Post-Combustion CO2 WAG Pilot in a Mature Field: Model Calibration and Optimization
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AbstractWe present a detailed history matching and process optimization of a CO2 WAG pilot at the West Ranch Field, Texas. The Petra Nova, a 50/50 joint venture between NRG and JX Nippon, operates a commercial scale post-combustion carbon capture facility at NRG's WA Parish generating station southwest of Houston. The industrially sourced CO2 is utilized for EOR in the West Ranch field, which is operated by Hilcorp Energy. A CO2 pilot was conducted to examine the potential for tertiary oil recovery by pattern-scale CO2 flooding and to better understand how pattern flooding will work in the fluvial geology of the reservoir. This paper discusses detailed modeling and history matching of the CO2 EOR pilot at the West Ranch field to understand the CO2 plume movement and optimize the flood design parameters.For history matching the CO2 WAG pilot, we started by initializing the pilot sector model and imposing multiphase boundary fluxes generated from full-field compositional simulation. The pilot model calibration followed a hierarchical two-step approach. First, we performed a large-scale update of the model permeability distribution by integrating bottomhole pressure and multiphase production data. Next, streamline-based local updates were used to further calibrate the permeability field to match CO2 breakthrough times at the producers. Sensitivity studies were conducted using the calibrated pilot model to evaluate the effects of WAG ratio, CO2 Pore Volume Injected (PVI), number of WAG cycles and Voidage Replacement Ratio (VRR) on the oil recovery efficiency and CO2 utilization factor. Finally, we carried out a multiobjective optimization of the CO2 WAG process based on the influential operational parameters. With this strategy, multiple scenarios that consider the trade-off between the oil recovery efficiency and CO2 utilization factor were generated.The history matched models capture the major trends observed in the producing Gas-Oil Ratio (GOR), oil production rate and CO2 mole fraction history at the wells. The updated models were independently validated in two ways. First, the models showed good agreement with reservoir saturation logs at two observation wells. Second, the models reproduced the CO2 recovery as a fraction of the injected CO2. These results imply that the history matched models are able to adequately capture the CO2 sweep profile in the pilot area. Sensitivity studies indicate CO2PVI and VRR (Voidage Replacement Ratio) as dominant parameters impacting oil recovery efficiency. The VRR and WAG ratio play a significant role in determining the CO2 utilization factor. A set of optimal operational parameters that utilize these decision variables was generated using a Design of Experiments (DOE) based multiobjective optimization workflow. This work presents, for the first time, modeling and optimization of a field-scale post-combustion CO2 WAG process.
