Some Problems In Pressure Build-Up
Authors: Hurst William , Haynie Orville K. , Christie Mitchell , Walker Richard N. 
Published: December 2007

Hurst, William, Petroleum Consultant, Houston, Tex. Haynie, Crville K., Christie, Mitchell, and Mitchell Co., Houston, Tex., Members AIME, and Walker, Richard N., Junior Member AIME Christie, Mitchell and Mitchell Co., Houston, Tex.,

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This paper deals with certain abnormalities as observed in pressure build-up, but instead of abnormalities per se, these are phenomena that begin to tell us something of the contiguous nature of the formation further removed from the well. In a sense, this is a broadening of the basis of what pressure buildups can mean that now extend into the realm of subsurface interpretations.

The problem treated is an actual assignment in the study of the Atoka Conglomerate in Wise County, Tex. Here it has been observed a departure from the straight-line Lord Kelvin effect of pressure build-up to reveal two such broken straight-lines, one following the other. This has been interpreted as gas replenishment from contiguous lenses feeding into the main sand body, for which mathematics have been formulated, based on the series problem of unsteady-state fluid flow.

To sustain this method by an entirely different application, a radial drainage formula was developed from work published by Hurst and van Everdingen for a constant-rate problem with a fixed exterior pressure at the boundary. This was purely an empirical correlation, and the results have more than met the writers' expectations as it showed that build-up time was a function of drainage radius, and independent of well radius or skin effect. Thus, for the times in pressure build-up where these abnormalities are observed to occur, yield drainage radii for the main sand body that are in substantial agreement with those established independently from the lens problem.

There are associated problems connected with this study. One is establishing the distance of a gas cap over an oil column, based on this very drainage formula; and the other is an estimation of static bottom-hole pressure interpreted from the problem cited of these early investigators, where interference between wells occur.

Introduction

What this paper presents is some factual representation of abnormalities that appear in pressure build-up.