DEVICE FOR PROVIDING A PASSAGE FOR A DRILL STRING

Abstract: A swivelsub (10) comprises a sleeve member (2) which is sealable and lockable by means of the annular preventer of a blowout preventer, with at least one end portion (3) of the sleeve being lockable to the drill string (1), and with means providing sealing and enabling relative rotational movement between said sleeve member (2) and the drill string (1). The swivelsub (10) forms a sealable and pressure controlling passage for a drill string in the drilling well and is particularly useful for cutting operations of casings in an abandoned well.

Description: The present invention relates to a method of providing a passage for a drill string and to a drilling assembly. In particular, the invention relates to a drill string swivel device or swivelsub which provides a sealable and pressure controlling passage for a drill string extending through a blowout preventer, a well head and into a well borehole. The swivelsub is particularly suited for cutting casings in an abandoned well. In offshore exploration drilling operations, wells are drilled down through the subsurface earth formations. As the drilling operations progress, casings are run into the bore hole in order to restrain the surrounding formations and simultaneously provide guidance for the drill string. The first drilling phase is carried out with drill bits of relatively large dimensions, and the bore hole is subsequently provided with casings having correspondingly large dimensions, e.g. 30". In the subsequent drilling operations, drill bits with decreasingly smaller dimensions are used, and the well is provided with casings of correspondingly smaller dimensions. This results in a stepped reduction of the casing dimensions as drilling operations reach greater depths. Thus, when drilling operations are completed, several casings are located one outside another immediately below the sea floor or in the proximity of the well head. Today, the authorities do not permit the well head with associated casings to be left on the sea floor after exploration drilling is completed. The casings have to be cut below sea floor level, and the well head, including the casing portions and associated equipment, is retrieved and removed from the sea floor. Casings are commonly cut approximately 10 m below sea floor level. At present no method exists for cutting casings in a controlled manner without preliminary perforation of the casing to check whether there is a pressure build-up between the casing to be cut and the adjacent surrounding casing. Commonly, a pressure build-up is expected between a casing of one dimension and the next externally located casing. To ensure that the high gas pressure between the casings is not able to cause a blowout, the casing is normally perforated just above the cutting area. Perforating is done before the cutting operation. In advance of perforating, a blowout preventer is closed to avoid a blowout. If no pressure build up occurs, the blowout preventer may be reopened and the perforation gun can be retrieved from the well. Subsequently the cutting equipment proper is inserted and the casing is cut and the upper severed portion is removed from the well. In the same way, the adjacent larger size casing is removed and the operations continue with casings of increasing dimension until all casings are cut and the sea floor is free of any equipment. If perforating before cutting is omitted, a hazard of a sudden pressure build-up as the cutting blades cut through the casing is present. In order to counteract this hazard, the blowout preventer has to be closed during cutting operations. In practice this is not possible without impairing the blowout preventer, since a stationary expandable rubber gasket or packer would have to be locked around a rotating drill string. This previously known method involving perforating the casing, and, possibly, cementing, requires relatively time consuming operations and, consequently, loss of rig time and increasing costs for the rig operator. In US-A-3,301,324 (Smith) there is described a swivel for supporting a drill string in a submerged casing head. As shown in Figure 2 of that specification, the swivel comprises a sleeve formed by a tubular housing 34 mounted on a portion 32 of the drill string 16. Bearings 58, 60, 64 and 66, allow rotation of the tubular housing 34 relative to the drill string portion 32, and upper and lower packing assemblies 76 and 78 provide a seal between the tubular housing 34 and the drill string portion 32. The tubular housing 34 is located relative to the drill casing 20 by a support member 110 which has a bevelled lower surface 112 that engages an upwardly facing shoulder 114 formed in the casing 20, and by a guide member 104 which locates in the casing 20. In US-A-3,934,945 (Hamilton et al) means for stabilising the drill rod of an earth boring machine comprises, as shown in Figure 1 of that specification, a sleeve 20 which is mounted on the drill rod 16 so as to be rotatable relative thereto, by rotating on bearings 22. The sleeve 20 is sealed relative to the drill rod 16, by a seal 34. According to the present invention, there is provided a method of providing a sealable and pressure controlling passage for a drill string comprising mounting on a portion of the drill string a swivel device which is internally sealed relative to the drill string portion, the drill string portion being rotatable relative to, but axially retained within, the swivel device, characterised by externally sealing the swivel device by means of an annular preventer of a blow-out preventer through which the drill string extends. Preferably the method includes sealing and locking the annular preventer