Reserve Estimation Using Decline Curve Analysis for Boundary-Dominated Flow Dry Gas Wells

Abstract

Diverse techniques have been developed to improve the estimated reserves for boundary-dominated flow dry gas wells. The various methods developed and published in various journals on how to estimate reserves range from material balance techniques to decline curve analysis. Among the various techniques, decline curves are found quite accurate in predicting good gas performance in the absence of well-known reservoir parameters. There are basically two issues that practically arise in applying decline curve analysis, particularly in boundary-dominated flow dry gas wells. First, it has been noted that it is difficult to match a decline exponent, especially at an early stage of well depletion, even with worthy quality data. Secondly, decline exponent is not constant from observation, but changes with declining production. So, the study has provided a new method based on numerical curve fitting to accurately match the Arps’ decline curve function, even at the early depletion stage, and account for the changing decline exponent. Once the match objective is satisfied, future predictions can be made with a reasonable degree of assurance. Finally, the study showed that for the Arps’ decline equation to be valid, the decline exponent must be between 0 and 1.