Based on the analyses of petrology，mineralogy and geochemistry，the formation phases of the carbonate cements and sedimentary environment in Jurassic clastic rocks in Lenghu V Tectonic Belt were studied.The experimental results demonstrated that the rocks of Lower Jurassic were mainly lithic sandstone and feldspar lithic sandstone with high content of clay minerals，which was up to 36.5%.The clay minerals in the Lower Jurassic were characterized by high content of kaolinite and low S% in I/S.Clastic rocks were mainly line contact and sature line contact，diagenetic stage of the Lower Jurassic clastic rocks was phase B of middle diagenetic stage；calcite，dolomite and ankerite were three main carbonate cements through observation under microscope.The carbon isotope (δ13C) of carbonate cements ranges from -15.6‰ to 9.2‰，and the average value is -3.2‰.The distribution was bimodal，one peak value was 4‰，consisting of samples coming from the upper section in Xiaomeigou Formation；the other one was -12‰，consisting of samples mainly coming from the lower section in Xiaomeigou Formation.The oxygen isotope (δ18O) had a wide range，ranging from -18.5‰ to -8.3‰，and the average value was -13.3‰.Combined with the observation under microscope，two phases of carbonate cements were distinguished according to isotope characteristic.The earlier carbonate cements were formed from eogenetic A phase to eogenetic B phase.The source of the carbon was inorganic，but it was mixed by the carbon from methane generation process.This mixing leads to positive bias of the δ13C，and make the indicated paleosalinity higher than the truth.The later carbonate cements were formed in phase A of middle diagenetic stage，and always filled in the cracks in clastic.The carbon came from decarboxylation of organic matters，so its δ13C was lighter.The carbon and oxygen isotopes together with element geochemistry showed that the climate in Low Jurassic was warm and wet，especially in the earlier time，sedimentary environment was fresh water.However，during the late stage，the climate became dry and cold，and sedimentary environment became fresh-brackish.
In recent years，the Yingxi area of the Qaidam Basin has formed a tonnage-scale reserve reservoir，which is mainly controlled by the wide-covering gray-rock reservoir，the high-quality salt rock cover，and the late uplift background，forming the large-scale tectonic-lithologic reservoirs of carbonate rocks.The Yingxi area is located in the Cenozoic main source rock development area in the western Qaidam Basin，and the middle and deep layers (Lower Ganchaigou Formation) have the inherent advantages of near to oil source.The predecessors believed that the crude oil in the deep reservoir was mainly from the Paleogene source rock，and have done a lot of research work on the oil source type and the development pattern of the high quality reservoir，but the process of oil charging has not been deeply studied.In this paper，the dynamic evolution of oil in the Yingxi area is analyzed systematically by means of reservoir quantitative grain fluorescence analysis，fluid inclusions petrography，homogenization temperature measurement and so on，combined with burial history and thermal history analysis.Yingxi middle-deep layer is characterized by rich middle density oil charging，while the result of QGF-E and TSF indicate that heavy and polarity oil exist in the reservoir.The reservoir mainly develop yellow and light blue fluorescent inclusions.Combined with the homogenization temperature of associated saline inclusions and burial and thermal history，it is concluded that the middle and deep layers of the Yingxi area mainly experienced the low-maturity oil charging in the late Lower Youshashan Formation (15Ma)，and the mature-highly matured oil charging in the late Upper Youshashan Formation (7Ma).Meanwhile，due to the influence of the late stage of Himalayan tectonic movement，the middle and deep reservoirs have experienced the process of oil charging and transferring to upward layers.
The organic-rich shale of Wufeng-Longmaxi Formations (Ordovician-Silurian) is one of the most important hydrocarbon source rocks and shale gas reservoirs in the upper Yangtze region of China.They contain abundant graptolites and the determination of their thermal maturity has always been a difficult problem.Based on the observation of abundant polished blocks，the graptolites were easily mistaken for vitrinite-like particles or bitumen.Abundant non-granular graptolites were observed in these sediments.Their biological and optical characteristics，which are different from bitumen or vitrinite-like particles，include complex and segmented structure，fusellar layers，abundant in-fill pyrites and strong anisotropy at the high-post mature stages.The bireflectance (Rmax-Rmin) values of the non-granular graptolites fall between 0.71% and 5.78%，indicating its behaviour similar to the optical biaxial material.The equivalent vitrinite reflectance values (EqVRO)，calculated from the mean maximum reflectance of non-granular graptolite，fall in the range of 2.75%-4.72%，1.05%-1.17% and 5.42%-5.58% for the studied samples from the southeastern Chongqing，Chengkou and Wuxi of northeastern Chongqing，respectively，indicating that the thermal maturity of the samples from southeastern Chongqing and Wuxi area is postmature，whereas the thermal maturity of the samples from Chengkou area is mature.
Recently great breakthrough in natural gas exploration has been obtained in mid-deep strata of the Yinggehai Basin，but the accumulation characteristics of the natural gas in mid-deep strata，especially in Ledong area is still indistinct because of the complicated geologic conditions.In this article，macroscopical geological analysis and microcosmic geochemical detecting techniques are used to research the gas accumulation difference in mid-deep intervals between Dongfang and Ledong areas.It is concluded that，compared with Dongfang area，extensive gas generation of the source rocks in Ledong area is relatively late but much faster，hydrocarbon gas began to accumulate at about 3.0Ma in Dongfang area while 1.7Ma in Ledong area.At the same time，there are some common ground in Dongfang and Ledong areas such as the hydrocarbon generation process and diapir activity controlling the gas accumulation，and the natural gas distribution is closely related to the diapiric activity energy.So，mid-deep intervals in diapir circumjacent areas with good physical properties will be priority exploration areas in Ledong area.
