This paper evaluates a field test of a low-tension tertiary flooding process using a petroleum sulfonate surfactant. Observation-well data process using a petroleum sulfonate surfactant. Observation-well data showed that with proper formation conditioning and sufficient surfactant the process effectively displaced all oil remaining after waterflood. Over-all production was 25 percent of expected, and various explanations for this performance are discussed. Introduction A regular 2-ha (5-acre), five-spot pilot test of a lowtension waterflood process was undertaken in a previously waterflooded Benoist sand in the Salem field, previously waterflooded Benoist sand in the Salem field, Marion County, 111. Part 1 of this paper presents the process and pilot descriptions, injection and production histories, and associated field operations. The objectives of this paper are to discuss parameters that may contribute to the process effectiveness and to evaluate the oil recovery performance. An accounting is made of flood components that were injected, produced, and retained in the formation. Both measured and predicted responses are reported. The use of tracers in predicted responses are reported. The use of tracers in allocating contributions from the four injectors to the producer and in detecting flow-path changes is described. producer and in detecting flow-path changes is described. Interpretation Techniques A computer model simulating tracer and chemical flooding in a stratified pattern was used to interpret pilot performance data. The reservoir was divided into five performance data. The reservoir was divided into five layers to represent the heterogeneity, and stream tubes were used to account for areal distribution of liquid. Within each layer and tube, flow was considered one dimensional, and crossflow between layers and tubes did no exist. The model incorporated the following features:Chemical transport accounting for dispersion, adsorption, and partitioning.Incompressible flow of aqueous and oil phases, with flow considered high-tension (immiscible) or low-tension (miscible-like) depending on the chemical environment.Non-Newtonian flow of polymer solution and permeability reduction because of polymer adsorption on the permeability reduction because of polymer adsorption on the rock. The following included in the pilot performance evaluation:Analysis of tracer data to verify quadrant flow patterns, fraction of production contributed by each patterns, fraction of production contributed by each quadrant, and vertical reservoir heterogeneity.The effect of the surrounding Benoist injectors and producers in conjunction with the adjacent aquifer. producers in conjunction with the adjacent aquifer.Estimation of chemical consumption based on tracer and chemical breakthrough volumes and concentration profiles at the observation and production wells.Comparison of simulated recovery performance with measured results. Flow Distribution Typical liquid distributions in vertically adjacent, high-and low-permeability flow intervals between one pilot injector and the producer are shown in Fig. 1. Also shown are the positions of the chemical banks at a given time. JPT P. 933
Previously published preliminary evaluations of a low-tension waterflood Previously published preliminary evaluations of a low-tension waterflood pilot reported less-than-expected oil recovery, partly the result of flow pilot reported less-than-expected oil recovery, partly the result of flow path distortion. Based on data from postflood tracer tests, tertiary path distortion. Based on data from postflood tracer tests, tertiary recovery was 37 to 43 % of the oil in the affected reservoir volume. Causes of the distortion and production shortfall are discussed. Complete reservoir definition when designing tertiary floods is necessary. Introduction In 1974, a joint Texaco Inc.-Mobil Research and Development Corp. test to evaluate a low-tension waterflood (LTWF) process was initiated in the Benoist sand at Salem Field, Marion County, IL. The process used a sequence of freshwater preflush, process used a sequence of freshwater preflush, chemical pretreatment, surfactant solution, a mobility-control (polymer) solution, and field brine. Descriptions of the process, its implementation, and preliminary evaluations are found in earlier studies. preliminary evaluations are found in earlier studies. Tertiary oil recovery was less than expected from the original flood plan, and various explanations of the flood performance were proposed. To provide additional information, further testing began in 1976. This paper describes the results of those tests and presents revised evaluations of the Salem LTWF pilot performance. pilot performance. Review To summarize pilot test performance briefly, the Salem LTWF program was designed to provide balanced injection with symmetrical fluid flow distribution in a 5-acre (20 x 10(3) m2), normal five-spot pattern. Four existing backup injection wells on 20-acre (81 x 10(3) m2) spacing (Fig. 1) were used to help confine the injected chemicals to the pilot area and to increase effectiveness of chemicals in the pilot. Studies indicated that 50 % of the injected chemicals should displace tertiary oil to the producing well, with the balance exiting the pattern.Oil recovery was substantially less than expected, only about 25 to 30 % of the recovery predicted using the concept of symmetrical displacement in all pattern quadrants, with recovery factors based on pattern quadrants, with recovery factors based on earlier laboratory investigations. Various explanations for the production shortfall were considered, including lower-than-expected oil displacement efficiency for the chemical system or a smaller pattern reservoir volume that actually was flooded and contributed to oil production. If the tertiary oil originated from a smaller swept reservoir volume, then the recovery efficiency assigned to the process obviously would be larger than that process obviously would be larger than that associated with a larger swept volume. Postflood Tests Postflood Tests To resolve the questions raised in preliminary evaluations, and to define better the amount of tertiary chemicals captured and the reservoir volume contributing to oil recovery, further testing began in 1976. A major goal of the postflood testing program was to ascertain whether flow path distribution was symmetrical (as intended) or distorted. Accordingly, for 1 month different tracers were injected into the respective injectors of the north and south quadrants. Response was measured using producing well samples. JPT P. 1185
Mitchell Energy Corp. has implemented a liquefied petroleum gas (LPG)/drive-gas miscible process in the Alvord (3000 ft Strawn) Unit in Wise County, TX, utilizing the U.S. DOE tertiary incentive program. The field has been waterflooded for 14 years and was producing near its economic limit at the time this project was started.This paper presents the results of the reservoir simulation study that was conducted to evaluate pattern configuration and operating alternatives to maximize LPG containment and oil recovery performance. Several recommendations resulting from this study were implemented for the project. On the basis of model predictions, tertiary oil recovery is expected to be between 100,000 and 130,000 bbl [15900 and 20700 m 3 ] or about 7% of the oil originally in place (OOIP) in the unit.An evaluation of the project performance through Dec. 1981 is presented. This portion of the paper was written after drive-gas injection had just been initiated and represents only a preliminary evaluation of the project. In July 1981 the injection of a 16% hydrocarbon pore volume (HCPV) slug of propane was completed. Natural gas is being used to drive the propane slug. A peak oil response of 222 BID [35.3 m 3 /d] was achieved in Aug. 1981 and production has since been declining. This compares with a peak rate of 400 BID [63.6 m 3 /d] during the waterflood, and an oil rate just prior to initiation of LPG injection of 7 B/D [1.1 m 3 /d]. The observed performance of the LPG flood indicates that the actual tertiary oil recovered will reach the predicted value, although the project life will be longer than expected. The results presented in this paper indicate that, without the DOE incentive program, the economics for this project would still be uncertain at this time.
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