METHOD AND SYSTEM FOR TREATING DRILL CUTTINGS SLURRIES AND THE LIKE

Abstract: Drill cuttings, and similar slurries or mixtures oily solid particles, are treated by a dryer apparatus (22) which vaporizes the liquid (36) and discharges (38) relatively large solid particles for disposal. Vapor and entrained solid fines are conveyed from the dryer (22) to a condenser (50) and then to a rotary drum vacuum filter (72) having a precoated filter media (100) disposed thereon. The solid fines are filtered by the filter media comprising diatomaceous earth or perlite and the clarified condensed liquid is conveyed to separator means (124) for separating oil, water and any other liquids present. The filter media stripped from the filter and contaminated with entrapped solid fines is conveyed (90, 92, 94) through the dryer means and disposed with the solids particles being discharged from the dryer (22). The system (10) is particularly adapted for offshore drilling operations (12) wherein the dried solids comprising drill cuttings and diatomaceous earth may be discharged to the sea (18) after separation from all contaminants such as oil and other liquids in the drilling fluid.

Description: The present invention pertains to a method and system for treating well drilling cuttings and similar slurries of oily solids wherein the slurry is subjected to a drying process and wherein a mixture of liquid having residual solid fines entrained therein is processed through a rotary vacuum type filter, particularly a precoat type filter. The generation of oil and gas well drill cuttings slurries and similar slurries of oily liquids and solids has presented longstanding problems with respect to suitable treatment and disposal methods which are environmentally acceptable. Slurries of oily liquid and solids mixtures may be subjected to a drying process as described in US-A-4,319,410 wherein the material is exposed to a relatively intense heat source and agitated to thoroughly evaporate as well as sometimes chemically alter the liquids present in the slurry. The dried solids may then be discharged directly back to the environment, particularly in the case of earth drill cuttings. However, the vapours produced in such drying processes must be treated further since they normally include entrained solids fines and such vapours are either not acceptable for direct discharge into the atmosphere or can be reused in a drilling process or the like. EP-A-200418 discloses a method of treating mixtures including liquids and solids such as earth drill cuttings and similar materials comprising subjecting the mixture to a drying process to vaporise the liquids and produce dry solids and condensing the vaporised liquids produced in the drying process. In this known method the condensed vapours are returned to the drilling operation for re-use. However, such condensed vapours usually have solids fines entrained therein which, desirably, should be separated out and conveniently disposed of. It is an object of the present invention, therefore, to provide for better separation and satisfactory disposal of solids fines from said condensed vapours. According to the present invention, the method of treating mixtures including liquids and solids such as earth drill cuttings and similar materials disclosed in EP-A-200418 is characterised by passing the condensed liquids which include solids fines entrained therein through a filter medium (100), said filter medium comprising a quantity of solids particles which when exposed to the condensed liquids and entrained solids fines allows the liquids to pass through the filter medium whilst entrapping the solids fines, removing said solids fines entrapped in said filter medium and subjecting the removed filter medium and entrapped solids fines to said drying process to dry the filter medium and entrapped solids fines and discharging with the dry solids produced by said drying process the filter medium and entrapped solids fines subjected to said drying process. The invention accordingly provides for the separation from the condensed vapours of the solids fines entrained therein, the drying of the separated solids fines and the disposal of the solids fines together with the dry solids produced from the original mixture treated by the drying process. The invention also consists in a system for treating mixtures such as a slurry containing at least solid particles and oil to dry said solid particles for disposal to the earth, said system as is disclosed in EP-A-200418 comprising: dryer means for receiving said slurry and operable to vaporise the liquids in said slurry and to discharge substantially dried solid particles for disposal and including means for discharging a flow stream of vapour comprising liquids vaporised from said slurry; and condenser means for condensing to liquid said flow stream of vapour; characterised, according to the invention, by filter means for receiving said flow stream of condensed liquid which includes entrained solids fines comprising a filter support surface and a layer of filter medium forming a coating on said support surface, means for causing said flow stream of condensed