Mechanical property evaluation of coal bed and favorable area prediction of coalbed methane (CBM) development based on well logging: A case study of No. 3 coal bed in Zhengzhuang Block, southern Qinshui Basin

Accurately grasping the mechanical properties of coal is of great significance to reservoir reconstruction and CBM development. Herein, the prediction model of shear wave time difference in coal reservoir based on multiple logging parameters and the brittleness index evaluation model based on dynamic and static mechanical parameter conversion were established for the research horizon of No.3 coal bed in Zhengzhuang Block. The brittleness index of coal reservoir in the study area was comprehensively evaluated by elastic parameter method. By this way, it is found that the brittleness index of coal bed in single well is obviously affected by “boundary effect” and in regional distribution. Besides, the brittleness index is positively correlated to the coal structure index, and put forward the classification standard of coal structure based on brittleness index. The brittleness index is negatively correlated with the compressive and tensile strength. In addition, the results of four-dimensional seismic fracture monitoring show that the coal in cataclastic structure has the best fracturing effect, followed by the coal in primary structure and granulitic structure successively. Finally, the favorable area of CBM development in the block was predicted with gas content and brittleness index as the main evaluation parameters, which provides a basis for the fracturing design of coal reservoir.