Like vertical wells, a horizontal well produced long enough to reach pseudosteady state is depleting the pressure in its drainage volume. Average pressure for a vertical well can be determined using correction plots designed to calculate average pressure for various vertical well position and drainage volume shape combinations. Because these were designed for pressure extrapolation strictly from the radial flow regime, it is not possible to use them to estimate average pressure for most horizontal wells. Using a general solution for the horizontal well arbitrarily located in a rectangular drainage area, curves are provided for the difference between the average pressure and the extrapolated pressure from the linear flow trend in the pressure buildup data. Knowing production time before the buildup, the well position and drainage volume shape, and the extrapolated pressure from the linear flow trend determined from the pressure buildup data, the new horizontal well correction plots enable estimation of average reservoir pressure. Correction plots have been determined for a wide variety of horizontal well position and reservoir shape combinations.
In 1954, Matthews, Brons and Hazebroek (MBH) proposed a method of determining the average pressure in a bounded reservoir. The MBH method was developed for use with a Horner plot. The technique is to extrapolate the Horner semilog straight line to infinite shut-in time, which corresponds to a Horner time function of 1 and provides the so-called "false pressure," p*. The MBH method then provides correction plots for various rectangular reservoir shapes showing the relationship between p* and the average reservoir pressure,, as a function of the production time before the start of the buildup.
