There are growing UHTP condensate gas reservoirs that have been discovered with the increase of exploration depth of offshore gas reservoir in recent years. The production of condensate water in these HTHP condensate fields increases significantly in the later stage of production， which makes it more difficult to analyze production dynamics and treat surface condensate water. In this study， experiments on the change of PVT water-gas ratio during development and the evaporation of formation water in long cores with decreasing reservoir pressure were conducted for three well areas in the abnormally high-pressure and high-temperature condensate reservoirs in the South China Sea. The difference of the condensate water-gas ratio of the three well areas with the decrease of gas pressure was compared， and the change characteristics of the condensate water-gas ratio obtained by the PVT test and the long core test under the formation temperature were discussed. The mechanism of formation water evaporation in long core simulating reservoir conditions is analyzed， which is higher than that in PVT cylinder. The simulation and prediction method of high-temperature condensate gas reservoir condensate water gas ratio is established and verified. The study shows： The fundamental reason why formation water evaporation in high-temperature and high-pressure condensate gas reservoir is higher than that in PVT cylinder is that the small pore diameter in the reservoir causes the critical properties of each component of condensate gas to deviate under the influence of pore diameter， which not only leads to the contraction of condensate gas in porous media， but also increases the saturated vapor pressure of formation water， resulting in the rise of dew point， and enhancing the mass transfer of formation water to condensate gas. The simulation and prediction method of formation water evaporation in high-temperature condensate gas reservoir can accurately predict the change of condensate water production.
The cross-scale storage and seepage media in carbonate reservoirs are distributed horizontally and vertically， with strong heterogeneity， which leads to complex gas production rules of gas wells. Therefore， it is necessary to explore the main controlling factors of gas well productivity by combining indoor physical experiments and mathematical model calculations on the basis of grasping the law of reservoir seepage. To this end， the gas seepage experiment under the original reservoir condition was first carried out， and then the quasi-threshold pressure measurement experiment， high-speed non-Darcy coefficient measurement experiment and stress sensitivity experiment were carried out in a targeted manner， and finally a trinomial capacity equation considering high-speed non-Darcy effect， low-speed non-Darcy effect and stress sensitivity was established. The numerical calculation results show that： （1） The productivity of gas wells is directly related to the type of reservoir. Fractured-cavity reservoirs have the best quality. Although the seepage capacity of porous reservoirs is weak， they still have certain exploitation value； （2） Stress sensitivity and high-speed non-Darcy effect should be considered in fracture-cavity reservoirs， and the combined effect of the two results in a loss of productivity of 41.82%； （3） The low-velocity non-Darcy effect of the vug-type reservoir is weak. If only stress sensitivity is considered， the resulting productivity loss is 12.53%； （4） Porous reservoirs have weak stress sensitivity. If only the low-velocity non-Darcy effect is considered， the resulting productivity loss is 23.42%. The above research results have important guiding significance for rational production allocation of gas wells in Dengying Formation gas reservoirs of Anyue Gas Field of Sichuan Basin and dynamic prediction of gas reservoir production and development.
For the tight sandstone reservoirs in the Ordos Basin， where the rock is compact， heterogeneous and the fracture shapes formed by conventional fracturing techniques are monolithic， a 3D reconstruction of the reservoir cannot be achieved. We have carried out the research on the law of balanced fracture initiation and extension of multi-cluster fracturing fractures in unconventional fracturing technology. Using the large size true triaxial simulation experiment system， based on the dimensional analysis method （π theorem） physical simulation experiment similarity criterion design， through multiple experimental proportioning， curing， mechanical testing and other methods， the artificial curing rock mass with mechanical parameters similar to the target layer is obtained， and a 30 cm × 30 cm × 30 cm artificial sample system was used to carry out the physical simulation experiment of unconventional volumetric fracturing. Taking the conventional fracturing technology as a reference， by changing the experimental conditions and design parameters， the non-equilibrium initiation and extension behaviors of fracturing fractures under five unconventional volume fracturing technologies， namely hydraulic pulse pretreatment， temporary plugging between clusters， flow limiting method， cyclic loading and unloading and pulse intermittent fracturing， were simulated， and the non-equilibrium initiation and extension laws of multi-cluster fractures were clarified. Compared with conventional fracturing， which has stress interference on the fracture and inhibits the fracture expansion， five unconventional volume fracturing methods can reduce the stress interference of multi-cluster fracturing， which is conducive to the uniform fracture initiation and expansion， and it is easier to obtain complex fractures and larger reconstruction volume. Among them， the effect of complex fracture networks is the best for inter-cluster block fracturing. It has developed and refined a balanced fracture and extension control technique for multiple cluster fractures in bulk fracturing， which has helped to improve the degree of 3D reconstruction of unconventional tight oil and gas reservoirs.
