Brittleness index is an important mechanical index to evaluate the fracturability of conventional oil and gas reservoirs. However, the brittleness index of an organic coal reservoir is more complex. In this study, based on array sonic logging and density logging data, coal brittleness index is calculated using an elastic parameter method in the Mabidong coalbed methane (CBM) block in southern Qinshui Basin. In combination with coal-body structure observation, the maceral analysis, and proximate data of coal cores, a comprehensive study of geological influencing factors of coal brittleness index has been carried out. According to coal fragmentation degree, the coal-body structure of coal seams can be divided into primary, cataclastic, and granulate structure. The average interval of brittleness index of primary, cataclastic, and granulate structural coals is 63.3-71.48, 73.01-74.85, and 77.41-82.77, respectively. The results indicate that generally the order of brittleness index is primary structural coal < cataclastic structural coal < granulate structural coal. Young’s modulus and the brittleness index have a good positive correlation. Poisson’s ratio and the brittleness index are negatively correlated in No. 3 coal seam but are positive correlated in No. 15 coal seam. The vitrinite content is positively correlated with brittleness index, and the inertinite content is negatively correlated. For the primary and cataclastic structure coal, the ash and volatile is positively correlated with the brittleness index. The correlation of brittleness index, macerals, and coal quality parameters in the primary structure coal is better than that of the cataclastic and granulate structure coal. The research results are helpful to guide the coal brittleness index and coal-body structure prediction in fracturing of CBM wells.

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沁水盆地马壁洞区块高位煤储层脆性指数及其影响因素

脆性指数是评估常规油气储层可压性的重要机械指标。但是，有机煤储层的脆性指数更为复杂。在这项研究中，基于阵列声波测井和密度测井数据，利用弹性参数法计算了沁水盆地南部马壁洞煤层气（CBM）区块的煤脆性指数。结合煤体结构观测，岩心宏观分析和近邻资料，对煤脆性指标的地质影响因素进行了综合研究。根据煤的碎裂程度，煤层的煤体结构可分为一次，碎裂和粒状结构。一次，碎裂，颗粒状结构煤分别为63.3-71.48、73.01-74.85和77.41-82.77。结果表明，脆性指数的顺序一般为一级结构煤＜碎裂结构煤＜粒状结构煤。杨氏模量和脆性指数具有良好的正相关。3号煤层的泊松比和脆性指数呈负相关，而15号煤层的泊松比与脆性指数呈正相关。镜质含量与脆性指数呈正相关，而惰质含量呈负相关。对于一级和碎裂结构煤，灰分和挥发物与脆性指数呈正相关。脆性指数，基团，一级结构煤的煤质参数要优于碎裂和粒状结构煤。研究结果有助于指导煤层气井压裂中的煤脆性指数和煤体结构预测。