A Modeling Study to Evaluate a Subsurface Bioreaction for Improved Oil Recovery

Abstract

Abstract Mature oil reservoirs contain substantial residual oil after waterflooding, creating an opportunity to implement technology solutions to increase oil production. In a subsurface bioreaction, residual oil is converted to hydrogen (H2) and carbon dioxide (CO2), creating a coupled mechanism of a bioreaction and fluid transport. The in-situ generated CO2 can contribute to incremental oil production and needs to be quantified via a fully coupled model. This study develops a compositional reservoir-simulation framework to evaluate the coupling between bioreaction, fluid transport, and improved oil production. A conceptual 3D inverted five-spot model was waterflooded for 10 years to establish residual oil conditions and subsequently treated for approximately 20 years by injecting a biotechnology through the central injector. Hexadecane was used as the representative oil. The model incorporated H2 and CO2 phase partitioning, aqueous solubility, molecular diffusion, three-phase relative permeability and hysteresis, and an Arrhenius-type hydrocarbon-conversion reaction. Reaction and fluid propagation were quantified using cumulative radial distributions. The biotechnology injection case was also compared with conventional CO2 injection using the same cumulative CO2 generated by the bioreaction. Sensitivities included reaction kinetics, biotechnology dosage and injection rate, permeability anisotropy, pattern size, and production control. The studied simulations show that bioreaction and fluid transport become increasingly decoupled as the process evolves over time. H2 and CO2 continue to migrate beyond the active reaction region, while reaction extent remains controlled by biotechnology transport and residual-oil availability. The biotechnology process simultaneously converts residual oil to H2 and CO2 and produces additional oil through multiphase displacement and CO2-oil interactions. The CO2-in-oil mole fraction maps demonstrate the differences in CO2-oil contact between the biotechnology injection and conventional CO2 injection cases. The sensitivity results further show that biotechnology availability, reservoir contact, and well operating conditions exert stronger control on overall process performance than the tested changes in intrinsic reaction kinetics. To derisk operations and study additional opportunities of a subsurface bioreaction, a fully coupled framework is required. This new framework connects oil degradation, fluid transport, and improved oil production within a single reservoir model and provides the basis for subsurface production optimization. The same process can be used to provide real-field development scenarios for biotechnology deployment applications.