Selection of optimal EOR for extra-heavy crude oil displacement from low-permeability reservoirs

The rapid decline in the number of conventional oil fields has been a global problem in recent decades, making the development of hard-to-recover reserves of heavy oil a priority task. Currently, the main methods that are being used for heavy oil recovery are thermal methods, such as injection of hot water, steam flooding, steam-assisted gravity drainage (SAGD), cyclic steam stimulation (CSS), and in-situ combustion (ISC). It is essential to select an efficient technology for the additional oil recovery after a prolonged interaction between the hot agent and the rock. An alternative method to increase oil recovery after heat treatment is a solvent injection, which aims to dissolve high molecular weight components and increase oil flowability. The main purpose of the study was to select the optimal sequential combination of thermal and non-thermal EOR for the maximum possible recovery of extra-heavy crude oil (EHCO). The effectiveness of the technology was assessed using 1-D physical modeling of the oil displacement process on a core model under reservoir conditions and subsequent analysis of the displaced fluid. The experiment was took place in several consecutive stages: injection of hot water, injection of steam, and additional oil displacement by injection of the solvent slug and water. The exposure of thermal methods reduced oil viscosity by 23 times and achieved an oil recovery factor (RF) of 40.2 %. Consecutive injection of solvent slug and water at the final stage allowed significantly increasing the RF by 38.5 % and reduces the content of high-molecular weight components. According to the results of the filtration experiment gas permeability of the core model increased by 9.5 times. Thus, the results obtained provide important information to evaluate the application of different EOR on fields with EHCO and confirm the possibility of achieving a high oil RF (78.6 %) with proper project design.