Quantifying Organic Matter and Its Pore Structure of Wufeng–Longmaxi Deep Shales by Small-Angle X-ray Scattering, Mercury Intrusion Capillary Pressure, and Field-Emission Scanning Electron Microscope

Organic matter (OM) pores are well developed in the deep marine shales of the Sichuan Basin, China. Understanding the morphology and connectivity of this pore system is crucial for making accurate predictions regarding accumulation and migration. This study aims to evaluate the influence of the pore size distribution (PSD) of OM on the overall pore structure of shale. Mercury intrusion capillary pressure and small-angle X-ray scattering are used in the assessment. A field-emission scanning electron microscope (FE-SEM) was used to study the pore morphology of OM, along with areal porosity and PSD calculated from the FE-SEM images. According to the findings of the study, solid OM particle sizes in deep shale are 1.92 times greater than the diameter of their connecting throat to the exterior. It has been observed that overpressure within shale reservoir pore spaces may prevent the destruction of the solid OM connecting channels by compaction. Although the deep shale exhibits porosity similar to that of the middle-shallow formation, it contains a greater proportion of closed pores, with 61.4%. In addition, the maturity of deep shale does not have a significant impact on the complexity of the pore structure. The findings of this study may provide a substantial theoretical basis for the exploration and development of deep shale gas resources.