liquid to pass through said filter medium to entrap said entrained solid fines and provide a substantially solids free flow stream of liquid, means for removing said solids fines entrapped in said filter medium from said filter support surface and means for conveying said removed filter medium and solids fines entrapped therein to said dryer means for drying and disposal together with said substantially dried solid particles from said dryer means. The invention will now be described, by way of example, with reference to the accompanying drawings. FIGURE 1 is a schematic diagram of an improved system for treating drill cuttings slurries and the like in accordance with the present invention; and FIGURE 2 is a detail, somewhat schematic view illustrating the operation of the filter medium and the filter apparatus used for separating the solids fines in the system of Figure 1. In the description which follows, like parts are marked throughout the specification and drawing with the same reference numerals, respectively. The drawing figures are not to scale and most of the features of the drawing are shown in somewhat schematic form in the interest of clarity and conciseness. Referring to Figure 1, there is illustrated a system for treating earth drill cuttings and the like to separate solid particles from a mixture of solids, oil and water. The system illustrated in Figure 1, and generally designated by the numeral 10, is particularly adapted for use in conjunction with treating drill cuttings from offshore drilling operations such as may be performed by an offshore drill rig 12. The drill rig 12 includes a platform 14 supported on suitable supports 16 above the surface of the sea 18. The drilling rig 12 includes conventional drilling equipment and a circulation system, not shown, for recirculating the drill cuttings evacuation fluid or "mud". The mud circulation system is mounted on the platform 14 and includes the system 10 for treating the drill cuttings in the form of slurry-like mixture which is separated from the circulation fluid and the conventional circulation system. Although the present invention is particularly useful for offshore well drilling operations, as well as onshore well drilling operations, those skilled in the art will recognize that the improvements provided by the system 10 may be utilized in treating various types of solids and oily liquid slurries, such as refinery waste streams, chemical processing waste streams, tanker ballast water and similar types of slurries. The system 10, in conjunction with the drilling rig 12, is particularly adapted to receive the drill cuttings slurry which has been separated from the recirculating drilling fluid and is charged into a feed stream 20 leading to a dryer apparatus generally designated by the numeral 22. The dryer apparatus 22 is particularly advantageously used in treating drill cuttings slurries and is characterized by a housing 24 in which a rotor 26 is disposed and is characterized by a plurality of spaced apart hollow circular disks 28. The disks 28 are adapted to receive a flow stream of hot fluid which enters the rotor 26 at one end 30 and is discharged at the opposite end 32 for recirculation through a heat source. The aforementioned fluid may be circulated in a way, not shown, which heats the housing 24, also. The dryer 22 includes an inlet port 34, a fluid vapour discharge port 36, and a dried solids discharge port 38. Dried solids particles of a size which, by mechanical and gravity flow, are discharged into the port 38 proceed through a conduit 40, which may be controlled by suitable valve means 41, to be partially recirculated back to the inlet port 34 by way of a conveyor 42 to adjust the consistency of the slurry mix entering the inlet port 34. At least a major portion of the dried cuttings are suitably discharged directly into the sea or to means, not shown, for transport to a suitable disposal site by way of the conduit branch 46. The process of drying the drill cuttings or similar solids generates a substantial amount of vapour as the liquids of the slurry are driven off, primarily by evaporation. Moreover, the solids fines resulting from various types of earth formations being drilled and from the drilling fluid additives may consist of certain claylike substances which are light enough to be carried off with the vapour flow exiting the dryer 22 through the discharge port 36. This flowstream of vapour and entrained solids fines is conveyed by a conduit 48 to a condenser 50. The condenser 50 is characterized as a closed vessel having an arrangement of liquid spray nozzles 54 discharging into a chamber 56 for condensing the vapour and entrained fines flow stream entering the chamber. The condenser 50 may include sieve trays or the like, not shown. The condensed mixture of liquids and solids fines is discharged from the condenser 50 through a conduit 58 into a collection or surge tank 60 which will provide for some separation of the heavier solids fines 62 which may collect at the bottom of the tank. However, the fineness and density of the solids typically driven off with vapours from the dryer 22 are such that