Effects of Wormhole Configurations on Performance of Cyclic Solvent Injection in Heavy Oil Systems

Abstract

In this study, the effect of three different wormhole configurations: single-linear, single-branched, and double-branched wormholes on the performance of cyclic solvent injection was investigated through extensive experimentation. A 2D rectangular sand-packed model with porosity and permeability of 31.96–33.2% and 4.3–10.4 d and heavy oil sample of viscosity 4440 mPa.s at T = 21 °C were used to represent a typical thin post-cold heavy oil production, respectively, with sands (post-CHOPS) reservoir. First, a series of cyclic solvent (15% C3H8–85% CO2) injection tests were carried out under operating injection pressure of Pinj = 730 kPa. After termination of each test, the residual oil saturation distributions on the top and middle layers of the sand-packed model were determined through additional tests. Thereafter, the double-branched wormhole network was subjected to another cyclic injection of 15% C3H8–85% CO2 to investigate the effect of a lengthier soaking time. The experimental results showed an improved heavy oil recovery factor (RF) (attributed to foamy oil phenomenon) as the number of wormhole branch increases. Therefore, better performance of CSI process was ascribed to larger wormhole coverage in the sand-packed model. The residual oil saturation profile also confirms this as larger wormhole coverage is required to produce oil during CSI process. However, lengthier soaking time in the presence of double-branched wormhole improved the incremental production of the early cycles, and increased the ultimate oil RF from 43.46 to 47.06% original oil in place. The findings of this paper further iterate the role of wormhole multi-branching systems in post-CHOPS reservoirs on the application of CSI schemes as a follow-up technique.