To address the difficult problem of poor understanding of the reservoir mobilization law of water-bearing sandstone gas reservoirs， a multi-point piezometric physical simulation experiment method and apparatus were used for long cores. Six natural matrix cores with permeability levels of 0.047，0.064，0.154，0.175，0.602， and 1.74×10-3 μm2 were selected， and a series of physical simulation experiments of depletion extraction were conducted under the conditions of water content saturation of about 0%，30%，40%，50%，60%， and 70%， respectively. The effects of reservoir matrix permeability and water saturation on the instantaneous gas production， pressure drop curve and characteristics of the reservoir， as well as the degree of reserve utilization （R） at different development stages （end of steady production， abandonment conditions and ultimate conditions） were investigated. The results show that： （1） the gas production capacity of reservoir matrix and the degree of reservoir utilization are controlled by both reservoir matrix permeability and water content saturation， but the sensitive threshold value is different in different stages of gas reservoir development. （2） Based on the characteristic diagram of the degree of utilization under the abandoned condition， a set of reserve utilization classification evaluation boundary map is constructed with the reservoir permeability and water content saturation corresponding to 60% and 80% of the reservoir utilization degree respectively as the indexes， and three levels of priority utilization， conditional utilization and potential utilization are divided， and the reservoir parameters corresponding to each level are clearly defined， which can provide prospective guidance for prioritizing and determining the sequence of reservoir utilization for high-quality reservoirs in the field.
The Ordovician Wulalike Formation in the northwestern margin of the Ordos Basin is a key area for exploration and evaluation of marine shale gas in northern China. In this paper， through the multi-method identification and quantitative evaluation of fractures and pores in multiple evaluation wells in the northwestern margin of the basin， the development characteristics， distribution rules and main controlling factors of fractures in the lower section of the Wulalike Formation were explored and revealed. Three preliminary conclusions were obtained： （1） Open bedding fractures are generally developed in the lower section of the Wulalike Formation at the northwest margin of the basin. Single fractures are either intermittent or continuous in steps. The width of the fractures is generally 0.1-0.2 mm， and the spacing of the fractures is generally 0.5-14.0 cm. The fracture development section is characterized by double or multiple peaks in the nuclear magnetic resonance standard T2 spectrum， and generally has the double track feature of positive amplitude difference on the deep and shallow resistivity logging curves. （2） The fracture section length and fracture porosity vary greatly. In the Majiatan-Gufengzhuang area in the southern exploration area， the fracture development degree is generally decreasing from west to east. In the Shanghaimiao area in the central exploration area， fractures are extremely developed， the continuous thickness of fracture section is generally more than 20 m， and the average value of fracture porosity is more than 1.3%. In the Tiekesumao area of the northern exploration area， the fracture development degree is generally worse than that of the central and southern areas， and also shows a weakening trend from west to east. （3） The highly brittle shale section rich in calcareous and siliceous is matched with the thrust fold and detachment since the Yanshanian period， which is the key controlling factor for the formation of fracture pores in the Wulalike Formation. Affected by the structural style and activity characteristics of different blocks， the development degree of fractures in different exploration areas is significantly different.
Tectonic uplift will not only reduce the formation pressure but also cause pore rebound which leads to changes in the physical properties of the formation. There are several errors without considering the pore rebound when the conventional methods are used to identify the disequilibrium compaction and calculating the overpressure. In order to accurately identify the disequilibrium compaction and calculate the disequilibrium compaction overpressure of the tectonic uplift area， this article introduces the impact of tectonic uplift on logging data firstly； then， a method to calculate disequilibrium compaction overpressure by combining pore rebound experiments and loading/unloading equations is introduced； finally， taking Yanchang Formation in Xiasiwan area of Ordos Basin as an example， the loading-unloading curve method was used to restore the disequilibrium compaction overpressure in Chang 7 Member of the Yanchang Formation. The results show that the logging curve characteristics at the end of the normal compaction section change by the pore rebound， that is， acoustic time difference and the density decrease， resistivity and neutron porosity increase； By comparing the calculation results of loading-unloading curve method， formation pressure simulation and equivalent depth method， it is found that the conventional calculation results of disequilibrium compaction without considering pore rebound are too large in the tectonic uplift area， which is not applicable in the tectonic uplifting area. Research shows that it needs to identify the logging curve characteristics that acoustic time， density decreases， and the resistivity， neutron porosity increases to identify the disequilibrium compaction， using the method of loading-unloading curve can restore the disequilibrium compaction overpressure in the uplift area more accurately， which provides a more effective research basis for pressure evolution， hydrocarbon accumulation and prediction in tectonically uplifted areas.