they remain in suspension or in an emulsionlike form with the liquids. The oil-water-solids mixture discharged from the condenser 50 into a chamber 61 formed within the collection or surge tank 60, must be subjected to further treatment to separate the oil and water from each other and from the solids fines. Typically, a layer 63 of relatively clarified liquid may exist in the chamber 61 while a sometimes frothy layer 65 containing a higher concentration of solids fines will rise to the surface of the mixture in the chamber. Accordingly, the condenser 50 may utilize a fluid stream taken from the surge tank 60 and discharged by way of a pump 66 through a heat exchanger 68 and recirculated to the array of nozzles 54 for use as the condensing fluid. The heat exchanger 68 may utilize sea water as the heat exchange medium for cooling the fluid stream being recirculated from the surge tank 60 through the heat exchanger 68 and the nozzle array 54 to the condenser 50. Further in accordance with the present invention, a mixture of oil, water (or other liquids), and solids fines in the surge tank 60, preferably from the layer 65, is discharged through a conduit 70 to a rotary drum vacuum type filter of a type which uses a precoat filter medium for separating relatively fine solid particles from liquids or slurrylike substances. The rotary drum vacuum filter is generally designated by the numeral 72 and is characterized by a rotating drum 74 having a suitable support structure, not shown, and a cylindrical filter medium support member 76 comprising a somewhat screenlike structure. The drum 74 is supported for rotation in a tank 78 into which the liquid and fines mixture from the tank 60 may be discharged by way of the conduit 70. The tank 78 is also in communication with a source of precoat filter media comprising a tank 80 which is connected to the tank 78 by a conduit 82 having a suitable shut-off valve 84 interposed therein. The tank 78 may also be drained by way of a conduit 86 having a shut-off valve 88 interposed therein and in communication with a conduit 90 and a suitable conveyor or pump, generally designated by the numeral 92. The pump or conveyor 92 is in communication with the feed conduit 20 by way of a conduit 94. Solids collected in the bottom of the surge tank 60 may also be conveyed through the conduit 94 by way of a branch conduit 96 having a suitable shut-off valve 98 interposed therein. The filter or separator 72 may be of a type commercially available such as from the Envirotech Corporation, Salt Lake City, Utah. The filter drum 74 is preferably precoated with a slurry-like filter medium to form a coating 100 of filter medium which may be provided by filling the tank 78 with the precoat medium and rotating the drum 74 to collect the medium on the surface of the element 76. When a suitable coating 100 is applied to the drum 74, the tank 78 may be drained of precoat material through conduits 86 and 88 or 93 and prepared for receiving the material to be filtered. Filtration of the liquid-solids slurry is carried out by drawing a vacuum on the drum interior space 104 formed by the drum 74 by a vacuum pump 106 connected to a liquid receiver tank 108. As the liquid/solids mixture is filtered through the medium coating 100, the solids fines are collected by the filter medium and, before the medium is blinded by the collection of solids, the coating 100 is continuously shaved to reduce the coating or layer thickness by an elongated knife blade 110. Figure 2 illustrates in somewhat schematic form the way in which the filter medium coating or layer 100 is continuously renewed by shaving a relatively thin layer 101 of the medium off the coating 100 as the drum 74 is rotated. As shown in Figure 2, a layer of precoated filter medium 100 entraps the solid fines 112 between the solid particles 114 of the precoated filter medium which typically comprises diatomaceous earth. As the drum 74 rotates, the knife edge 110 shaves off layer 101 from the coating 100 which has the greatest density of accumulation of solids 112. This layer of precoated filter material and collected solids is discharged into a trough 120, Figure 1, and is conveyed by way of the conduit 90, the conveyor 92 and the conduit 94, to the feed stream conduit 20 leading to the dryer 22. The knife 110 is connected to a suitable mechanism, not shown, for advancing the knife through the filter medium layer 100 until the layer is shaved down to a thickness which requires replacement. The filtered liquids such as oil and water withdrawn through the filter drum 74 into the tank 108 may then be discharged to a suitable separator 124, Figure 1, for separation of the water and oil into separate discharge streams. Both of the streams 126 and 128 may be reused in the drilling fluids circulation system, as required, or suitably disposed of in other acceptable ways. A particular advantage of the system 10 resides in the arrangement of the filter 72 which provides for a filter medium which may be disposed of and treated together with the solids fines which are removed from the filtrate fluid. Since the filter medium comprising the solid particles 