Study on optimization of well pattern and well spacing for CBM development：Taking Daning Block as an example

CBM well pattern optimization design and deployment is a key part of CBM development plan formulation. Reasonable well pattern deployment can not only optimize CBM production, but also reduce CBM development costs and improve economic benefits. In response to this problem, taking Daning block in the Ordos Basin as the research object, the coal seam conditions and coal reservoir characteristics in the study area were systematically analyzed, and the suitable well type and well pattern orientation for CBM development were determined. The results show that the No.5 coal seam of Shanxi Formation in the Daning block has the characteristics of large thickness, simple structure, high gas content and low permeability. The well type of CBM development should be mainly directional wells, supplemented by horizontal wells, with the corresponding well pattern for large-scale development, and the well pattern orientation is NE66°; using the CBM productivity numerical simulation software COMET3, the current use of the Daning block is analyzed. The productivity was predicted based on the well pattern and well spacing, and the productivity under the open scheme of different well pattern and well spacing was simulated and evaluated. Numerical simulation results show that the CBM recovery rate is only 19.03% after 3086 d of well pattern and well spacing used in the current CBM development in the Daning block, indicating a low degree of CBM resource production. When the well spacing is 300 m×80 m and 400 m×100 m (that is, the well spacing ratio is 4∶1), the cumulative gas production of a single well in the five-spot well pattern is the largest. That is, when the well row spacing ratio is 3∶1), the cumulative gas production of a single well in the rectangular well pattern is the largest. Therefore, it is considered that the five-point well pattern should be selected when setting the well row spacing ratio of 4:1 in the Daning block, and the 3:1 Rectangular well pattern should be selected for the well spacing ratio of 1. After the well pattern and well spacing are optimized, the CBM recovery rate reaches 44.18% and 36.85% respectively, and the CBM resource production degree is greatly improved.