Effect of an Invaded Zone on Pressure Transient Data from Multi-Probe and Packer-Probe Wireline Formation Testers in Single and Multilayer Systems

Abstract

Abstract A three-dimensional r-θ-z single-phase fully-implicit finite-difference model for a vertical well has been developed to examine how the presence of invaded zones affects the multiprobe and packer-probe pressure measurements in single-layer and multilayer (crossflow) systems. Invasion zones are modeled as composite zones concentric with the wellbore, that have different rock and fluid properties (permeability, porosity, viscosity and compressibility) from those of the native uninvaded formation. The results show that for multi-probe wireline testers, the sink (or the flowing) and horizontal probe pressure responses are highly affected by the invaded region properties, while the vertical probe pressures are mainly influenced by the properties of the uninvaded zones. For packer-probe testers, similar results are obtained; i.e., the vertical probe pressures are mainly influenced by the properties of the uninvaded zones, while the packer interval pressures at early times are influenced by the invaded zone properties. It is shown that if the invaded zones are incorporated into the interpretation process using the model developed in this work, simultaneous matching of spatially available wireline formation tester pressure data sets using nonlinear regression can provide estimates of both invaded and uninvaded zones parameters. A synthetic example of a multi-probe test is presented to confirm the theory and procedures developed in this work.