Detection of no-flow boundaries is an integral and important aspect of well test analysis. Identification of no-flow boundaries assists in defining the reservoir system and is used in determining the areal extent of a reservoir. Existing procedures for detection of boundaries rely heavily on the use of type curves. These type curves have been derived for use with drawdown data, and do not necessarily work with buildup data.;A direct method for detecting no-flow boundaries in rectangular reservoirs using only buildup data, without reference to drawdown type curves, has been developed. This direct method of boundary detection introduces the concept of Boundary Influenced Difference of Pressure, or BIDP, which relies on using an infinite acting reservoir as a frame of reference. The BIDP is defined as the difference between the "Infinite-Acting Reservoir" pressure and the "Boundary Influenced" pressure. This differencing procedure removes the effect of the infinite-acting behaviour and accentuates the boundary effects. The BIDP thus contains the "boundary information". Additionally, by utilizing the semi-log derivative of the BIDP the number of boundaries is indicated and the distance to those boundaries may be calculated.;Furthermore, this method does not rely on the duration of producing time, as do the existing traditional methods of boundary detection. This direct method depends only on the duration of shut-in time, and is not affected by the duration of producing time. Thus boundaries can be detected for relatively short producing times and longer shut-in times.;The method is illustrated with examples using synthetic data. The application of the method to "noisy" data is also demonstrated.
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