Paleo-Environment Induced Full-Scale Pore Variation in the Low Matured Shale: A Case Study of the Third Member of the Jiufotang Formation at the Lujiapu Rift Basin, Northeast China

Abstract

Shale in the third member of the Jiufotang Formation at the Lujiapu Rift Basin is a new potential target for shale oil exploration and has rarely been studied before. In order to study pore structure and its controlling factors, shale compositions are mainly analyzed by X-ray Diffraction (XRD), and the characterization of full-scale pore structures is studied by the field-emission scanning electron microscope (FE-SEM), low-temperature N2 adsorption, and high-pressure mercury intrusion porosimetry (high-pressure MIP). According to composition and micro-texture, shale samples in the third member of the Jiufotang Formation are classified into three types: laminated organic matter-lean shale (TOC < 2%), unlaminated organic matter-intermediate shale (2% < TOC < 4%) and laminated organic matter-rich shale (TOC > 4%). Most shale samples are dominated by interparticle pores, with many of them filled by diagenetic minerals. All the shale samples are most developed in mesopores, whose development is mainly controlled by quartz content. And macropores with a diameter of 10,000 nm~100,000 nm are the secondary developed pores, which are influenced by both the paleoenvironment and diagenesis (especially clay transformation). Full-scale pore variations in laminated organic matter-lean shale, unlaminated organic matter-intermediate shale, and laminated organic matter-rich shale are ultimately related to their paleoenvironments.