Implications of thin laminations on pore structure of marine shale reservoir: Goldwyer Formation case study from Western Australia

Abstract

The pore structure of a shale reservoir is a major control on hydrocarbon potential, yet shale pore systems are complex and affected by various factors. This paper focuses on the differences in pore structure between thinly laminated and massive black shale (MBSh) beds in the Ordovician Goldwyer-III shale, Canning Basin, Western Australia. A multiscale approach included image logs, core descriptions, thin sections, scanning electron microscope and X-ray diffraction analysis with low-pressure nitrogen and carbon dioxide gas adsorption tests. The results indicate that the Goldwyer shale comprises laminated beds of quartz silt and shale with thin beds of organic-rich clay, plus minor interbedded carbonate bands or concretions. The pore types are subjected to rock type, and the thinly laminated shale (LSh) is enriched in intergranular and intragranular pores. In contrast, the MBSh mainly comprises organic matter pores. The LSh is slightly enriched in mesopores but has negligible micropores. The mesopores are wedge-shaped and associated with an inorganic matrix of clay and pyrite. In comparison, the MBSh contains both mesopores and micropores. These pores are slit-like and related to organic matter and clay. The clay content and total organic carbon fluctuations control the development of mesopores and micropores in both the laminated and MBSh beds in the Goldwyer-III shale. The MBSh layers are suggested as the most important rock types for fluid flow via pore systems due to higher total pore volume, specific surface area and gas adsorption capacity.