Enhanced Oil Recovery Through the Use of Chemicals-Part I

Abstract

Distinguished Author Series articles are general, descriptivere presentations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleumengineering. Introduction Chemical enhanced oil recovery (EOR) includes processes in which chemicals are injected to improve oil recovery. Chemical methods are one of three categories of EOR, the others being thermal and miscible. Table 1 shows the different processes in these categories as defined by the Crude Oil Windfall Profit Tax Act of 1980. A comparison of field project activity in the three categories is shown in Table 2. Thermal activity is the highest, followed by chemical. Note that the number of chemical projects more than doubled between 1980 and 1982. Miscible CO2 injection accounts for most of the miscible category. Projects in the chemical category of Table 2 are broken down further in Table 3 in terms of the three chemical EOR methods. Micellar/polymer projects are those in which surfactant is injected into the formation. Projectsare those in which surfactant is injected into the formation. Polymer projects refer to a spectrum of uses including near-wellbore Polymer projects refer to aspectrum of uses including near-wellbore treatments, complete polymer-augmented water floods, and a combination of both. Caustic refers to projects where alkaliis injected to increase pH and to produce surfactants in situ. With all three chemical EOR methods, activity has increased significantly between 1980 and1982. In Part 1, each of the three chemical methods is discussed separately. The history of each method is presented along with field projects and laboratory developments. In Part 2 (to appear next month), reservoir heterogeneities are considered in relation to their effect on process performance. Next, information is presented on chemical flooding performance. Next, information is presented on chemical flooding simulators, and procedures are described for their use. Then, U.S. government incentive programs and their effect on chemical EOR development are considered. Finally, the risk vs. reward associated with chemical EOR is illustrated by some economic calculations. Micellar/Polymer Flooding Two kinds of surfactant systems are being developed for this chemical method. Work on the first system began in the late 1920's; it involves a largePV (up to 50%) of a low concentration (less than 2.5%) active surfactant solution. This development has led to the so-called low-tension water flood process. Most often, polymer is used in the surfactant solution to increase itsviscosity, thereby giving mobility control to the system. Development of the second system began in the late 1950's. Here a small PV (5 to 15%) of a high-concentration (5 to 12%) active surfactant is used. The small-PV development led to patent processes such as Mara flood (TM) and Uniflood (TM). Both systems are followed by polymer solution for mobility control. During the1960's and early 1970's, surfactant/polymer field tests in the U.S. mostly used single-pattern well configurations. The area covered in these projects was relatively small. For example, 3/4-acre pilot tests with one injector and four producers were not uncommon. JPT p. 1581