Evolution Characteristic and Implication of Coalbed Methane Desorption Stages Division for Tectonically Deformed Coals

This paper discusses the evolution characteristic and implication of coalbed methane (CBM) desorption stages division with the tectonic deformation degree based on the CH4 isothermal adsorption/desorption experiments and desorption efficiency for the primary coal and tectonically deformed coals (TDCs). The results show the pressure drops for the three desorption stages divided contributing to the CBM productivity increase with the tectonic deformation degree. This evolution characteristic indicates the CBM productivity of the strong brittle and ductile deformation TDCs is greater than that of the primary coal and weak brittle deformation TDCs, while the actual productivity is prohibited by the special reservoir properties of low strength, low permeability, and stimulation difficulty. This study demonstrates the two reservoir stimulation methods of the staged hydraulic fracturing of horizontal well in roof strata and the double string screen pipe completion and flushing of horizontal well can be considered adaptive for the strong brittle and ductile deformation TDCs reservoirs. Also, the special water drainage and depressurization management need to be adopted in different TDCs reservoirs. The reasonable flow pressure for CBM production can be estimated by the evolution characteristics of the three key pressures and desorption stages division with the tectonic deformation degree. In summary, this study is of great significance for achieving high and stable CBM production in TDCs reservoirs.

Automated summary

This paper discusses the evolution characteristic and implication of coalbed methane (CBM) desorption stages division with the tectonic deformation degree based on the CH4 isothermal adsorption/desorption experiments and desorption efficiency for the primary coal and tectonically deformed coals (TDCs). The results show that the pressure drops for the three desorption stages divided contributing to the CBM productivity increase with the tectonic deformation degree. The study also identifies the reservoir stimulation methods suitable for different TDCs reservoirs and emphasizes the need for special water drainage and depressurization management. The evolution characteristics of the three key pressures and desorption stages division with the tectonic deformation degree can estimate the reasonable flow pressure for CBM production. This study is of great significance for achieving high and stable CBM production in TDCs reservoirs.