Tortuosity of pore channels in tight rocks as a key parameter in fluid flow ability

Abstract

Tortuosity is a significant parameter in porous materials analysis. Not only, when it comes to rocks or soils but also cellular materials, alloys or cells, the multiple definitions exist for tortuosity and several purposes. Geometrical tortuosity describes the pore network paths; on the other hand thermal, diffusional, electrical and hydraulic tortuosity refers to the transport processes in the pore network. Computed X-ray tomography (CT) is the best solution in tortuosity estimation, thanks to the 3D images. In particular, computed X-ray tomography, together with mercury porosimetry (MICP), pulse- and pressure-decay permeability methods (PDP), as well as electrical parameter measurements (EPM), links and expands the information about the tortuosity into the greater meaning. The geological material was composed of tight, low-porosity and low-permeability gas-saturated rocks cored from the present depth of deposition below 3000 m, containing different lithologies, as sandstones, mudstones, limestones, and dolomites. The research presents the novel approach in the identification and analysis of the main pore channels based on 3D CT images. Algorithm of the central axis identifies and analyzes the whole main flow path and calculates tortuosity. High correlation was observed between the tortuosity and Swanson parameter from mercury porosimetry data. Moreover, the high correlation was detected between the tortuosity and saturation exponent from electrical parameter measurement in analyzed tight low-porosity and low-permeability deposits. Multilinear regression (MLR) allows estimating absolute permeability taking CT, MICP and EPM parameters into consideration. Combination of these parameters in one equation with high determination coefficient gives credence in estimating preliminary absolute permeability (PDP) based on the data which is executed as standard core analysis (MICP and EPM) and data from the non-invasive method (CT).