Geological structure identification of coalbed methane reservoir based on trend surface and curvature analysis algorithms

The geological structure affects the occurrence of coalbed methane (CBM), and identifying its structural characteristic boundaries is significant for CBM development. Based on the 3# coal seam top elevation observation data of the South Shizhuang CBM district in Qinshui Basin, this study comprehensively used trend surface analysis, curvature analysis and multi-element overlay analysis to study the geological structure characteristics of this area and identify its geological structure boundaries. First of all, through the analysis of the fitting degree test and significance test, it was proved that the fourth-order trend surface can be better used to identify the geological structure characteristics in this area. On this basis, the geological structural units of the study area were identified on a regional scale, and the study area was divided into the northwest depression zone, the middle fold area and the eastern slope zone. Then, by using the contour curvature analysis method, the fold geological structure boundaries were identified on a local scale, and combined with the coal seam roof elevation model for optimization and adjustment, 73 fold structural boundaries were finally identified, including 37 anticlines and 36 synclines. The results showed that: (1) The fold structures of the 3# coal seam in the South Shizhuang CBM district are primarily wide and gentle secondary folds, with symmetrical wings and a roughly NNE trend. (2) The northwest depression zone is dominated by syncline structure. (3) In the middle fold zone, anticlines and synclines are evenly distributed. (4) The eastern slope zone is dominated by anticline structure and has small terrain fluctuations, making it a favourable area for CBM development. The identification results can provide a reference for the exploration, planning and development site selection of CBM resources in the study area.