The Power Law decline analysis method has been offered as a way for predicting gas reserves in low permeability reservoirs, by matching early transient data but not over-predicting reserves as can happen when using hyperbolic decline and a high b-exponent.
This paper compares the goodness-of-fit and reserve prediction results of the Power Law versus the Modified Hyperbolic decline method; the Modified Hyperbolic being a hyperbolic decline with an imposed limit on how low the decline can become, thereby also avoiding reserve over-prediction.
Linear flow is a common occurrence in tight gas wells. For this situation, the modified hyperbolic decline (which has a direct theoretical connection) is better suited than the power law decline. Furthermore, for low values of n, Power Law appears to degenerate into hyperbolic decline.
Using synthetic and real production data, is it demonstrated that, for the most part, data matched using Power Law can also be matched using Modified Hyperbolic decline. Modified Hyperbolic decline is well understood and accepted by the industry; on the other hand, the Power Law is complex and its constituent variables are not intuitive.