Density-Based Production-Data Analysis of Gas Wells With Significant Rock-Compressibility Effects

Abstract

Summary The state-of-the-art analysis of the production performance of gas wells relies on material-balance concepts combined with pseudopressure and pseudotime for rate-time decline analysis and reserves estimations. In many cases, rock compressibility and reservoir pore-volume (PV) change are either neglected or accounted for by replacing gas compressibility with total compressibility values. In this work, we extend the applicability of a rescaled exponential and density-based decline-analysis approach (Ayala and Ye 2013a, b; Zhang and Ayala 2014a, b) for the decline analysis of gas systems experiencing significant rock-compressibility effects. We formally derive the density-based analytical techniques that rigorously capture formation-compressibility effects during the analysis of gas-well-production data during boundary-dominated flow, which proves crucially important for high-pressure and/or large-formation-compressibility gas-reservoir systems. The proposed formulation enables the calculation and correct prediction of well performance and original gas in place (OGIP) by incorporating formation compressibility and the change of reservoir PV effects, which may prove crucially important in high-pressure and/or relatively large-formation-compressibility gas reservoirs. We also present the associated straight-line analysis technique used for OGIP determination on the basis of the density approach applicable to constant-bottomhole-pressure production and variable-flow-rate/pressure-drop systems.