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原文传递 IMPROVED EFFICIENCY OF MISCIBLE CO2 FLOODS AND ENHANCED PROSPECTS FOR CO2 FLOODING HETEROGENEOUS RESERVOIRS

题名：	IMPROVED EFFICIENCY OF MISCIBLE CO2 FLOODS AND ENHANCED PROSPECTS FOR CO2 FLOODING HETEROGENEOUS RESERVOIRS
作者：	Reid B. Grigg David S. Schechter
关键词：	flooding；prospect；improved；ects；misc；permeability；fici；nced；gene；saturation
摘要：	The goal of this project is to improve the efficiency of miscible CO2floods and enhance the prospects for flooding heterogeneous reservoirs. This report provides results of the first year of the three-year project that will be exploring three principle areas: • Fluid and matrix interactions (understanding the problems): interfacial tension (TFT), phase behavior, miscibility, capillary number, injectivity, wettability, and gravity drainage. • Conformance control/sweep efficiency (solving the problems): reduction of mobility using foam, diversion by selective mobility --eduction (SMR) using foam, improved injectivity, alternating water and gas injection, and using horizontal wells. • Reservoir simulation for improved oil recovery (predicting results): gravity drainage, SMR, CO2- foam flooding, IFT, injectivity profile, horizontal wells, and naturally fractured reservoirs. The study of the effect of oil saturation on foam showed that in a single, relatively homogeneous core, C02-foam improves CO2 breakthrough time and oil recovery. In composite core samples with two permeability regions parallel to the flow direction, the C02-foam systems significantly improved the CO2 sweep efficiency in the low permeability region compared with similar runs when CO2 alone was used. When foam was used as a displacing agent, breakthrough time of CO2 was substantially delayed in the high permeability region in both isolated and communicating composite core systems. During oil displacement, foam improved sweep efficiency by a diversion of CO2 from the high permeability to the low permeability region. A foam flood is more effective in assisting oil recovery in an isolated coaxial core system than in a capillary contact core system. Mixed surfactant foaming agents were tested to set if mixtures were detrimental or synergistic when analyzing foaming properties, and as a prelude to the search for effective, inexpensive sacrificial agents to be used to satisfy reservoir rock adsorption requirements. Mixed systems were found that demonstrated substantial mobility reduction and favorable selective mobility reduction when coinjected with CO2. A mixture of an anionic alpha olefin sulfonate and an anionic ethoxylated alcohol sulfate was tested that generated a more stable foam than its individual components. One mixture of a nonionic and an anionic surfactant was found to have better foaming stability, mobility reduction and SMR than the anionic surfactant alone. Studies of surfactant foam quality were performed during this first year. The effect of CO2 fraction on the total mobility of C02-brine (non-surfactant system) was inconclusive, but had an apparent minimum between CO2 fractions of0.333 and 0.667 and increased with increasing flow rate. The total mobility of CO2-surfaciant solution decreased with increasing foam quality and increased with increasing flow rate. Thus, the foam resistance factor increased with increasing foam quality and decreased with increasing flow rate. Simulation studies on a foam pilot area resulted in an acceptable history match model. The simulated results of the foam test simulation were consistent with the foam pilot test results. The foam model was found to be adequate for field scale C02-foam simulation. The results confirm that the communication path between the foam injection well and a production well had a strong impact on the production performance. A laboratory study to aid in the development of a gravity drainage reservoir was undertaken on the Wellman Unit. Reservoir performance, slim tube, large-diameter tube and gravity-stable corefloods in Wellman Unit whole core at reservoir conditions demonstrate excellent displacement efficiency with Sor after less than 10% CO2. The MMP of Wellman Unit oil is 1600+/- 50 psig over a range of GORs from 150 to 600 scf/bbl. Reducing the pressure from above the MMP to near the MMP and below the MMP does not reduce efficiency in laboratory coreflooding. The data suggests the bottomhole pressure could be reduced from the current level of above 2000 psig to near the MMP of 1600 psig with no reduction in displacement efficiency. The reduction in CO2 purchases would be a positive benefit from this strategy. The reduction in reservoir pressure, however, is constrained by voidage replacement issues. Gravity-stable coreflooding results, from transition zone core taken from the Wellman Unit, demonstrate that oil not mobilized by water influx in the transition zone can be effectively mobilized with CO2 0ver a range of injection pressures. Experiments were begun meant to duplicate situations of injectivity loss in WAG flooding and identify factors affecting the injectivity loss. Initially, four cores were tested. The preliminary results indicate that for a given rock the injectivity loss depends on oil saturation in the core during WAG flooding. The injectivity loss is higher in cores with high in-situ oil saturations during WAG flooding. This effect is being verified by more experimental data.
报告类型：	科技报告