Transient pressure analysis of gas wells producing at constant pressure

• Published in: Journal of petroleum science & engineering 2003-10, Vol.40 (1), p.89-102
• Main Authors: Nashawi, Ibrahim Sami, Qasem, Fuad H, Gharbi, Ridha
• Format: Article
• Language: English
• Subjects: Applied sciences; Constant pressure; Crude oil, natural gas and petroleum products; Crude oil, natural gas, oil shales producing equipements and methods; Energy; Exact sciences and technology; Formation damage; Fuels; Gas reservoirs; Gas well production; Non-Darcy flow; Prospecting and production of crude oil, natural gas, oil shales and tar sands; Transient rate-decline
• ISSN: 0920-4105; 1873-4715
• DOI: 10.1016/S0920-4105(03)00105-0

A comprehensive investigation of the validity of applying the constant-pressure liquid solution to transient rate-decline analysis of gas wells is presented. Pseudo-pressure, non-Darcy flow effects, and formation damage are incorporated in the liquid solution theory to simulate actual real gas flow around the wellbore. The investigation shows that for constant-pressure gas production, the conventional semilog plot of the inverse of the dimensionless rate versus the dimensionless time used for liquid solution must be modified to account for high-velocity flow effects. Especially when reservoir permeability is higher than 1 md and the well test is affected by non-Darcy flow and formation damage. In addition, a systematic method for determining formation permeability, mechanical skin factor, and non-Darcy flow coefficient from a single constant-pressure production test also is presented. The working equations are written to allow graphical analysis of the variable rate with time that is analogous to analysis of the constant-rate production test. The procedure is simple and straightforward. It does not require type-curve matching or correlations. The applicability of the proposed method is illustrated using several simulated examples. The input formation permeability varies from 0.1 to 5 md. The ratio of the bottomhole pressure to the initial reservoir pressure ranges from 0.1 to 0.8.