Pore characterization of marine-continental transitional shale in Permian Shanxi Formation of The Southern North China Basin

Xiaoguang Yang,Shaobin Guo

doi:10.1177/0144598720912346

Xiaoguang Yang, Shaobin Guo

Open Access

https://doi.org/10.1177/0144598720912346

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Abstract

Organic-rich marine-continental transitional shale is widely developed in the Permian Shanxi Formation in the Southern North China Basin. In this study, shale samples from the southern and northern wells of the basin were characterized by X-ray diffraction, high-pressure mercury intrusion porosimetry, low-pressure gas adsorption (N2 and CO2) and argon ion polishing-field emissions scanning electron microscopy. The pore types and structures of shale micropores, mesopores and macropores are qualitatively described; their pore size distribution and volume are quantitatively characterized; and the influencing factors of the pore volume are analyzed. The results show that the marine-continental transitional shale pores exhibit an unbalanced multimodal distribution with four peaks at 0.4–0.8 nm, 2–4 nm, 10–50 nm, and >10 µm. The mesopore volume is dominant, accounting for 40–70% of pores. The mesopores of the samples are slit-shaped pores and ink bottle-shaped pores. Since there is a desorption hysteresis loop on the N2 adsorption-desorption curve, most of them belong to the H4 type, and ye23-8 belongs to the mixed H2 and H4 type according to the IUPAC classification scheme. The slit-shaped pores are mainly interlayer pores and interparticle pores in clays, and the ink bottle-shaped pores are tiny dissolved pores and organic matter pores. Ro has negative correlation with the volumes of the mesopores and macropores, but it does not affect the volume of micropores. TOC has a positive correlation with the macropore and micropore volumes, and it has a negative correlation with mesopore volume. The relative contents of kaolinite and I/S have a positive correlation with the mesopore and macropore volumes. The relative content of illite has a negative correlation with the mesopore and macropore volumes. The relative content of chlorite has a negative correlation with the mesopore volume.

Highlights

The exploration and development of shale gas in China have reached breakthroughs in recent years, and the marine shale gas in southern China has gained industrial production capacity (Jiang et al, 2016a; Zhang et al, 2004; Zou et al, 2010)
Marine-continental transitional shale has the advantage of producing shale gas due to its high brittleness, its thin layers arranged into thick cumulative layers and its potential for microcrack development (Ren et al, 2007; Zhao et al, 2005)
The shale samples are characterized by XRD, mercury intrusion porosimetry (MIP), N2/CO2 adsorption and AIP-FESEM

Summary

Introduction

The exploration and development of shale gas in China have reached breakthroughs in recent years, and the marine shale gas in southern China has gained industrial production capacity (Jiang et al, 2016a; Zhang et al, 2004; Zou et al, 2010). In addition to marine shale gas, marine-continental transitional shale gas has certain exploration potential. The gas generation ability of marine-continental transitional coal measure strata has been widely recognized (Gong et al, 2018; Wang et al, 2019; Zhang et al, 2019; Zhao et al, 2018). Marine-continental transitional shale has the advantage of producing shale gas due to its high brittleness, its thin layers arranged into thick cumulative layers and its potential for microcrack development (Ren et al, 2007; Zhao et al, 2005). The associated reservoir characteristics and development of marine-continental transitional shale need to be studied further

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Conclusion