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沁水盆地太原组、山西组及下石盒子组煤系地层气测异常现象极为普遍,具有巨大的天然气勘探潜力。但其中烃类聚集程度差异较大,裂缝发育程度是影响烃类聚集差异的主导因素。岩石孔隙纵横比反演对孔缝形态基础研究、地震反演、物理模拟、天然气疏导保存及井区优选等方面具有重要参考价值。以沁南樊庄区块固县井区山西组一口煤层气井的全波列测井资料为基础,提出基于寻优算法+微分等效介质理论组合模型的岩石孔隙纵横比α反演方法。首先基于寻优算法提取原生结构煤岩及其顶板砂岩、砂质泥岩基质矿物及干岩样骨架模量,然后利用微分等效介质理论模型对煤系地层岩石孔隙纵横比α进行反演。研究结果表明,所研究原生结构煤以近球形孔隙空间系统为主;顶板致密黏土质砂岩以微裂缝空间为主;砂质泥岩中存在孔隙和裂缝多重空间系统。利用该方法可以对地层裂缝发育段进行有效识别,吻合率为92%。对于砂质泥岩或泥包砂类型岩石而言,微裂缝主要存在于砂质中,该类岩石α与孔隙度负相关,与泥质含量正相关。无论砂岩、泥岩还是煤岩,裂缝系统的沟通或疏导能力都要强于孔隙系统,当存在有利气源、疏导体系、裂缝系统及保存条件时,理论上均可富集成藏。α研究在裂缝参数提取、岩石存气能力、孔隙沟通能力、渗透能力及天然气疏导保存成藏等方面均具有一定参考价值,对指导煤层气或煤成气科学勘探开发选区具有现实意义。
The anomalous gas measurements of coal measures in the Taiyuan Formation, Shanxi Formation and Xiashihezi Formation in the Qinshui Basin are extremely common and have great potentials for exploration of natural gas. However, the degree of hydrocarbon accumulation varies greatly, and the degree of fracture development is the dominant factor affecting the hydrocarbon accumulation. The inversion of rock pore aspect ratio has important reference value in basic research of pore morphology, seismic inversion, physical simulation, natural gas diversion and well area selection. Based on the data of full-wave well logging of a coalbed methane well in Shanxi Formation in Block Guzhuang, Fanzhuang, Qinnan, this paper proposes an inversion method of rock pore aspect ratio α based on the combination model of optimization algorithm and differential equivalent medium theory. First, based on the optimization algorithm, the skeleton modulus of primary structural coal rock and its roof sandstone, sandy mudstone and dry rock sample were extracted. Then, the differential equivalent medium theory model was used to invert the rock pore aspect ratio α of coal measure strata. The results show that the primary structural coal studied is mainly near-spherical pore space system; the top dense clay sandstone is dominated by microcrack space; and the porous mudstone contains multiple pore and fracture space systems. This method can effectively identify the development of fractures in the formation, with an anastomosis rate of 92%. For sandy mudstone or muddy sand type, the microcracks mainly exist in the sandy soil. The α of this kind of rock is negatively correlated with the porosity and positively correlated with the mud content. Regardless of sandstone, mudstone or coal, the fracture system has stronger ability to communicate or divert pores than the pore system. In the case of favorable gas source, drainage system, fracture system and preservation conditions, the reservoirs can theoretically enrich and accumulate. α study has some reference value in the aspects of fracture parameter extraction, rock gas storage ability, pore communication ability, permeability and natural gas drainage and accumulation.