Digital rock physics involves high-resolution imaging of rocks, creation of 3D digital (or virtual) rocks, and sophisticated rock property computations. The state-of-the-art CT scanners currently in use allow complicated reservoir rocks to be imaged at resolutions ranging from +50 microns (μm) to a few nano-meters, suitable for analyzing conventional as well as unconventional rocks like tight sandstones, carbonates and shales. Precise separation and capture of the actual pore space in a rock and its solid matrix enables numerical simulations of multi-phase fluid flows within the pores, and makes possible fast and accurate computations of essential rock properties. Key reservoir parameters, such as porosity, absolute and relative permeability, can be computed within a few hours up to a couple of weeks.
Unlike traditional physical measurements, digital imaging-based computational rock physics is not constrained by the shape and size of rock samples under investigation, and therefore can be applied to while-drilling cuttings analysis, an important consideration for expensive deep gas drilling.
Such technologies are particularly suitable for complex reservoir characterization and resource assessment for unconventional tight gas sand and/or shale exploration and exploitation, for this type of reservoirs often, if not always, exhibit extreme heterogeneities in flow characteristics.
Some examples of practical applications include but are not limited to: detailed pore geometry (pore size, connectivity and distributions) study, deterministic volumetric appraisal for ultimate gas resources and risk assessment, flow simulations at pore scales, drill cuttings rock physics (strength, Young's modulus, porosity-permeability profiling) to guide vertical and horizontal well stimulation engineering, effects of clay, minerals and diagenetic processes, partial water saturation, and fracture network characterization.
In this paper, the concepts and procedure of digital rock physics will be fully introduced. In addition, we will present some case studies from unconventional plays to demonstrate its applicability.