Wells – Valves – closures or changeable restrictors – Fluid operated
Patent
1991-10-08
1993-03-16
Britts, Ramon S.
Wells
Valves, closures or changeable restrictors
Fluid operated
166323, E21B 3408, E21B 3410
Patent
active
051936194
DESCRIPTION:
BRIEF SUMMARY
This invention relates to well control apparatus, and concerns in particular that apparatus employed in discontinuing a well testing procedure, especially an oil well testing procedure.
BACKGROUND OF THE INVENTION
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 placing in 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 lowered into the well a test string--a length of tubing containing the tools required for testing. The flow of fluid from the formation of interest into the well bore and thus to the test tools is controlled by a valve known as a sub-surface control valve.
The operation of the various tools include in the downhole test string 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 actuated by changes in annulus pressure are at present much in vogue, and it is this type of actuation mechanism that is to be employed with the apparatus of the invention.
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. The achievement of such a fixed reference pressure is the subject of our co-pending British Patent Application No. 89/07,098.1 (Publication No: 2,229,748A; FN P1049).
Following completion of the well testing procedure, it is necessary safely to "shut down" the test tools, and then to remove the test string from the packer assembly and pull it to the surface. These operations do, however, require careful control and planning. In the case of pressure-differential-actuated test tools, for example, the string will, at the end of testing, still contain the high pressure reference gas which has been used in creating the required differentials. It is extremely desirable for this gas in some way to be vented before the string reaches the well head, so that there are no potentially dangerous pressures trapped within the tools when the test string is received at the surface.
Additionally, it is an advantage if there be incorporated within the test string some means of isolating the upper portion of the tubing thereof, and of subsequently providing a route for communication between this tubing and the annulus, so that tubing-contained well liquid above the test string can then be circulated out of the tubing before it is raised to the surface. The isolation is conveniently accomplished using a ball valve suitably placed near the top of the test string, and such a ball valve particularly suitable for effecting this isolation is described in our co-pending British Patent Application No. 89/09,903.0 (Publication No: 2,231,069A; FN P10
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Buchanan Robert D.
Edwards Jeffrey C.
Johns Ray
Britts Ramon S.
Exploration and Production Services (North Sea) Ltd.
Tsay Frank S.
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