Abstract
Static reservoir pressures are required for gas material balance plz vs. Gp plots. A new method has been developed that uses wellbore storage distorted early time pressure buildup data to determine original gas in place (OGIP). Analysis of fundamental concepts has led to the development of an equation that relates the static plz value to the transient plz value in the presence of wellbore storage effects. A chart is presented that allows the user to deten-nine the error in the OGIP estimate for different shut-in times. This chart is parametrized with respect to permeability, thickness and flow rate and is applicable to reservoirs with a permeability greater than 0.5 md. The method will allow analysis of wellbore storage distorted data from wells in low permeability gas reservoirs. The analysis is based on the conventional plz vs. Gp plot and is easy to apply. The use of short term pressure buildup data will greatly reduce testing costs. Shut-in times of less than 24 hours can be used to determine OGIP in some cases. The method has been shown to be applicable for reservoirs with a permeability of 0. I md or greater (k> 0. 1). An analytical and numerical simulation approach has been used in the development of the method. A radial flow, homogeneous gas reservoir model is used. An analytical and numerical simulation approach has been used in the development of the method. A radial flow, homogeneous gas reservoir model is used. The range within which this method may be effectively applied has been demonstrated. This range is based on the CDe e2s parameter, where CDe is the effective dimensionless storage coefficient and s is the skin factor. CDe is required to remain constant between successive shut-in periods and during the shut-in as well. Low permeability gas wells with large pressure drawdowns prior to buildup cannot be analyzed with the method due to large variations in CDe - The method provides the gas field operator with a simple and effective technique to use short term storage distorted buildup data in deten-nining the OGIP. The new technique will result in considerable cost reduction and time saving during buildup testing.
Deshpande, Anil (1993). Applying the isochronal, transient p/z method to gas wells exhibiting wellbore storage effects. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1993 -THESIS -D456.