Oil production forecasting by decline curve analysis

Abstract

The subject of analyzing oilwell production-decline curves is examined in detail. The problem is approached from the standpoints of raw data validity, techniques of data handling, modes of graphic representation, and final interpretation procedures. Forms of analysis based on mathematical treatments, factors of analogy and experience, and predicted reservoir behavior efforts are discussed. It is evident that all of the methods of decline curve analysis are subject to gross forecasting error in specific situations. Examples are given to illustrate the over-all problem of reliability. The accepted method for classifying decline curves is reviewed. The mathematical definition for hyperbolic decline is found to be too restrictive and a broader definition is suggested. Gradual or abrupt changes in the producing rate of a well due to reservoir depletion, fluctuation in bottom-hole producing pressure, and changes in conditions in or immediately adjacent to the wellbore, are examined. A method is presented utilizing comparative theoretical and actual productivity index behavior that can be useful in predicting future rates of production.