Density-based decline performance analysis of natural gas reservoirs using a universal type curve

Modern natural gas reservoir decline performance analysis has traditionally relied on the use of oil type curves along with the concepts of pseudopressure and pseudotime. Alternatively, it also employs empirical curve fitting of rate-time production data for reserve and future performance analysis. In this work we show that the use of a density approach leads to the formulation of a new-generation type curve applicable to the analysis of unsteady state of natural gas wells under boundary dominated flow (BDF). The resulting gas reservoir decline equation applies to any gas well producing at constant bottomhole pressure under BDF. On the basis of this decline model, a single-line, universal type curve is derived for any gas fluid and reservoir properties producing under a constant drawdown condition. New-generation analytical procedures for gas well performance analysis are presented, which does not necessitate the calculation of pseudopressure or pseudotime. Explicit OGIP predictions are thus enabled from the proposed universal type curve matching. The proposed single-line type curve is demonstrated to successfully match rate-time production BDF data and reliably estimate fluids in place for a number of numerical simulations and field cases. It is also demonstrated that the proposed formulation can be alternatively implemented in terms of straight-line analysis of 1/q^b_gsc versus time data plots.