Analysis of Decline Curves

Abstract

Since production curtailment for other than engineering reasons is graduallydisappearing, and more and more wells are now producing at capacity and showingdeclining production rates, it was considered timely to present a brief reviewof the development of decline-curve analysis during the past three or fourdecades. Several of the commoner types of decline curves were discussed in detail andthe mathematical relationships between production rate, time, cumulativeproduction and decline percentage for each case were studied. The well-known loss-ratio method was found to be an extremely valuable toolfor statistical analysis and extrapolation of various types of curves. Atentative classification of decline curves, based on their loss ratios, wassuggested. Some new graphical methods were introduced to facilitate estimationof the future life and the future production of producing properties wherecurves are plotted on semilogarithmic paper. To facilitate graphical extrapolation of hyperbolic-type decline curves, aseries of decline charts was proposed, which will make straight-lineextrapolation of both rate-time and rate-cumulative curves possible.