Pore Connectivity Characterization Using Coupled Wood’s Metal Intrusion and High-Resolution Imaging: A Case of the Silurian Longmaxi Shales From the Sichuan Basin, China

Abstract

Pore connectivity is crucial for shale gas production. However, the three-dimensional (3D) characteristics and distribution of pore networks and, more fundamentally, the underlying role of different pore types on pore connectivity in shales are inadequately understood. By comparing the 3D pore connectivity derived from direct microstructural imaging of pores filled with Wood’s metal at a pressure corresponding to the finest accessible pore throat in the resolution ranges that may be achieved by X-ray micro-CT and SEM, it is possible to evaluate pore connectivity of different types of shales. The pore connectivity of three shales including a mixed mudstone, siliceous shale, and argillaceous shale from the Silurian Longmaxi Formations is investigated via combined broad ion beam (BIB) polishing, and SEM and X-ray micro-CT imaging after Wood’s metal injection at a pressure up to 380 MPa. The three shales show significant differences in pore connectivity. The mixed mudstone shows excellent pore connectivity in the matrix; the siliceous shale shows an overall poor connectivity with only a small amount of OM (organic matter) pores immediately adjacent to microfractures displaying interconnectivity, while the pores in the argillaceous shale, dominated by plate-like clay pores, are largely not interconnected.

An Innovative Percolation Theory‐based Method for Characterizing Shale Pore Connectivity

“…As inorganic pores are the main pore type at the micrometer scale in the shale samples investigated, Sample W-23, the laminated calcareous shale, has the best inorganic pore connectivity; Sample D-36, the laminated siliceous shale, ranks second; while Sample J-24, the massive siliceous shale, has the worst inorganic pore connectivity. This quantitative evaluation result is consistent with the qualitative assessment from previous research (Yu et al, 2021). Samples with low Pc are both laminated shales with well-developed microfractures, indicating that such fractures can significantly enhance the pore connectivity (Figs.…”

“…2) from the Silurian Wufeng and Longmaxi formations in the Fuling District, Chongqing, SE Sichuan Basin were selected for investigation. Wood's Metal Alloy was injected into the shales under high pressure using the procedure of Yu et al (2021) before X-ray micro CT imaging to improve the contrast of pores. Wood's Metal Alloy is a low melting point metal that can be pressed into shale pores in a molten state under high pressure at 85-100℃, and filled in shale pores in a solid form after cooling to room temperature.…”

Decoding the nanoscale porosity in serpentinites from multidimensional electron microscopy and discrete element modelling

“…Such delamination is probably due to pressure relief during the progressive 'unloading' of the serpentinite as it approaches or reaches the Earth's surface. Furthermore, the intermittent drying of the sample either within the lithosphere or during sample preparation could have resulted in similar delamination porosity, mirroring the phenomena observed in clay (Desbois et al 2009;Rodriguez et al 2014;Yu et al 2021). In general, decompression leads to fractures and affects macroscopic-scale properties of rocks, such as the elastic modulus, without significantly altering their microscopic structures (Auzende et al 2015; Wei et al 2017).…”

Pore Connectivity Characteristics and Controlling Factors for Black Shales in the Wufeng-Longmaxi Formation, Southeastern Sichuan Basin, China

“…Low-pressure N 2 adsorption and MICP are effective methods for measuring pore volumes and characterizing types of pores in porous media [35]. The characteristics of samples from the WF-LMX Formation during N 2 adsorption and MICP measurements are displayed in Figures 3 and 4, respectively, and the associated pore size distribution data are presented in Table 2.…”