The Ordos Basin is an important natural gas resource base in China， of which the Upper Paleozoic is the main gas-bearing layer， which has both tight gas reservoirs， unconventional shale gas and coalbed gas reservoirs. Many unconventional gas reservoirs have been found in the east of the basin， but less research has been done in the west of the basin. This paper focuses on the typical lithology of the main Upper Paleozoic accumulation layer in the middle of the Tianhuan Depression - the tight sandstone of the Xiashihezi Formation and the dark mudstone of the Shanxi Formation. Argon-ion polishing Scanning Electron Microscope （SEM） and nuclear magnetic resonance technique （NMR） were used to analyze the distribution status and morphological characteristics of micro-nano pore seams， and CT scanning technology was used to reconstruct its pore space， restore its in situ three-dimensional state， and comprehensively explore the pore space characteristics of the Upper Paleozoic in the salt pond area of Ordos Basin. The results show that：（1） The average porosity measured by the NMR of the 8th tight sandstone in the Xiashihezi formation of the study area was 6.47%， the average saturation of the movable fluid was 43.42%， mainly in type III reservoirs. CT scans show that the average connectivity porosity is 6.08%， with 80.62% pore connectivity， and the overall connectivity is good. （2） The overall porosity measured by CT scanning of dark mudstone in the Shanxi Formation was low， between 0.78% to 1.62%， with an average of 1.23%， a large number of inorganic nanopores and microfractures were developed， and the organic matter pores did not develop， which was related to the overall TOC in the Yanchi area located in the western part of the basin and the type of kerogen was mainly type III. The results of NMR and CT scanning techniques of tight sandstone in the Xiashihezi Formation show that the reservoir is highly heterogeneous. The inorganic mineral pores and micro nano fractures of the dark mudstone of the Shanxi Formation are the main oil and gas storage spaces. The existence of a large number of micro nano fractures may be the main reason for the high production of some gas wells. The research conclusion is helpful to the exploration and development of Upper Paleozoic oil and gas reservoirs in the western Ordos Basin and the evaluation of resource quantity.
The Lower Cambrian Longwangmiao dolomite is a crucial deep carbonate reservoir with great hydrocarbon potential in the Sichuan Basin， and most existing studies have focused on the central Sichuan area， while research on the dolomite of the Longwangmiao Formation in the eastern Sichuan area is relatively weak. Therefore， three field sections （Xishui Tuhe， Pengshui Banzhigou and Wuxi Xujiaba） in east Sichuan were selected for the study， and the characteristics of dolomitizing fluids and dolomite genesis mechanisms of the Cambrian Longwangmiao Formation in eastern Sichuan Basin were investigated by conducting lithological and rare earth element characteristics studies. The result shows that： （1） Three main types of dolomite developed in the study area are micrite dolomite， silty dolomite and fine-crystalline dolomite. The rare earth elements are low in various dolomites and the total rare earth content decreases as the crystal size increases， while the （Nd/Yb） SN values increase， indicating a gradual increase in dolomitization degree. （2） The gradual decrease in Ce/Ce* values and the increase in U content from micrite dolomite to fine-crystalline dolomite indicate a decreasingly oxidative environment of dolomite formation and a more closed diagenetic system. （3） The similar seawater-normalized REE partition pattern of the investigated dolomites to that of the micrites， showing positive Ce anomalies and right dip， and no significant positive Eu anomalies. These characteristics suggest that the dolomitizing fluids are likely related to seawater uninfluenced by hydrothermal fluids. （4） In summary， the micrite dolomite and the silty dolomite of the Longwangmiao Formation in the east Sichuan area were formed by evaporative concentration dolomitization during the syngenetic-penecontemporaneous phase and seepage-reflux dolomitization during the shallow burial phase， respectively， and the fine-crystal dolomite was formed by secondary enlargement of the precursor dolomite during the middle-deep burial phase. （5） In addition， combined with the sedimentary background and physical characteristics， the silty dolomite is considered to be the most important reservoir rock type of the Longwangmiao Formation in the east Sichuan area， and the early seepage-reflux dolomitization within restricted platform is most favourable to reservoir development.
