This study presents a technical evaluation of a large-scale miscible gas huff n puff pilot project, highlighting the reasons for its success over four years of Enhanced Oil Recovery (EOR) operations. Field results show a notable 37% uplift to-date compared to the scenario without EOR.
We built and calibrated a compositional, fully coupled fracture-reservoir model to assess and guide pilot operations. This model was calibrated to completion data, primary production data, and the results of multiple huff n puff cycles, all on a unified and consistent platform. Key model objectives included: 1. characterizing the stimulated rock volume (SRV), 2. properly capturing all mechanisms involved in the complex Huff n Puff process, 3. optimizing huff n puff cycling operations, and 4. estimating uplifts and incremental oil recoveries.
The integration of geomechanics and reservoir models facilitated history matching completion data, primary production, and EOR response. By modeling the hydraulic fracturing process, we effectively estimated well injectivity and captured the behavior of hydraulic fractures, which are influenced by net effective stress on the proppant. Our findings indicate that unpropped portions of the hydraulic fractures may open and close during gas cycling, potentially leading to inefficient gas recovery. This modeling approach helped us avoid such issues.
The calibrated model was used to perform a parametric evaluation to optimize injection cycling. Sensitivity analyses allowed us to estimate target injection pressures, volumes, and flowback strategies, guiding us into maximizing economic value.
Modeling results indicate that greater gas volumes do not always translate into increased value. While oil rate uplift improves with higher gas injection volumes, diminishing economic returns may be observed beyond certain thresholds. Field observations and the modeling study also indicate that Gas Utilization Factors (GUFs) are expected to rise in every cycle. Consequently, gas injection requirements significantly increase in subsequent cycles to achieve similar well responses, while oil production peaks decline with each cycle due to depletion in the near-fracture SRV.
This study presents a robust modeling framework for the design, evaluation, optimization, and economic enhancement of Miscible Gas Huff n Puff pilots in unconventional reservoirs. The insights gained are critical for informing future EOR projects and maximizing recovery efficiencies. As oil production from unconventional oil basins in the United States continues to experience decline, EOR becomes increasingly critical. EOR will have a substantial impact on increasing recoveries, accelerating production, and extending asset life for the unconventional plays in the United States, unlocking billions of barrels in additional recoverable resources.