Detecting Linear Barriers by Type Curve Analysis: Supri TR 61.

摘要

The effect of a linear barrier (the semi-infinite system) on the pressure behavior of a single well test has been recognized for many years. The characteristic doubling of slope on a semilog graph has been used to determine the existence of a fault and to determine its distance from the well tested. The equations governing this behavior are quite straightforward and understandable; hence the presence of a sealing fault is often used as an explanation for anomalous pressure behavior even when it is not justified. Alternatively, when a change in slope is not observed, the absence of a second straight line is used to calculate a minimum fault distance. Although, this is reasonable in theory, the radius of investigation method normally used for this calculation will overestimate this distance. This study uses the pressure derivative and equivalent drawndown time, to present type curves for a semi-infinite system on a single log-log graph. This presentation allows the determination of permeability, skin and fault distance from a single match. The type curves can be used to analyze data from either drawdown or buildup tests, and there is no restriction on production time in the case of buildup testing. Prior to this study, there was no method available to analyze buildup data from a semi-infinite system following a short flow period. The value of the log-log presentation is that it allows for verification that the correct model is being used. Since the pressure derivative is merely the slope of the semilog graph, a minimum distance to a barrier can be calculated from the type curve when only infinite acting data are available. Type curves are also presented for the case of a well with wellbore storage and skin producing in the presence of a boundary. These type curves show that reasonable values of wellbore storage and skin can completely mask the effects of a boundary. 27 refs., 21 figs. (ERA citation 14:010688)