114 and a water-like substance which provides the precoat slurry may be treated by the dryer 22 and the solid particles 114 which are dried by the dryer discharged into the environment, the solids separated from the drill cuttings slurry or a similar based stream, together with the filter medium, may be treated in the same manner and disposal efforts are minimized. The filter medium or material making up the layer or coating 100 may be of a type commercially available, such as a diatomaceous earth composition manufactured under the trademark Celite by Johns Manville Corporation, Denver, Colorado. In a preferred method of operating the system 10 in accordance with the present invention, the filter 72 may be prepared for receiving a flow stream of condensate and solids fines from the tank 60 by precoating the element 76 with a suitably thick layer 100 of filter medium. Assuming that the tank 78 is initially empty, it is then at least partially filled with the filter medium slurry from the tank 80 by way of the conduit 82. The valve 88 is in the closed position to prevent loss of filter medium from the tank 78. When a suitably thick layer 100 is applied to the drum 74, the tank 78 is emptied and excess filter medium returned to tank 80. A feed stream of drill cuttings slurry is presented to the dryer 22 through the conduit 20 and the dryer is operated to vaporize the liquids in the slurry stream for discharge from the dryer to the condenser 50. An initial charge of liquid such as clear water may be present in the chamber 61 for being pumped through the circuit comprising the pump 66, the heat exchanger 68, and the nozzle array 54. Dried cuttings are discharged from the dryer 22 through the conduit 40 and at least a portion of the cuttings may be recirculated as needed to control the consistency of the feed stream entering the port 34. The mixture of vapour and solid fines entering the chamber 56 is condensed, discharged into the tank 60 and allowed to undergo a gravity separation process. When the liquid and solid fines mixture in the tank 60 reaches a level which will allow it to be discharged into the conduit 70, the tank 78 is filled with this mixture and the pump 106 is started to commence drawing the mixture onto the filter medium layer 100 whereby the liquid filters through the layer and into the chamber 104 while the solid fines are collected and entrapped in the filter medium. The knife 110 is operated to begin shaving a thin layer of filter medium from the layer 100 and entrapped solid fines off and into the trough 120 whereby it is conveyed by the conduits 89 and 90, the conveyor 92 and conduit 94 to the feed stream inlet conduit 20 for treatment by the dryer 22. It is contemplated that the relatively viscous layer of filter medium and entrapped solids fines filtered from the drill cuttings liquids and fines mixture will progress through the dryer 22 and tend to agglomerate with larger solids particles, be suitably dried to evaporate the liquids and whereby then the solids fines and dried filter medium agglomerated on to other solids particles will be discharged as dried solids through the conduit 40. Liquid withdrawn through the chamber 104 into the tank 108 is then pumped into the separator 124 for separation into respective water and oil fractions for further treatment. For example, the oil may be stored and used as an additive for the drilling fluid and the clarified water may be handled in a similar manner or discharged directly overboard into the sea. When the precoated filter medium layer 100 has been reduced to a thickness that will no longer provide suitable filtration, the flow of filtrate to the tank 78 is cut off, the tank drained through the conduit 86 and the conveyor 92 back to the dryer 22 and a fresh charge of filter medium is discharged into the tank 78 to recoat the drum 74. During this time the level in the tank 60 may be allowed to build up to prevent shutdown of the dryer 22 and the condenser 50 or the recoating of the filter 72 may be carried out during shutdown of drilling operations for various reasons. Those skilled in the art will appreciate that the method of the present invention and the system 10 provide a unique improvement in the handling of slurries of solids which cannot be separated and treated by prior art methods. The use of the system 10 in offshore as well as onshore drilling operations and in other applications for handling oily solids slurries is particularly advantageous. The rotary type dryer apparatus is particularly and surprisingly advantageous for handling slurries of solids, oil and water of a type typically produced in well drilling operations, and may be included in a system of a type disclosed in U.S. Patent Application Serial No. 796,349 filed November 8, 1985, in the name of James L. Skinner (& EP-A-224353, published 03.06.87), and the condensing system for the vapour and solids fines stream is also described and claimed in U.S. Patent Application Serial No. 727,311 filed April 19, 1985, also in the name of James L. Skinner (& US-A-4683963, published 04.08.87), both applications being assigned to the assignee of the present invention.

