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Relationship between shale gas reservoir pores structures/connectivity and organic matter/inorganic matrix in Wufeng-Longmaxi formation of Southeast Sichuan basin, China
  • Jianyang Song,
  • Luofu Liu
Jianyang Song
China University of Petroleum-Beijing

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Luofu Liu
China University of Petroleum Beijing
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Abstract: In Sichuan basin, the Longmaxi-Wufeng formation is rich of the shale gas, and the study of control factors of pores structure and connectivity are extremely significant for exploration of shale gas. Organic matter and inorganic matrix attribute to shale reservoir characters strongly. Though this work has been carried out by others before, it still has some arguments for this topic. In this project, we collected rock samples from oilfields, we did SEM, CO2 adsorption CH4 adsorption N2 adsorption, high pressure mercury injection, microscope observation, NMR, XRD, TOC test some related experiments. Analytical results show that TOC contents of the samples range from 0.96% to 6.12%, and the Wufeng-Longmaxi formation shale organic matter content is high. The samples porosity and permeability range from 0.49%-9.55% and 0.0006mD-0.73mD respectively, and the I/S of clay mineral amount ranges from 10%-60%. A plenty of graptolites were observed in the formation under microscope, and reflectivity of graptolites and solid bitumen can reveal that organic maturity is high in the formation. The higher the TOC percentage of sample, the higher the graptolite reflectance is. There are hydraulic fractures under microscope and SEM observation, and some of hydraulic fractures formed by stress, and some of them formed by hydrocarbon generation. Inorganic pores including bedding fracture, structural pores, intercrystalline pores, intergranular pores and dissolved pores and organic pore including corrosion pores, gas pores, bitumen spherulite pores can be observed. We observed quartz, calcite, feldspar under SEM to identify their cementation, filling, different periods’ growth, and aeolotropism. Based on these analysis data, authors inferred the shale diagenetic evolution is at the diagenetic B period, the mineral bitumen mass and solid bitumen macerals organic matters are contributed to the shale gas mainly, and by calculating the plane porosity by MATLAB, the fractal dimension is about 2.57. Pores diameters of these samples range from 1-55nm, and the maximum is 4nm. Most pores are around medium pores. In summary, shale gas migrates obeying non-Darcy flow along pores/fracture several nanometers, and gas migration affected by organic matter mainly in Wufeng-Longmaxi formation in Southeast Sichuan basin, China.