During the initial flowback after hydraulic fracturing in unconventional wells, fluid rates (oil, gas, and water) and pressures are typically recorded on an hourly basis. Therefore, even though flowback may only take a few weeks, there are hundreds of available data points. The authors have developed an innovative approach to predict short-term cumulative oil production and long-term oil EUR using hourly flowback data, theory-based calculations, and empirical correlations.
Unconventional wells produce in the linear flow regime in early time. During this period, the production depends on pressure, fracture surface area, and reservoir and fluid properties, which can be lumped into one term obtained from the slope of the RTA superposition time plot. Most wells exhibit a linear flow signature during the flowback period, so this slope is easily obtained. Hundreds of Permian wells with hourly flowback data were analyzed to obtain the slope. The initial pressures for these wells divided by this slope were plotted against their corresponding one-year cumulative oil production and EUR. From this analysis, correlations for both one-year cumulative oil production and EUR have been established.
Using these correlations from historical wells, the one-year cumulative oil production and oil EUR of a new well can be estimated with just a few weeks of flowback data since the main parameters (pressure, fracture surface area, and reservoir and fluid properties) impacting production performance can be obtained. We named the EUR from this RTA linear flow-based correlation LinearFlow-EUR.
The authors validated this innovative method based on hourly flowback data in new wells in different benches in both the Midland Basin and Delaware Basin. We also validated the method with dynamic reservoir simulation. The correlations can generally predict one-year cumulative oil production and oil EUR within reasonable ranges, even though the correlations are only based on linear flow regime, not considering the pseudo-steady state depletion.
This new method provides an early performance indication for new wells, new benches, or new areas. The application of the method could speed up completion trials and appraisal processes tremendously while optimizing field development plans.
