GB2273668A

GB2273668A - Drilling fluid recovery

Info

Publication number: GB2273668A
Application number: GB9226755A
Authority: GB
Inventors: Tony Johnson; Steven Love
Original assignee: FBG Ltd
Current assignee: FBG Ltd
Priority date: 1992-12-23
Filing date: 1992-12-23
Publication date: 1994-06-29
Anticipated expiration: 2012-12-23
Also published as: GB9226755D0; GB2273668B

Abstract

Oil well drilling fluid is fed from the well by chutes 13 into a tank 12 having four inclined perforate sides and an imperforate base, all spaced from corresponding sides and base of an outer tank 11, which receives the fluid, from which cuttings have been removed by combination of settling and filtering. Tank 12 has impervious areas 30a on side 30 beneath chutes 13, and the perforations are otherwise arranged in two bands extending horizontally round the tank. All perforations taper in the downstream direction, and perforations in the lower band are smaller in diameter than those in the upper band. The tank 12 may comprise metal plates, and its floor may be removable to provide access to the floor of tank 11, which slopes outwards to outlets 41. To remove accumulated solids from tank 12, an excavator (Fig. 4) moves along a supporting frame 70, which is attached to one side of tank 11 by hinged joints to allow it to be folded up when not in use. <IMAGE>

Description

DRILLING FLUID RECOVERY The present invention relates to apparatus for recovering drilling fluids particularly although not exclusively, apparatus for recovering drilling fluids used in earth boring drilling rigs such as oil drilling rigs.

Drilling bits are generally known to be provided at the lower end of an assembly of pipe sections secured in a sequential end-to-end array and known as a "drill string".

The drill string is rotated in order to turn the bit whilst advancing the bit down into the earth to gouge or cut out portions of an earth formation during the downward travel of the string.

It is also well known to provide such bits with flow channels for directing drilling fluids, commonly referred to as drilling mud, from inside the drill string through the bit around the cutters in order to keep the bit cool. This also flushes cuttings from around the bit upwardly in the annulus around the drill string. The particles removed by the drill bit flows up with the fluid.

The drilling fluid is either water or oil based and is usually a formulation determined by the type of material being drilled. One consideration in formulating the drilling fluid is that specific gravity should be such as to provide sufficient buoyancy to the removed particles to enable them to be conveyed to the surface.

At the drill head the drilling fluid including particles is fed to separators which serve to separate the fluid out from the particles for recovery and re-use. The separators usually comprise at least one shaker screen which separate the bulk of the particles to form a wet slurry and fluid.

The fluid is passed through a series of sealing and conditioning tanks to a centrifuge for a final separation stage before being reused.

The slurry is normally fed to an excavated pit at the well head.

The slurry still contains an appreciable amount of fluid and an aim of the present invention is to recover this fluid for re-use.

Another drawback is that the slurry pits are expensive to construct and maintain. The pits are also potentially an environmental hazard due to the presence of the drilling fluid and so special precautions are normally exercised in order to prevent contamination of the surrounding environment. Also, once drilling has been completed, removal of the pits and re-instatement of the environment is an expensive exercise.

Therefore, it is desirable to eliminate the expense of maintenance and construction of the slurry pits and avoid environmental hazard of the pits.

According to one aspect of the present invention there is provided a separator having a main tank and a settlement tank located within and spaced from the main tank, the settlement tank having perforated side walls enabling fluid to pass through to the main tank for collection.

Preferably the bottom of the settlement tank is spaced from the bottom of the main tank.

Preferably the bottom of the settlement tank is removable for providing access to the lower region of the main tank.

Preferably the sides and bottom of the settlement tank are defined by metal plate.

Preferably the perforated sides are defined by a series of apertures spaced along the sides.

Preferably the apertures are arranged in at least two bands extending parallel to the bottom of the settlement tank, the band located nearer to the bottom having apertures of a smaller size than its neighbouring band located further away from the bottom.

Preferably the apertures have an inlet opening located on the inside face of the settlement tank sides and an outlet opening on the outside face of the settlement tank sides, the inlet opening being relatively narrower to the outlet opening.

Various aspects of the present invention are hereinafter described with reference to the accompanying drawings in which: Figure 1 is a schematic perspective view of a separator according to one embodiment of the present invention; Figure 2a and 2b are more detailed front and end views respectively of part of the separator shown in Figure 1; Figure 3 is a cross-sectional view through part of the separator shown in Figure 1; Figure 3a is an enlarged view of part of one side wall shown in Figure 3; Figure 4 is an end view of the separator shown in Figure 1; Figure 5 is a plan view of a modified separator; Figure 6 is a front view of the separator shown in Figure 5; Figure 7 is a schematic longitudinal section through the separator shown in Figure 1.

