Uncertainty Analysis Results for a Proposed Simultaneous Miscible Gas CO2 and Polymer Injection SIMGAP Pilot in a Giant Carbonate Reservoir in Abu Dhabi.

Bhushan, Yatindra (ADNOC Onshore) | Ali Al Seiari, Reem (ADNOC Onshore) | Igogo, Arit (ADNOC Onshore) | Hashrat Khan, Sara (ADNOC Onshore) | Al Mazrouei, Suhaila (ADNOC Onshore) | Al Raeesi, Muna (ADNOC Onshore) | Al Tenaiji, Aamna (ADNOC Onshore)



A reservoir simulation study has been performed to assess the enhanced oil recovery benefits for a proposed pilot on Simultaneous Injection of Miscible Gas (CO2) and Polymer (SIMGAP) in a giant carbonate reservoir (B) in Abu Dhabi. The model has been used to carry out uncertainty analysis for various input parameters and analyze their impact on pilot performance. The paper discusses the uncertainty analysis in detail.

Reservoir-B consists of B_Upper and B_Lower layers which are in full hydrodynamic equilibrium. However, in the southern and western parts of the reservoir, the B_Upper layer has permeabilities that are one to two orders of magnitude higher than the B_Lower layer. The reservoir is on plateau production under waterflooding, however, it is observed that there is water override in B_Upper. The B_Upper layer is being waterflooded very efficiently, while the B_Lower layer remains largely unflooded and forms the key target for enhanced oil recovery (EOR).

The proposed SIMGAP pilot plans to inject polymer into the B_Upper layer and CO2 into the B_Lower layer with producers in the B_Lower layer. The pilot will utilize a line drive pattern at 250m spacing using 3000 ft horizontal wells. There will be two central horizontal injectors (one in B_Upper and the other in B_Lower) and two horizontal producers (one on either side of the central injectors).

Pilot uncertainty analysis cases have been run by varying different parameters that could impact the pilot performance. The parameters that have been varied are polymer viscosity, polymer adsorption, residual resistance factor, thermal stability of polymer, residual oil to miscible flooding (Sorm), residual oil to water flooding (Sorw), Krw end point, high perm streaks, fracture possibility and extension to B_Upper or B_Lower layers, three phase oil relative permeability models, maximum trapped gas saturation, dense zone permeability and pore volume uncertainty. In addition, a grid sensitivity study was undertaken to test the sensitivity of the process to varying levels of dispersion. The results suggest that the key uncertainties which have impact on recovery are polymer viscosity, polymer adsorption, residual oil saturation to water and CO2, presence of high perm streaks and maximum trapped gas saturation values. Vertical observation wells located between the injector and producer wells (equivalent to 0.3 to 0.4 PV of CO2 injection in B_Lower), will be used to confirm whether the SIMGAP process has been successful in containing CO2 in the B_Lower layer and thereby suppressing crossflow.