault blocks and nosing structures of various origin, but also different types of hydrocarbon accumulation modes. In order to improve the success rate of oil and gas exploration in complex fault depression, based on the theory of light hydrocarbon microleakage, microbial-geochemical detection technologies, including Microbial Quick-Screen (MQS) , Microbial Oil Survey Technique (MOST) and Sorbed Soil Gas (SSG) dection are applied to directly detect the change of microbial value and acid desorption hydrocarbon anomaly on the surface of the favorable exploration target area, predict the oil and gas properties of the underlying favorable target area, and identify the distribution range and oil and gas properties of the oil and gas reservoirs. The results show that there is a good correlation between the distribution of microbial anomalies and the known oil and gas areas and oil and gas wells, which indicates that the microbial-geochemical detection technology has good applicability and reliability in the Bayanhushuu fault depression of Hailaer Basin. The MOST+SSG technology combination is applied to further identify the favorable anomaly area, and it is considered that the western steep slope of Bayanhushuu fault depression is a long-term oil and gas advantageous accumulation area with large microleakage intensity. It is pointed out that the two nosing structures in the western steep slope belt are favorable areas for further oil and gas accumulation.