Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
Bureau Seminar, February 27, 2004
of Permeability from Well Logs Based on
Verdin, Department of Petroleum and Geosystems Engineering
of this study is an active over-pressured tight-gas reservoir. Conventional
core porosity and permeability, together with capillary pressure were
used to determine rock types and flow units in a key cored well. The dominant
non-wetting phase saturation from capillary pressure curves is used to
estimate pore throat radii and permeability at different confinement pressures.
Subsequently, a study is performed to assess the influence of mud-filtrate
invasion on borehole array induction logging tools. Flow units defined
from core analysis are taken as horizontal layers to simulate the process
of mud-filtrate invasion with a two-dimensional chemical flood simulator
that includes the effect of salt mixing between mud filtrate and connate
water. Radial resistivity profiles are obtained from the simulated profiles
of water saturation and salt concentration using Archie's law. It is found
that matching the simulated flushed-zone resistivities with the shallow
resistivity readings requires that Archie's parameters, m and n, be specific
functions of rock type.
Based on the analysis at the key well, detailed petrophysical assessments are performed in additional wells in the same field. Simulations of mud-filtrate invasion are carried out in each well with the only free parameter being absolute permeability. All of the remaining petrophysical parameters required for the simulation of invasion are either estimated from well logs or else extrapolated from the key well. Matching the shallow and deep resistivity logs with the corresponding resistivities yielded by the simulation of mud filtrate invasion provides the desired estimate of absolute permeability. This technique embodies a novel, efficient, and accurate methodology to estimate in-situ permeability from a basic suite of logs.