Simulation of WFT Responses in Heterogeneous Reservoirs. Consequences on Permeability Evaluation at Different Scales

Because the viscosity of the fluid produced during WFT acquisition is usually poorly known, these data are undervalued for characterising permeability in heterogeneous reservoirs. Moreover, interpretation of pressure transient during WFT provides different values of permeability for draw-down and build-up. Several authors explain these differences only with the anisotropy of the permeability field. In this work, synthetic heterogeneous reservoirs are generated through stochastic simulations of anisotropic permeability fields. Flow simulations of WFT are then conducted in these models, and lead to propose a very new interpretation for the permeability values obtained from WFT. Drawdown permeability is an estimate of the permeability near the probe. Very close to the tool, the pressure drop is only driven by the very small scale permeability, while build-up pressure is controlled by the permeability in a larger volume, according to the extension of the sedimentary structures in which the test is conducted. As far as the driving parameters for both drawdown and buildup permeability from WFT are now identified, one can expect: -to characterise permeability at two different scales, few cm3 (near the probe) and few m3 (in the volume investigated by the WFT). -to deliver additional information on heterogeneity of permeability field.