Another Concept for Final Buildup Pressure

A method is developed for determining final static reservoir pressure buildup based upon the assumption that the change of the quantity [Ps - Pw] decreases at a constant rate with time. It is actually an application of the infinite series. The pressure measured in the well is assumed to be the average static reservoir pressure less the additive effect at any one time of the differential in pressure across the skin, differential in pressure between the higher permeability parts and the surface of the rest of the reservoir bounding them and differential in average pressure at the boundary of the higher permeability parts and static reservoir pressure. Thus the actual plot of the log [Ps - Pw] may be the addition of several straight line functions at any one particular time. A great deal of field data has been analyzed using this method; results indicate that it is capable of giving accurate results in every case. Other information besides final static pressure buildup may be obtained from the plot of log [Ps - Pw] vs shut-in time. The method presented in this paper has the following advantages:The time the well is produced prior to shut-in is not required.The skin effect or damage ratio can be observed from the plot of log [Ps - Pw] vs shut-in time at a glance.A qualitative measurement of the effect of the non-uniformity in permeability of the reservoir can be made. Introduction In 1937, M. Muskat proposed that the log of Ps - Pw would form a straight line when plotted against shut-in time during pressure buildup.