This study presents a modeling lookback of a two-well Enhanced Oil Recovery (EOR) miscible gas Huff-n-Puff project focused on reconciling differences between observed field behavior and initial model predictions. This project consisted of two horizontal parent wells drilled from the same pad in opposite directions. The incremental uplift of oil in these projects can be substantial and is necessary to extend the economic life of the well. However, the field response differed from the original modeling forecasts, motivating a comprehensive modeling investigation to better understand the controlling mechanisms.
The original Huff-n-Puff pilot modeling was performed using a non-coupled reservoir simulator and focused solely on the production and gas injection processes. This model proved to be overly optimistic, and it was determined that there were more processes occurring than could be fully captured. Two new models were independently developed for each well using a fully coupled fracture and reservoir model whereby the entire lifecycle of the wells were captured in one continuous simulation, including the fracturing, primary production, gas injection and post injection processes. Finally, a third model was created to reconcile all history matching parameters from both wells into one overall model, simultaneously matching the entire lifecycle of each well.
The outcome of the modeling revealed several major considerations. First, although the primary production of each well could be history matched independently, it was difficult to match historical production from both wells with the same set of ‘reasonable’ petrophysical and reservoir parameters. Second, the injection pressures, rates, and subsequent production of the Huff-n-Puff could not be matched with the primary production reservoir parameters until the injection capacity of the lateral was limited. Finally, it was found that limiting lateral contribution during the injection and post injection production phases could also be used to match the primary production phase, allowing the entire lifecycle of the well to be successfully modeled for both wells.
The use of a fully coupled fracture and reservoir simulator was paramount in understanding the processes that make a Huff-n-Puff project successful and highlights the importance of well selection. It was learned that the injection capacity of the well was directly related to the primary production, and the original stimulation size, primary production depletion considerations, and lateral contribution are factors that need to be considered when choosing a pilot.