关键词: 煤系, 多层合压, 裂缝扩展, 反演模型, 可压性分析, 压裂层位

Abstract: Multi-layer combined pressure is a key technology to improve multiple types of gas-bearing gas layers. However, due to the large difference between coal lithology and sandstone and shale, fracture propagation is more complicated than single-layer fracturing, especially the existence of coal seams makes the change of fracture shape unpredictable, which brings technical difficulties to fracturing design and implementation. For this reason, through indoor experiments to measure the peostress of coal seam roof and floor, establish multi-layer finite element inversion model, carry out in-situ stress inversion calculation of coal seam, and the feasibility of the combined pressure of different types of formations is analyzed. The results show that the error of the inversion calculation result is less than 5%, and the credibility is high; the conditions of the multi-layer combined pressure penetration layer are: the fracture is a vertical fracture, the fracture pressure difference is small (<5MPa), and the combined pressure layer difference is less than 18-20m; When multiple reservoirs are combined, the upper reservoir is in better condition, try to avoid pressing the lower coal seam; when the lower coal seam cracks, the proppant mainly supports the lower coal seam, and for the upper strata, the supporting effect is relatively poor.Cracks from the coal seam can take advantage of the stress shielding effect to increase the length of the seam in the coal seam when the coal seam is in the upper part, and the sandstone gas layer is in the lower part. The research results can provide guidance for the calculation of the stress of each layer, the judgment basis and conditions of the combined pressure, and the selection of the crack initiation layer when the multi-layer combined pressure is calculated.