GB2094676A

GB2094676A - Method and means for treating oil-base drilling mud to remove oil-free drill cuttings therefrom

Info

Publication number: GB2094676A
Application number: GB8107721A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1981-03-11
Filing date: 1981-03-11
Publication date: 1982-09-22

Abstract

The cuttings after being separated from the drilling mud at (1), are transported to a screenbowl decanting centrifuge (11) by means of a first wash liquid (7). The cuttings are separated from the first liquid in the solid bowl section (13) of the centrifuge (11), and subsequently passed on into the screenbowl section (19) of the centrifuge, in which section they are contacted with a second wash liquid (20). <IMAGE>

Description

SPECIFICATION Method and means for treating oil-base drilling mud to remove oil4ree drill cuttings therefrom The present invention relates to a method and means for treating oil-base drilling mud. In particular, the present invention relates to a method and means for treating oil-base drilling mud to remove oil-free drill cuttings therefrom.

In drilling wells penetrating subsurface formations with the object of producing or recovering from such formations valuable materials, such as hydrocarbon fluids, use is made of rotary drilling equipment.

When drilling the well, drilling mud is circulated through the well, the mud performing functions as cooling and lubricating the drilling bit, and raising to the surface cuttings that are broken out of the formation by the action of the bit. At the surface, the cuttings are mechanically separated from the mud and the mud is pumped down the well after being regenerated. The cuttings are disposed of at a suitable location.

Enviromental problems occur, however, when the drilling mud contains hydrocarbon constituents. The liquid content of this type of mud (hereinafter also indicated as oil-base mud) consists at least partly of a mixture of hydrocarbons. These hydrocarbons will coat and/or soak the cuttings that are broken out of the formation and subsequently lifted to the surface and it will be appreciated that such cuttings cannot be disposed of without subjecting them to a treatment aimed at removing the hydrocarbons therefrom.

Various techniques of removing the hydrocarbons (hereinafter also referred to as oil) from the cuttings have already been suggested and tried in the field.

USA patent specification No. 3,693,951 describes separation of the cuttings from the mud and subsequently burning the oil from the cuttings. This system, however, requires the use of a relatively large furnace, which is not attractive for use on offshore platforms. USA patent specification No.

3,860,019 describes the use of a vibrating screen to which the cuttings - after having been separated from the mud - are supplied in combination with a detergent. The cleaned cuttings are dumped into the sea after having been separated from the wash liquid. Further, USA patent specification No.

4,040,866 describes the use of a solvent that is mixed with the cuttings whereafter the mixture is passed into a centrifuge to separate the cuttings from the solvent and the oil dissolved therein. If desired, sea water may be added to wash the solvent and the oil dissolved therein from the cuttings by centrifugal action.

It has now been found that better results can be obtained by treating the cuttings and the solvent liquid in a screen bowl decanting centrifuge comprising a solid bowl decanter, a cylindrical screen and a screw conveyor. Centrifuges of this type are known per se and do not require any detailed description. By applying this type of centrifuge in treating the cuttings separated from an oil-base mud, the solvent and the wash liquid are not mixed with one another, which simplifies the regeneration and re-use of these liquids. A further advantage is that the space required for the cleaning operation is considerably reduced. Another advantage is the reduction of the residual oil content of the cuttings after the cleaning operation.

The method according to the invention for treating oil-base drilling mud to remove oil-free drill cuttings therefrom includes the steps of first passing the drilling mud through a separator to separate the cuttings from the mud, then mixing the cuttings with a first wash liquid and passing the mixture of cuttings and first liquid into a screen bowl decanting centrifuge comprising a solid bowl section, a screen bowl section and a screw conveyor, wherein the cuttings are first separated from the first liquid in the solid bowl section and thereafter passed on in the centrifuge by the screw conveyor into the screen bowl section of the centrifuge where the cuttings are contacted with a second wash liquid prior to being discharged from the centrifuge.The means according to the invention for treating oil-base drilling mud to remove oil-free drill cuttings therefrom includes a mechanical separator for separating the cuttings from the mud, a chamber for mixing the cuttings with a first wash liquid, and a screen bowl decanting centrifuge for separating the cuttings from the first wash liquid and subsequently treating the cuttings with a second wash liquid in the screen bowl section thereof.

