Horner and MBH Methods

The Horner and MBH methods are used to analyze the buildup data only for infinite-acting reservoirs. This is not true; Horner's method can be used to estimate the reservoir parameters in finite reservoirs just as in infinite-acting reservoirs. The difference occurs only in late-time data when boundary effects influence the data as shown in Figure 5-7.

Figure 5-7: Horner plot of pressure buildup data from a well in a finite reservoir

For an infinite-acting reservoir, an estimate of p _i is obtained by extrapolating the straight-line section of the Horner plot to infinite shut-in time. For finite and developed reservoirs, the extrapolated pressure is not a good estimate of p _i and generally has been called the false pressure, p ^*. As shown in Figure 5-7, the extrapolated false pressure, p ^*, is higher than the average reservoir pressure at the instant of shut-in unless the drainage region is highly skewed. Using the concept of the false pressure, we may rewrite Eq. 5-18 as

Ramey and Cobb ^[12] show that P ^* is related to p _i by

where

Although it is commonly believed that the Horner...