3D SIMULATION STUDY ON THE PERFORMANCE OF TOE-TO-HEEL AIR INJECTION (THAI) PROCESS IN FRACTURED CARBONATE SYSTEMS

S. M. Fatemi, R. Kharrat

Abstract


THAI (“toe-to-heel” air injection) is a novel thermal enhanced oil recovery method that has been studied in the case of conventional sandstone systems. It involves vertical injection and horizontal producer wells in a line drive configuration and is regarded as a promising tool for some reservoirs. However, its applicability on fractured carbonate rocks as an in-situ combustion-based method remains questionable. The aim of the present work was to study the feasibility of the THAI process in the presence of parallelepiped networked fractures to study how the presence of networked fractures affects on the process outcome. Both conventional and fractured THAI models and the effect of different operational and reservoir parameters on the process performance have been considered. Networked fractures reduced the performance of the THAI process. Parameters such as ultimate oil recovery factor, °API quality of the produced oil, front temperature and sweep efficiency were all reduced in non-conventional model as compared to the conventional one, but the process has high performance even after. In the case of networked fractures, the air injection rate should be optimized since the ultimate oil recovery is reduced after a limit, and there is also higher possibility of carbonate rock decomposition, oxygen breakthrough and water emulsions production for higher injection rates. Heterogeneity ratio reduction from 1000 to 100 has a significant effect on process performance since the combustion fronts in matrix and fractures systems have higher opportunity to become coupled together. THAI process start up should be optimally chosen for a system, considering the fact that the higher initial oil saturation at the start, leads to the higher ultimate oil recovery.

Keywords


in-situ combustion; toe-to-heel air injection; carbonate fractured reservoirs

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