The first wash liquid may be any liquid suitable for transporting the cuttings in the form of a suspension and simultaneously diminishing the contact between the cuttings and between the cuttings and the oil or hydrocarbons adhering to the cuttings or present in the pore space of the cuttings. A suitable first wash liquid is the liquid that is used in the drilling mud as the continuous phase, such as diesel oil, a heavy kerosene topped crude oil, and mixtures thereof.

The second wash liquid is applied to remove the traces of the first wash liquid and oil or hydrocarbons dissolved therein from the cuttings. Suitable second wash liquids are any organic solvents for dissolving the liquid or liquids that form(s) the continuous phase of the oil-base mud from which the cuttings are separated.

Any decanter centrifuge allowing a separate washing treatment of solid particles after these particles have been separated from a liquid in the decanting section thereof may be applied in carrying out the present invention. An example of such cetrifuge is the "Broadbent Screen Bowl Decanter Centrifuge" manufactured and marketed by Thomas Broadbent & Sons Ltd., Huddersfield, England.

The invention will be described by way of example in more detail with reference to the drawing which shows schematically a system wherein the present method may be carried out.

Oil-base drilling mud comprising cuttings is pumped from the well (not shown) to a shale-shaker 1 via the conduit 2. The shaker is of the known type and when in operation, separates the cuttings from the mud. The mud is returned via conduit 3 to the mudpit 4, whereas the cuttings 5 are passed on to the mixing chamber 6, where they are brought into contact with the first wash liquid that is supplied to the chamber 6 via the conduit 7.

Means (not shown) known per se are present in the mixing chamber 6 maintaining the cuttings in suspension in the first wash liquid. Such means may be rotatable paddles that are actuated by an electric motor. The contact between the cuttings and between the cuttings and the oil or hydrocarbons adhering thereto is decreased by this contact with the wash liquid. The suspension of the cuttings and the first liquid is transported via the conduit 8 and the central channel 9 in the shaft 10 of the centrifuge 11 to the openings 12 in this shaft. In the centrifuge, the suspension is collected in the solid bowl section 13 of the centrifuge where the cuttings 14 are separated from the first liquid that is decanted (see arrow 15) from the centrifuge and collected in the splash guard 16 from which it is removed via the conduit 17 for re-use.Prior to such re-use, the wash liquid may be cleaned in a manner known per se.

Separation of the cuttings from the wash liquid takes place by the combined action of the solid bowl 13 that is being rotated at high speed by means (not shown) and the screw conveyor 18 that is being rotated at a slightly lower speed (by means not shown).

The screw conveyor 18 displaces the separated and dried cuttings 14 to a screen bowl section 19 wherein the cuttings are treated with a second wash liquid 20 that is supplied via conduit 21, central channel 22 and openings 23 in the shaft 10 of the centrifuge. This second wash liquid washes the traces of the first wash liquid from the cuttings by dissolving the first wash liquid together with the oil or hydrocarbons dissolved in this first wash liquid.

The second liquid is drained from the screen bowl 24 through the openings 25 therein and subsequently passes via the splash guard 26 and the conduit 27 to a storage (not shown) where it is retained for re-use.

If desired, it may be cleaned prior to such re-use in a manner known per se.

Subsequently, the cuttings that are now free from any oil and washing liquid are passed on by the screw conveyor 18 to the outlet 28 from the centrifuge, and into the collector guard 29, from which they are removed via the outlet conduit 30. The cuttings can then be disposed by dumping them on a suitable spot.

Itwill be appreciated that the use of the screen bowl decanting centrifuge allows the cleaning of the drill cuttings in an efficient manner to a degree at which the cuttings can be dumped on land or in the sea without fear of pollution of the enviroment.

Claims

1. Method for treating oil-basedrilling mud to remove oil-free drill cuttings therefrom, the method including the steps of first passing the drilling mud through a separator to separate the cuttings from the mud, then mixing the cuttings with first wash liquid and passing the mixture of the cuttings and the first liquid into a screen bowl decanting centrifuge comprising a solid bowl section, a screen bowl section and a screw conveyor, wherein the cuttings are first separated from the first liquid in the solid bowl section and thereafter passed on in the centrifuge by the screw conveyor into the screen bowl section where the cuttings are contacted with a second wash liquid prior to being discharged from the centrifuge.

2. Means for treating oil-base drilling mud to remove oil-free drill cuttings therefrom, said means including a mechanicai separator for separating the cuttings from the mud, a chamber for mixing the cuttings with a first wash liquid, and a screen bowl decanting centrifuge for separating the cuttings from the first wash liquid and subsequently treating the cuttings with a second wash liquid in the screen bowl section thereof.