Pressure Analysis of Gas Wells in Multilayered Reservoirs with Skin, Storage and Non-Darcy Effects.

Abstract

This paper presents the first study of transient drawdown and buildup pseudopressure behavior of a gas well located in multilayered infinite acting reservoirs where wellbore storage, skin and turbulence intensity effects were taken into account. A mathematical model was developed to investigate the pseudopressure function and its derivative for different situations with regard to wellbore and reservoir characteristics. It was found that pseudopressure function ψD, for all cases considered in this study, is characterized by a unit slope line (during early period) followed by a transition period and then a pseudoradial flow period during later period. The pseudopressure derivative function(ψ'D*tPD) is characterized by a unit slope line, a curvature and then a constant value. The effect of the contrast in kh product on ψD and ψ'D*tPD was found to be significant compared to the effect of both skin factors and φh products. Type curves were developed for buildup and drawdown testing analyses. The drawdown type-curves can be used to analyze buildup test data as long as the duration of buildup test is less than the producing time before shutting-in the well. The fractional production rate from different layers can be evaluated using the mathematical model presented in this study. The results of a flowmeter survey can be used to evaluate the contrast in kh product of different layers.