Permeability of Unconsolidated Sand Sidewall Cores Through Data Base Regression Analysis

Allen W. Britton

Sidewall core samples provide a valuable tool for formation evaluation in unconsolidated heavy-oil reservoirs in California. Porosity, oil and water saturations, cation exchange capacity and sieve analysis for gravel-pack design are a few of the measurements that can be made on these cores. Permeability measurements, however, can easily be low by a factor of 4 due to mud solids invasion and compaction of the sidewall at the time of bullet sampler impact.

A data base of conventional core information, which does not suffer from sidewall data limitations, has been established. Regression analysis of this data base (1,237 conventional samples) containing measured porosity, permeability, and grain-size distribution data can be used to estimate permeability values for unconsolidated sand sidewall core samples. Sidewall data required are a measured porosity and a grain size distribution. Estimated permeability data for 35% of a controlled group of samples correlated within 10% of measured values. Ninety-seven percent of the control group estimated permeabilities correlated with measured data within a factor of 2. Estimated data fell both higher and lower than measured data, removing the erroneous low bias of sidewall measured data.

Therefore, the data base estimated permeabilities for altered sidewall cores provide values more representative than measured values and furnish improved data for formation characterization and evaluation.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.