GB2207159A - Method and apparatus for monitoring mud and cuttings - Google Patents

Abstract

A mixture of mud and cuttings from a well is fed to a shale shaker screen (2) which allows the major part of the mud to pass to a holding tank (8). Cuttings together with fluid and residual mud pass to a container (4) in which a secondary separation of mud and fluid is effected by a weir (6). The cuttings are accumulated batchwise in the container (4) until the batch reaches a predetermined amount as determined by a load cell (14), at which point the cuttings are discarded. The total weight of cuttings separated is recorded by a totaliser (19). <IMAGE>

Description

Method and Apparatus for Monitoring Mud and Cuttinqs This invention relates to a method and apparatus for monitoring mud and cuttings in well drilling.

When drilling oil wells, drilling mud is circulated continuously through the well to carry cuttings from the drill bit to the surface and to cool and lubricate the bit.

At the surface the cuttings are separated from the mud and discarded, and the mud is recycled through the well.

However, the separated cuttings remain admixed with oil, and this can present a considerable environmental problem when the well is offshore and the cuttings are dumped into the sea. Control and reduction of the extent of pollution by the discharged oil is therefore desirable.

At present the measure of pollution is quantified by retorting periodic samples of cuttings and determining the percentage of oil in each sample, but this method does not allow for variations of the proportion of oil between sampling and does not give any indication of the total amount of oil discharged; nor does it take account of gross mud losses due to rig heave or other causes.

According to the present invention there is provided a method of monitoring mud and cuttings, comprising receiving a mixture of mud and cuttings from a well, substantially separating the cuttings from the mud, collecting the separated cuttings in a batchwise manner, monitoring the amount of the cuttings collected in each batch and discarding each successive batch of the cuttings after collection of a predetermined amount of the cuttings.

Preferably, oil, residual mud and other fluid carried by the cuttings after separation are further separated from the cuttings to reduce the pollutive content of the cuttings.

The cuttings may be discarded by dumping in the sea or may be otherwise disposed of.

The separation of the cuttings may for example be performed by feeding the mixture to a perforate screen which may be shaken or otherwise moved to allow the mud to pass through while retaining the cuttings. The cuttings may be directed from the screen to a container having weighing means such as a load cell for monitoring the amount of cuttings collected.

The container preferably is actuated to empty its contents on attainment of the predetermined amount of cuttings, for example by interrupting the integrity of the container for release of the contents or by inverting the container.

Further according to the invention there is provided apparatus for use in monitoring mud and cuttings, comprising means for receiving a mixture of mud and cuttings from a well, means for separating the cuttings from the major part of the mud, means for receiving the separated cuttings from the separating means for collection in a batchwise manner, and means for monitoring the amount of the cuttings in said receiving means.

The receiving, separating and collecting stages of this invention are preferably conducted continuously.

The collecting means preferably has additional separating means for further removal of oil, residual mud and other fluid from the cuttings. Such additional separating means may be for example a weir or a filter member such as a perforate screen.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a flow diagram illustrating a method of the invention; Fig. 2 is a perspective view schematicaaly illustrating part of the apparatus of one embodiment of the invention; and Fig. 3 is a detailed side view of a solids collection box used in the apparatus of Fig. 2.

Referring first to Fig. 1, a shale shaker 2 is disposed on an oil rig to receive a mixture of mud and cuttings from a well being drilled. The shaker 2 allows mud to pass through it under gravity while retaining cuttings from the drilled formation, along with a quantity of fluid which adheres to the cuttings. The cuttings and fluid are passed from the shaker 2 into a solids collection box 4 having a weir 6 over which excess fluid flows as the box 4 fills. The fluid passes into a holding tank 8 disposed below the box 4 and from there is either pumped back into the mud active system 12 through a pumping unit 10 or overflows from the tank 8 and passes to the active system 12 under gravity.

The cuttings which collect and are retained in the box 4 are continuously weighed by a load cell 14 located below a platform 16 forming the base of the box 4 until a predetermined weight is achieved. At this point the side walls of the box 4, which are together of unitary construction, are moved relative to the platform 16 until they are clear of the platform 16 as shown by the broken lines 18, and the cuttings then fall through the open bottom of the box 4 into the sea. The sides of the box 4 are then returned to their original position on the platform 16 to receive further cuttings from the shaker 2.

