WO1993012321A1

WO1993012321A1 - Apparatus for filtering cuttings from drilling fluid

Info

Publication number: WO1993012321A1
Application number: PCT/GB1992/002296
Authority: WO
Inventors: William Woodburn
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-12-10
Filing date: 1992-12-10
Publication date: 1993-06-24
Anticipated expiration: 1994-06-10
Also published as: GB9411729D0; GB2276562B; GB2276562A; GB9126185D0

Abstract

Apparatus for filtering cuttings from drilling fluid comprises a filter disposed in an endless recirculating loop (10), an inlet (30) for receiving drilling fluid and cuttings from a drilling well and disposed to direct the drilling fluid and cuttings onto the filter (10), and an outlet (50) disposed to receive filtered drilling fluid from the filter (10), for supply of the filtered drilling fluid to a drilling well.

Description

Apparatus for Filtering Cuttings from Drilling Fluid

This invention relates to apparatus for filtering cuttings from drilling fluid. It is particularly although not exclusively adaptable for use on an oil well drilling rig to filter cuttings from used drilling fluid enabling the filtrate to be recycled and reused.

The pumping of drilling fluid down a well and back to the rig while drilling is important for a number of reasons including bit lubrication and cooling, providing a well data source and retrieval of cuttings. Retrieval of cuttings is particularly important since failure to do so leads to loss of drilling efficiency and damage to the bit.

Currently a common means of filtering uses a shale shaker, which comprises a stainless steel mesh screen clamped in an iron frame. Drilling fluid contaminated with cuttings is fed onto the screen of the shale shaker while the whole assembly vibrates. Cuttings are retained and drilling fluid passes through the screen and can be returned to the well.

The shale shakers may run 24hr/day in a salt water environment, must typically bear heavy loads and are subjected to high forces by the vibration mechanism; therefore corrosion due to the salt water environment, and the stress to which the apparatus is subjected cause frequent mechanical failure of the prior art.

The use of dissimilar metals for the construction of the shale shakers such as a stainless steel screen and a low grade mild steel frame causes rapid degradation of the frame in a salt water environment. A typical method of fixing the screen in place consists of gluing the screen between the two halves of the frame using an epoxy adhesive. The epoxy bonds only to a surface layer of the low grade mild steel of the frame. When this surface layer corrodes due to the high salt atmosphere on many rigs, the screen becomes detached. Another method of clamping the screen in place frequently used is to pierce sharp points on the frame through the mesh, creating areas with enhanced vulnerability to tearing and corrosion. Tears in the screen may be patched but only with a loss of filtration area that can represent a high proportion of the area available for filtration.

In addition, many screens comprise several layers of mesh of a differing pore size clamped together for strength. This can cause problems when the vibration of the screen moves the layers relative to one another creating a sawing effect which can induce a perforation in the screen very quickly. Hence the life of an average screen might be no more than 2 weeks.

In addition to the corrosion and stress disadvantages, the existing filtration methods lack efficient screen cleaning mechanisms, frequently becoming blocked and developing blind spots. This causes leaking of unfiltered liquid over the screen, shorter screen life and increased maintenance time to clean or replace the screen.

As a result of the high maintenance requirements of existing shale shakers, rigs must carry spare frames and spare screens of several different pore sizes. Each machine may have -between 3 and 8 screens, each weighing 12-22 kg, thus adding to the weight to be borne by the rig. This can be a significant disadvantage on floating platforms.

According to the present invention there is provided apparatus for filtering cuttings from drilling fluid, comprising filter means disposed in an endless recircultrating loop, an inlet for receiving drilling fluid and cuttings from a drilling well and disposed to direct said drilling fluid and cuttings onto said filter means, and an outlet disposed to receive filtered drilling fluid from said filter means for supply of the filtered drilling fluid to a drilling well.

The filter means may comprise a mesh preferably woven from stainless steel, although other materials, for example a synthetic plastics material may also be used. The mesh size may be selected to remove particles above a given size from the drilling fluid and is preferably between 80 x 80 and 325 x 325 mesh (according to the A.P.I designation system commonly known in the art) although other mesh sizes may additionally or alternatively be used.

The filter means preferably has a web attached to the sides thereof, most preferably by an encapsulation of example stitching or stapling of the web to the filter means may also be used.