around a sleeve member of the swivel device, and locking at least one end portion of the swivel device to the drill string portion. The method may also include clamping a separate split locking collar of the swivel device around the drill string portion. Advantageously the method may include passing oil through passages in a wall of a sleeve member of the swivel device so as to fill with oil an annulus between an internal wall of the sleeve member and an external wall of the drill string portion. There is also provided in accordance with the present invention a drilling assembly comprising a portion of a drill string, and a swivel device mounted thereon, the swivel device comprising a sleeve member rotatably mounted on the drill string portion, and means providing sealing between said sleeve member and said drill string portion and enabling relative rotational movement therebetween, characterised in that the assembly includes an annular preventer of a blow-out preventer, the annular preventer including expandable packing means for preventing a blow-out, the swivel device being positioned on the drill string portion in cooperation with the annular preventer with the expandable packing means in sealing and locking engagement with the sleeve member of the swivel device. The assembly may suitably include at least one end portion which is lockable to the drill string portion for rotation therewith. In use the sleeve member is tightened and locked by means of surrounding expansion gland packings, i.e. of the kind present in an annular preventer. The lockable end portion is suitably a separate split locking collar which may be attached around a drill string. Advantageously, the means for providing sealing and relative rotational movement comprise thrust bearings and radial bearings and one or a plurality of seals cooperating with the sleeve member and the through running drill string. The drill string in question may be a specially prepared pipe section with external portions complementary with internal portions of the locking collar and it may have portions with a smooth surface for cooperation with said seals. The sleeve member may, advantageously, be provided with through passages in the sleeve wall for filling oil in the space formed between the inner wall of the sleeve and the outer wall of the drill string. By means of a device according to the present invention, at least in preferred embodiments thereof, primarily damage of the blowout preventer is avoided. Additionally, it is fully possible to save 6-24 hours of rig time due to the fact that the preliminary perforating of casings is avoided. Completely controllable cutting operations may be carried out with a swivelsub according to the invention, at least in preferred arrangements. Other and further objects, features and advantages will appear from the following disclosure of an embodiment of the invention which is at present preferred and which is shown by way of example in the accompanying drawings in which:- Figure 1 is an elevational section through a blowout preventer including a swivelsub according to the invention; Figure 2 shows a drill string portion; Figure 3 is a longitudinal section through a sleeve member and a locking collar of the swivelsub shown in Figure 1; Figure 4 is a diagrammatic view of the sleeve and the collar of Figure 3, mounted on the drill string portion of Figure 2; Figure 5 is a more detailed view of the sleeve member according to Figure 3; Figure 6 is a sectional view of the locking collar of Figure 3 presented in more detail with associated seals and bearings; Figure 7 is a plan view of part of the locking collar of Figure 6; and Figure 8 shows the arrangement of bearings and seals of the embodiment on the drill string portion, in more detail. Referring to Figure 1 a sectional view of a blowout preventer 12 provided on a well head 18 is illustrated. From well head 18 one or a plurality of casings 20 extend down into the subsea earth formations. In the upper portion of blowout preventer 12 an annular preventer 14 is provided. Commonly, the latter is intended for sealing off the annulus between the drill string 16 and the inside passage through the annular preventer 14. The drill string, or more precisely, the cutting string 16 extends through the entire blowout preventer 12 with the lower end of the cutting string 16 being provided with a cutting tool 15 for cutting casing or casings 20. The swivelsub or drill string swivel 10 is interposed in the cutting string 16 at a predetermined level relative to the cutting tool 15 and level with the annular preventer 14. The annular preventer 14 is normally provided with expandable rubber packings or packers which, when activated, surround and seal off the drill string. This inherent feature of an annular preventer is utilized in the present invention in that the expandable packers are activated to embrace the swivelsub and consequently shut off the annulus in order to enable control of the well pressure. For a more detailed disclosure of the swivelsub 10, reference is made to Figure 2 which is a diagrammatic view of a drill string portion or mandrel 1 within the swivelsub 10. This portion comprises a steel core having an internal bore diameter of 71 mm in order to enable liquid to be circulated through the core. The mandrel has a 4.5" I.F. A.P.I. threaded portion at both ends (box and pin). At the lower end (Figure 2), a shoulder 22 is provided to receive axially directed thrust forces of the swivelsub. At the upper end of the mandrel, machined profiles are provided which are adapted for standard slips and lifting elevators (not shown). Figure 3 is a sectional view of sleeve member 2 which is provided outside the mandrel 1 and contacts