Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
  • E21B17/10—Wear protectors; Centralising devices, e.g. stabilisers
  • E21B17/1078—Stabilisers or centralisers for casing, tubing or drill pipes

Definitions

• CENTR LISERS This invention relates to centralisers. During the construction of oil and gas wells a bore is drilled into the ground. Casing is then lowered into the bore and the annular space between the casing and the bore filled with cement.
• the centralisers comprise two spaced apart bands which can be slipped over the casing and a plurality of spring bows which extend between and are connected to the bands.
• centralisers with rigid members instead of spring bows.
• Examples of such centralisers are shown in GB-A-2 171 436 and GB-A- 682 362.
• the overall diameter of such centralisers is somewhat smaller than the bore so that said centralisers can be readily moved along the bore. Whilst such centra ⁇ lisers are not as versatile as centralisers with spring bows they do provide a reasonable centralising action.
• the disadvantage of such centralisers is that if part of the bore collapses and it is necessary to with ⁇ draw the casing some of the rigid members are nearly always broken off as the casing is withdrawn. This is extremely undesirable since the broken fragments can later be carried to the surface and obstruct or damage flow control equipment.
• the present invention provides a centraliser which is provided with at least one rigid member which, when said centraliser is mounted on casing / will substantially irreversibly collapse against said casing when subjected to a lateral load of from 5 to 30 tonnes.
• the rigid member will substanti- ally irreversibly collapse against said casing when subjected to a lateral load of from 10 to 25 tonnes.
• the rigid member will substantially irreversibly collapse against said casing when subjected to a lateral load of from 18 to 22 tonnes.
• the casing will substantial ⁇ ly irreversibly collapse against said casing when sub ⁇ jected to a lateral load of from 5 to 10 tonnes with 8 tones being most preferred.
• the rigid member is of generally U-shape cross section.
• the rigid member comprises a crushable material.
• the rigid member is preferably provided with a reinforcing member to provide the centraliser with acceptable tensile strength.
• the reinforcing member may comprise, for example a metal such as steel or aluminium although it could also comprise a plastics material.
• the reinforcing member may be provided with protrusions and/or adhesive to improve the adhesion between the reinforcing member and the crushable material and to reduce the probability of any broken pieces separating from the centraliser. More generally stated, it is preferred that the reinforcing member co-operates with the crushable material to inhi ⁇ bit broken pieces of said rigid member separating from said centraliser.
• Figure 1 is a vertical cross-section through one embodiment of a centraliser in accordance with the present invention
• Figure 2 is a side view of the centraliser shown in Figure 1;
• Figure 3 is a horizontal cross-section taken on line III-III of Figure 2;
• Figure 4 is a side view of a second embodiment of a centraliser in accordance with the present invention.
• Figure 5 is a horizontal cross-section taken on line V-V of Figure 4.
• centra ⁇ liser which is generally identified by the reference numeral 1.
• the centraliser 1 comprises an upper ring 2 and a lower ring 3 which are spaced apart and connected by six rigid members 4 which are welded to the upper ring 2 and the lower ring 3 at their respective ends.
• each rigid member 4 is of generally U-shape cross-section.
• each rigid member 4 is approximately 180mm.
• the maximum width of each rigid members 4 is approximately 45mm and the thickness of the wall of the rigid members 4 is approximately 2mm.
• the centralisers 1 are mounted at the desired spacing. Conveniently, the centralisers 1 are secured between two stop collars to prevent them moving along the casing.
• the casing In normal use the casing is simply lowered into a bore and cemented in position, the rigid members 4 acting as centring members. If the casing has to be withdrawn for any reason prior to cementing, for example due to collapse of part of the wellbore, the casing is simply raised by the draw works.
• the obstruction exerts a force on the centra ⁇ liser 1. If the force is sufficient the rigid members 4 irreversibly collapse thereby enhancing the prospects of the centraliser 1 remaining in one piece on the casing.
• the rigid members 4 could be of any convenient cross-section, for example semi circular, arcuate or trapezoidal. If desired, the rigid members could be locally weakened to facilitate their collapse.
• the rigid members could comprise two generally aligned sections joined by, for example an epoxy resin bonding the sections together but formulated to fail under a desired load.
• the rigid members comprise two generally aligned sections connected by a shear pin intended to fail at a desired load. Whilst both the alternatives just described are within the scope of the present invention the embodiment shown in Figures 1 to 3 is preferred as there is believed to be less chance of parts becoming detached from the centra ⁇ liser after collapse of the rigid members.
• the rigid members could be made of a crush ⁇ able material, for example a cellular material. Such an embodiment is shown in Figures 4 and 5.
• a centraliser 11 which comprises an upper ring 12 and a lower ring 13 which are spaced apart and connected by six rigid members 14.
• Each rigid member 14 comprises a thin reinforcing member 15 of metal, for example steel or aluminium, which is embedded in a crushable material comprising polyurethane foam 16.
• Each of the thin reinforcing members 15 is welded to the upper ring 12 and the lower ring 13 at its ends.
• the polyurethane foam 16 In use, if the centraliser 11 is withdrawn through an obstruction the polyurethane foam 16 irreversibly collapses thereby enhancing the prospects of the centra ⁇ liser 11 remaining in one piece on the casing.
• the polyurethane foam 16 is designed to irreversibly col ⁇ lapse under a lateral load of about 20 tonnes.
• the reinfor ⁇ cing members 15 could be separate and distinct from the rigid members 14 which could simply comprise a crushable material such as polyurethane foam. Whilst preferably made of metal, the reinforcing members 15 could also be made of plastics material.
• the arrangement described with reference to Figures 4 and 5 is preferred as it provides a conve ⁇ nient method of mounting the rigid member 14 to the upper ring 12 and lower ring 13. Since our initial work we have discovered that the rigid member is preferably designed to substantially irreversibly collapse against the casing when subjected to a lateral load of as little as 5 to 10 tonnes with 8 tonnes being most preferred.

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• Engineering & Computer Science (AREA)
• Geology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Mining & Mineral Resources (AREA)
• Physics & Mathematics (AREA)
• Environmental & Geological Engineering (AREA)
• Fluid Mechanics (AREA)
• Mechanical Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Casings For Electric Apparatus (AREA)
• Earth Drilling (AREA)
• Stackable Containers (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Priority Applications (7)

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Publications (1)

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Cited By (6)

Citations (9)

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• 1995
  • 1995-09-25 WO PCT/GB1995/002272 patent/WO1996009459A1/en active IP Right Grant
  • 1995-09-25 DE DE69524109T patent/DE69524109T2/de not_active Expired - Fee Related
  • 1995-09-25 EP EP95932810A patent/EP0782660B1/de not_active Expired - Lifetime
  • 1995-09-25 CN CN 95195249 patent/CN1159848A/zh active Pending
  • 1995-09-25 AU AU35705/95A patent/AU691665B2/en not_active Expired
  • 1995-09-25 BR BR9509169A patent/BR9509169A/pt not_active IP Right Cessation
  • 1995-09-25 CA CA002198619A patent/CA2198619C/en not_active Expired - Lifetime

Patent Citations (9)

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