Referring to the drawings, there is shown a separator 10 according to the present invention which includes a main tank 11 in which is housed a settlement tank 12. The separator 10 is positioned to receive slurry from a pair of chutes 13 extending from shaker screen separators (not shown).

The main tank 11 comprises a bottom 14 which stands on elongate beams 15. Extending upwardly from the bottom 14 is a pair of opposed side walls 17, 18 and a pair of opposed end walls 19, 20. The walls 17 to 20 are generally vertical.

The settlement tank 12 comprises a bottom 22 which is spaced from the bottom 14 of the main tank and is supported on cross-members 26 secured to side walls 17, 18. A plurality of cross-members 26 are provided spaced longitudinally along the tank 11. At least one leg 27 which contacts bottom 14 is preferably provided at an intermediate position along each cross-members 26 to provide added support for the cross-members 26.

The bottom 22 is preferably defined by imperforate metal plates 22a which are detachably secured to selected cross-members 26 by fixing means such as bolts. Accordingly, the plates 22a may be removed to provide access to the lower regions of the main tank 11 for say cleaning purposes.

The settlement tank 12 further comprises opposed side walls 20, 31 and opposed end walls 32, 33.

The walls 30 to 33 are preferably formed from metal sheet having a lower edge supported on the cross-members 26 and an upper edge secured to an upper portion of the adjacent side or each wall of the main tank 11. The metal sheet is preferably steel sheet which is about 6 mm thick. The lower edge of walls 30 to 33 is spaced inwardly from the neighbouring wall of the main tank 11 so as to provide the settlement tank with inclined walls thereby providing a relatively wide open top to the settlement tank and a relatively narrow bottom.

The inclined walls of the settlement tank 12 encourages deposited slurry to reside at the bottom of the tank 12 and facilitates drainage of fluid as will be described below.

In addition, the inclined nature of the walls of the settlement tank also facilitates removal of particulate material therefrom by means of an excavator.

At least the side walls 30, 31 are perforated in order to enable fluid contained in slurry deposited in the settlement tank to drain therethrough and into the main tank 11. Walls 32, 33 may also be perforated.

Preferably the area 30a of wall 30 directly beneath the chutes 13 is imperforate to enable the slurry to run down the wall 30.

Preferably the main tank 11 is provided with an inclined floor 40 which encourages fluid draining from the settlement tank 12 to flow towards either end of the main tank 12. Outlet ports 41 are provided at each end of the main tank 11 for discharging fluid from the tank 11.

Preferably the outlet ports 41 are conducted via conduits (not shown) to a centrifugal type separator (not shown) normally provided at the well head to provide a final separation operation on the fluid before reuse.

The side walls 30, 31 are preferably perforated by means of at least two bands of apertures 44 and 46 running parallel to the bottom 22. The band 44 which is located nearest bottom 22 preferably contains a plurality of rows of apertures 48 which are spaced both horizontally and vertically apart by about 4 inches (10 cm). The apertures 48 in band 44 preferably each have an inlet opening formed on the inside face of the side walls 30, 31 which is about 6 mm in diameter.

The band 46 located further away from the bottom 22 preferably includes a plurality of rows of apertures 48 which are similarly spaced from one another as for the apertures 48 in band 44. However, the apertures 48 in band 46 each have an inlet opening formed on the inside face of side walls 30, 31 which is about 8 mm in diameter.

Preferably all the apertures 48 are counter-sunk from the outside face of walls 30, 31 so as to define an outlet opening for each aperture which is relatively wider than their inlet opening. This is advantageous as it helps to prevent blockage of the apertures by particulate material bridging across the outlet opening.

The provision of separate bands 44, 46 of differently sized apertures is preferred since the fluid tends to rise on the slurry bed formed within the settlement tank and so the larger diameter apertures which are located further away from the bottom 22 enable the surface fluid to drain rapidly away whilst the smaller size apertures in the band 44 closer to the bottom serve to permit a relatively slower drainage of fluid whilst holding back particulate material.

In order to empty the settlement tank 12 of particulate material, it is preferred to use an elevated excavator 50. Accordingly, an elevated track 51 is preferably provided attached to one longitudinal side of the separator 10 to thereby enable the excavator to traverse at an elevated position along the settlement tank 12.

Since the excavator 50 is elevated, its bucket and boom assembly 55 is able to reach down into the tank 12 without having to reach over and above the side of the tank.