Broken soft and low permeability coal seam，with high gas content，high gas pressure，grant resource potential，and low mechanical strength，developed well in China.Formation of hole along the coal seam drilling is difficult，and the key science and technology problem in CBM efficient development and the mine gas control of this coal seam area have always been difficult to extract gas.No.8 coal seam of Luling coal mine is in broken soft，high gas，outburst，low permeability，difficult extraction，easy drill ability of roof.Introducing horizontal well and multistage fracturing techniques，constructing horizontal well along the coal seam roof，using a complete set of developing techniques: pumping bridge plug multistage，multistage clustering directional perforation，piecewise directional fracturing step by step，and adopting the sand technologies of first low to high，first coarse to fine，applying slug-style sand technology duly，multiple sets of north-east main vertical fracture belts with high seepage ability were formed in the coal seam.Through fine drainage management technology，the horizontal well creates a record that daily CBM production is more than ten thousand cubic meters.The successful application of multistage fracturing in horizontal well along the roof of broken soft and low permeability coal seam，breaking through the concept that “structure coal is forbidden zone to develop CBM”，filling the techniques gap in surface CBM efficient development and coal mine gas control of difficult extracting coal seams area.
Coalbed methane resources are rich in Manasi mining area of Southern Junggar Coal-field，but the enrichment rules of coalbed methane are complex because of complex structures，multi-layer seam，particulate hydrodynamic field.With analytical data of mining area，coal mine，oil and gas exploration，we study many factors which influence the enrichment of coalbed methane，such as coal rank，structural，sedimentary，hydrogeology.The results show that tectonic movement form Qingshuihe and Manasi syncline，swamp on plain control the growth of thick coal seam，sealing conditions which controlled by fan delta fluvial facies and lacustrine facies，the underground water dynamic system which controlled by burning area can hinder the dissipation of coalbed methane.The above factors control the enrichment and reservoir formation model of coalbed methane in the Mansi mining area.The research shows that south Manasi and Qingshuihe synclinal shafts which have higher coal rank，good mineralization of groundwater and good sealing condition are enrichment area of coalbed methane.
Tight reservoir with poor physical property，complex seepage characteristics and strong heterogeneity result in the difficulty in the development，so the study of reservoir horizontal and vertical heterogeneity and the establishment of a multi-layered and multi-stage (different scales) seepage model based on multi-stage seepage experiments in heterogeneous layers is essential for improving oil recovery.Firstly，three kinds of experiments are carried out：Slippage effect，starting pressure gradient and stress sensitivity.Experimental results show：when the reservoir effective permeability is between 0.01×10-3μm2 and 1.0×10-3μm2 and the gas reservoir pressure is higher than 10MPa，the effect of slippage effect on the production is less than 3% which can be ignored；there is no starting pressure gradient in single gas flow in tight gas reservoir；for the gas-water two-phase seepage in high water saturation reservoirs，due to the role of capillary force，the macro performance of the reservoir is the starting pressure phenomenon；compared with the matrix core，the stress sensitivity of the micro-crack core permeability is stronger and stress-sensitive lag is also stronger.Then，considering the starting pressure gradient and the stress sensitivity，the Multi-Layered and Multi-Stage seepage model of tight sandstone gas reservoir is established.Finally，the sensitivity analysis of model parameters was carried out by using the relationship between dimensionless quasi-pressure and dimensionless time.Research shows：the interlayer parameters mainly affect the later stage，the larger the ratio of the formation coefficient of the fracture，the greater the later pressure drop，so the fracturing scale is uniform when the production is in several layers，otherwise the pressure between the layers differentiates significantly，likely to cause a single layer of gas overriding and gas flow；in addition，the permeability modulus of the deformed medium，the elasticity ratio of the medium and the starting pressure gradient in in-layer parameters all affect the transition and the late stage.Therefore，it is very important to maintain the pressure at the later stage of gas reservoir development.
High well head pressure，big well control risks，high bottom hole temperature，poor data stability and severe tubing damage etc.are the challenges existing in the operation of formation pressure monitoring and well productivity testing of abnormal high pressure gas reservoir which limits the application scale of conventional productivity testing.Through the research on the methods of gas well productivity evaluation，based on the bottom hole flow pressure determined by well head oil pressure while considering the dynamic parameters to evaluate the single well productivity using the dynamic production data of gas field and on the basis of this to calculate the gas well formation pressure P，laminar flow coefficient a，turbulent flow coefficient b，the gas well deliverability equation was established to evaluate the real-time productivity of gas field and to determine the reasonable productivity of single well and reasonable production of gas field.The application example shows that the relative error of AOF is only 2.75% between gas well absolute open flow(AOF) confirmed by surface dynamic production data and AOF measured by actual bottom hole pressure which proved the rationality of evaluation of gas well productivity by using of surface dynamic production data.Application of this new method not only saves testing operation cost and eliminates the testing risk，at the same time it provides a scientific basis for gas reservoir dynamic analysis，tracking data simulation and gas reservoir management，and offers reference and guiding suggestion for similar abnormal high pressure gas reservoir development.
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