March 2023: A New Approach to Apply Decline-Curve Analysis Under Variable Pressure Drop Conditions

Abstract Decline-curve models inherently assume constant bottomhole flowing pressure (BHP) conditions. This is a poor assumption for many unconventional wells. For this reason, the application of decline-curve models might lead to incorrect: (a) flow regime identification and (b) estimated ultimate recovery (EUR). This work presents a method to incorporate variable BHP conditions for any decline-curve model. We validate the technique against synthetic cases and illustrate its application for tight-oil and shale gas wells using different decline-curve models. The technique is computationally inexpensive, history-matches production of unconventional wells more accurately than traditional decline-curve analysis, and provides improved estimates of the bottomhole and initial reservoir pressures. The major contribution of this work is the remarkable simplicity yet robustness of the solution to variable pressure decline-curve analysis. Bio Leo Ruiz Maraggi is a reservoir engineer within the State of Texas Advanced Resource Recovery program at the Bureau of Economic Geology. His research interests include conventional and unconventional oil and gas resources, subsurface Hydrogen and CO2 storage. Leo holds a BS degree in Chemical Engineering from University of Buenos Aires (Argentina), MS and PhD degrees in Petroleum Engineering from The University of Texas at Austin.