Global Laboratory Experience of CO2-EOR Flooding

Abstract

Abstract Primary and secondary drive oil production mechanisms are coming short in meeting the ever increasing global oil demand. Currently, many tertiary recovery-EOR projects are in the design or implementation stage in many parts of the world to help meeting this extra global oil demand. Good number of these projects involves certain kinds of CO2 gas injection. To help match the technical results of these projects and their economic viability under the current oil prices, the industry should learn from the lessons of the available global field, pilot and laboratory technical evaluation experiences. This is to avoid unnecessary losses in time and money and to make the best incremental oil recovery possible. To master the performance of CO2 flooding and provide accurate data for designing an oil development plan, a comprehensive investigation of CO2 flooding phase behavior and mechanisms based on laboratory study needs to be conducted. This is a challenging prospect technically and economically. The results of a large number of CO2 gas injection laboratory technical evaluations have been reported in the literature. This paper tries to give a serious and comprehensive review of the past global experience of laboratory CO2-EOR flooding, and reports the best practices of laboratory technical evaluations and to highlight the uncertainties and limitations of these evaluations. A large number of technical papers were reviewed to describe the laboratory experiments that are most performed for CO2 flooding evaluation. The main issues that could be addressed using laboratory technical evaluation are covered including PVT properties of different CO2-Oil mixtures, effect of Rock Pore Structure on CO2 Miscible Displacement, effect of WAG and Wettability on CO2-EOR Flooding, assessment of Asphaltene Deposition, and effect of Slug Size on Oil Recovery by CO2 Miscible Flooding and finally CO2 flooding in naturally fractured reservoirs. Finally, the paper reports on the proper utilization of any attainable laboratory data and its limitations. 1. Introduction Oil recovery factor (RF) is usually broken as a product of macroscopic or volumetric displacement efficiency, EV, and microscopic displacement efficiency, ED. The macroscopic displacement efficiency, EV is a measure of how effectively the displacing fluid contacts the volume of a reservoir both areally (EA) and vertically (EI). It is governed by the reservoir heterogeneities, well patterns, and differences in the fluid properties of the displacing and displaced fluids 1. Microscopic displacement efficiency, on the other hand, relates to the displacement or mobilization of oil at the pore scale. It is a measure of the effectiveness of injected fluid to mobilize the oil from the pores in the rock where the injected fluid has contacted the oil. There are many factors that affect the microscopic displacement efficiency, including: reservoir pressure and temperature, oil composition, fluids phase behavior and properties, saturation history of rock-fluid system, diffusion, solvent flow rate and residence time, slug size, dispersion, dead-end pore volume, and rock pore geometry and structure 1. There is a limitation on what can be done about the naturally occurring reservoir heterogeneities such as anisotropy and layered heterogeneities. Oil recovery could be improved, however, by optimizing well patterns, well placements, and drilling new wells. The choice of the fluid in any EOR process, on the other hand, should control the injected EOR fluid/produced oil mobility ratio, viscosity ratio, density differences, and interfacial tensions in a way to improve both the volumetric sweep and the microscopic displacement efficiencies.