Porosity-preserving mechanisms of marine shale in Lower Cambrian of Sichuan Basin, South China,Gas Science and Engineering

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Porosity-preserving mechanisms of marine shale in Lower Cambrian of Sichuan Basin, South China
Gas Science and Engineering Pub Date : 2018-07-01 , DOI: 10.1016/j.jngse.2018.05.002
Xin Li , Zhenxue Jiang , Pengfei Wang , Yan Song , Zhuo Li , Xianglu Tang , Tingwei Li , Gangyi Zhai , Shujing Bao , Chenlu Xu , Fan Wu

Abstract Porosity preservation is of great significance in the capacity of gas shale reservoir. Whether pore space can be preserved at the later diagenetic stage controls the capacity of shale reservoir. In this study, porosity-preserving mechanisms of marine shale from Lower Cambrian, both inside and at the margin of Sichuan Basin, South China, were investigated via a combination of the X-ray diffraction (XRD), organic geochemistry analysis, gas adsorption analysis and focused ion beam milling-scanning electron microscopy (FIB-SEM) in both two-dimension (2-D) and three-dimension (3-D). The results showed that there was little difference in mineralogical compositions between samples of Qiongzhusi shales and Niutitang shales that brittle minerals and clay were predominate components. The mean value of the total organic carbon (TOC) of Qiongzhusi shales was 1.44 wt% lower than that of Niutitang shales (4.37 wt%), whereas Qiongzhusi shales were at relatively lower thermal maturity stage with equal-vitrinite reflectance (Ro) ranging from 2.66% to 2.8% compared with Niutitang shales (3.06% These observations suggest that brittle mineral grains can function as rigid frameworks or grain supporters due to high brittleness which preserves ductile matrix relating pores (OM-hosted pores and clay associated pores) from collapse by sharing the effective stress; in addition, either excessive OM abundance (TOC>5.0 wt%) or over thermal maturity (Ro>3.3%) is detrimental to pore preservation; moreover, poor sealing ability of shale systems might deteriorate pore preserving ability through losing overpressure environment or stress supporting mechanism.

更新日期：2018-07-01

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