When drilling for oil, it is not uncommon that the length of the drill string exceeds 6000 meters. The drill string is usually composed of lengths of pipe about 10 meters long. In the course of a drilling operation, the entire drill string has to be drawn up and disassembled several times for replacing the drill bit, rigging up and cementing casings, and for other reasons. During a "trip", as the withdrawal of the drill string is known, the drill string is normally broken down in lengths of three pipes, i.e., about 30 meters, and these stands or "thribbles" of pipe are temporarily stored verti¬ cally in the derrick.

The normal procedure earlier was to have two derrickmen up in the derrick for guiding the screwed-apart stands of pipe to the side for racking the pipe lengths in the derrick, and this procedure is still followed to some extent today. This job, in addition to requiring the labor of two men, is both difficult and dangerous. The difficulties and risks increase in offshore drilling, especially when using drilling vessels and other floating platforms, and various solutions for semi- and fully-automatic handling and temporary storage of stands of drill pipe have been proposed and utilized in practice. The most advanced systems today comprise pipe- racking equipment which takes hold of the stand of pipe that has been pulled up by the hoisting equipment on the derrick before the length of pipe has been screwed apart from its neighbors, and after disengagement transports the pipe laterally to a storage automat in the derrick. The storage automat comprises a storage platform on the drill floor, and at least one so-called finger board, which is spaced a suitable vertical distance above the storage platform and contains grooves for receiving the respective stands of pipe. On each of the fingers of the finger board, wherein the spaces between the fingers form the grooves for receiving

-BURE U

OMPI

the pipes, there are remotely controlled locking means which secure the individual lengths of pipe within the grooves. When the drill string is to be reassembled and guided down into the well once again, the lengths of pipe are retrieved one at a time from the vertical storage rack by means of the racking equipment. The pipe racking equipment consists primarily of horizontal arms with a grab/support claw an one end of the arm that is intended to engage with a length of pipe. The arms can be moved toward and away from the line of drilling (the well), and toward and away from the vertical storage rack. At least one of the arms can be moved vertically, for raising and lowering the stand of pipe.

Although the handling and racking of stands of pipe in the derrick can thus be said to be fully mechanized, there is a - need for improvements on the prior art systems. The pipe racking equipment, i.e., mainly the arms, should be able to execute more movements, and the arms should be able to be controlled accurately and stopped precisely at selected locations for depositing and retrieving the stands of pipe at the rack. The finger board has several parallel receiving grooves with associated access openings, and the respective stands of pipe must be guided into the correct groove during racking. There is therefore a need for simplifying the mechanized handling of pipe to enable the pipe racking to be accomplished with fewer, but controlled and defined, move¬ ments. This can be obtained by ensuring that the stands of pipe are deposited in and removed from the vertical storage rack at the same, fixed location, the lengths of pipe being moved in a defined manner between the line of drilling, where the drill string is located, and the fixed access opening to the rack, i.e., the place where a stand of pipe enters the groove of a finger board and is retained in that groove, the respective grooves being brought successively, as needed, into a position in which the groove opening coincides with the fixed deposit/retrieval location.

An embodiment of this type provides the advantage that racking

OMPI ^~~

is performed between two fixed, defined positions, namely, the line of drilling and the rack access opening, and the racking operation therefore is accomplished with few and defined movements of the racking members. When the racking equipment comprises horizontal racker arms with a grab/ support head that is movable laterally within the derrick frame, the grab/support head is preferably mounted on a support arm that is pivotable about a vertical axis and is carried by the racker arm, said support arm also being telescopic so that the grab/support head can be moved relative to the axis of rotation of the support arm. For racking the drill string, the racker arm moves between two distinct positions, i.e., from the line of drilling to a position in which the length of pipe held by the grab, by pivoting the support arm, is moved into a position vis-a-vis the fixed entrance to the rack. Thereafter, the grab/ support head is moved in a direction toward the rack entrance and toward the groove in the finger board that has been brought into alignment with said entrance. This ove- ent will also be distinct and defined, since the movement of the pipe into the groove is translational, stopping when the the pipe abuts against a barrier in the groove or against another stand of pipe already deposited within the groove. Removal of pipe from the rack occurs in a similar manner, by reversing the above movements.

