Advanced characterisation of tight unconventional rocks

Abstract

Tight unconventional rocks have become an increasingly common target for hydrocarbon production. Exploiting these resources requires a comprehensive reservoir description and characterisation program to accurately estimate reserves and identify properties that control production. In particular, this requires mapping the porosity at multiple scales and understanding the coupled contributions of fractures, variable pore types, microporosity and mineral heterogeneity to flow, petrophysical response, reserves assessment and recovery processes. This extended abstract describes a formation characterisation study based on the integrated analysis of data in 2D and 3D at multiple scales on sets of plugs from three unconventional tight gas plays: coal, tight gas and shale. Heterogeneity and geological rock typing is considered at the core scale by classical 3D imaging techniques. Mineralogy and secondary microporosity characterisation is mapped at the plug scale with different modes of 3D X-ray micro-CT analysis coupled with SEM and SEM-EDS analysis. In particular, the pore connectivity and production potential is probed. SEM and FIBSEM imaging is then used to reveal the porous microstructure of the key phases at the nano-scale in 2D and 3D. This information, collected at multiple scales, is integrated to provide an understanding and quantification of the pore structure and connectivity of these complex rocks. Petrophysical properties that impact the storage capacity and production characteristics are then computed for each key phase and data up-scaled to the plug scale using standard procedures. Results compare favourably with core analysis data, where available. The presentation slides for this speech have not been made available to APPEA at this stage.