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

Abstract

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 environment 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 photoelectric 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.

Keywords

• interbedding of sandstone and mudstone
• high bound water volume
• conductive mineral
• abnormal low resistivity
• coal measures