Umm Gudair/Abduliyah Tayarat reservoir is a challenging EOR target because of its high oil viscosity, low permeability, and carbonate mineralogy. A previous feasibility study indicated that a hybrid EOR thermal and chemical method combined with IOR techniques could produce significant amount of oil from this reservoir. The objective of this study was to identify the most viable reservoir-specific EOR/IOR approach taking into account techno-economic considerations.
With the latest well logging data, production history, and petrophysical measurements, the Tayarat reservoir simulation model was revisited. Consequently, this simulation model was updated and calibrated to reflect field and lab observations. In addition, lab tests that demonstrated good transport and oil recovery performances of a selected polymer in low permeability reservoir cores were modeled to provide parameters for field-scale scoping simulations. Sensitivity studies were conducted to evaluate the effects of injection temperature, viscous fingering, well configuration, etc. A simple economic analysis was conducted to demonstrate the economic benefits of the proposed hybrid EOR/IOR method.
Calibrated by history matching the actual production data, the Tayarat reservoir model included a barrier zone that would prevent influx from a bottom aquifer. A better match was obtained by assuming that the reservoir is strongly water wet, which is consistent with the latest laboratory imbibition and contact angle measurements. Reservoir transmissibility was increased to represent possible fractures/microfractures in the carbonate reservoir. Scoping simulations based on a selected sweet spot of the Tayarat reservoir showed that primary recovery was ineffective due to the lack of a bottom aquifer, and waterflood recovered significantly more oil. A hybrid thermal/chemical EOR process was more effective when a preflush of hot water was considered to heat up a portion of the reservoir ahead of chemical injection. When viscous fingering was neglected, oil recovery could be erroneously as high as 50% more compared to the case when viscous fingering was modeled. Simulation results showed that about 19% of OOIP could be recovered using the hot waterflood followed by hot polymer flood, i.e. about 130% higher than conventional waterflood corresponding to a water cut of 95%. The chemical cost for incremental oil produced with our most promising approach was $10/bbl of incremental oil.
This integrated laboratory and simulation study should provide meaningful insights into tackling challenging low permeability and/or heavy oil carbonate reservoir using novel chemical EOR techniques.