In-Situ Visualization and Characterization of Filter-Cake Deposition Using Time-Lapse Micro-CT Imaging

This work establishes and verifies a laboratory method for accurate, noninvasive, and nondestructive in-situ measurement of filter-cake, or mudcake, properties using high-resolution X-ray microcomputed tomography (micro-CT). Accurate in-situ characterization of mudcake properties is of vital importance for understanding mudcake deposition during mud-filtrate invasion and, more broadly, the deposition of filter cake during industrial filtration processes. The developed laboratory method involves the injection of pressurized drilling mud into a borehole located at the center of a cylindrical rock core sample. Radial mud-filtrate invasion is induced by maintaining the outside of the core sample at a lower pressure. Mudcake is deposited on the borehole wall while mud filtrate flows into the surrounding pore space of the core sample. Simultaneously, the core sample is continuously scanned using high-resolution X-ray micro-CT, allowing for three-dimensional (3D) in-situ visualization and characterization of the deposited mudcake. Analysis of experimental results is aided by a new set of filtration equations that are generalized for use with either water-based mud or invert emulsion drilling fluids, such as oil- or synthetic oil-based mud. Each experiment produces a time-series data set consisting of injected mud volume and the corresponding in-situ average mudcake thickness, porosity, and permeability. Results are presented for experiments involving injection of water- and synthetic oil-based drilling mud. We observe that experimental measurements agree well with modeled results when mudcake is thin compared to the size of the borehole—a condition that would be satisfied under most normal field conditions. Initial results also suggest that the developed method may be capable of providing accurate in-situ 3D measurements of local filter-cake properties during compressible cake filtration, which has significant implications for a wide range of industrial applications.