Slips positioning apparatus for a well operation

A slips positioning apparatus for a wellhead installation is installed in a fixed position relative to the blow out preventer and allows releasable locking of the slips relative to well center and driving movement of the slips relative to well center. The slips positioning apparatus includes a slips-mounting structure for accepting connection of the slips; an installation structure for mounting the apparatus rigidly above the blow out preventer and relative to well center. The installation structure is a plate that defines a first plane. The apparatus further includes a first and a second linear guides configured for movement of the slips-mounting structure relative to the installation structure along respective first and second directions in planes substantially parallel with the first plane; and first and second linear actuators for moving the slips-mounting structure respectively along the first and second linear guides. Slips are mounted on the slips mounting structure and positioned, including releasably locked and/or driven, by the apparatus relative to well center.

FIELD

The invention relates to a well operation apparatus and in particular a wellhead apparatus for positioning the slips in a well operation.

BACKGROUND

Wellbore operations employ pipe strings, sometimes called drill, production or work strings, each used for drilling and/or servicing. The pipe string can comprise a bottom hole assembly such as, when drilling, a drill bit attached to sections of drill pipe. As the well is drilled or serviced, additional sections of drill pipe are added to the pipe string to extend its length until the bottom hole assembly is deep enough to reach a depth of interest. Sections of pipe are joined together using threaded connections on the pipe, often referred to as “pin” and “box” connections, where the pin of one section of pipe is threaded into the box of an adjoining section of pipe. When the pipe string is removed from the wellbore, the sections of pipe can be removed from the pipe string by unthreading the connections and setting aside a pipe section.

While servicing or drilling wells, a BOP (blowout preventer) is installed on the wellhead. The purpose of the BOP is to close off the well in the event of an emergency and to seal the well while normal servicing or drilling operations are being conducted. To prevent the drill string from falling into the well, a device called “slips” are employed. The slips are a mechanical device with a set of jaws that allow the drill string to be moved up out of the well, with the slips acting to arrest automatically the drill string if it starts falling into the well. The slips can be unlocked to allow controlled movement of the drill string into the well, when desired.

Currently, the slips are positioned atop the BOP and are free to slide around relative to the BOP. This allows the driller to move the drill string with respect to the well casing and slips will slide to follow the string. It is desirable to move the drill string with respect to the well casing because often it is a requirement for multiple strings to be positioned in the well side by side and, so, the string to be controlled is off center.

However, the slips, being free to slide, are difficult to use in a slant rig. The slant orientation may tend to pull the slips to the low side. In addition, since the movement of the slips cannot currently be controlled, it is difficult to move and hold the slips in a position suitable to locate the drill string, as desired by the driller. Because of this, dangerous, time consuming and inefficient methods may be employed to move the slips and the drill string to the desired location and to counteract gravitational issues when operating in slant.

SUMMARY

In accordance with a broad aspect of the present invention, there is provided a method for positioning a slips relative to a well center of a wellbore, the method comprising: operating a slips positioning apparatus including: a slips-mounting structure for accepting connection of the slips; an installation structure for mounting the apparatus rigidly relative to well center, the installation structure having an upper surface defining a first plane; a first linear guide configured for movement of the slips-mounting structure relative to the installation structure along a first direction in a plane substantially parallel with the first plane; a second linear guide configured for movement of the slips-mounting structure relative to the installation structure along a second direction in a plane substantially parallel with the first plane; a first linear actuator for moving the slips-mounting structure along the first linear guide; and, a second linear actuator for moving the slips-mounting structure along the second guide; and actuating the first linear actuator to position the slips along the first direction.

In accordance with another broad aspect of the present invention, there is provided a wellhead installation comprising: a blowout preventer; a slips positioning apparatus installed in a fixed position relative to the blow out preventer, the slips positioning apparatus comprising: a slips-mounting structure for accepting connection of the slips; an installation structure for mounting the apparatus rigidly relative to well center, the installation structure having an upper surface defining a first plane; a first linear guide configured for movement of the slips-mounting structure relative to the installation structure along a first direction in a plane substantially parallel with the first plane; a second linear guide configured for movement of the slips-mounting structure relative to the installation structure along a second direction in a plane substantially parallel with the first plane; a first linear actuator for moving the slips-mounting structure along the first linear guide; and a second linear actuator for moving the slips-mounting structure along the second guide; and slips mounted on the slips-mounting structure.

In accordance with another broad aspect of the present invention, there is provided a slips positioning apparatus for installing slips relative to well center, the slips positioning apparatus comprising: a slips-mounting structure for accepting connection of the slips; an installation structure for mounting the apparatus rigidly relative to well center, the installation structure having an upper surface defining a first plane; a first linear guide configured for movement of the slips-mounting structure relative to the installation structure along a first direction in a plane substantially parallel with the first plane; a second linear guide configured for movement of the slips-mounting structure relative to the installation structure along a second direction in a plane substantially parallel with the first plane; a first linear actuator for positioning the slips-mounting structure along the first linear guide; and, a second linear actuator for positioning the slips-mounting structure along the second guide.

