Simulation study and economic analysis of steam-assisted vapor extraction for heavy oil recovery in thin reservoirs

Abstract

Solvent-based recovery processes such as vapor extraction (VAPEX) showed a potential to produce heavy oil resources from thin reservoirs. However, their practical application is rather limited due to their low oil production rate. The main reason is a small heavy oil-solvent diffusivity that depends largely on the heavy oil viscosity. Previous studies showed that the heavy oil viscosity can be greatly reduced by increasing its temperature. This study proposes a steam-assisted solvent vapor extraction process to improve heavy oil production. This new process produces heavy oil in a cyclic manner. Each cycle contains a very short steam-injection period and a relatively long solvent-injection period. Steam is first injected at a certain pressure and temperature, which is intended to heat the heavy oil not far away from a chamber boundary. Solvent is then injected to dissolve into the heated and less viscous heavy oil around the chamber. Field-scale simulation results show that first, elevating the temperature of heavy oil beyond a chamber boundary slightly (e.g., from 20 °C to 70 °C) can greatly boost the diffusivity between oil and solvent and thus increase the solvent penetration depth and solvent injectivity. Then, as a typical result, the oil production rate of the new process is about 12.2 times that of a pure cold solvent injection process at an expense of just 2.6 times the solvent usage, and its performance is especially outstanding in a thin heavy oil reservoir. Moreover, even compared with steam-assisted gravity drainage (SAGD), the performance of the new process is very promising; it achieves 1/3 of the oil production rate of SAGD with just 1/8 of the cumulative steam-oil ratio of SAGD.

Keywords

• Cyclic process
• VAPEX
• SAGD
• Steam
• Solvent
• Temperature elevation