GB2114192A - Improved swivel stem for delivering fluid to a rotary drill string - Google Patents

Abstract

An oil field swivel stem has a rotatable section 16 having an internally threaded portion (22) for receiving a threaded saver sub connector (24) adapted for connection to the drill string. An intermediate passage (30) joins the threaded portion (22) and the through-passage (20) in the rotatable section (16). A flow guidance piece (40) is adapted to fit within the intermediate passage (30) and also has a through-passage (32) axially aligned and generally mateable with the through-passage (20) of the rotary section (16). An elastomeric ring (42) mounted between an outer end face of the flow guidance piece (40) and saver sub (24) serves as a compression spring between the two, urging the inner end face of the flow guidance piece into engagement with the wall of the intermediate passage (30). Thus drill fluid is prevented from wetting the threaded portion of the rotary section, reducing the occurrence of fatigue failures therein. <IMAGE>

Description

SPECIFICATION Improved swivel stem for delivering fuel to a rotary drill string This invention relates to swivel stems for rotary well-drilling equipment, and more particularly to improvements for reducing the frequency of fatigue failures therein.

In conventional oil-field equipment, fluid is supplied to a rotary drill string to flush cuttings from the bottom of the well. A swivel stem connects a supply of drill fluid line to the rotary drill string. The stem has adjoining fixed and rotary sectons attachable to the supply line and drill string, respectively. The sections each have a through-passage connected in fluid-tight relationship. The exit end of the passage in the rotary section has an internally threaded portion for receiving a threaded saver sub, serving to connect with the stem to the rotary drill string.

High stress levels occur in the wall of the rotary section due to suspension of entire weight of the drill string therefrom. Often an undercut is provided (as shown in Figure 3) to prevent scratches due to thread runout during machining.

Despite provisions of the undercut to prevent stress raisers, fatigue failures still have occurred at the last thread engaged by the saver sub.

It is therefore a primary object of this invention to provide an improvement in swivel stems for rotary well-drilling equipment which is designed to reduce the occurrence of fatigue failures.

According to the present invention a swivel stem for delivering fluid to a rotary drill string comprises a housing a pair of sections mounted adjoining each other in the housing, each of the sections having a passage therethrough and being located so that their passages are mateably aligned and connected in fluid tight relationship, one of the sections being adapted to receive fluid from a supply line and the other being rotatable about the axis of its passage and having an internally threaded portion adapted to receive a threaded drill string connector, the rotatable section having an intermediate passage joining its first mentioned passage and its internally threaded portion, a flow guidance piece adapted to fit within the intermediate passage so as to prevent the occurrence of flow turbulence eddies therein the flow guidance piece having a passage therethrough extending from an inner end remote from the threaded portion of the rotatable section to an outer end adjacent thereto, and an elastomeric ring for mounting between adjoining end faces of the flow guidance piece and a drill string connector, for urging an inner end face of the flow guidance piece into engagement with the wall of the rotatable section intermediate passage, when compressed by such a connector, whereby, wetting of the intermediate passage by the drill fluid is avoided, thus reducing the occurrence of corrosion fatigue failures in the rotatable section of the stem.

Preferably the elastomeric ring extends radially outward so as to abut the wall of the intermediate passage at least when compressed, thus preventing wetting of the threaded portion of the rotary section by the corrosive drill fluid.

The invention will now be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevation view of a swivel stem partially in section to show improvements therein according to the present invention, Figure 2 is an enlarged view of the sectioned portion of Figure 1, and Figure 3 is an enlarged half-section similar to the view of Figure 2 but showing a prior art swivel stem with a conventional undercut.

Referring to Figure 1 swivel stem 10 has a housing 12 with a fixed section 14, and an axially rotatable section 16 mounted therein. A bail 19 is provided for suspending the stem from a hook in a drill tower. Sections 14, 1 6 have through passages 1 8, 20 connected in fluid-tight relation by conventional sealing means (not shown).

