A case study on 3D characterisation of pore structure in a tight sandstone gas reservoir: The Collyhurst Sandstone, East Irish Sea Basin, northern England

Abstract

Pore systems of tight-gas reservoirs control important parameters such as flow capacity, producible pore volumes, hydrocarbon flow rates and storage which are complex to characterise and to quantify. Detailed understanding of 3D pore structure is vital in predicting tight-gas reservoir productivity. This study investigates the pore architecture of a sandstone sample from Collyhurst Sandstone Formation, northern England, a tight gas reservoir. X-ray Computed Tomography (XCT) was employed to quantify the pore system (pore size, shape, geometry, and connectivity). Three types of pores were identified: inter-grain pores which are at the boundary of detrital grains and/or authigenic minerals, intra-grains pores which are pores within the detrital mineral grains, and intra-cement pores which are pores within the cement phase (authigenic minerals). The first pore type is primary in origin, whereas the latter two are secondary pores. A centerline tree and a pore network model (PNM) algorithm were applied for pore network analysis and a porosity value was estimated. The image-based porosity value was validated with laboratory experimental measurement. 3D image estimates 3.1% volume porosity, while 4.6% was recorded from the laboratory experiment. Spatial quantification of pore types and analysis of pore connectivity of the studied sandstone improves understanding on gas flow behaviour and gas storage. Furthermore, the results are useful in predicting permeability and multi-flow phase properties in a tight gas reservoir.