An Investigation of Gas Well Testing Under Constant-Bottomhole Pressure Conditions, High-Velocity Flow Effects, and Formation Damage

摘要

This paper presents an investigation of the validity ofapplying the constant-pressure liquid solution to transient ratedeclineanalysis of gas wells. Pseudo-pressure, non-Darcyflow effects, and formation damage are incorporated in theliquid solution to simulate actual real gas flow in the vicinityof the wellbore. The study shows that for constant-bottomholepressure gas production the conventional semilog plot of theinverse of the dimensionless rate versus the dimensionlesstime used for liquid solution has to be modified to consider thehigh-velocity flow effects. This is especially true when thereservoir permeability is higher than 1 md and the well test isaffected by non-Darcy flow and formation damage.This paper also presents a novel systematic method todetermine the formation permeability, mechanical skin factor,and non-Darcy flow coefficient from a single constantpressureproduction test. The working equations are written insuch a way that allows a graphical analysis of the variable ratewith time that is analogous to the analysis of constant-rateproduction test. The analysis procedure is simple andstraightforward. It does not require type-curve matching orcorrelations. The applicability of the proposed method isillustrated using several simulated examples. The inputformation permeability varies from a low value of 0.1 md to ahigh value of 5 md. The ratio of the downhole pressure to theinitial reservoir pressure ranges from 0.1 to 0.8.