Filter cleaning apparatus is preferably disposed adjacent the filter means at a position (with regard to the direction of movement of the filter means) before the inlet. The cleaning apparatus may comprise a mechanical or ultrasonic vibrator and/or a spray wash.

Motive force for the filter means may be provided in the form of, for example, a pneumatic, hydraulic or electric motor.

Preferably the filter means is guided during its movement by sprockets engaging in apertures along the filter means, and may pass over guide rollers.

An embodiment of the present invention will now be described by way of example, with reference to the accompanying drawings in which:-

Fig. 1 is a side view showing internal detail of apparatus for filtering cuttings from drilling fluid in accordance with the invention;

Fig. 2 is an end sectional view of the apparatus shown in Fig. 1; and

Fig. 3 is an expanded sectional view across a filter of the apparatus shown in Fig. 1.

Referring now to the drawings, apparatus 1 for filtering cuttings from drilling fluid according to the invention has a casing 5 in which is mounted a filter 10 woven from stainless steel having a mesh size of 325. The filter 10 is arranged in an endless loop and moves longitudinally on a path 15 defined by pairs of sprocket wheels 20, 21, 22, 23, 24, 25, 26, 27 and 28. Sprocket wheels 20, 21, 22, 23, 24 and 25 are disposed at the ends of rollers which further support the filter. The filter 10 is driven longitudinally by a pneumatic motor (not shown) which powers the rotation of the sprocket wheels 20. The sprocket wheels 21-28 idle and act only to guide the filter 10 around the path 15. The filter 10 is gripped by sprocket teeth 29 on each sprocket wheel which teeth 29 extend through apertures 36 in the filter 10. Sagging of the filter 10 resulting from heavy loads is mitigated by an adjustable filter tensioning device 19.

The filter 10 is guided at sections of the path 15 by guide rails 35 into which slot 'T^* pieces 37 extending from a flexible neoprene web 38 the base of which encapsulates at 39 the weave of the filter 10 at each edge 11. The flexible neoprene web 38 is liquid-impermeable and a seal is thus formed at the edges 11 of the filter 10. The guide rails 35 also act to stretch laterally the filter 10. At the sprocket wheels 20, 21, 24, 25 and 26, the path 15 of the filter 10 changes direction, and at these points, the flexible neoprene web 39 deforms to accommodate the curvature of the turn.

The filter 10 is supported by three support bars 17 which are equally spaced apart across the filter 10. The filter 10 has reinforced neoprene wear strips 18 extending along it to coincide with and contact the support bars 17.

The use of the support bars 17 and wear strips 18 strengthen the filter 10 and allow the use of synthetic plastics in its composition. Synthetic plastics were unusable for filters on previous shale shakers due to the weakness of the material and its tendency to sag. The use of synthetic plastics in the filter's construction mitigates the problems of corrosion associated with the use of dissimilar metals previously discussed.

The apparatus 1 has an inlet 30 which communicates with a drilling fluid circulation system so as to receive therefrom a suspension of cuttings in drilling fluid. The inlet 30 opens above a decline 15a of 45° to the horizontal in the path 15 of the filter 10 between the sprocket wheels 25 and 26.

The path 15b of the filter 10 inclines from the sprocket 26 at an angle of 10° to the horizontal, thus creating an area 31 where a pool 45 of drilling fluid and cuttings collects.

At areas 31 and 32 on the path 15b, the filter 10 is subjected to lateral vibration by mechanical vibrators 47. The amplitude of this vibration is low and is applied in a plane of the filter 10 which is resistant to stress and therefore causes little fatigue to the filter 10 or the apparatus 1.

At area 32 on the path 15b, the filter 10 is guided and laterally stretched by guide rails 35. Drilling fluid passing through the filter 10 at areas 30, 31 or 32 on the path 15 falls into a chute 50 and drains through an outlet orifice therefrom (not shown) into the drilling fluid circulation system for return to the well. Particulate matter retained on the filter 10 falls from it under gravity as the filter 10 passes around the sprocket wheels 20; residual cuttings still remaining on the filter 10 may be dislodged by a mechanical vibrator 55 held in contact with the internal surface of the filter 10.

The filter 10 is then washed after passing the sprocket wheels 22 by liquid sprays 60 and is laterally stretched and guided by guide rails 35 along the path 15d. The washed area of filter 10 then returns to the inlet 30 via path 15e.

