This paper investigates the effect of higher concentrations (0-100%) of CO2, H2S, and N2 on natural gas well deliverability,reserve estimation, and pressure test analysis quantitatively.Physical properties of natural gases such as viscosity andcompressibility are corrected according to the concentrationsof the contaminant gases such as CO2, N2, and H2S present init. These contaminant gases have profound impact onpressure test analysis. The Carr et all1 viscosity correctionchart allows adjusting the viscosity up to 15% concentrationof these contaminant gases. However, Wichert and Aziz2compressibility correction chart allows up to 80%concentration of the CO2 and H2S.Tiab3 developed an analytical method to estimatepseudopressure function for 0-100% combined-concentrationof CO2, H2S, and N2. His pseudopressure was first re-plottedto simplify the procedure and then it was used to analyze thedeliverability, pressure tests, and decline curvesquantitatively. The analysis was performed with Carr et all1viscosity correction chart, pure CO2 properties, and then withTiab's corrected pseudopressure. Pure CO2 properties wereused due to the fact that the sample data has 98.256% CO2.During this study it was observed that the compressibilityfactor has a little effect on analysis since it is a volumerelatedproperty. Viscosity, however, has the largest effect onthe analysis since pressure is transmitted through the fluid inthe porous media and viscosity works against it. It was alsoobserved that the numerical method of calculatingpseudopressure function introduced successive error in theanalysis. Number of pressure data points also contributed tothe error in numerical integration of the pseudopressurefunction. Analysis of field as well as simulated examplesresulted an absolute error range of 13-75% in thepermeability estimation in pressure tests, 77% indeliverability tests, and 20-95% with pressure derivative.Error in AOF was observed as 15% and as high as 32 %in reserve estimation.
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