Affected by the breakup of Rodinia supercontinent， rift basins were widely developed in the Yangtze block， North China block and Tarim block during the Nanhua Period. The existence of deep rift basins played an important role in controlling the late tectonic evolution of the basin and the distribution of deep oil and gas. The Sichuan Basin is located in the western margin of the Yangtze block. Because there are few wells in the basin that reveal the stratigraphic characteristics of the Nanhua System， the research on the structural characteristics and genetic mechanism of the Nanhua rift in the Basin is relatively low. This paper takes the Nanhua rift in central area of Sichuan Basin as the research object， uses the method of drilling and seismic combination to analyze the geometric characteristics of the rift basin， recover the kinematic process， and preliminarily explore the genetic mechanism of the rift basin under the constraints of the regional tectonic background. The research reveals that： （1）NE trending narrow and long rifts dominated by extensionism developed in Nanhua Period in the central area of Sichuan Basin， the boundary of which is mostly “fault overthrust” or “double fault”， The internal horst graben type and ladder type faults are developed. （2）The tectonic evolution of the rift valley is divided into three main stages： the opening stage of the rift basin， the synsedimentary stage and the sedimentary overlap stage. The formation and evolution of the Nanhua rift valley has an obvious control effect on the structural deformation of the overlying strata， and then affects multiple sets of source-reservoir associations and oil and gas distribution in the basin. （3）Based on the results of previous petrogeochemical studies， it is comprehensively believed that the Nanhua rift in Sichuan Basin developed in the environment of continental crust thinning after plate subduction and collision， showing the nature of intracontinental rift. The fault activity under the extensional tectonic background is the key factor affecting the development of Cambrian carbonate hydrothermal solution reservoir and the formation of natural gas reservoir.
Based on the previous research results of the dolomite reservoir of the Permian Maokou Formation in the Sichuan Basin， the authors made a systematic geochemical analysis of the dolomite reservoir of the Maokou Formation in the Well JT1 of the Bajiaochang structure by means of thin section observation， cathodoluminescence， carbon and oxygen isotope and in-situ laser microanalysis， and discussed the genetic mechanism of the dolomite reservoir. According to the research： （1） The shoal facies dolomite reservoir of a section of Mao 2 Member of Maokou Formation in Well JT1 is mainly developed in the shoal facies deposition at the edge of the platform depression， and the development of the reservoir is controlled by the sedimentary facies belt and dolomitization. （2） There are two stages of dolomitization in the Maokou Formation. The first phase of dolomitization mainly formed fine-medium crystalline dolomite， mainly semi-euhedral to euhedral crystals， with weak cathodoluminescence intensity， mainly dark red to red light. δ13C VPDB value and ∑REE concentration are equivalent to those of micritic limestone， and rare earth elements have the characteristics of Ce negative anomaly and Y positive anomaly. It indicates that the dolomitization fluid is mainly confined seawater at the same period. The second stage of dolomitization forms saddle-shaped dolomite， and the intensity of cathodoluminescence is the strongest， red to bright red light， with obvious positive δEu anomaly features， high 87Sr/86Sr ratio， low Sr content but high Mn content， and high fluid inclusion homogenization temperature and salinity， indicating that its dolomitization fluid is deep high-salinity hydrothermal brine. （3） The dolomitization time is syngenetic - penecontemporaneous to shallow burial period， the first stage of dolomitization occurs， and Mg2+ in limited seawater metasomatizes sparry bioclastic limestone， forming a large number of intercrystalline dissolution pores and crystals. Because dolomite has a stronger anti-compaction effect than limestone， the pore space is better preserved； in the burial period， affected by tectonic movement， the second stage of dolomitization occurred， mainly forming saddle-shaped dolomite， filling in the pore space formed by the first stage of dolomitization. It has a destructive effect on the reservoir.
Middle Jurassic Lianggaoshan Formation in Fuxing area is regarded as one of the important fields of shale oil and gas exploration in Sichuan Basin. Source rock potential and reservoir quality of Lianggaoshan Formation were analyzed via integrated analysis of organic geochemistry property and pore types and pore microstructure， and thereby favorable intervals for shale oil exploration were defined. Finally， shale oil exploration potential of Lianggaoshan Formation in Fuxing area is discussed. Results show that， shallow lake to semi-deep lake organic rich shale was developed at the Lianggaoshan Formation in the Fuxing area， which is characterized by fair-good source rocks with medium organic matter abundance， good organic matter type， moderate thermal maturity and high hydrocarbon generation potential. Shale reservoirs at No.④ layer have medium storage capacity， but good oil and gas property and good movable potential. It is a favorable shale oil exploration target. The Lianggaoshan semi-deep lacustrine shale at Bashansi Syncline in Fuxing area has a solid foundation for in-situ condensate or light oil enrichment with good shale oil exploration prospects.