DESCRIPTION OF VARIOUS EMBODIMENTS

The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

A slips positioning apparatus between the slips and the top of the wellhead such as the top of BOP, secures and moves the slips with respect to well center as defined by the wellhead/BOP will improve the ease and safety with which the slips can be employed and positioned. The slips positioning apparatus is installed, and acts, between the slips and a rigid installation point on the wellhead. The apparatus, also referred to herein as a slips table, provides XY linear guides and releasable locks and/or drivers to position the slips relative to well center. The apparatus includes a slips-mounting structure for accepting connection of the slips, an installation structure for mounting the apparatus rigidly relative to well center and linear slidable guides and the releasable locks and/or drivers for positioning the slips-mounting structure, and thereby the slips, along the X and Y directions relative to the installation structure and substantially orthogonally relative to a center axis of the apparatus.

It has been determined that a linear actuator, such as an hydraulic cylinder or a screw drive, may function as both the releasable lock and the driver to both move and lock position of the slips table components along the linear slidable guides. Double acting hydraulic cylinders may be particularly useful.

Referring toFIG. 1, a wellhead4is shown during an operation to handle a pipe string, herein a drill string3. A BOP2is mounted to the wellhead. Slips1are coupled onto a slips positioning apparatus, herein called slips table5, and the slips table is coupled to the top of the BOP2. Slips1can be controllably moved along directions X and Y by slips table5. Directions X and Y are two substantially perpendicular directions, each of which are substantially orthogonal relative to a center vertical axis through the slips table. The center vertical axis of the slips table can be aligned parallel with well center, defined inFIG. 1as axis C.

Referring also toFIGS. 2 and 3, the slips table apparatus5includes a base plate11, X direction linear actuators12, a center plate13, Y direction linear actuators14and a top plate15.

Each of the base plate, the center plate and the top plate include a central hole20,22,24, respectively. Each central hole passes through its plate from top to bottom. As such, the plates each have perimeter side edges11a,13a,15asurrounding the central holes. Perimeter side edges need not be continuous, as shown by plate15, wherein the central hole24extends to a side edge. In particular, one side of the plate has a passage24aconnecting to the central hole24.

Base plate11is configured, as by bolt apertures26, for rigidly mounting on the surface structure above the BOP2, such as on the BOP's uppermost end. Base plate11can be coupled to the surface structure with its central opening20centered on well center, for example with its central opening substantially concentrically positioned relative to the upper opening of BOP2. For example, the base plate may have a pattern of apertures26to work with the BOP flange. For example, there may be four slotted apertures26that are concentric with a center point of hole20. This arrangement may be equi-radial with the pattern on the top of the BOP, which generally matches a standard oilfield pipe connection flange bolt pattern. There are standard connection flange bolt patterns for different pipe diameters and pressure ratings. The base plate may be configured for the particular flange bolt pattern of the wellhead on which it is to be used. Apertures26in the base plate may be slotted to allow for some adjustment, such as rotational adjustment of the slips table during installation.

While the slips table5is typically installed on the upper end of the BOP, the slips table could be installed on a casing flange, if there is no BOP, or on the rig floor.

In one embodiment, base plate11includes a pedestal27in which bolt apertures26are positioned. Pedestal27is on the underside of base plate11such that edges11aprotrude laterally beyond, and are slightly raised above, pedestal27.

Top plate15is configured, as by provision of holes32and/or hardware such as bolts or studs33to accept installation of the slips1. The selection and arrangement of holes/hardware may vary depending on the type of slips to be employed. The central hole24may have a diameter to at least match the opening diameter of the slips, which will be selected based on the well and string sizes of the operation.

In one embodiment, top plate15includes a pedestal34on which studs33are positioned. Pedestal34extends upwardly on the upper side of the top plate such that edges15aprotrude laterally beyond and below pedestal34. Pedestal34spaces the underside of slips1out of the way of plate15riding in rails30.

Center plate13is sandwiched between top plate15and base plate11. Center plate13defines at least a part of the linear guides, such as slide bearings. Linear actuators12,14allow driven movement of the top plate relative to the base plate along x and y-axis orthogonal to the center axis x, which may be installed in alignment with the well center axis C.

Center plate13is configured for slidably coupling to base plate11. In particular, center plate13is coupled to base plate11but there is a connection, such as rails28, between center plate13and base plate11that permit the center plate to move relative to the base plate. For example, in the illustrated embodiment there are rails on the underside of center plate13that engage slidingly on the side edges of base plate11. The rails may be formed by a pair of facing returns spaced apart a distance just slightly more than the width of the base plate and with a height such that the thickness of the base plate is retained between the returns and the underside of the center plate. The movement of center plate is substantially along a plane parallel with a plane defined along the expanse of the upper surface of the base plate. Rails28allow translation of center plate13relative to the base plate while holding the plates against separating in the Z direction. Stops may be provided to limit the range of motion and thereby to prevent overextension.

