Abstract

Decline curves are frequently used to predict performance and to evaluate ultimate reserves or remaining production life of well or fields. The use of decline curves is with one basic assumption that the past controlling factors will also control the future life of the wells. An extrapolation of past trends is valid only if the characteristics remains unchanged.

Arps 1) has summarized the different types of production decline curves along with the mathematical bases underlying their use. Three common types of decline curves are constant percentage decline or exponential decline, hyperbolic decline and harmonic decline.

In searching as tools for prediction of future performance, curve-plotters pursued two line of investigation, i.e. visual and mathematical. In some instances, for considerable periods of time, production performance was approximated by a straight line, when plotted versus time on semilog paper. The departure from a straight line prompted by more scattering of the data used in the construction of production decline curves may make the fit of a smooth curve to the plot rather ambiguous, and dependent on the personal bias of the analyst.

This paper presents a Computerized decline analysis system used to analyse production history, provide log-log and semi-log plots of history and projections, and produce production forecast reports.