Coalbed methane geology of Pingdingshan fault uplift

Pingdingshan exploration area is located in Pingdingshan fault uplift (Pingdingshan concealed zone) in the west of South North China Basin. Pingdingshan fault uplift is a residual basin (slice) divided by the late tectonic movement of Carboniferous-Permian coal-bearing basins in North China, which is covered by Mesozoic and Cenozoic sedimentary caprocks. Coal exploration has proved that it is a NW-trending compound syncline structure, and Carboniferous and Permian coal-bearing strata are exposed in the west, so it is difficult to trap Carboniferous and Permian strata by fault cutting, and the compound syncline structure is more complicated. Pingdingshan exploration area is located in the south-central part of compound syncline, and the exploration block is a wide and gentle syncline with northwest direction. There is a Baishigou anticline between the northwest Likou syncline and the Lingwushan syncline, and high-angle normal faults in the northwest and northeast directions are developed. Coal-bearing strata are Taiyuan Formation of Upper Carboniferous and Shanxi Formation of Lower Permian, with more than 40 layers of coal with a thickness greater than 20 m, of which Shanxi Formation 2- 1 coal is the most developed, with a large thickness and stable distribution, and it is the main coal seam, followed by Shangshihe Formation 4 coal. 2- 1 coal seam is 0.69~9.06 meters thick, generally 3 ~ 6 meters thick. It is bright and semi-bright coal with low ash content, with 14.2% ~ 18.05% in the south and 1 1.00% ~ 65438 in the north. The coal and rock are fat coal, coking coal and lean coal, and the coal rank increases from syncline wing to core. The gas content in coal seam is high, generally 6 ~ 12m3/t, and the highest is 15.52 m3/t, which increases with the increase of buried depth of coal seam. It is speculated that the gas content of syncline core can reach more than 9 m3/t ... According to the observation of mine outcrop and borehole core, the cleavage of coal seam is developed, and exogenous cracks are developed near fold axis and fault, so the permeability of coal seam may be good. The exploration area covers an area of 650 km2, and it is estimated that the CBM resources of 2- 1 coal will reach 400× 108m3. The inclined core area in this area is about 180 km2, 2- 1 coal thickness is 3-7m, buried depth is 700- 1000m, and gas content is 8- 10m3/t, so it has a certain prospect for coalbed methane exploration.

Pingdingshan 1 2 CBM exploration wells drilled in Pingdingshan fault uplift (hidden zone) have achieved preliminary exploration results, which can be used for reference. In the interval of 655.87~848.60 m, Pingdingshan Coal Mine 1 well encountered No.8, No.9, 10 and 1-5 coal seams; Pingdingshan No.2 Coal Mine encountered two thin coal seams with thickness less than 0.5 m at 693.48~698.69 m, and 58, 9, 10 and 15, 16, 17 coal seams at 777.98 ~ 972.24 m. 58 coal volatile into 19.649 coal and 10 coal volatile into 15.82% ~ 29.36%, fixed carbon 36.90% ~ 56.84%, ash into16.98% ~ 47.28. 1-5 coal contains volatile 16.53% ~ 24.89%, fixed carbon 57.05% ~ 70.02% and ash 12.60% ~ 24.89%. 15 coal contains 23.4 1% ~ 24.34% volatile matter, 65. 12% ~ 67.76% fixed carbon and 8.82% ~ 10.54% ash. The volatile fraction of coal 16 and 17 is 16.77% ~ 2 1.60%, the fixed carbon is 39. 17% ~ 65.57%, and the ash fraction is12.87%. According to the maceral analysis of coal and rock, the vitrinite and semivitrinite content of 58 coal is 77. 18% ~ 85.8%, sericite content is 14.2% ~ 22.4%, and chitin content is 0 ~ 0.5%. The vitrinite and semivitrinite contents of E 9 coal and 10 coal are 69.8% ~ 87.0%, wool coal is 12.3% ~ 29.7%, and shell coal is 0.5% ~ 1.2%. The vitrinite and semivitrinite contents of No.2 and No.4 coals are 84. 1% ~ 9 1.4%, and the silky content is 8.6% ~ 15.9%. The vitrinite and semi-vitrinite content of 15 coal is 82.4% ~ 92.5%, sericite content is 7.3% ~ 17.7%, and shell content is 0 ~ 0.2%. The vitrinite and hemivitrinite contents of 16 and 17 coals are 62.2% ~ 85.4%, sericite 13.3% ~ 37.3%, and shell 0 ~ 1.3%. The macerals of the above coal groups are mainly vitrinite and semivitrinite. The vitrinite reflectance of E8 coal is 1.24% ~ 1.35%, E8 coal is 10, 1.25% ~ 1.32%, and E2 coal is1.

Through the determination of coal and rock gas content in Pingmei 1 well and Pingmei 2 well, it is concluded that the gas content of E8 coal is 4.66 ~ 12.40m3/t, that of Pingmei 1 well E9 coal is 6.88 ~ 9.79m3/t, and that of Pingmei 2 well E9 coal and1t. 8.35 ~ 9.66m3/t of Pingmei No.2 well 1-4 coal, 5.43 m3/t of 1 5 coal, 6.00 ~ 7.92m3/t of 16, 17 coal, 3.23. According to the gas analysis of Pingdingshan Coal Mine 1 Well, the CH4 content of No.8 and No.9 coal is 95.2% ~ 99.6%, while that of anthracite coal is 90% higher and 40% ~ 80% lower. According to the gas analysis of Pingdingshan No.2 well, the CH4 content of 45% samples is 60% ~ 90%, and that of 50% samples is 20% ~ 60%. According to the isothermal adsorption of coal and rock, Langmuir volume of coal is 20.98 ~ 25.67cm3/g, Langmuir pressure is 1.77 ~ 3. 18mpa, and critical pressure is 0.9 1 ~ 1.653 MPa:e9. The Rankine volume of 10 coal is 18.44 ~ 18.53 MPa2, the Rankine volume of No.4 coal is 25.39 cm3/g, the Rankine pressure is 1.63 ~ 1.87 MPa and the critical pressure is 0.934 MPa. 15, 16 and 17 coals have a rank volume of 25.48 ~ 26.88cm3/g, a rank pressure of 3. 16 ~ 3.70mpa and a critical pressure of 0.750 ~1.570. ..

Refer to Atlas of China Coalbed Methane Basin, Structural Outline of Pingdingshan Syncline, Distribution Map of Coalbed Methane Exploration Wells in Pingdingshan Syncline, Coal Seam Thickness Map of Shanxi Formation of Lower Permian in Pingdingshan Syncline, Coal Seam Thickness Map of E of Lower Permian in Pingdingshan Syncline, Coal Seam Thickness Map of D of Lower Permian in Pingdingshan Syncline and Cumulative Thickness Map of A, E and D of Lower Permian in Pingdingshan Syncline. Coal and rock metamorphic degree map of lower Permian Shanxi Formation in Pingdingshan syncline, methane content map of lower Permian Shanxi Formation in Pingdingshan syncline, pentane methane content map of lower Shihezi Formation in Pingdingshan syncline, isothermal adsorption curve of flat coal 1 well pentane, and isothermal adsorption curve of flat coal 1 well pentane.