GB2531931A - Hang-off device - Google Patents

Abstract

A hang-off device 8, or spider, for holding a tubular string 6 extending through a drill floor 3 of a drilling, production or work over facility, said device comprising rams 11a/11b;12a/12b that are displaceable from a disengaged position with the tubular string 6 and an engaged position with the tubular string. The device comprises at least two sets of rams 11a/11b; 12a/12b having different internal diameters in the engaged position. On of the sets of rams 12a/12b may be arranged above another set of rams 11a/11b. The rams may be guided on tracks set in side walls. A second set of rams may have a collar extending upwards, the collar having an internal diameter larger than the tubular string and an external diameter smaller than the internal diameter of an elevator tool.

Description

Hang-off device The present invention relates to hang-off devices for tubular elements, so-called spiders, i.e. pipe and tube grippers that are adapted to hold a tubular string extending through a drill floor, typically while the string is being assembled or disassembled.

Conventionally, slips have been used to hold tubular strings temporarily while 10 they are being assembled or disassembled. The slips are placed between the string and the opening in the drill floor, through which the string is extending, typically in connection with the rotary table.

The following prior art references show examples of slips: US 2006/225891, US 15 2014/131051 and WO 97/49944. These examples use slips of varying diameters to grip tubulars of different diameters.

The recent years, however, instead of using slips or any other hang-off means placed directly in the rotary table, these means have been replaced by a device usually called a tubing spider. Spiders are rams that are linearly moveable transverse to the axis of the tubular that it is intended to grip. The spider is arranged on top of the drill floor and resting on the rotary table. It comprises rams that are slidable in parallel with the drill floor to grip and hold selectively the tubular string while an elevator or similar is used to connect or disconnect a tubular section at the upper end of the tubular string. The spider is applied as a hang-off point for, e.g., each riser joint section to be run while making up the connection to the next riser joint section. Examples of such spiders are shown in US 2014/166297 and US 6237684.

However, some offshore operations require the running of different types of, e.g., riser sections, with varying outer diameters and/or varying hang-off diameters. Examples of such operations could be completion operations using a landing string set-up: i.e. a completion riser run within a marine riser, or running of special riser joints in a work-over operation such as for instance tension or safety joints with larger outer diameter than a standard riser. In such operations, the spider will have to be changed in the middle of the operation to allow for running of different diameter tubulars, or slips have to be used in addition to the spider.

Changing between different types of spiders and/or splitting spiders to allow for passage of nonconforming riser section outer diameters, add to operational time and to possible HSE risk. To reduce operational time and HSE challenges, a spider capable of running riser joint sections with varying hang-off points and diameters is proposed.

Consequently, the present invention provides a special spider that has at least two sets of rams with different internal diameter when the rams are brought together to grip a tubular string, as defined in the appended claim 1.

The invention will now be explained in detail, referring to the enclosed drawings, in which: Figure 1 shows schematically the spider of the invention placed on a mobile drilling unit, Figure 2 shows the spider of the present invention in cross section in a fully open state, Figure 3 shows the spider of the present invention in cross section gripping a tubular with the large diameter rams, Figure 4 shows the spider of the present invention in cross section gripping a tubular with the small diameter rams, Figure 5 shows the spider of the present invention in isometric view in a fully open state, Figure 6 shows the spider of the present invention in isometric view with the large diameter rams closed, Figure 7 shows the spider of the present invention in isometric view with the small diameter rams closed, Figure 8 shows the spider of the present invention in planar view in a fully open state, Figure 9 shows the spider of the present invention in planar view with the large 10 diameter rams closed, Figure 10 shows the spider of the present invention in isometric view with the small diameter rams closed, Figure 11 shows an isometric view of the spider of the present invention with a tubular section held in an elevator, Figure 12 shows the same as in figure 11, but with the small diameter rams gripping the tubular section, and Figure 13 shows the same as in figure 12, but with a riser connection tool ready to connect an additional tubular section.

Figure 1 shows schematically a mobile drilling unit (MODU) 1 with a derrick 2 and a drill floor 3. A rotary table 4 is arranged around an opening 5 in the drill floor 3. A riser 6 extends through the drill floor 3 and down to the seabed 7. The riser is suspended in a draw-work 9. A spider 8 according to the invention is arranged on top of the rotary table 4. The spider 8 will be explained in detail below.