Rotatable section 1 6 has an internally threaded portion 22 for receiving a threaded saver sub 24 therein. Saver sub 24 serves as a connector for attaching the stem to a rotary drill string.

Referring now to Figure 2, the improvements made in the stem according to the present invention include an intermediate passage 30 joining passage 20 and threaded portion 22 of the rotatable section. Generally, the intermediate passage is longer than the conventional undercut previously used (see Figure 3) and has a sloped or arcuate-shaped wall joining at threaded portion 22, and passage 20. The sloped or arcuate portion extends for more than half i.e. a major portion of the length of intermediate passage 30, thus substantially reducing the peak stress level in the wall of the rotatable section from that which exists when an undercut is provided.

A flow guidance piece 40 is adapted to fit within intermediate passage 30 and has a through passage 32 axially aligned and generally mateable with passage 20 in the rotatable section. The piece 40 as shown is a hard urethane material, but it may be of any structurally sound material, for example metal similar in composition to the stem itself. An elastomeric ring 42 is provided between an outer end face of piece 40 and saver sub 24. The ring is of relativeiy soft rubber and when compressed preferably abuts the wall of the intermediate passage to prevent wetting of the threads by drilling fluid. An annular packing space 44 is provided in piece 40 so as to be engageable by a shoulder on ring 42 in order that the ring will remain in proper position during insertion of the piece in the rotatable section.

Desirably the sidewall 46 of the packing space slopes radially inward toward its base so that the ring is more securely mounted.

A second elastomeric ring 50 may be provided to more completely seal the joint between the inner end of the flow guidance piece and the intermediate passage. This latter ring may serve to prevent access of drill fluid to the threads. In that case the first mentioned ring would not necessarily need to abut the wail of the intermediate passage in order to prevent wetting of the thread area by drilling fluid. This second ring may be mounted in an annular slot in the inner end face of the flow guidance piece.

Thus an assembly is provided which is easy to assemble and is effective in preventing fatigue failures in swivel stems.

Claims (6)

Claims

1. A swivel stem for delivering fluid to a rotary drill string and comprising a housing a pair of sections mounted adjoining each other in the housing, each of the sections having a passage therethrough and being located so that their passages are mateably aligned and connected in fluid tight relationship, one of the sections being adapted to receive fluid from a supply line and the other being rotatable about the axis of its passage and having an internally threaded portion adapted to receive a threaded drill string connector, the rotatable section having an intermediate passage joining its first mentioned passage and its intemally threaded portion, a flow guidance piece adapted to fit within the intermediate passage so as to prevent the occurrence of flow turbulence eddies therein the flow guidance piece having a passage therethrough extending from an inner end remote from the threaded portion of the rotatable section to an outer end adjacent thereto, and an elastomeric ring for mounting between adjoining end faces of the flow guidance piece and a drill string connector, for urging an inner end face of the flow guidance piece into engagement with the wall of the rotatable section intermediate passage, when compressed by such a connector, whereby, wetting of the intermediate passage by the drill fluid is avoided, thus reducing the occurrence of corrosion fatigue failures in the rotatable section of the stem.

2. Apparatus as claimed in claim 1 further comprising a second elastomeric ring adapted to be mounted between the inner end face of the flow guidance piece and the wall of said intermediate passage for sealing the joint therebetween.

3. Apparatus as claimed in claim 1 or 2 wherein the flow guidance piece has a packing space extending around the exterior periphery of the outer end face thereof, and the first elastomeric ring has a shoulder engageable in said space serving to retain the ring in position on the flow guidance piece during insertion thereof into the rotatable section.

4. Apparatus as claimed in claim 1,2 or 3 wherein the rotatable section intermediate passage has a wall extending along a major portion of the length thereof aligned at an acute angle with respect to the axis of its first mentioned passage.

5. Apparatus as claimed in claim 4 wherein the portion of said wall extending at an acute angle to the axis of the rotatable section first-mentioned passage is of arcuate shape.

6. A swivel stem for delivering fluid to a rotary drill string substantially as herein described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.