Assessment of Permeability from Well Logs Based on Core Calibration and Simulation of Mud-filtrate Invasion

This paper describes the application of a new methodology to estimate permeability of clastic rock formations based on the numerical simulation of the physics of mudfiltrate invasion. The methodology assumes a key well with a complete suite of well logs and rock-core laboratory measurements of porosity, permeability, capillary pressure, and relative permeability. For additional wells in the same field, absolute permeability is estimated by matching the shallow resistivity measurements with the electrical resistivity in the flushed zone yielded by the simulation of mud-filtrate invasion. We describe the application of this methodology to the estimation of permeability in three wells penetrating the same over-pressured tight-gas sands of the East Texas Bossier formation. Conventional rock-core porosity and permeability measurements, along with capillary pressure, are used to determine rock types and flow units in the cored key well. Estimates of permeability based on a modified version of Winland’s equation agree with the measured permeability of the available rock-core samples. Simulations of mud-filtrate invasion account for the dynamic process of immiscible flow between mud-filtrate and in-situ gas as well as for salt mixing between mud-filtrate and connate water. Moreover, the simulations properly reproduce the effect of mudcake buildup along the borehole wall. Two-dimensional spatial distributions of water saturation and salt concentration * Currently with University of Oklahoma