Improving CO2 Efficiency for Recovering Oil in Heterogeneous Reservoirs

This document is the First Annual Report for the U.S. Department of Energy under contract No., a three-year contract entitled: ?Improving CO2 Efficiency for Recovering Oil in Heterogeneous Reservoirs.? The research improved our knowledge and understanding of CO2 flooding and includes work in the areas of injectivity and mobility control. The bulk of this work has been performed by the New Mexico Petroleum Recovery Research Center, a research division of New Mexico Institute of Mining and Technology. This report covers the reporting period of September 28, 2001 and September 27, 2002. Injectivity continues to be a concern to the industry. During this period we have contacted most of the CO2 operators in the Permian Basin and talked again about their problems in this area. This report has a summary of what we found. It is a given that carbonate mineral dissolution and deposition occur in a formation in geologic time and are expected to some degree in carbon dioxide (CO2) floods. Water-alternating-gas (WAG) core flood experiments conducted on limestone and dolomite core plugs confirm that these processes can occur over relatively short time periods (hours to days) and in close proximity to each other. Results from laboratory CO2-brine flow experiments performed in rock core were used to calibrate a reactive transport simulator. The calibrated model is being used to estimate in situ effects of a range of possible sequestration options in depleted oil/gas reservoirs. The code applied in this study is a combination of the well known TOUGH2 simulator, for coupled groundwater/brine and heat flow, with the chemistry code TRANS for chemically reactive transport. Variability in response among rock types suggests that CO2 injection will induce ranges of transient and spatially dependent changes in intrinsic rock permeability and porosity. Determining the effect of matrix changes on CO2 mobility is crucial in evaluating the efficacy and potential environmental implications of storing CO2 in the subsurface. Chemical cost reductions are identified that are derived from the synergistic effects of cosurfactant systems using a good foaming agent and a less expensive poor foaming agent. The required good foaming agent is reduced by at least 75%. Also the effect on injectivity is reduced by as much as 50% using the cosurfactant system, compared to a previously used surfactant system. Mobility control of injected CO2 for improved oil recovery can be achieved with significant reduction in the chemical cost of SAG, improved injectivity of SAG, and improved economics of CO2 injection project when compared to reported systems. Our past work has identified a number of mobility control agents to use for CO2-foam flooding. In particular the combination of the good foaming agent CD 1045 and a sacrificial agent and cosurfactant lignosulfonate. This work scrutinizes the methods that we are using to determine the efficiency of the sacrificial agents and cosurfactant systems. These have required concentration determinations and reusing core samples. Here, we report some of the problems that have been found and some interesting effects that must be considered.

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