Integrated pore-scale characterization of mercury injection/imbibition and isothermal adsorption/desorption experiments using dendroidal model for shales

Distinct from conventional reservoirs, shale formations have limited pore connectivity and unique pore spatial-distributions. Consequently, theoretical pore-network models developed for conventional formations are not representative of the pore topology within unconventional rocks. This paper presents a theoretical pore-network model, dendroidal model, based on the analysis of reconstructed pore-scale model extracted from Scanning Electron Microscope images. Dendroidal model is a semi-acyclic model, which characterizes the poor connectivity of void space without sacrificing the interaction between main flow paths. Dendroidal model infers pore-body distribution based on the hysteresis effect of isothermal adsorption/desorption measurements and characterizes pore-throat distribution using mercury injection capillary pressure data. The use of dual-compressibility model in pore-network model construction eliminates the effect of compressibility of both void space and matrix. Total organic carbon (TOC) content and minerology determine the composition of pore bodies and pore throats. The difference in mercury intrusion and extraction caused by trapping hysteresis and contact-angle hysteresis affects the stochastically distributed parameters, including pore-throat length, pore-throat cross-sectional morphology, coordination number and pore-body spatial distribution. We used shale core samples from Marcellus and Wolfcamp formations to validate the dendroidal models by calculating the absolute permeability without slippage effect. This newly developed pore-network model integrates aforementioned seven distinct types of experimental data to capture the realistic pore structures within shales.