Loudon Surfactant Flood Pilot-Overview and Update

Abstract

Abstract A successful surfactant (microemulsion) flood pilot test in a watered-out portion of the Weiler pilot test in a watered-out portion of the Weiler sand, Loudon Field, Illinois (USA) was completed in October, 1981. The microemulsion system tested was designed to be effective in the presence of high-salinity formation water containing 104,000 ppm (mg/l) total dissolved solids (TDS) without use of a preflush. The test was conducted in a single, 0.68-acre preflush. The test was conducted in a single, 0.68-acre (2752 m2) 5-spot operated in a manner that approximated a confined pattern. The test was highly successful, recovering 60% of the oil remaining after waterflood. Cores from a post-flood well drilled within the pattern have confirmed the low final oil saturations and low surfactant retention achieved in the flood. Although oil recovery was excellent, loss of nobility control in the polyner drive bank and premature breakthrough of lower-salinity drive water premature breakthrough of lower-salinity drive water were observed part-way through the test. Laboratory and field studies conducted since flood termination have confirmed that loss was caused by bacterial degradation of the xanthan biopolymer used. Several biocides were tested in the laboratory and in a field injection experiment to determine their effectiveness against the bacteria contaminating the pilot. Formaldehyde was shown to kill bacteria within the formation, have negligible adsorption on reservoir rock, and permit propagation of undegraded polyner. Based on these test results, formaldehyde should protect xanthan biopolymer from bacterial degradation in future microemulsion floods at Loudon. Introduction Exxon is conducting a field pilot program to evaluate the potential of a microemulsion flooding process which can be used in high-salinity reservoirs process which can be used in high-salinity reservoirs without a brine preflush. Since the bulk of tertiary target oil amenable to surfactant flooding exists in reservoirs having brine salinities greater than 30,000 ppm (ng/l) TDS (defined here as "high salinity"), considerable incentive exists to develop such a process. Use of a preflush has certain disadvantages: flood life is extended, which increases operating costs; the preflush nay not contact all reservoir rock later contacted by lower-mobility micellar/polyner fluids, thereby reducing process performance; and large volumes of low-salinity water performance; and large volumes of low-salinity water nay not always be available for use in a preflush process. process. The pilot test was conducted in the Loudon Field, Fayette county, Illinois (USA). The reservoirs in this field are Mississippian Chester sandstones ranging in depth from 1400 to 1600 ft (427 to 488 n) subsurface. As shown in Table 1, the formation water contains about 104,000 ppm (ng/l) TDS including over 4000 ppm of divalent ions. Reservoir temperature is 78 deg. F (25.6 deg. C), oil viscosity is 5 cp (5 mPa s), and formation porosity averages about 19%. The Loudon reservoirs are in an advanced stage of depletion after 13 years of primary production and 31 years of water-flooding. It is estimated that at the economic limit of waterflooding slightly more than half of the OOIP will remain trapped as residual oil. Bragg et al. previously reported details of the pilot test, which was located on the Lewis Ripley pilot test, which was located on the Lewis Ripley lease in the Loudon Field (see Fig. 1). The test was conducted in a single, normal 5-spot pattern of 0.68 acres (2752 n2) operated in a manner to approximate a confined 5-spot. Fig. 2 shows the pilot well pattern at the reservoir sand depth of 1550 ft (472.4 n). In addition to the four injectors and central producer, the pattern contained five fiberglass-cased logging observation wells to allow use of induction and carbon/oxygen logs to monitor changes in oil saturation during the flood. The test was conducted in a small pattern to permit completing a field evaluation within a two-year permit completing a field evaluation within a two-year period and rapidly integrating results into an ongoing period and rapidly integrating results into an ongoing research program. P. 537