Does Solvent Injection Enhance In-Situ Combustion of Viscous Oils?

Abstract

Abstract Application of cyclic solvent injection into heavy and viscous crude oil followed by in-situ combustion of heavy residues is explored from a laboratory perspective. The solvent reduces oil viscosity in-situ and extracts the llighter crude-oil fractions. Combustion cleans the near well region as well as thermally stimulates production. Both solvent injection and in-situ combustion are technically effective. The combination of the two methods has, however, never been tried to our knowledge. Hamaca (Venezuela) and West Sak (Alaska) crude oil were employed. First, ramped temperature oxidation studies were conducted to measure the kinetic properties of the oil prior to and following solvent injection. Pentane, decane, and kerosene were the solvents of interest. Second, solvent was injected in a cyclic fashion into a 1-m long combustion tube. Then, the tube was combusted. Hamaca oil presented good burning properties in all cases. The pentane extracted lighter components of the crude prefferentially depositing effective fuel for combustion. West Sak oil, however, did not exhibit stable combustion properties following solvent injection, even when metallic additives were added to enhance the combustion. We were unable to propagate a burning front within the combustion tube. Nevertheless, the experimental results show that this combined solvent-combustion method is applicable to a broad range of oil reservoirs. Introduction This article investigates the effect of solvent injection on the subsequent performance of in-situ combustion. The work is based on experimental results obtained with a combination of these two successful in-situ upgrading processes for viscous oils. By mixing with oil, the solvent decreases the oil viscosity and upgrades the crude by depositing in-situ the heavy ends. A large part of the oil's light ends are recovered and the heavy ends that are markedly less interesting are left behind. The solvent injection in then followed by an in-situ combustion. The latter burns the heavy ends left from the solvent injection and enhances the production by decreasing the oil viscosity. The combustion also upgrades the oil through thermal cracking. For our experiments, two oils of particular interest within the scope of our study were used. The first set of experiments employed crude oil from Hamaca (Venezuela) where the field location requires important costs of transporting crude to upgrading facilities. The second set was conducted with West Sak oil (Alaska) where steam injection currently appears to be unsuitable because of permafrost. While the presence of oil in the Orinoco heavy-oil belt, in Central Venezuela, has been known since the 1930's, the first rigorous evaluation of the resources were made in the 1980's and the region was divided into four areas: Machete, Zuata, Hamaca, and Cerro Negro. It contains between 1.2 and 1.8 trillion recoverable barrels[1] of heavy and extra-heavy oil. The 9–11º API density crude is processed at the Jose refinery complex on the northern coast of Venezuela. The cost of transporting heavy oils to the northern coast provides an incentive to investigate how in-situ upgrading can decrease these downhill costs. In 2003, the total production from these projects was about 500,000 bbl/d of synethetic crude oil. This figure is expected to increase to 600,000 bbl/d by 2005.[2]