ABSTRACT

The Fry In Situ Combustion Test was conducted in a 3.3 acre site in the Robinson sandstone. Six observation wells were cored through the reservoir during various stages of expansion of the combustion front. These cores were sampled for porosity, permeability, grain density, formation factor, saturation exponent, residual fluids, and clay content. These data and core examination show the reservoir consists of three sandstone units, each having distinct reservoir properties. Several combinations of logging devices were run in the observation wells to evaluate their effectiveness in tracking the front laterally and in estimating the degree of combustion vertically. Gamma-ray neutron, density, induction, and focused resistivity logs were run open hole in two wells after combustion. Core, GRAPE and density log porosities were compared to neutron-derived porosities and both gas saturation and invaded zone water saturations were calculated. Both methods outline the vertical variations in combustion. In two wells, no logs were run before casing was set. Conventional neutron logs were run through casing but it was necessary to construct departure curves for the conditions encountered. Gas saturations were calculated using the neutron-derived porosities and core or GRAPE porosities. This technique yields a qualitative picture of the vertical combustion distribution. A small diameter neutron device was run through tubing in one well. In this case, the device was run before the front reached the well and again after combustion occurred. This technique permits evaluation of the vertical extent of combustion using just the ratio of the two response curves. Of the combinations listed, the neutron, density and focused-contact resistivity program was most effective in open hole for quantitative determinations of the degree of vertical combustion. In cased holes, the neutron device was satisfactory for picking the burned zone but the logging program was not designed for quantitative interpretation.

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