Field Test of an Aqueous Surfactant System For Oil Recovery, Benton Field, Illinois

Abstract

In this pilot study, which involved drilling five process wells, three observation wells, and four evaluation core holes, there were four injection phases: 1. a preflood, 2. a slug of chemical solution, 3. a drive solution, and 4. a fresh-water flood. Although the oil cut in the pilot increased appreciably, the chemical system would have to be modified pilot increased appreciably, the chemical system would have to be modified for commercial application of the process. Introduction A tertiary process for recovering oil left by conventional waterflooding has been applied in a 1-acre pilot in the Benton field, Franklin County, III. The pilot was a five-spot pattern with three observation wells drilled around one injection well to provide data for early evaluation of the process (see Fig. 1). The process tested in the pilot consisted of four injection phases: 1. a preflood of low-salinity water to displace the high-salinity formation water from the vicinity of the injection wells; 2. a slug of chemical solution that contained a surfactant 3. a controlled-mobility drive solution 4. an ordinary waterflood with fresh water. The chemical slug used in Phase 2 was based upon work by Hill et al., carried out in the Shell Development Co. Bellaire Research Center. Adsorption and mobility experiments in small Benton cores provided the technological design requirements for the chemical system. However, both technological and economic factors were considered in arriving at the final design. During the operation of the pilot, one of the injectors experienced poor receptivity and was abandoned before significant chemical was injected. After the four phases had been injected, four core holes were cored through the objective zones and swab-produced to provide data on reservoir conditions. Reservoir Characteristics The Tar Springs sandstone in the Benton flood unit is a northwest-southeast trending distributary channel bordered on both sides by delta fringe deposits. The 1-acre pilot site was located in the fringe portion in the southern part of the field (see Fig. 2). Only the upper 20-ft sand interval was included in the chemical pilot, with impermeable layers separating this interval pilot, with impermeable layers separating this interval from the remaining sand, This site was selected because of suitable sand thickness, low-permeability layers above and below the sand representing layering in much of the field, and sand quality representative of most of the field. Restriction of the test to the 20-ft interval reduced the cost of the project and the time required to complete the test. The interval selected for the pilot can be sub-divided into three zones on the basis of sedimentary features, average permeability, and frequency distribution of permeability. The upper zone (Zone A) averages 8 ft in thickness and consists of ripple-bedded, very fine-grained sandstones; the middle zone (Zone B) averages approximately 4 ft in thickness and consists of medium-scale, cross-bedded, fine-grained sandstone; the lower zone (Zone C) averages 10 ft in thickness and is similar in appearance to Zone A. These three zones appear in the same order in all wells at the pilot site. Porosity averages about 17 percent. Pore volume in Zone B was 4,970 bbl. JPT P. 195