Movement of center plate13relative to the base plate may be driven by linear actuators12, such as hydraulic cylinders. There may be a pair of linear actuators positioned symmetrically relative to plate11to permit smooth operation. Each linear actuator12may be connected at one end to base plate11and at its opposite end to the center plate. The linear actuators12drive center plate13slidingly over base plate11.

In the illustrated embodiment, for example, rails30are on the upper side of center plate13. Rails30engage slidingly on the side edges15aof top plate15. The rails may be formed by a pair of facing returns spaced apart a distance just slightly more than the width of the top plate and with a height such that the thickness of the top plate is retained between the returns and the upper side of the center plate. Rails30allow translation of top plate15relative to center plate13while holding the plates against separating in the Z direction. Stops may be provided to limit the range of motion and thereby to prevent overextension.

Movement of top plate15relative to the center plate along rails30may be driven by linear actuators14, such as hydraulic cylinders as shown. There may be a pair of linear actuators14positioned substantially symmetrically relative to plate15to permit smooth sliding movement. Linear actuators14may be connected at one end to top plate and at their opposite end to the center plate to drive top plate slidingly over center plate.

In the assembly table, rails28are oriented substantially orthogonally to rails30such that motion therefrom is in two substantially perpendicular directions.

Actuators12and14are each in communication40a,40bwith an actuator control system42. The pairs of actuators can thereby be controlled by an operator to move the slips table along the X and/or Y-axis. In the illustrated embodiment, communications40a,40bare through hydraulic lines (not shown) and manifolds44a,44bare provided for supporting connection of the hydraulic lines between actuators12and14and a main hydraulic supply controlled by actuator control system42.

In use, the base plate11is mounted in a fixed position relative to the BOP2with well center axis C passing up through hole20. For example, the base plate11may be rigidly fixed to the top of the BOP with hole20concentrically oriented relative to the BOP top opening.

The center plate13is installed over base plate11with rails28fitting over the edges11aof base plate11. This locks the center plate to the base plate against movement in all axis except the X direction. In particular, the center plate is free to slide with respect to the base plate along direction X. Linear actuators12are connected between the base plate and the center plate to impart a drive force to the center plate to move in the X direction.

The slips1are rigidly fixed to the top plate15. The top plate is installed over center plate13with side edges15aslidingly engaged within rails30. The rails lock the top plate to the center plate in all axis except the Y direction such that the top plate is free to slide with respect to the center plate along the Y direction. Linear actuators14are connected between the top plate and the center plate to impart force to move the top plate along rails30in the Y direction.

As the base plate, center plate and top plate are all furnished with a central hole, the drill string can pass through the whole assembly. These holes have a diameter at least as large as the size of the BOP opening or wellbore inner diameter. This is typically 7⅙″ to 13⅝″ in land based well service applications. Holes20,22,24, therefore, are large enough and the range of motion of the linear actuators is large enough so that the drill string can be moved to any location within the well bore inner diameter without contacting the slips table apparatus. Instead, the motion of the drill string is constrained only by the inner diameter of the well bore. The cylinders may be sized with a stroke length appropriate to retain engagement of the plates. In other words, the cylinder stoke lengths may be selected to avoid driving the plates too far, such that the plates remain engaged with each other.

In one embodiment, linear position sensors, such as transducers46, are provided to permit position sensing and to enhance automation options for the cylinder control.

By driving actuators12,14, the slips can be moved in any combination of the X and Y directions even while the drill string3is installed in the well and passing through slips1. Actuators12may be driven independently of actuators14. Once positioned, the actuators may be lockable such that once stroked to position slips1, they may lock the position of the slips relative to well center. Slip positioning apparatus, therefore, may be useful in a slant rig operation, where well center is off vertical. All driving operations may be conducted remote from the slips, which offers reduces risk of injury to personnel. With transducers46providing positional feedback, the location of the slips relative to the well center can be determined remotely as well.

The stroke lengths of actuators12,14may be similar or dissimilar, depending on the range of motion desired. It is desirable in some situations, for example, to be capable of fully removing the slips off the drill string. To allow for this to occur, the Y direction linear actuators14are furnished with a stroke long enough to move plate15entirely out of overlapping position with hole20and side edges15aand/or rails30are long enough to accommodate this range of motion, while retaining plate15engaged by plate13. This allows the slips to be fully pushed off and laterally away from the drill string, as shown inFIG. 4, once slip gate50is removed from its receptacle in slip bowl52. In particular, once slip gate50is removed, the actuators14can drive plate15along the Y direction such that the plate hole24and passage24amove past and away from opening22and drill string3. This carries slips1laterally away from the drill string into a parked position. Control system42can have a function to prevent the actuators14from driving the plate15when the slips are engaged on a drill string.