Reservoir characteristics and gas-bearing property of Wufeng-Longmaxi shale in well HY2, Hefeng area
Tóm tắt
Survey well HY2 reveals the reservoir characteristics of the Wufeng-Longmaxi shale and its gas-bearing properties in the Dahegou anticline, Hefeng area. Through analysis of the organic geochemical character, X-ray diffraction whole-rock mineralogy, SEM, isothermal adsorption, and live desorption experimental data, the Wufeng-Longmaxi shale is characterized. It has a high organic carbon content, an advanced thermal maturity, mainly clastic brittle minerals, and an ultralow porosity and permeability. By comparing data from well HY2 with those from well LD1, which is located in the Lianghekou syncline, Laifeng-Xianfeng area, the shale quality of the two wells is generally consistent. For the shale in well LD1, the average organic carbon content is 1.58%, average vitrinite reflectance is 2.94%, average porosity is 1.0%, average clay mineral content is 36.0%, and average quartz + feldspar content is 54.19%, while for the shale in well HY2, the average organic carbon content is 4.43%, average vitrinite reflectance is 2.65%, average porosity is 1.23%, average clay mineral content is 29.0%, and average quartz + feldspar content is 64.20%. The isothermal adsorption experimental results show that the average Langmuir volume of Wufeng-Longmaxi shale in well HY2 is 2.40m3/t, but the total gas content of well HY2 is low, with a maximum gas content of only 0.08 m3/t, while the average total gas content of well LD1 is 1.72m3/t. On the basis of fine description of well rock core, it is found that the vertical fractures developed in the upper part of the Linxiang Formation underlying the Wufeng-Longmaxi shale at well HY2 which were filled with calcite, and the cross-section of the core shows extensive microcracking. This result indicates that the Dahegou anticline was damaged to a certain extent after shale gas accumulation due to tectonic movement. Therefore, the destruction of preservation conditions in geological history is the main reason for the low gas content of well HY2.
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