华北东部晚古生代过渡相煤系地层低阻成因、控制因素与地质意义

Genesis,controlling factors and geological significance of low resistivity in Late Paleozoic transitional coal measures in Eastern North China

华北东部晚古生代过渡相煤系地层中低阻层发育,明确其成因类型、控制因素以及地质意义,可以充分揭示其中所包含的地质信息,对于相关层系油气资源评价和勘探部署具有积极意义。本文以华北东部太原组和山西组中低阻层为研究对象,综合运用岩心、薄片、扫描电镜、碳氧同位素和测录井资料,围绕其成因类型、控制因素和地质意义开展研究。结果表明:华北东部晚古生代过渡相煤系低阻层主要发育在太1段和山2段,成因类型包括砂泥岩薄互层、高束缚水体积和发育导电矿物,沉积作用和成岩作用控制了低阻的形成;太1段低阻的成因为砂泥岩薄互层和高束缚水体积,潮汐作用导致的潮汐成因层理和微细孔隙发育促进了障壁海岸背景下太1段低阻的形成,山2段低阻的成因为菱铁矿的密集发育,稳定的覆水还原环境和沉积有机物的成岩演化共同控制了三角洲背景下山2段低阻的形成;太1段的低阻和高毛细管束缚水体积指示着潮坪沉积,说明太原组自下而上为一个海退的过程,是对早二叠世早期冈瓦纳冰川迅速扩张和全球海平面快速下降的响应,山2段的低阻和高光电吸收截面指数指示着三角洲前缘沉积,说明山西组由一期三角洲沉积组成。

Low-resistance layers are common in Late Paleozoic transitional coal measures in eastern North China.To clarify their genesis types,controlling factors and geological significance can fully reveal the geological information contained therein,which is of positive significance for the evaluation and exploration deployment of oil and gas resources in the relevant layers.Taking the low-resistance layers in the Taiyuan and Shanxi Formation in eastern North China as research object,their genesis types,controlling factors and geological significance were investigated based on the comprehensive use of cores,thin sections,SEM,carbon and oxygen isotopes and logging data.The results show that low-resistance layers in the Late Paleozoic transitional coal measures in eastern North China are mainly developed in the Tai 1 Member and the Shan 2 Member,and the genesis types include thin interbedding of sandstone and mudstone,high bound water volume and the development of conductive minerals,sedimentation and diagenesis control the formation of the low-resistance layers.The low resistivity of the Tai 1 Member can be attributed to thin interbedding of sandstone and mudstone and high bound water volume,tidal stratification and abundant micro-pore caused by tidal action promote the formation of low resistance in Tai 1 member under the barrier coast background.The low resistivity of the Shan 2 Member can be attributed to the dense development of siderite,stably reducing envir-onment in water column and diagenetic evolution of sedimentary organic matter jointly control the formation of low resistance in the Shan 2 Member under the delta background.The low resistivity and high capillary bound water volume of the Tai 1 Member indicates tidal flat deposition,suggesting that the sedimentary evolution of the Taiyuan Formation is a process of regression,which is in response to the rapid expansion of Gondwana glacier and rapid global sea level fall in the early stage of early Permian.The low resistivity and high photoelec-tric absorption cross-section index of the Shan 2 Member indicates deltaic front deposition,suggesting that the Shanxi Formation consists of one phase of delta deposition.