Wells – Valves – closures or changeable restrictors – Fluid operated
Patent
1991-09-26
1993-11-09
Neuder, William P.
Wells
Valves, closures or changeable restrictors
Fluid operated
166324, E21B 3410
Patent
active
052594564
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to tools used in the testing of subterranean wells, and concerns in particular the mechanism by which such tools--especially but not exclusively those for use in hydrocarbon-bearing wells--are operated.
2. Description of The Prior Art
Whether at sea or on land, the first stages in the production of a new hydrocarbon well--an oil well--are the drilling of the well bore itself through the various formations within the earth's crust beneath the drilling rig, followed by "casing" (the introduction and cementing into position of piping which will serve to support and line the bore) and the introduction into the bore, at the depth of a formation of interest, of a device known as a packer, into which inner tubing (of smaller diameter than the casing) can subsequently be lodged.
The next work carried out is normally some programme of testing, for the purpose of evaluating the production potential of the chosen formation. The testing procedure usually involves the measurement of downhole temperatures and pressures, in both static and flow conditions (the latter being when fluid from the relevant formation is allowed to flow into and up the well), and the subsequent calculation of various well parameters. To collect the necessary data there is used a test string--a length of tubing containing the tools required for the testing--that is lowered into the well bore to the required (test) depth. Either the packer has previously been placed at that depth, and the test string is then set into the packer, or the packer is sent down as part of the test string, and then set into place in the bore; in any event, once the string is set in the packer and the packer is set in the bore, the tubing of the string is isolated from the surrounding well.
One essential component of the test string is a valve known as the downhole valve, which is used to control the flow of fluid out of the formation and into and up the well tubing. The density of drilling fluid in the tubing above this valve is adjusted such that its hydrostatic pressure at the depth of the formation is lower than the formation fluid pressure. Thus, when the valve is opened, formation fluid is permitted to enter the well bore through perforations in the casing and flow into the tubing string (and possibly to the surface therethrough). This contrasts with the situation during drilling, when the drilling mud must exert a hydrostatic pressure greater than the formation fluid pressure in order to prevent the formation fluid's escape to the surface.
The operation of the various tools included in the downhole test string, including the opening and closing of the downhole valve itself--and, consequently, the control of the testing procedure--can be effected using one of three main types of mechanism. These types are those actuated by reciprocal motion of the pipe string (the inner tube, of which the test string constitutes a part), by rotational motion of the pipe string, or by changes in the pressure differential between the tubing and the annular space which surrounds it in the well--hereinafter referred to simply as "the annulus". Test strings wherein the tools thereof are activated by changes in annulus pressure are at present much in vogue, and it is this type of mechanism with which the invention is particularly concerned.
A mechanism of the annulus pressure-responsive type requires the provision and maintenance of a fixed "reference" pressure within the tool. This, used in conjunction with an adjustable (and higher) annulus pressure, allows the establishment of the chosen pressure differential necessary to control the operation of the appropriate component of the test string.
To ensure that the downhole tools operate within a narrow known band of applied annulus pressure, it is essential that a constant reference pressure be established within the tool string. A convenient such pressure to trap is the hydrostatic ambient (annulus) pressure experienced by the string after it has been lowered d
REFERENCES:
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patent: 4429748 (1984-02-01), Beck
patent: 4448254 (1984-05-01), Barrington
patent: 4655288 (1987-04-01), Burris, II et al.
patent: 4736798 (1988-04-01), Zunkel
patent: 5101904 (1992-04-01), Gilbert
Buchanan Robert D.
Edwards Jeffrey C.
Johns Ray
Exploration and Production Services (North Sea) Ltd.
Neuder William P.
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