MECHANISMS FOR OIL RECOVERY BY STEAM ALKANE CO-INJECTION
Dan Marchesin | Silva, J. D.
Steam injection is a cheap and widely used method for enhanced oil recovery. However, some portion of oil is not recovered because it remains trapped in the pores of the reservoir after the passage of the injected steam. To increase recovery efficiency, Dietz proposed at the end of the 70’s the co-injection of a small fraction of volatile oil. His intention was that the volatile oil injected ideally would condense with the steam, forming a bank of light oil capable of dissolving and displacing the heavy oil contained in reservoir, improving the recovery. The mechanism that describes this gain is therefore related to the formation of a volatile oil condensation bank that pushes the heavy oil inside the reservoir. We establish a model capable of capturing these effects. It allows describing the behavior of the flow of oil in a uniform porous medium in local thermodynamic equilibrium. To understand the mechanisms that allow the improvement in oil recovery we solve Riemann problems for the conservation laws governing the injection of volatile oil in the reservoir. In this work we will focus in the subproblem of volatile oil gas injection into a porous medium containing oil. The understanding gathered by means of this simplification constitutes a key step towards the understanding of the co-injection problem. Also the injection of light alkane possesses a relevance of its own: during off-shore production it is not always possible to utilize commercially the produced gas. Therefore, this gas can be reinjected into the reservoir to maintain the reservoir pressure. For a combination of initial data and oil parameters we found a “cleaning wave” in which a volatile oil condensation wave arises when it encounters dead oil in the reservoir and pushes it. This is the first time this problem was solved exactly.