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CO2-Eor 101: An Overview of CO2 Enhanced Oil Recovery

Ian J. Duncan, Enhanced Oil Recovery: Legal Framework for Sustainable Management of Mature Oil Fields

CO2-EOR is sometimes referred to as tertiary oil production. In this sense primary production phase occurs when a new oil reservoir is discovered and the initial production is driven by the energy provide by the pressure of the oil and in some cases, natural gas. For oil close to saturation in natural gas, as the reservoir pressure decreases this gas exsolves (referred to by industry as the bubble point) with a sudden increase in viscosity of the oil and drop in production of the well. Where the oil is strongly under-saturated with gas, the reservoir pressure can decrease substantially before injection of fluids for pressure maintenance is required to prevent this effect. As the reservoir pressure gets lower and the flow rate of wells decrease, “artificial lift” may be employed to get oil to the surface and prolong production. At some point decreasing production and the cost of lifting the oil make primary production uneconomic. At this point as little as 10%, or as much as 70 or 80%, of the original oil in place (OOIP) may remain in the reservoir. In the majority of oil fields 50 to 70% of the original oil remains. Such fields may be a suitable target for secondary production strategies, the most common of which is water flooding.

In secondary production new wells are drilled to injection water, typically in the center of a cluster of four or more production wells. In