Minimization of Disparity between Well test and Log Driven Permeabilities through Combination of Rock-physics And Advanced Logs with Proper Averaging Technique

Abstract

Minimization of disparities between welltest and log-derived average permeabilities has always been an issue, particularly in carbonates where complex pore structures add on challenges to permeability estimation from wireline log data. The disagreement between permeability averages from logs and well tests originates from the combined effects of measurement-scale of static porosity components for permeability models, dual flow system of fractures and matrix, tensorial nature of permeability and the averaging techniques used. The proposed workflow exploits rock-physics templates to identify and to quantify secondary porosity. Rock-physics templates employ conventionally derived total porosity and shear modulus as inputs. Fracture and vug porosity identified by the proposed workflow through rock-physics agree with other qualitative and quantitative evidences of non-primary porosity obtained from NMR, Image logs and core data1. Matrix and connected-vug permeabilities are computed, calibrated and integrated via "Chen-Jacobi" connectivity-driven model2 by using NMR and acoustic log data. Fracture permeability is estimated from "fracture aperture" and fracture-porosity by using image log data and rock-physics algorithms. The final permeability profile is computed with a selective-replacement step. This step ensures that in co-presence of matrix, connected vugs and fracture permeabilities at a given discrete depth level, the greater one would dominate and replace the lesser one. The final step in efforts of lessening the disparity between averages of wireline-driven and well test/DST permeabilities for a given interval is the usage of proposed averaging technique for the integrated wireline-driven permeability profile. The rock-physics templates used in this study combine Kuster and Toksoz3 "inclusions" theory with the Dvorkin-Nur4 granular media model (1996). We have observed appreciable correlations between secondary porosity driven from shear velocities against the secondary porosity determined from NMR and Image logs and core data. These correlations further provide routes for newer permeability models that can be solely based on the rock-physics. Comparisons of permeability averages computed from wireline-driven permeability profiles against DST or welltest permeability showed significant improvements toward parity via proposed methodology and averaging technique. The workflow presented in this study is to guide the reader through numerous steps of the proposed algorithm in detail.