Abstract:
Production practices applied to maximize gas recovery from water drive gas reservoirs differ from those applied to volumetric ones. It necessitates appraising of reservoir drive mechanism at the earliest for maximum gas recovery. Normally P/Z, a diagnostic plot, is used to assess the drive type of a gas reservoir and estimate the Gas Initially in Place (GIIP). However, P/Z plot fails to recognize water encroachment during initial reservoir life for some reservoir-aquifer systems. There are some other diagnostic plots as well, such as energy plot, which are used to estimate GIIP and detect presence of aquifer attached with gas reservoirs. All these plots utilize correlations based on cumulative gas withdrawal and PVT properties evaluated at corresponding reservoir pressure. Pressure used to evaluate PVT properties is assumed to be acquired under complete stabilized conditions and representing reservoir depletion stage. However, in case of low permeability reservoirs it is not practical to shut-in wells long enough to achieve pressure stabilization. This paper presents comparative evaluation of these diagnostic plots for the above mentioned aspects of their application. 3-D homogenous gas reservoir simulation models are constructed to evaluate and identify the plot that detects presence of aquifer more efficiently with least gas withdrawal. Behavior of these plots for shut in times of varying duration is evaluated as well. Heterogeneous reservoir models are used to asses the effect of reservoir depositional heterogeneity, on the capability of these plots to diagnose drive mechanism and estimate GIIP.
Page(s):
199-208
DOI:
DOI not available
Published:
Journal: Proceedings SPE-PAPG Annual Technical Conference, Volume: 0, Issue: , Year: 2008