Which is the Most Attractive IOR Method to Produce the Venezuelan Highly Viscous Oil Resources in the Energy Transition Era? A Comprehensive Review of Research and Field Applications

Abstract Venezuela has been a potential producer of highly viscous crude oils for more than a century, thanks to its large resources located at the Lake Maracaibo and Eastern Venezuela basins in the Orinoco Oil Belt. Despite these huge resources, Venezuelan oil production is going through one of the greatest crises in its history, presenting a dramatic production decline, for which the application of Improved Oil Recovery (IOR) methods with low environmental impact (low carbon emissions, low water consumption, etc.) is crucial to increase oil production. The main methods applied in Venezuelan highly viscous oil reservoirs (heavy, extra-heavy and bituminous oil reservoirs) have been cold production with sand by vertical and horizontal wells with artificial lift pumps, waterflooding, thermal IOR/EOR methods (steam drive-based methods), chemical EOR (CEOR) methods, namely polymer and surfactant-polymer (SP) flooding, hybrid methods (e.g. thermal combined with solvents or CEOR methods), among others. Research works in CEOR methods for Venezuelan highly viscous oil reservoirs have shown that high oil recoveries may be possible for oils with viscosities up to 13,400 mPa.s. On the other hand, for the case of bituminous oil reservoirs (e.g. viscosities up to 50,000 mPa.s) thermal IOR methods and combinations with chemicals, nanoparticles, or solvents may increase oil production significantly. The methods reviewed in this article are: waterflooding, chemical flooding (e.g. polymer, surfactant, alkali and a combination of them), steam drive methods (e.g. CSS, In-situ Combustion and SAGD), solvent flooding, microorganisms and hybrid methods. Based on research and field tests, CEOR methods may lead to increased oil recovery of extra-heavy oils with low carbon emissions compared to thermal EOR methods, thus making SP flooding and low salinity polymer flooding among the most attractive technologies. Depending on the type of chemicals evaluated, recovery mechanisms such as mobility control, IFT reduction, ion exchanges and/or wettability alteration might be most efficient. It also appears that hybrid methods have achieved the highest recovery at the laboratory scale (e.g. In Situ Combustion with nanoparticles). For the medium-heavy oil reservoirs of the Maracaibo Lake Basin, waterflooding combined with infill well optimization and microorganism flooding are encouraging IOR methods with low environmental impact. The greatest challenges in the application of these technologies are related to technical and economic considerations that will be decisive for the implementation of the IOR processes at the pilot scale and/or massification at the field scale aiming to increase Venezuelan oil production in this era of the energy transition.