Preferably, the storage rack is formed as a carousel, wherein the finger boards are substantially circular and rotatable about a common vertical axis, with radially extending fingers and intermediate grooves therebetween. By rotating the finger boards, preferably utilizing a common, central, vertical column, the grooves can successively be brought into a predetermined orientation, with the groove opening ready to receive/release a stand of pipe, and this groove opening then represents the access opening of the rack. At this location a guide means can also be arranged, if desired, and in that case the guide means would then represent the access opening of the rack.

In a preferred embodiment, the carousel comprises one or more fixed annular frames which are concentric with the axis of rotation of the carousel, each ring having a minimum aperture corresponding to the cross section of the bundle of pipe strings that the carousel can hold. Each ring is discontin¬ uous, having a gap at the perimeter which forms the access opening to the rack.

Preferably, two storage carousels are placed on each side of a joint racker- assembly, with the rack access openings facing toward each other.

Within the individual grooves of the finger board, simple snap-locks may be used for retaining the lengths of pipe in the groove. Alternately, remotely controlled latch mechanisms or the like could also be used. The annular frames form an outer safeguard for the pipe bundles, and the perimeter gaps in the rings form the fixed access openings to the racks.

The invention will be described in greater detail in the following with reference to the accompanying drawings, wherein:

Figure 1 is a schematic drawing, in cross section, of a derrick equipped with an assembly in accordance with the invention,

Figure 2 shows the derrick of Figure 1 in plan view, with a horizontal section through the derrick along line II-II in Figure 1, drawn on a larger scale, and

Figure 3 shows the derrick in cross section as in Figure 1, with a bundle of pipe strings stored vertically in the derrick.

The derrick is designated by reference numeral 1, and the line of drilling is designated by 2. The drill string is not

shown, but during a drilling operation it will extend down into the well 3 along the line of drilling 2. The necessary equipment for drilling, such as hoisting equipment with elevator, kelly, rotary table, etc., is not shown, as the equipment utilized is known per se.

In the derrick 1, laterally of the line of drilling 2, two storage racks 4 and 5 are placed for temporary storage of stands of pipe during a "trip". Racking equipment is placed between the two racks 4,5, in this case comprising a lower racking assembly 6 and an upper racking assembly 7. The lower racking assembly 6 comprises essentially a racker arm 8 which in this case is movably supported by a horizontal support member 9. A column 10, rotable about a vertical axis, is mounted on the racker arm 8 and carries a support arm 11 at the upper end thereof. The support arm 11 is telescopic and the telescopic arm carries a grab/support head 12 formed for grasping and holding a stand of pipe 13, see Figure 3. The horizontal support 9 is mounted in a guide 14 that permits upward and downward movement of the support member 9, as indicated by the twin-headed arrow at the guide 14.

The upper racking assembly 7 is constructed in the same way as the lower assembly, but its horizontal support member 15 is fixedly attached to the derrick 1. The grab head 16 on the upper assembly can be formed like the grab head 12 , but it does not need to be made for supporting weight, as its function is only to hold about the pipe and guide it.

The racks 4 and 5 are identical, but mirror images of each other when in position, and only the rack 4 will be described. A central column 17 is pivotally mounted on the drill floor 18 and on a bracket 19 at a higher point on the derrick 1, respectively. At its base, the central column 17 carries a circular storage platform 20, and spaced apart vertically above this platform, the central column carries

-βURi- __OMPJ

^• WϊprJ-

a lower and an upper finger board, 21 and 22, respectively. The two finger boards are identical, having radially extending fingers with intermediate grooves opening toward the peri¬ meter of the circular finger board. Per se, the finger boards

