This paper discusses and evaluates a fast, reliable and conservative method of estimating the gas initially in place; reservoir properties—permeability, drainage area and skin for volumetric dry-gas reservoirs using a nonlinear flowing material balance and in the absence of a representative average reservoir pressure history.
This approach uses reliable pseudopressure-normalized rate (PPNR) vs. pseudopressure-normalized cumulative production (PPNC) data. In theory, it considers a pseudopressure-normalized (PPNR) rate vs. pseudopressure-normalized pseudocumulative production (PPNPC). A modification to existing theory is to use a pseudocumulative production function, a polynomial which accounts for variations of the viscosity-compressibility product with fractional recovery. This function transforms the flowing material balance to a nonlinear equation. Pseudosteady-state data are used and matched by polynomial regression on spreadsheets to obtain the various coefficients of the nonlinear equation. The production characteristics are then inferred from the constant and the coefficient of the unit exponent. The 3rd and 4th degree nonlinear equations have shown to give excellent results based on the depletion characteristics of the reservoir. This theoretical-empirical approach can easily be adopted in production data analysis and will predict reliably whilst ensuring a reduction in production data noise and the rigours of digital type-curve matching. We demonstrate the application of this method using simulated and field production data.