The Alcohol Slug Process for Increasing Oil Recovery

Abstract

The primary purpose of this investigation was to define the basic mechanism of the miscible displacement of oil and water from porous media by various water-driven alcohol slugs. The first portion of this investigation deaIt with use of a single alcohol (isopropyl) as the slug material. In later studies two distinct process variations were developed, wherein the total alcohol slug consisted of two or more slugs of different alcohols. The first of these utilized methyl alcohol and isopropyl alcohol, while the second variation used normal butyl alcohol and methyl alcohol as the composite slug. These techniques were shown to have distinct advantages over the simple, onealcohol process and represent an important extension of the original process. The porous medium used in this study was I-in. diameter, 100-ft long, unconsolidated core. The porosity of this system was 35 per cent, and the permeability was approximately 4 darcies. Total pore volume of the core was 5,700 cc. All displacements were conducted at an injection rate of 5 to 6 cc/min, which corresponded to a frontal advance of 5 to 6 ft/hr. Most of the alcohol slug runs were initiated in a previously waterflooded system; however, several were conducted at irreducible water saturation. The oils used were naphtha, SoItrol-C and Kendex 0837, having viscosities of 0.52, 1.5 and 16 cp at 20°C, respectively. Kendex 0837 was used in only one run. Individual displacements were conducted by injecting the desired size and type of alcohol slug, which was then driven or displaced in turn by water. The basic data obtained from each run were the composition-time histories of the effluents. From these data it was possible to study the displacement mechanism and to determine the oil recovery. Data from 30 such runs were obtained. In the first series of runs, isopropyl alcohol (IP A) was used as the alcohol slug. This alcohol is completely miscible with either oil or water; however, miscibility of the three-component system (oil-water- IP A) requires a relatively high concentration of IP A. Hence, the displacement is not of the miscible type unless the IP A content is maintained above some critical value. Slug volumes ranging from 8 to 16 per cent of total core pore volume were used in several runs in both the naphtha and Soltrol-C systems. Complete (100 per cent) naphtha recovery from a previously waterflooded core required a 13.5 per cent IP A slug. Complete SoItrol recovery required a 17 per cent slug under the same conditions.