Analysis of Unsteady Responses of Natural Gas Reservoirs via a Universal Natural Gas Type-Curve Formulation

Abstract

AbstractGas decline curve analysis has traditionally relied on the use of liquid (oil) type curves along with the concepts of pseudopressure and pseudo-time and/or empirical curve fitting of rate-time production data using Fetkovich type curves for gas well performance and reserve estimations. In this work, we show that a single-line, universal type curve can instead be derived for the analysis of unsteady state of natural gas wells under boundary dominated flow (BDF). The proposed decline equation is presented in its analytical, closed functional form and is shown to model production from any gas well producing at constant bottomhole pressure under BDF. On the basis of this decline model, a universal type-curve is formulated for type curve matching of natural gas well producing under BDF, for any constant drawdown condition, and regardless of intrinsic reservoir and fluid properties. New-generation analytical procedures for gas well performance analysis are presented, which does not necessitate the calculation of pseudo-pressure or pseudo-time. Explicit OGIP predictions are thus enabled from the proposed universal type curve matching. The importance of conducting unambiguous reserve estimations based on rate-time data and reliably predicting future well performance cannot be overstated. The proposed single-line type curve is demonstrated to do so by successfully matching rate-time production BDF data and reliably estimating fluid in place for a number of numerical simulations and field cases. It is finally shown that the proposed formulation can be alternatively implemented in terms of straight-line analysis of 1/qgscb versus time data plots.