In order to explore the impact of tectonic deformation on the pore-fracture structure of shale reservoir， two sets of deformation （fault and fold） Longmaxi Formation shale samples in northeastern Chongqing were systematically collected， and a variety of material composition and pore structure characterization experiments were carried out. And the transformation mechanism of pore-fracture structure caused by different tectonic deformation （fault and fold） was further analyzed. The experimental results show that， compared with Liaozi samples， Tianba samples have relatively lower TOC content and clay mineral content， while quartz mineral content is relatively higher； Fault belt shale samples with strong deformation contain relatively more mesopores and macropores， and micropores tend to decrease， while fold belt shale samples with strong deformation contain relatively more macropores， and both micropores and mesopores tend to decrease； The total pore volume of fault belt shale has increased with the increase of deformation degree， because the large intergranular pores， microfractures and microchannels in the sample are specially developed， which greatly improves the reservoir and permeability of shale reservoir； The total pore volume of fold belt shale has decreased， specifically， the developed intergranular pores， microfractures and microchannels can only enhance the local reservoir and permeability of shale reservoir， but will not lead to long-distance migration and escape of shale gas. The research results will provide a theoretical basis for the subsequent evaluation of shale gas resources in complex structural areas in China.
In order to discuss the geological characteristics of deep Longmaxi Formation shale reservoir in Zhaotong Shale Gas Demonstration area in the southwest margin of the Upper Yangtze River， taking Leibo area as an example， on the basis of field geological survey and indoor experimental data， and through regional geological data， a systematic study was carried out on the petrological characteristics， sedimentary facies distribution， organic geochemical parameters， and reservoir space types and characteristics of Longmaxi Formation shale in the study area. The mineral components in the study area are mainly quartz and clay minerals， with an average of 36.3% and 34.85% respectively， and contain a small amount of carbonate minerals， feldspar and pyrite； TOC content is 0.12%-5.94%， with an average of 2.12%； The two areas near Zhongdu town-Nan'an town and the east of Leibo county are high TOC value areas and sedimentary centers in the study area. The sedimentary facies are mainly deep-water continental shelf， which evolved to the West into shallow water continental shelf. TI value is 36.5-82.5， mainly type Ⅱ1 kerogen； RO is 2.34%-2.72%， with an average of 2.48%， which is at over mature stage； The average porosity is 8.99% and the average pore diameter is 5.682 nm. The pore types are mainly organic matter pores， mineral dissolution pores and micro fractures. The pore morphology is mainly nano-sized open quadrilateral parallel plate pores and densely stacked spherical intergranular pores， with a small amount of open cylindrical pores and fracture structures. The porosity of shale shows a positive correlation with permeability. Compared with the major shale gas producing areas at home and abroad， the lower shale of Longmaxi Formation in the southwest margin of Sichuan Basin shows the characteristics of high TOC content， high organic matter abundance， high maturity， high content of brittle minerals and development of organic matter pores. According to its hydrocarbon generation capacity and exploitability， it is divided into source rock section and reservoir dominated section. The upper member of Longmaxi Formation is characterized by low TOC content， high clay mineral content and developed microcracks. It is a non-source rock and a cap dominated interval.
In order to clarify the pore structure properties and key controlling factors of dominant lithofacies in normal pressure shale reservoirs， by taking the marine shale reservoirs of Wufeng-Longmaxi formations in Lintanchang area， southeastern Sichuan as an example， the pore structure of different lithofacies was quantitatively characterized， and their key controlling factors and gas content differences were analyzed. The findings show that the lithofacies of Lintanchang area can be classified as organic-rich siliceous shale facies （S-H）， organic-rich mixed shale facies （M-H）， organic-poor argillaceous shale facies （C-L）， and organic-poor mixed shale facies （M-L）； Ink bottles or slit shaped make up the main pore morphology of the four different types of pores shape. Mesopores dominate the pore distribution in the southern portion of Lintanchang area， whereas micropores and mesopores dominate the northern portion. S-H and M-H lithofacies have a higher connection than C-L and M-L lithofacies do； Organic matter， followed by brittle mineral content， are the main factors on the pore development of S-H and M-H lithofacies. Organic matter and clay mineral composition primarily control the pores of C-L and M-L lithofacies； Fracture is an another important factor affecting pores， and shale reservoirs in the north of the Lintanchang area have higher vertical gas content than those in the south， which is presumed to be caused by fractures. We believe that the gas reservoir adjustment and pore pressure relief caused by fractures are important factors for the differences in pore parameters， gas content and production between the north and south part of Lintanchang area. Subsequent attention should be paid to the comprehensive impact of fractures and faults on its productivity.
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