A Field Test of Surfactant Flooding, Loudon, Illinois

Abstract

Illustrated here are procedures that were used to interpret a pilot test of tertiary recovery employing an aqueous solution of petroleum sulfonates. Information derived from a comprehensive tracer program indicated that the effectiveness of the recovery process was reduced by an excessive mixing of surfactant solution with high-salinity formation brine. Introduction One of the more difficult phases in the development of any new oil recovery process is the design, implementation, and interpretation of pilot tests. Such tests are usually quite expensive, yet represent only one of the many possible sets of operating conditions. Consequently, the operator should take every possible precaution to choose an optimum set of conditions precaution to choose an optimum set of conditions and to design a pilot that provides maximum opportunities for interpretation. Previous laboratory work had pointed to the effectiveness of surfactants of the type described in the patent literature for use in improved secondary or patent literature for use in improved secondary or tertiary recovery applications. Laboratory studies of these materials had ranged from detailed chemical investigations to floods in reservoir cores, as well as linear and areal models cut from outcrop rock samples. Interspersed with the laboratory studies were field tests that evaluated the injectivity of surfactant systems and pattern oil recovery. This paper describes a surfactant pilot test conducted in a watered-out portion of the Loudon field, Illinois, during the period 1969-1971. In addition to having the usual goal of determining the level of operability in this field, the test was specifically designed to determine (1) the extent of surfactant adsorption-fractionation and the resulting effect on oil recovery, (2) the degree of mobility control achieved and its effect on sweep efficiency and oil recovery, and (3) any additional problems not uncovered in the relatively simple laboratory systems. Process Development Process Development The properties of Loudon crude are such that the only surfactants found that gave acceptable interfacial tensions exhibited excessive adsorption as well as low salinity and divalent ion (calcium and magnesium) tolerance. Fortunately, the clay type and content of Loudon rock are such that adsorption levels did not appear prohibitive. Low salinity tolerance necessitated the use of fresh injection water with the surfactant and a low-salinity preflush to protect the surfactant from contacting high-salinity (104,000 ppm total solids) formation water. Divalent ion protection could be accomplished by either complexing or precipitating these ions. However, high costs associated with complexing agents suggested that the only practical solution would be precipitation with an inexpensive salt such as sodium carbonate. Laboratory data suggested that permeability reduction associated with such precipitation would not be severe. A dualbase system was developed so that divalent ion protection would be provided by sodium carbonate, while the majority of the rock base consumption would be satisfied by a less expensive material, ammonia. The surfactant used in the test was Feed D (SO3) sulfonate described elsewhere. JPT P. 793