To quantify and compare the accuracy of a series of progressively earlier-time forecasts generated from various available production decline analyses methods modified with the industry’s first physics-based analytical solution for predicting inevitable severe degradation in transient oil decline associated with transition to boundary-dominated flow (BDF).

Abundant production data from horizontal wells recovering oil from unconventional reservoirs indicates the widespread use of late-life assumptions for BDF transitions—regardless of well spacing and stimulation intensity—has proven overly optimistic. Reliable early-time production forecasts are critical to ensuring deployed capital is adequately offset by future revenue from production and shortening model-measure-optimize cycle times.

Gas-to-oil ratios were integrated into various production decline analysis methods after Lapierre (2021) in order to proactively modify initial transient forecast segments in anticipation of the inevitable transition to BDF. Forecasts were generated for ten multi-well drilling units in the Permian Basin which manifest historical BDF transitions. Hyperbolic transient decline segments were fit through progressively longer periods of early production data (i.e., first 12, 18, and 24 months) to generate initial, 2–stream transient forecast segments. The proactive termination of transient forecast segments after S. Lapierre (2021) was used to generate complete 2–segment, 2–stream production forecasts. Actual transition points are objectively determined from full production histories.

All ten selected cases manifest historical transitions to BDF within the first 30 months of production rather than within the multi-decade timeframe assumed by using static, late-life BDF assumptions of transition to BDF. Furthermore, all cases were observed to transition within a highly dynamic range of instantaneous hyperbolic declines all greater than 25% as opposed to the time-of-transition implied by the traditional use of single-digit minimum declines.

The time-to-transitions predicted by the application of Lapierre (2017) were observed to closely match those actually observed; however, the predicted transitions tended to be slightly later than the observed indicating a tendency for slightly optimistic recoveries.

The improved accuracy of early-time forecasts can shorten the model-measure-optimize cycle for horizontal shale oil infill drilling. Furthermore, the improved accuracy of early-time forecasts offered by the novel method for the proactive prediction of impending BDF from only transient data can greatly enhance the reliability of reserves analysis when only limited 2–stream production data is available.