Wells – Processes – Assembling well part
Reexamination Certificate
2001-04-14
2003-07-15
Tsay, Frank S. (Department: 3672)
Wells
Processes
Assembling well part
C166S081100, C175S218000
Reexamination Certificate
active
06591916
ABSTRACT:
The present invention relates to a method for drilling wells, particularly drilling for hydrocarbons.
In drilling wells for hydrocarbons, particularly petroleum, the drill string is rotated to drive the drill bit and mud is circulated to cool lubricate and remove the rock bits formed by the drilling.
As the drill penetrates into the earth, m ore tubular drill stems are added to the drill string. This involves stopping the drilling whilst the tubulars are added. The process is reversed when the drill string is removed e.g. to replace the drilling bit. This interruption of drilling means that the circulation of the mud stops and has to be re-started on recommencement of the drilling which, as well as being time consuming is and expensive, can also lead to deleterious effects on the walls of th e well being drilled and can lead to problems in keeping the well ‘open’.
Initial Patent Application PCT/GB97/02815 of Oct. 14
th
1997
A method for continuous rotation of the drill bit whilst adding or removing tubulars is described in patent Application PCT 97/02815.
In this application there is provided a method for drilling wells in which a drill bit is rotated at the end of a drill string comprising tubular members joined together and mud is circulated through the tubular drill string, in which method tubular members are added to or removed from the drill string whilst the circulation of mud continues.
The method provides for supplying mud, at the appropriate pressure in the immediate vicinity of the tubular connection that is about to be broken such that the flow of mud so provided overlaps with flow of mud from the top drive, as the tubular separates from the drill string the flow of mud to the separated tubular is stopped e.g. by the action of a blind ram or other preventer or other closing device such as a gate valve.
The separated tubular can then be flushed out e.g. with air or water (if under water) depressured, withdrawn, disconnected from the top drive and removed. The action of the preventer is to divide the tubular connection into two parts e.g. by dividing the pressure chamber of the connector connecting the tubular to the drill string. The drill string continues to be circulated with mud at the required pressure.
In a preferred embodiment of the invention a tubular can be added using a clamping means which comprises a coupler, and the top end of the drill string is enclosed in and gripped by the lower section of the coupler, in which coupler there is a blind preventer which separates the upper and lower sections of the coupler, the tubular is then added to the upper section of the coupler and is sealed by an annular preventer and the blind preventer is opened and the lower end of the tubular and upper end of the drill string joined together.
In use, the lower section of the coupler below the blind preventer will already enclose the upper end of the drill string before the tubular is lowered and when the tubular is lowered into the coupler the upper section of the coupler above the blind preventer will enclose the lower end of the tubular.
The tubular can be added to the drill string by attaching the lower section of the coupler to the top of the rotating drill string with the blind preventer in the closed position preventing escape of mud or drilling fluid. The tubular is lowered from substantially vertically above into the upper section of the coupler and the rotating tubular is then sealed in by a seal so that all the drilling fluid is contained, the blind preventer is then opened and the tubular and the drill stand brought into contact and joined together with the grips bringing the tubular and drill string to the correct torque.
The lower end of the tubular and the upper end of the drill string are separated by the blind preventer such that the tubular stand can be sealed in by an upper annular preventer so that when the blind preventer is opened there is substantially no escape of mud or drilling fluid and the tubular stand and drill string can then be brought together and made up to the required torque.
To remove another tubular from the drill string the tubular spool or saver sub under the top drive penetrates the upper part of the pressure chamber, is flushed out with mud and pressured up; the blind ram opens allowing the top drive to provide circulating mud and the spool to connect to and to torque up the into the drill string. The pressure vessel can then be depressured, flushed with air (or water if under water) and the drill string raised until the next join is within the pressure chamber, the ‘slips and grips’ ram closed, the pressure chamber flushed with mud and pressured up and the cycle repeated.
Preferably the coupler includes rotating slips which support the drill string while the top drive is raised up to accept and connect another tubular.
The coupler may be a static coupler connected to and above the wellhead BOP stack with a top-drive or mobile coupler handling the tubulars above the static coupler working hand-to-hand.
The coupler may be a mobile coupler disconnected from the wellhead BOP stack with a top-drive or second mobile coupler handling the tubulars above it working hand-to-hand and thereby allowing the string to move steadily in the vertical plane when tripping is in progress or allowing drilling to continue while a tubular stand is being added.
The coupler may be a mobile coupler disconnected from the wellhead BOP stack with one or more identical mobile couplers, above, which take it in turns to become the bottom coupler thereby working hand-over-hand and also facilitating steady movement of the string when tripping is in progress or drilling is continuing while a tubular is being added to the string.
The method disclosed in Patent Application PCT/GB97/02815 locates the grips and slips either inside or outside the coupler pressure hull.
I have now devised an improved structure and method of continuous drilling.
According to the invention there is provided a well head assembly which comprises a BOP stack above which there are positioned sequentially:
(i) a lower annular preventer
(ii) lower grips and slips adapted to engage a downhole drill string
(iii) a blind preventer
(iv) upper grips and slips adapted to engage a tubular to be added to the drill string and
(v) an upper annular preventer
in which the upper grips and slips are able to pass through the blind preventer when the blind preventer is in the open position.
This is illustrated in
FIG. 1
of the accompanying drawings and the sequence of operation of adding a tubular to the string is illustrated in FIG.
2
.
The Grips and Slips Function
The grips are the means of gripping the tubulars strongly enough to transfer a rotational force or torque, by friction surfaces shaped to fit the external surface of the tool joint, or the shaft of the tubular, or by powered rollers, both methods of which are common in conventional iron roughnecks.
The slips are the means of applying an axial force to the tubular to prevent it slipping, by wedge action and or by obstructing the passage of the upset of the tool joint, as is common in conventional slips.
The grips & slips combine the functions of gripping and slipping either by modifying the profile of the friction pads, rollers or slips or by integrating the separate grips and slips to operate in concert.
The orientation of the well head assembly refers to the well head assembly when in position on a drill string.
The gripping mechanism with or without integrated slips may be achieved by simply altering the materials and profile of the inserts of the conventional Rotary BOP, Diverter, Preventer, or Rotating Control Head. Alternatively the gripping may be achieved by conventional methods of wedge, lever, motorised rollers screw or other mechanical means caused by hydraulic, electrical or mechanical means such as is currently applied within collett connectors, casing tongs rotary power slips or current iron roughnecks.
In use, the invention enables a tubular to be added to a drill string when a drill string is rotating and drilling mud is flowing. Th
Bartlett & Sherer
Coupler Developments Limited
Sherer Ronald B.
Tsay Frank S.
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