A Computer Analysis Of Shaly Sands Using Multiple Porosity Logging Devices

Current techniques of evaluating shaly sands require an assumption regarding the manner of occurrence of the argillaceous material. This paper describes an approach where this is no longer necessary providing the total responses can be adequately described. The solution of a system of linear equations representing the neutron, density, and velocity log responses, plus an additional equation based upon the SP or gamma ray, appears to provide a satisfactory solution for the evaluation of effective porosity. The shaly sand model is not an explicit solution for the quantities of shale, sand, clay and porosity but a trial and error procedure. The proposed procedure allows the consideration of more than one type of clay, flushed zone gas saturation, and another mineral component. The results of these calculations are not specific quantities but rather a range of values for porosity, shale and clay percentages. The values of porosity computed by the technique have been found to be relatively insensitive to clay type, matrix velocity, and compaction correction. The compaction correction coefficient does affect the computed percentages of shale and clay, however.