The filter 10 may be repaired if damaged by applying a patch of suitable material, and the lost filter area resulting will generally be small in proportion to the large overall area of the filter 10. If the filter 10 becomes badly damaged or blocked it may be replaced by slowly moving the male-female filter joint 8 to a point between the upper 65 and lower 66 loading brackets, releasing the tension and disconnecting the two ends of the old filter 10, loading a roll of new filter 12 onto the lower loading bracket 66 and joining the ol 10 and new 12 filters at the male-female joint (not shown) . The combined filters 10, 12 can then be moved slowly around the path 15, unrolling the new filter 12 from the lower loading bracket 66 and rolling in the old filter 10 at the upper loading bracket 65 until the male-female joint 9 between them is again between the upper 65 and lower 66 loading brackets. The old 10 and new 12 filters can then be separated, the two ends of the new filter 12 can be joined at 9 and the tension re-applied. If the filter requires replacement due to an incorrect pore size instead^*of damage it may first by cycled through the apparatus several times in the absence of drilling fluid and with the activation of the cleaning means to clean the filter 10 before removal and storage.

In use, a suspension of cuttings in liquid drilling fluid is fed continuously onto the moving filter 10 at the inlet 30. Liquid drilling fluid may pass through the filter 10 at this point but cuttings larger than the filter's pore size are retained on the outer surface of the filter 10. As the filter 10 moves on its path 15a, cuttings are transported from the inlet 30 to the pool area 31. The neoprene web 38 seals the edges 11 of the filter 10 and prevents the escape of unfiltered liquid drilling fluid. The deformation of the web 38 as the filter 10 changes direction at the sprocket wheels 26 is minimal. As the filter 10 moves along path 15b, cuttings deposited from suspension in the pool 45 are transported out of the pool 45 and up the "beach" area 32 by the movement of the filter 10. During its movement up the beach area 32, the deposited cuttings are subjected to vibration which facilitates the draining of any drilling fluid still associated with them. The drilling fluid passing through the filter in areas 30, 31 or 32 falls into the chute 50 and can drain from the apparatus 1 through the outlet (not shown) , and thence return to the drilling fluid circulation system for recycling to the well.

When the cuttings have reached the sprockets 20 on the path 15b, they are substantially free of drilling fluid and upon passing the sprockets 20, fall under gravity from the filter 10. Any cuttings that remain on the filter are removed either by the mechanical vibrator 55 or by the spray wash 60, thereby continually provided a substantially clean filter surface at the inlet 30. Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims

1 Apparatus for filtering cuttings from drilling fluid, comprising filter means disposed in an endless recircultrating loop, an inlet for receiving drilling fluid and cuttings from a drilling well and disposed to direct said drilling fluid and cuttings onto said filter means, and an outlet disposed to receive filtered drilling fluid from said filter means for supply of the filtered drilling fluid to a drilling well.

2 Apparatus according to Claim 1 wherein the filter means comprises a woven mesh.

3 Apparatus according to Claim 2 wherein the filter means has an API mesh designation of between 80 x 80 and 325 x 325.

4 Apparatus according to Claim 1, 2 or 3 wherein the filter means is of stainless steel.

5 Apparatus according to Claim 1, 2 or 3 wherein the filter means is of synthetic plastics material.

6 Apparatus according to any one of the preceding claims wherein the filter means has a web attached to the sides thereof.

7 Apparatus according to Claim 6 wherein the web encapsulates a portion of the edge of the filter means.

8 Apparatus according to any one of the preceding claims wherein filter cleaning apparatus is disposed adjacent the filter at a position, with regard to the direction of movement of the filter means, before the inlet.

9 Apparatus according to Claim 9 wherein the filter cleaning apparatus comprises a mechanical vibrator.

10 Apparatus according to Claim 9 wherein the filter cleaning apparatus comprises an ultrasonic vibrator.

11 Apparatus according to Claim 9 wherein the filter cleaning apparatus comprises a spray wash.

12 Apparatus according to any one of the preceding claims wherein the motive force for recirculation of the filter means is provided by a pneumatic motor.

13 Apparatus according to any one of Claims 1-11 wherein the motive force for recirculation of the filter means is provided by a hydraulic motor.

14 Apparatus according to any one of Claims 1-11 wherein the motive force for recirculation of the filter means is provided by an electric motor.