Improving Chemical Flood Efficiency With Micellar/Alkaline/Polymer Processes

Abstract

Summary A laboratory study was undertaken to find more efficient, lower-cost chemical systems for the recovery of waterflood residual oil. Our investigation emphasized alkaline-augmented processes because alkali is much less expensive than surfactant. The strategy was to replace some of or all the high-cost surfactants in a micellar formulation with lower-cost alkali and still maintain the high tertiary oil recoveries obtained with micellar flooding. Baseline oil recoveries in Berea corefloods were determined for two interfacially active crude oils with micellar/polymer (MP) and alkaline/polymer (AP) systems. A combination process was then developed in which a small micellar slug is injected first, followed by a larger AP slug. This process is referred to as a micellar/alkaline/polymer (MAP) flood. Phase-behavior studies guided the design and optimization of all three chemical processes in the coreflood experiments. Detailed effluent analyses and in-situ mobility measurements provided information about possible oil recovery mechanisms. Well-designed MAP systems recovered more possible oil recovery mechanisms. Well-designed MAP systems recovered more than 80% of the waterflood residual oil, comparable to the best MP systems These recoveries were achieved with only one-third the surfactant and cosurfactant required in the MP system. AP systems recovered less oil than either the MAP or MP systems. The chemical efficiency (ratio of the total chemical cost to oil recovered) of the MAP systems was better than the efficiency of the MP systems and comparable to that of AP systems. Similar results were obtained for both crude oils. Introduction Micellar flooding has received much attention in laboratory studies and field tests in recent years. This process is attractive because the displacement efficiency of an effective micellar flood can be almost 100% in zones swept by surfactant. However, this EOR process has yet to be implemented on a commercial scale because process has yet to be implemented on a commercial scale because of economic considerations. A recent Natl. Petroleum Council study I of EOR in the U.S. projects that the production from chemical flooding with current technology will be only 17% of production from all EOR processes. Micellar flooding alone is not likely production from all EOR processes. Micellar flooding alone is not likely to begin widespread application until the 1990's and will account for only 14% of future EOR. One major impediment to the commercialization of micellar flooding is the high cost of the surfactant and cosurfactant required to mobilize the residual oil in the reservoir. In this paper, our objective is to reduce the amount of surfactant needed for an effective chemical flood. Specifically, we investigated the use of inexpensive alkaline agents as substitutes for the more expensive surfactant chemicals. The results of this study are used to compare the performance and characteristics of the combined surfactant/alkaline performance and characteristics of the combined surfactant/alkaline process with that of surfactant and alkali alone. Others have reported a beneficial synergistic effect from combining surfactant and alkali in a chemical flood. When properly designed, adding surfactant to the alkaline slug can increase oil recovery significantly in laboratory corefloods. With polymer included for mobility control, the oil recovery can be as high as that obtained with a conventional micellar flood. Some authors suggest that the proper combination of these chemicals lowers interfacial tension (IFT) and reduces surfactant adsorption. Other possible benefits from alkali include a favorable change in wettability possible benefits from alkali include a favorable change in wettability and enhanced mobility control from the creation of emulsions. Two California crude-oil/brine systems (denoted A and B) were selected for this laboratory study. Initial work identified an MP system that displaced Oil A well in laboratory coreflood tests. Similar experiments with Oil B and an AP system showed that this process effectively displaced this higher-acid-number crude oil. The next stage of our investigation focused on combining alkali and surfactant to improve the oil recovery and chemical efficiency for both candidate reservoirs. The objective for Reservoir A was to maintain the high recovery obtained for the existing MP design, but with a significant decrease in the amount of expensive surfactant and cosurfactant. The objective for Reservoir B was to improve significantly upon the oil recovery for alkaline or AP floods by adding a minimal amount of surfactant. As a result, an improved MAP process was designed for both reservoirs.