⁵ are made like prior art finger boards with parallel grooves and fingers, but in this case the grooves and fingers are oriented radially, see Figure 2, on which some of the grooves 23 and fingers 24 are shown. In the rack 4 in Figure 2, four grooves are shown as being full, and one empty. In the rack

10 5 there is one full groove, one groove containing one stand of pipe, and one empty groove. The grooves and fingers are distributed around the entire periphery, and in the exemplary embodiment each of the finger boards has a total of 24 grooves, or the capacity to hold 96 pipe strings (four stands

15 of pipe in each groove). , and the two racks together can thus contain 192 stands of pipe. Assuming that each stand of pipe is 30 meters long, this arrangement provides storage capacity for 5,760 meters of pipe. The storage capacity could be increased by increasing the dimensions of the racks.

20

The mode of operation of the assembly of the invention will be explained in further detail with reference to the draw¬ ings. Let us assume that a drill string, represented by the line of drilling 2, has to be pulled up from the well 3. By

25 means of an elevator (not shown) , the drill string is drawn up so that the uppermost stand of pipe is above the level of the drill floor 18. The racker assemblies 6 and 7 are then actuated and the respective grab heads 12 and 16 take hold around the pipe. The stand of pipe is unscrewed in a manner

30 known per se. During this operation, the lower racker assembly 6 is moved vertically into a position in which the grab head 12 grips around the stand of pipe 13 (see Figure 3) . The elevator is released and the stand of pipe is unscrewed. The stand of pipe is now supported by the grab/support head

35 12. At the top, the stand of pipe is held by the grab head 16. By an upward movement of the lower racker assembly 6, the stand of pipe 13 can be elevated as required (Figure 3) .

The drill string remaining within the well is suspended from the rotary table by means of. slips, as known per se. From the position shown in Figure 3, the racker arms 8 and 26 are driven back from the line of drilling 2, to a position corresponding to that shown in Figure 1. The grab heads 12 and 16 are pivoted 90° one way or the other as indicated by the arrows in Figure 2, and the support arms 11 and 27 are extended, whereby the heads 12,16 are moved toward the selected rack 4 or 5. The receiving groove in the selected rack has already been brought into position through a corres¬ ponding rotation of the carousel. This rotary movement occurs in clearly defined stages, corresponding to the groove subdivision. Two annular frames 28 and 29 are mounted on the derrick 1. The apertures of the rings are adapted to the cross section of the pipe bundle 30 which can be placed in the carousel. Each annular frame has a gap in the perimeter, at 31 and 32 respectively, thereby forming openings which are in alignment with the receiving groove lying internally thereof. The stand of pipe 13 that is being racked is guided through the gaps 31,32 into the receiving grooves in the two finger boards 21 and 22. The pipe string is moved inwardly until it meets some resistance, after which the stand of pipe is lowered down onto the storage platform 20 by moving the lower racker assembly downwardly in the guide 14. The grab heads 12,16 are opened and guided back to the drill string at the line of drilling 2 with corresponding movements in reverse.

To retrieve stands of pipe from the pipe rack, the above procedure is reversed.

It should be understood that the carousel always rotates to a defined position and that all racking movements are distinct, from a fetching position to a delivery position. This provides more reliable operation and requires less inter¬ ference by the operator, and results in less damage to the pipes and threads during handling. The stands of pipe can

be secured in the receiving grooves with simple snap-locks, or remotely controlled flaps could be utilized. The annular frames 28,29 provide an additional safeguard around the racked pipe bundle. A retainer ring 31 is also preferably arranged around the storage platform 20.

The racking assembly can be constructed in various ways, which will be familiar to the skilled person, without depart¬ ing from the scope of the present invention. Instead of rotatable columns 10, the support arms 11,27 could rotate about fixed columns, or optionally rotate directly on the racker arms 8,26. The columns 10 could optionally be tele¬ scopic. Different modifications could also be imagined for the racker arms, etc. The important point is that all move- ments are distinct. Hydraulic actuators are preferably utilized, especially for the radial movements of the grab heads 12,16 toward and away from the pipe racks.