A Relationship Between Pore Structure and Residual Oil Saturation in Tertiary Surfactant Floods

Abstract

Photomicrography and mercury porosimetry have been used jointly to determine the pore-size distributions of various sandstone samples. The two curves differed drastically from each other for all samples. Two unconsolidated packs consisting of uniform 250u glass beads and mixed 44-250u beads, respectively, as well as the sinters prepared from them, were also investigated. An index, D, measuring the difficulty of recovering waterflood residuals in tertiary surfactant floods has been constructed from the two different porosimetry curves. Reasonably good correlation porosimetry curves. Reasonably good correlation bas been obtained between D and residual oil saturations found in tertiary surfactant floods. Introduction: This paper presents our first results in a continuing study of pore structure and oil recovery. The problem of how pore structure might influence oil recovery has been discussed by several authors. There is, however, no known method whereby one could rank various porous media (e.g., different sandstones) on the basis of pore structure in the order of decreasing amounts of expected residual oil saturations assuming identical conditions of flooding (identical oil, water, wetting and pressure gradient for the various sands. In this pressure gradient for the various sands. In this work we have taken an initial step toward this ideal objective. The prime target of the treatment has been the problem of correlating the extent of recovery of waterflood residuals by tertiary surfactant floods with the pore structure. The degree of difficulty presented by the pore structure in the way of recovering the isolated oil masses left behind by a waterflood has been expressed in the form of an index that is calculated from a mercury porosimetry and a photomicrographic pore-size distribution curve obtained on the sample. pore-size distribution curve obtained on the sample. The degree of correlation obtained amounts to a promising start in the case of tertiary surfactant promising start in the case of tertiary surfactant floods, and there also appears to be some correlation between the residual oil saturations found in the waterfloods and the pore structure. In this paper we are considering only the case of water-wet formations and moderate viscosity ratios.