Claims: A method of treating mixtures including liquids and solids such as earth drill cuttings and similar materials comprising subjecting the mixture to a drying process to vaporise the liquids and produce dry solids and condensing the vaporised liquids produced in the drying process, characterised by passing the condensed liquids which include solids fines entrained therein through a filter medium (100), said filter medium comprising a quantity of solids particles which when exposed to the condensed liquids and entrained solids fines allows the liquids to pass through the filter medium whilst entrapping the solids fines, removing said solids fines entrapped in said filter medium and subjecting the removed filter medium and entrapped solids fines to said drying process to dry the filter medium and entrapped solids fines and discharging with the dry solids produced by said drying process the filter medium and entrapped solids fines subjected to said drying process. The method set forth in Claim 1, characterised by: drawing the condensed liquid and solids fines mixture through said filter medium (100) with a vacuum pump (106) to provide a liquid mixture substantially free of solids fines. The method set forth in Claim 2, characterised by separating liquids produced in the filtrate. The method set forth in Claim 1, characterised by condensing the vapours and entrained solids fines by exposing the vapour and solids fines mixture to a stream of condensed vapours and entrained solids fines in a closed vessel (60). The method set forth in Claim 1, characterised by applying said filter medium (100) to a generally cylindrical drum (74) and removing applied filter medium from said drum after collection of a predetermined amount of solid fines from said mixture of condensed liquids and solids fines. The method set forth in Claim 5, characterised by conveying to a drying apparatus, together with a flow stream of slurry to be dried, the filter medium and entrapped solids fines removed from said filter drum. The method set forth in Claim 1 and in which said mixture comprises a stream of drill cuttings and drilling fluid in an offshore well drilling operation in the form of a slurry of oil, water and solids, including solids fines, characterised by discharging solids dried in said drying step including dried filter medium and entrapped solids fines in a dried oil free condition into the sea. The method set forth in Claim 7, characterised by separating liquid separated from said solids fines into a water fraction and an oil fraction and recirculating at least said oil fraction for use in said drilling fluid. The method set forth in Claim 7, characterised by selecting said filter medium from a group consisting of diatomaceous earth and perlite. A system for treating mixtures such as a slurry containing at least solid particles and oil to dry said solid particles for disposal to the earth, said system comprising: dryer means (22) for receiving said slurry and operable to vaporise the liquids in said slurry and to discharge substantially dried solid particles for disposal and including means (36) for discharging a flow stream of vapour comprising liquids vaporised from said slurry; and condenser means (50) for condensing to liquid said flow stream of vapour; characterised by filter means (74,100) for receiving said flow stream of condensed liquid which includes entrained solids fines comprising a filter support surface (76) and a layer of filter medium (100) forming a coating on said support surface, means (104,106) for causing said flow stream of condensed liquid to pass through said filter medium to entrap said entrained solid fines and provide a substantially solids free flow stream of liquid, means (110) for removing said solids fines entrapped in said filter medium from said filter support surface and means (92,94) for conveying said removed filter medium and solids fines entrapped therein to said dryer means for drying and disposal together with said substantially dried solid particles from said dryer means. The system set forth in Claim 10, characterised by means (108) for receiving said flow stream of liquid separated from said solid fines and separator means (124) for separating oil in said liquid from water in said liquid. The system set forth in Claim 10, characterised in that said condenser means (50) includes means for contacting a liquid flow stream with said flow stream of vapour and entrained solid fines to condense said vapour, said liquid flow stream comprising at least in part liquid condensed from said flow stream of vapour. The system set forth in Claim 12, characterised by a heat exchanger (68) interposed in a circuit including said condenser means for recirculating at least part of the vapours condensed in said condenser means for use as a liquid for contacting said vapour to condense said vapour and entrained solid fines. The system set forth in Claim 10, characterised by a surge tank (60) including a chamber (61) for receiving condensed vapour and entrained solid fines to permit settling of at least some of said solid fines in said condensed vapour, and conduit means (70) leading from said tank to said filter means for conveying liquid with entrained solid fines to said filter medium. The system set forth in Claim 10, characterised in that said filter means includes a rotary vacuum drum filter (74) including a foraminous member (76) forming said filter support surface and means (78) are provided for receiving a quantity of said filter medium for coating said filter medium on said member, means (120, 89, 90, 92, 94) also being provided for discharging filter medium to said dryer means. The system set forth in Claim 15, characterised by means (110) for shaving a layer of filter medium from said filter drum (74) progressively to remove filter medium contaminated with entrapped solid fines, and means (120, 89, 90, 92, 94) for conveying said filter medium with entrapped solid fines to said dryer means (22). The system set forth in Claim 10, characterised in that said filter medium is selected from a group consisting of diatomaceous earth and perlite.

Inventors: BEER, GARY L., LI, YING H.
Applicants: ATLANTIC RICHFIELD COMPANY
Application year: 1987
Main classification: E21B21
IPC codes: B01D37, B01D33, E21B21