the shoulder 22 with its lower end portion. A splittable locking collar 3 is located at the opposite end of sleeve 2. The locking collar 3 has an internal shape which is complementary to a flange portion on the mandrel 1, as shown in Figure 2. Each end of the sleeve 2 is provided with thrust bearings, radial bearings and seals provided for cooperation with locking collar 3, shoulder 22 and mandrel 1, respectively. Figure 4 illustrates the assembled swivelsub 10 with sleeve 2 enclosing a spaced portion of the drill string 1. The lower end of sleeve 2 is in contact with shoulder 22, and locking collar 3 is clamped about the mandrel 1. Locking collar 3 and shoulder 22 are, thus, stationary relative to the mandrel 1 and rotatable relative to the sleeve member 2. As mentioned, sleeve member 2 is intended to be fixedly restrained by expanding rubber packers in the annular preventer 14. In this way the sleeve member 2 may be kept stationary and the annulus may be shut off at the same time as it is possible to rotate the mandrel 1 or the cutting string 16. Figure 5 is a longitudinal section of sleeve 2 in more detail. Apertures 24 are indicated for filling, preferably light oil, into the annulus between the mandrel 1 and the internal wall of sleeve member 2. It will also appear from the Figure how bearings and seals are to be assembled in the end portions of sleeve 2. The components are presented in Figure 6, in the correct sequence of assembly where radial bearing 5 is initially inserted into sleeve 2. Said bearing or bushing may, for example, be manufactured from Ni-bronze. Then a retaining ring 4 is inserted into a groove 26 provided in the sleeve 2, followed by a suitable seal 6, and another retaining ring 4 intended for location in a corresponding groove 27 on sleeve 2. An internal bearing 7, for example made of polyacetate-pom, is located between internal bearing 7 and locking collar 3. As will be apparent from Figures 6 and 7, the attachment of the locking collar 3 on the mandrel 1 may be provided by bolts and bolt holes, as indicated. Figure 8 illustrates in further detail the order in which the bearing and sealing components are assembled in sleeve 2 and their engagement with the mandrel 1. Thus it will be seen from the shown embodiment that the bearings and seals are kept stationary in relation to the sleeve 2, but the arrangement may naturally be the opposite, i.e. said components may be stationary on the mandrel 1, though this arrangement appears to be less convenient.

Claims: A method of providing a sealable and pressure controlling passage for a drill string (16) comprising mounting on a portion (1) of the drill string (16) a swivel device (10) which is internally sealed relative to the drill string portion (1), the drill string portion (1) being rotatable relative to, but axially retained within, the swivel device (10), characterised by externally sealing the swivel device (10) by means of an annular preventer (14) of a blow-out preventer (12) through which the drill string (16) extends. A method according to claim 1 including sealing and locking the annular preventer (14) around a sleeve member (2) of the swivel device (10), and locking at least one end portion (3) of the swivel device (10) to the drill string portion (1). A method according to claim 2 including clamping a separate split locking collar (3) of the swivel device (10) around the drill string portion (1). A method according to any preceding claim including passing oil through passages (24) in a wall of a sleeve member (2) of the swivel device (10) so as to fill with oil an annulus between an internal wall of the sleeve member (2) and an external wall of the drill string portion (1). A drilling assembly comprising a portion of a drill string (16), and a swivel device (10) mounted thereon, the swivel device (10) comprising a sleeve member (2) rotatably mounted on the drill string portion (1), and means (5,6,7,8) providing sealing between said sleeve member (2) and said drill string portion (1) and enabling relative rotational movement therebetween, characterised in that the assembly includes an annular preventer (14) of a blow-out preventer (12), the annular preventer (14) including expandable packing means for preventing a blow-out, the swivel device (10) being positioned on the drill string portion (1) in cooperation with the annular preventer (14) with the expandable packing means in sealing and locking engagement with the sleeve member (2) of the swivel device (10). An assembly according to claim 5 in which the swivel device (10) includes at least one end portion (3) which is lockable to the drill string portion (1) for rotation therewith. An assembly according to claim 6 in which said lockable end portion (3) is a separate split locking collar (3) for clamping around the drill string portion (1). An assembly according to claim 5, 6 or 7 in which the said means for providing sealing and relative rotational movement comprise thrust bearings (7,8), radial bearings (5), and one or a plurality of seals (6) cooperating with between said sleeve member (2) and said drill string portion (1). An assembly according to any of claims 5 to 8 in which the drill string portion (1) includes an external portion (23) designed to be complementary to an internal portion of an end portion (3) of the swivel device (10). An assembly according to any of claims 5 to 9 in which the said sleeve member (2) is provided with passageways (24) for filling oil into an annulus between an internal wall of the sleeve member (2) and an external wall of the drill string portion (1).

Inventors: GLEDITSCH, SVEIN
Applicants: GLEDITSCH, SVEIN
Application year: 1988
Main classification: E21B33
IPC codes: E21B17, E21B33, E21B29