Preferably the excavator digs the particulate material out of the settlement tank and deposits the material into a container 60 such as a skip for removal of the material from the site for controlled disposal.

The elevated track 51 is preferably mounted on a support frame 70 which is pivotally mounted along one longitudinal side to one side wall of the main tank 11.

The frame 70 preferably comprises a pair of longitudinally extending support members 80, 81 which are spaced laterally apart and secured to laterally extending support members 84. Each support member 84 is pivotally connected at one end to the side wall of the main tank 22 via a bracket 85. The frame 70 is therefore movable between a raised position whereat it extends perpendicular from the side wall and a lowered position whereat it extends generally parallel to the side wall.

A plurality of retractable ground engaging legs 72 are pivotally attached to the opposite side of the support frame 70 to maintain the frame 70 in its raised position. When in their ground engaging position, each leg 72 is connected at its lower end with the adjacent side wall of the main tank 11 via a strut member 73. Each strut member 73 is pivotally attached at one end to the side wall of the main tank 11 so as to be movable in a vertical plane located perpendicular to the side wall of the main tank 11.

When in its lower position, the opposite end of each strut is detachably secured to its associated leg 72 via a bracket 75 mounted on leg 72 and when in its raised, stowed, position the opposite end of each strut is detachably secured to the side wall of the main tank 11 via a bracket 76 mounted on the side wall.

Each leg is preferably made from steel tube and is pivotally attached at its upper end to support member 81 via a bracket 78 to be movable in a vertical plane which is parallel to the longitudinal axis of support member 81 between a lower position and a raised, stowed, position.

A latch mechanism 90 is provided for each leg 72 and is mounted on support member 81 so as to be connectable with the bracket 75 when the leg is moved to its raised position. The latch mechanism 90 preferably comprises a retractable plunger 92 which is insertable into an aperture (not shown) formed in bracket 75. Channel members 95 defining tracks 51 are mounted directly on support members 80, 81.

It will be appreciated that the separator 10 of the present invention is transportable from site to site and so does not require a special pit to be excavated at the well head.

In addition, the separator 10 enables valuable drilling fluid to be recovered for re-use from the slurry discharged from the normal shaker separators and so avoids costly waste of fluid and costly precautions against contamination of the environment.

In addition, the separator 10 is conveniently emptied of particulate material by means of an excavator which is able to deposit the material in a container for transport away from the well head to a disposal site where the material can be disposed of under controlled conditions.

It is envisaged that the separator 10 shown in Figure 1 may be modified as shown in Figures 5 and 6 by the inclusion of an additional tank compartment 50 separate from the tank 12. Conveniently, tank compartment 50 is arranged to receive solid material from the centrifuge which can then be removed by the excavator.

Claims

1. A separator having a main tank and a settlement tank located within and spaced from the main tank, the settlement tank having perforated side walls enabling fluid to pass through to the main tank for collection.

2. A separator according to claim 1 wherein the bottom of the settlement tank is spaced from the bottom of the main tank.

3. A separator according to claim 2 wherein the bottom of the settlement tank is removable for providing access to the lower region of the main tank.

4. A separator according to any preceding claim wherein the sides and bottom of the settlement tank are defined by metal plate.

5. A separator according to any preceding claim wherein the perforated sides are defined by a series of apertures spaced along the sides.

6. A separator according to claim 5 wherein the apertures are arranged in at least two bands extending parallel to the bottom of the settlement tank, the band located nearer to the bottom having apertures of a smaller size than its neighbouring band located further away from the bottom.

7. A separator according to claim 5 or 6 wherein the apertures each have an inlet opening located on the inside face of the settlement tank sides and an outlet opening on the outside face of the settlement tank sides, the inlet opening being relatively narrower to the outlet opening.

8. A separator according to any preceding claim wherein the side walls of the settlement tank are inclined to provide the settlement tank with a narrower bottom than the bottom of the main tank.

9. A separator according to any preceding claim including a chute for depositing slurry into the top of the settlement tank, the region of the side wall located beneath the chute being imperforate.

10. A separator according to any preceding claim wherein the main tank has an inclined floor for facilitating drainage of fluid.

11. A separator according to any preceding claim including an elevated track located adjacent to the top of the settlement tank to enable an excavator to empty particulate material within the settlement tank.

12. A separator according to claim 11 wherein the track is movably attached to the main tank for movement between a collapsed transport position and an erected work position.

13. A separator substantially as described herein with reference to and as illustrated in the accompanying drawings.