Probability Ranges for Reserve Estimates From Decline Curve Analysis

Abstract

Abstract An estimate of the production expected from a property is frequently accomplished by extrapolating historic production data to a minimum economic flow rate. For a particular analyst, deterministic reserve estimates from decline curve analysis gives a specific answer or value for a given production data set. A method has been developed which yields probable production rates and volumes based on the analyst’s deterministic estimate of the future well performance. The objective is to quantify the uncertainty in reserve estimates from production decline curve data. The statistical concepts of linear regression and prediction limits have been incorporated in a method which utilizes the analyst’s decline exponent (b), decline rate (Di), and production rate (qi) estimates. The method is flexible in that any portion of the historic production data may be utilized if the analyst believes the production parameters of the well have changed over the life of the well. The prediction limits yielded by the method are analogous to probability values and could be used in property value comparisons. The method was applied to the deterministic reserve estimates made by seven practicing engineers in SPE paper 26388, "A Comparison of Probabilistic and Deterministic Reserve Estimates: A Case Study,"1 The results of this approach will be compared to the subjective probabilistic reserve estimates made by the engineers in the study by Hefner.