Figures 2, 5 and 8 show the spider 8 of the invention in a fully retracted state, in cross-section, isometric view, and planar view, respectively. The spider 8 rests on top of the rotary table 4 through a load ring 10, which is arranged within the opening 5 in the drill floor 3. The load ring 10 may be a separate component or be a part of the rotary table 4 or a part of the spider 8. The load ring 10 transfers loads from the spider to the rotary table.

The spider 8 of the present invention comprises two sets of rams; a set of large diameter rams 11 a, 11 b, and a set of small diameter rams 12a, 12b. The large diameter rams 11a, 11 b are arranged closest to the drill floor 3 and the small diameter rams 12a, 12b are arranged on top of the large diameter rams 11a, 11 b.

As shown in figure 5, the rams are received in tracks 13, 14 in sidewalls 15, and they are horizontally slidable along these tracks.

The rams 11a, 11 b and 12a, 12b provide two separate hang-off points for tubular sections, as will be described below. In figures 2, 5 and 8 the rams have been fully retracted to allow a component 16, such as diverter housing or a tension joint attached to the riser string, to pass through the opening 5 in the drill floor. Such components may have an outer diameter that is only slightly less than the internal diameter of the rotary table 4.

In figures 3, 6 and 9, the large diameter rams 11a, 11 b have been moved, e.g., by hydraulic cylinder arrangements (not shown) towards each other. This creates an opening through the spider 8 with a diameter suitable for hanging off a riser section 17 with a relatively large diameter. The riser section 17 has a shoulder 18 (in this case below an end flange 19) that can rest on the rams 11a, 11b. The rams 11a, 11 b will in turn rest on the load ring 10. In this configuration of the invention, the smaller diameter rams 12a, 12b are radially retracted to provide a minimum opening as large as the inner diameter of the load ring 10.

As shown in figures 6 and 9, the large diameter rams 11a, llb have cut-outs at 30 the ends facing one another. This is to accommodate peripheral lines that may be clamped on the outside of a riser string.

When a smaller diameter tubular section 20, such as workover riser, completion risers, casings and drill pipes, is to be hanged-off, the small diameter rams 12a, 12b are moved towards one another, as shown in figures 4, 7 and 10. The predefined diameter of the opening formed by these rams 12a, 12b, which is significantly smaller than the large diameter formed by the large diameter rams 11a, 11b, is adapted to grip a shoulder 21 on the tubular section 20. The rams are displaced by, e.g., hydraulic cylinder arrangements (not shown), and the rams 12a, 12b may slide on top of the large diameter rams 11 a, 11 b or in the tracks 14 shown in figures 5 -7. The load on the rams 12a, 12b is transferred to the large diameter rams 11a, 11 b and from there to the load ring 10.

The rams 12a, 12b also each carry one half of a collar section 22 that, when the rams are brought together forms a cylindrical part with a predetermined outer diameter. The significance of this will be explained below.

Figure 11 shows the spider 8 of the invention, through which a tubular section 20 of relatively small diameter extends. The tubular section 20 hangs in an elevator 23, which grips the section 20 below a collar 24 (see figure 4).

In figure 12 the small diameter rams 12a, 12b have been brought together around the tubular section 20. The elevator 23 is lowered and the collar 22 of the rams 12a, 12b is received in an annular space between the elevator 23 and the tubular section 20. Hence, the upper edge of the collar 22 may be received by the shoulder 21 of the tubular section 20. Each half of the collar 22 is preferably bolted to the rams 12a, 12b by a plurality of bolts 26. Thereby the collar 22 can be replaced by a different collar or by a planar gripping plate, according to the needs.

Figure 13 shows the tubular section 20 hanging in the rams 12a, 12b and a riser connection tool 25 arranged around the upper part of the tubular section to connect a further section 26 to the first tubular section 20.

Above, a spider having two sets of rams is described. It is within the ambit of the invention to arrange additional set of rams, preferably in a layered arrangement, one set of rams on the top of another. Each set of rams may also comprise more than two rams that are moved into engagement with the tubular string from different directions.