Boring or penetrating the earth – Boring a submerged formation
Reexamination Certificate
1999-08-06
2002-07-23
Bagnell, David (Department: 3673)
Boring or penetrating the earth
Boring a submerged formation
C175S321000, C166S355000
Reexamination Certificate
active
06422324
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of, and an apparatus for, sinking bore holes, in particular exploratory and extraction bore holes.
Exploratory bore holes are intended for the purpose of examining deposits and to make it possible to take samples of the material present in the deposit. Exploratory bore holes are sunk, in particular, when the deposit is at a considerable depth and/or bodies of water lying above the deposit, such as seas or oceans, preclude the possibility of sinking exploratory shafts.
Extraction bore holes serve the purpose of loosening deposit contents from soil strata. An example for extraction bore holes which may be mentioned is the extraction of marine sediments with diamond inclusions deposited on the sea bed. Such diamond-containing deposits have usually formed upstream of estuaries in the form of reasonably sized layers spread out over a rocky base. For extracting the diamond-containing sediment material, use is usually made of apparatuses which comprise a drill head which is lowered to the sea bed with the aid of an extensible drill-pipe string extending from a floating platform. Floating platform is to be understood as any arrangement of which the height above the sea bottom or ocean floor depends on the water level at any one time. Drilling vessels are particularly suitable here.
In order to make the drill head rotate, this rotational movement being required for the drilling operation, either said drill head is arranged in a rotationally fixed manner on the drill-pipe string and the latter is made to rotate with the aid of a rotary drive (powered rotary head) arranged above the platform, or the drill string is mounted in a rotationally fixed manner on the platform and there is provided a drive which makes the drill head rotate with respect to the drill string.
The overburden which is loosened during the drilling operation is usually delivered up to the platform, through the interior of the drill string, by so-called “reverse circulation” —for example by using the known air-lift method—and at the platform is fed, via a pipe bend which is provided at the top end of the drill string and is in connection with the inner volume thereof, to arrangements in which diamonds and overburden are separated in a known manner.
Since the prerequisite for a satisfactory drilling result is that the drill-head end side which is equipped with at least one cutting tool always butts throughout the drilling operation, with an approximately constant advancement pressure against the end side of the bore hole, the platform comprises an arrangement which allows a vertical movement of the platform, called for example by sea swell, without this resulting in the advancement force fluctuating to any great extent or in the drill head being lifted off from the sea bed at all. Such arrangements comprise pneumatic or hydraulic/pneumatic piston/cylinder arrangements which are usually connected to a relatively large equalizing volume and are connected, for example, on the cylinder side to the drill string and, on the piston side, to an arrangement which bears the drill string, for example a drilling derrick. The equalizing volume connected to the cylinders means that the platform can execute vertical movements without the force with which the drilling tool butts against the sea bed changing to any considerable extent. If the fastening point of the piston/cylinder arrangement on the platform side is located beneath those on the drill string, then it is possible, by adjusting the pressure in the equalizing reservoirs, for the contact pressure of the drill head on the sea bed to be adjusted to a desired value from a maximum of the resultant weight.
Although such arrangements for equalizing vertical movements of the platform have frequently been used for some time now, it is disadvantageous that the drill string has to project out of the top side of the platform at least by half the maximum expected displacement of the vertical movement of the platform—in relation to the central position thereof—and it is also only at this height that it is possible to fit the pipe bend which is necessary for discharging the overburden to the separating arrangement. This is disadvantageous because, on the one hand, the center of gravity of the platform is displaced upward to a considerable extent, as a result of which the period in which the weather is favorable enough for use of the platform is reduced, and, on the other hand, the overburden has to be delivered up to the level of the pipe bend. This is associated with high energy outlay, in particular, when the platform is located at its lowest level, for example in a wave trough, since the energy outlay depends on the height of the pipe bend above the water surface.
U.S. Pat. No. 3,319,726 discloses an apparatus which is intended for sinking bore holes in the sea bed and in the case of which, in order to equalize the vertical movement of the platform, the drill string comprises two telescopically interengaging drill-string parts which can be displaced axially relative to one another. Serving for mounting the inner and outer drill-string parts is a high-outlay arrangement which comprises a plurality of seals and floating pistons for pressure equalization, is filled with a hydraulic fluid and is fully encapsulated toward the outside against the penetration of sediment. The disadvantage with this apparatus is that it involves high outlay to produce.
Furthermore, U.S. Pat. No. 3,259,198 and U.S. Pat. No. 3,669,993 disclose apparatuses in the case of which the drill string comprises a telescopic part which is intended to equalize, inter alia, the movement induced by the sea swell. In the case of these apparatuses, the drilled maternal is delivered upward via the interior of the drill string by fresh water being fed to the bore hole under pressure. For this purpose, the drill string contains two concentrically arranged tubes which form an annular gap between them. The fresh water is fed by way of the annular gap, and the drilled material is transported away by way of the inner tube. The drill strings of these apparatuses too involve higher outlay to produce.
SUMMARY OF THE INVENTION
The object of the invention is thus further to develop a method and an apparatus of the abovementioned type so as to improve on these disadvantages.
This object is achieved by an embodiment of the method and by an embodiment of the apparatus set out below.
Since, in the case of the method according to the invention, the drill string comprises at least two telescopically interengaging drill-string parts which, during a vertical movement of the platform, induced for example by the sea swell, execute a movement relative to one another, it is no longer necessary for the drill string to project beyond the platform by at least half the maximum expected vertical deflection of the platform; rather, it is possible for the top end of the drill string to be located directly above the platform surface. As a result, on the one hand, this considerably reduces the height of the center of gravity of the platform, with the result that, in relation to those platforms in the case of which the vertical movement is equalized above the platform, it is also possible to use this platform in rough seas, and, on the other hand, the now likewise lower pipe bend considerably reduces the delivery height which is necessary for lifting the overburden, with the result that, with the energy requirement remaining the same, the delivery quantity can be increased or else, with the delivery quantity remaining the same, the energy requirement can be lowered. The negative pressure which prevails in the interior of the drill string when use is made of a reverse circulation method, preferably the air-lift method, which is know per se from FR 2523205 for example, means that a certain quantity of surrounding water is always sucked in through the annular gap which is inevitably located between the telescopically interengaging drill-string parts, so that there is always water circulating around thi
Tibussek Fritz
Von Wirth Hermann-Josef
Bagnell David
Foley & Lardner
Singh Sunil
Wirth Maschinen-und Bohrgeratefabrik GmbH
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