Downhole Shut-Off Tool
Authors: Gazda I.I. , Cantlon H.L. , Kingelin G.F. 
Published: December 2007

The early time buildup pressure response resulting from a surface shut-in of low to intermediate productivity wells can be dominated by wellbore storage (after production) and/or fluid segregation effects for extended time periods. The purpose of this paper is to periods. The purpose of this paper is to introduce a new downhole shut-off tool that reduces the wellbore volume during the shut-in period and allows the buildup pressure and period and allows the buildup pressure and temperature measurements to be made with surface recording downhole pressure/temperature instruments. Potential savings in well testing costs, minimizing afterflow and segregation effects and the possibility of acquiring early-time information on naturally fractured systems, nearby impediments, and hydraulic fractures, are motivating factors for conducting a buildup test by means of a subsurface shut-in.

Shutting in the well near the formation face reduces the wellbore volume thus virtually eliminating the effects of fluid compressibility and fluid segregation.

Introduction

Several different types of downhole shut-in tools, have been used in the past. Most of these attempts had some difficulties because of temperature, differential pressure, chemical wad mechanical problems. Due to advances in material mad design problems. Due to advances in material mad design technology, a new tool was developed to overcome these problems. For the engineer faced with the problem of making decisions on stimulation at the problem of making decisions on stimulation at the wellsite, the use of the downhole shut-off tool with surface recording pressure temperature instruments in pre-frac and/or post-frac well testing offers a solution. The quality control of the data can be maintained and sufficient data can be gathered to allow evaluation at the wellsite.

During the past twenty years, transient pressure analysts have been dealing with the pressure analysts have been dealing with the effects that change the pressure response of the well in the early part of a buildup before the "Horner straight line" develops. These effects on the pressure response include wellbore storage, phase segregation, various types of skin effect phase segregation, various types of skin effect such as perforations, partial penetration, fractures, washouts, inclined wellbore, aid non-Darcy flow, to name a few. To be able to evaluate the various skin effects including the fracture characteristics in low producing gas wells, the, downhole shut-in tool virtually eliminates the long duration of wellbore storage and/or phase segregation effects such that the effects of the skin can be evaluated. It can be readily seen that there is a tremendous advantage in shutting in the well near the formation to enhance gathering well test data that can be used to describe the reservoir near the wellbore.

THEORY

The idealized theory of pressure buildup assumes that after production and fluid phase segregation in the wellbore does not exist. Tn practice however, the well is normally shut-in at practice however, the well is normally shut-in at the wellhead allowing the after production and fluid phase segregation effects to dominate the pressure response of the well for a time period. pressure response of the well for a time period. Chen and Brigham state that the buildup time necessary to reach "Horner straight line" (after production has ceased dominating the pressure production has ceased dominating the pressure response) can be estimated by

(1)

where

Vw = wellbore volume available for fluid compression (bbl)

C = compressibility of the wellbore fluid (1/psi)

S = skin factor (dimensionless)

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