Analysis On Generation And Reservoir Characteristics Of Permian Gas Hydrate In Permafrost Region,Southern Qinghai Province,China

Natural gas hydrate is a new type of clean energy source with enormous reserves. The exploration,development and utilization of natural gas hydrate are of great significance. Qinghai Tibet Plateau permafrost region is the most important regions in China, which has the largest area, the best continuity and the stable thickness of frozen soil. In order to evaluate the metallogenic potential of gas hydrate in the Qinghai Tibet Plateau Permafrost region, drilling operation of TK1 well was conduct by Oil and gas resources survey center of China Geological Survey in 2014 at Kaixingling, and TK2 well in 2015 at Wuli. All kinds of data in this paper are mainly derived from these two wells.According to the field logging data and core sample test data, sedimentary environment, source rock and reservoir characteristics are analyzed, and the preliminary conclusion of gas hydrate formation in Permian strata in the study area is obtained: (1). Based on the field logging data, combined with the results of the identification of biological fossils, geochemical test and XRD test results, the sedimentary facies of TK1 well and TK2 well are fully understood. The formation of TK1 well is a transitional facies,located at the active continental margin. And the formation of TK2 well is a set of volcanic rock, located in the island arc. There may be a back-arc foreland basin between the two well. The swamp coal seams, the fine grained sedimentary rocks of the delta front and marine mudstone can be regarded as potential source rocks. The delta channel sand bodies, neritic sand bodies and pyroclastic rocks all have the potential of reservoir formation. (2). The results of rock pyrolysis, biomarker and vitrinite reflectance of source rock samples are integrated, and the characteristics of source rocks in the study area are preliminarily understood. It is known that the organic matter of the source rocks in the two wells is mainly mixed type; the kerogen maturity is high; the TOC is high, but the S1+S2 is very low. Comprehensive analysis shows that the source rocks in the strata are not capable of hydrocarbon generation and expulsion at the present stage. However,after the recovery of organic matter abundance, the overall evaluation is very good,which means that a large amount of oil and gas have been produced and discharged at a certain stage in the evolution of source rocks. (3). According to the records of abnormal gas in the drilling process of TK2, combined with neutron porosity logs and cores observation, favorable reservoirs were screened. And the samples were checked by thin section observation, pore permeability test and mercury injection experiment. It is considered that the reservoir space of the two wells is dominated by fractures,and the porosity is less important. The fracture zone,the macro fissures and micro fissures which have not been fully filled, can improve the physical properties of the reservoir greatly. The contribution of primary porosity to reservoir physical properties can be ignored. And the dissolution pore has a positive effect on the physical property of reservoir. Overall, physical property of layers is good.