Recently, produced gas has been employed in numerous pilot projects for enhanced oil recovery (EOR) in several unconventional plays, and successful cases have been reported. In the meantime, well interference (or conformance issues—crossflow of the injected gas between wells) was also identified as a critical issue for most of the pilots. However, this effect was largely ignored in most of the previous studies. In this study, systematic experimental modeling and simulation activities were conducted to evaluate the technical feasibility of increasing oil production through produced gas EOR in the Bakken considering well interference. A field site with a clear well interference effect was selected from the core-producing area in the Bakken to make sure the results were representative. Data from 77 wells in the targeted area were collected to develop a multiple-well, multiple-fracture (MWMF) simulation model, which can reproduce the historical data and predict the possible EOR response under realistic constraints. Embedded discrete fracture modeling (EDFM) was employed to construct fractures in the model to improve the simulation efficiency. Minimum miscibility pressure and swelling tests were conducted to further understand the fluid behavior and gas–oil interactions during the EOR process. Based on operational data collected from previous pilots, a series of simulation cases were designed to predict the EOR performance and study the sensitivity of the oil production response to the EOR operations with the well interference effect considered.

Both experimental and simulation results showed that a high gas injection rate is required to yield meaningful EOR results. Results suggested that up to 60% incremental oil recovery (compared to the depletion-only operation) could be achieved in the primary huff ‘n’ puff (HnP) well using gas injection rates of 17 MMscfd. The production performance of offset wells strongly depended on the stimulated reservoir volume (SRV) around these wells. An offset well with a large SRV close to the HnP well could also have a maximum of 58% incremental oil recovery when the gas injection rate reached 17 MMscfd. However, a negative EOR effect was also observed in another offset well with a small SRV. In the meantime, over 70% of the injected gas could be recovered from the site for recycling injection. The MWMF model employing the EDFM technique can simulate interference between wells effectively. This effect is especially important in the gas injection process as the injected gas will easily flow from the injector to offset wells where the fractures are connected. Sensitivity analysis results indicated that the chance of success for an EOR operation increases by optimization of design parameters, including careful well selection, reasonable timing of EOR initiation, sufficient gas injection, and optimized cycle design.

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