The readings from the load cell are continuously monitored by a weight totaliser 19 which controls the actuation of the box 4 and keeps a tally of the total weight of cuttings collected.

Referring now to Figs. 2 and 3, the shale shaker 2 comprises a pair of vertically spaced horizontal mesh screens 20, 22 whose mesh size is selected to prevent through passage of cuttings while allowing passage of mud. The shaker 2 moves continuously in a reciprocating motion which causes cuttings held on the screens 20, 22 to move to an open end 24 from which the cuttings fall into the solids collection box 4.

The box 4 is generally rectangular in plan, having side walls 26 which rest on and are movable in a direction "A" across the platform 16 on guides indicated at 27 by means of a pair of hydraulic rams 28 disposed one at each end of the box 4 and secured to a support wall 30.

One side wall 26 of the box 4 has a mesh panel 32 of similar mesh size to the screens 20, 22, and a portion of that wall around the panel 32 terminates at its upper end in the weir 6. A container 34 collects fluid passing through the mesh panel 32 and over the weir 6, and a pipe 36 leads the fluid from the container 34 to the holding tank 8 (Fig. 1).

In Fig. 3 there is shown a pair of traction shafts 38 which extend between end walls of a cuttings ditch 42, the shafts 38 being provided as guides (replacing the guides 27 of Fig. 2) for the box 4 as it travels across the platform 16. Also, neoprene scrapers 40 extend downwardly from the side walls 26 of the box 4 to seal against the platform 16 while the box 4 is filling with cuttings; the scrapers 40 are sufficiently flexible to travel across the platform 16 on actuation of the ras 28.

In the apparatus of this embodiment of the invention the box 4 collects cuttings discharged from the shale shaker 2, continuously weighs them and records the total weight of cuttings collected. When used in conjunction with a percentage by weight measurement, this will give an accurate.

assessment of total oil discharged. This can also be used to give an indication of whether more solids are being generated than would be expected in a gauge hole.

Further, the apparatus and method allow for a quantity of mud carried by the wet cuttings, or gross mud losses, to be returned to the mud active system; this could amount to over 5 BBL per day.

The system can be fully automatic and no operator is required. Normal maintenance can be carried out by the rig personnel.

The cumulative weight of solids discharged can be displayed for recording daily or at the end of each section; an output directly to the rig computer can also be incorporated.

Modifications and improvements may be made without departing from the scope of the invention.

Claims (12)

1. A method of monitoring mud and cuttings, comprising receiving a mixture of mud and cuttings from a well, substantially separating the cuttings from the mud, collecting the separated cuttings in a batchwise manner, monitoring the amount of the cuttings collected in each batch, and discarding each successvie batch of cuttings when it reaches a predetermined amount.

2. The method of Claim 1, in which the cuttings being collected undergo a secondary separation for removal of oil and other fluid, including residual mud, carried by the cuttings.

3. The method of Claim 1 or Claim 2, in which the total weight of successive batches of cuttings is accumulated over a predetermined time period.

4. Apparatus for use in monitoring mud and cuttings, comprising means for receiving a mixture of mud and cuttings from a well, means for separating the cuttings from the major part of the mud, means for receiving the separated cuttings for collection in a batchwise manner, and means for monitoring the amount of cuttings in said receiving means.

5. The apparatus of Claim 4, in which the receiving and collection means also comprises further separating means for removal of oil and other fluid, including residual mud, carried by the cuttings.

6. The apparatus of Claim 5, in which said further separating means comprises a weir.

7. The apparatus of Claim 5 or Claim 6, in which said further separating means comprises a filter member.

8. The apparatus of any of Claims 4 to 7, in which said separating means comprises a moving perforate screen.

9. The apparatus of any of Claims 4 to 8, in which said receiving and collection means comprises a container, and means for moving the container to empty it of contents when the contents reach a predetermined amount.

10. The apparatus of Claim 9, in which the monitoring means comprises means for weighing the container and its contents.

11. A method of monitoring mud and cuttings, substantially as hereinbefore described with reference to the drawings.

12. Apparatus for use in monitoring mud and cuttings, substantially as hereinbefore described with reference to and as illustrated in the drawings.