US3901254A

US3901254A - Pollution-free well cuttings disposal apparatus

Info

Publication number: US3901254A
Application number: US403999A
Authority: US
Inventors: Marvin O Stearns; James A Gill
Original assignee: NL Industries Inc
Current assignee: NL Industries Inc
Priority date: 1973-10-05
Filing date: 1973-10-05
Publication date: 1975-08-26
Anticipated expiration: 1992-08-26

Abstract

Apparatus for cleaning oily mud from cuttings at offshore drilling locations and disposing of the cuttings without the formation of an oil slick comprising a cuttings washer in which the cuttings are sprayed with a wash liquid and then conveyed to a partially submerged down pipe and discharged therein below the water level, whereby the cuttings fall to bottom, releasing their oily coating which rises within the down pipe to a submersible pump therein which pumps the released oil to a receiver for optional recycling into the mud system.

Description

United States Patent 11 1 Stearns et al.

1451 Aug. 26, 1975 [54] POLLUTION-FREE WELL CUTTINGS 3,563,255 2/1971 Morris 134/133 DISPOSAL APPARATUS 3,688,781 9/1972 Talley, Jr... 134/110 X 3,765,430 10/1973 Muller 134/109 [75] Inventors: Marvin O. Stearns, London,

England; James Houston Primary Examiner-Robert L. Bleut ge Attorney, Agent, or Firm-Delmar H. Larsen; Roy F. [73] Assignee: NL Industries, Inc., New York, NY. House; Robert L. Lehman [22] Filed: I Oct. 5, 1973 57 ABSTRACT [21] Appl. No.: 403,999 1 Apparatus for cleaning oily mud from cuttings at offshore drilling locations and disposing of the cuttings [52] 1 2 851 5 9 gig/ 2 12 without the formation of an oil slick comprising a cuttings washer in which the cuttings are sprayed with a II}!- wash and h conveyed to a partially Flld of Search merged d and discharged therein below the 175/88 208; 209/159; 210/216 water level, whereby the cuttings fall to bottom, re-

leasing their oily coating which rises within the down [56] References cued pipe to a submersible pump therein which pumps the UNITED STATES PATE T released oil to a receiver for optional recycling into 2,576,283 11/1951 Chaney 175/208 X e d system. 2,950,724 8/1960 Roederer, Jr. 134/183 3,378,018 4/1968 Lawter 134 109 5 Clams 4 Drawmg Flgul'es /4 /5 Z3 TI /0 POLLUTION-FREE WELL currmos DISPOSAL I APPARATUS This invention relates to the art of rotary well drilling in offshore locations using oily drilling fluids, and more particularly to an apparatus and process which permits the economical disposal of cuttings without polluting the body of water where the drilling takes place.

As is well known, the increasing worldwide demand for petroleum has led to increased drilling in offshore locations, such as the Gulf Coast of the United States, the Pacific Coast, the North Sea, and elsewhere. Such drilling is carried out by the rotary process, in which cuttings dislodged by the bit are raised to the surface by means of a drilling fluid or a mud, which fills the bore hole and is circulated continuously during drilling, being pumped downwardly inside the drill string to the bit and thence upwardly in the annular space between the drill pipe and the walls of the bore hole. At the surface, the mud is freed of cuttings by mechanical means and is then recirculated down the hole through the hollow drill pipe as before.

In many locations, it is preferred and may even be indispensable to utilize a drilling fluid having oil as its continuous phase. Such a fluid is commonly known as an oil base or oil emulsion mud. When this is the case, it will be readily appreciated that the cuttings brought to the surface will be coated with a film of oil. Simply disposing of the cuttings by dumping them overboard results in at least a portion of the oil film eventually coming to the surface of the body of water as an oil slick, which is an intolerable situation and indeed is prohibited by laws and regulations in most countries of the world. Since the cuttings are of substantial total volume, disposal by transporting them to land is not only expensive, but is not always a complete solution regardless of expense because oil soaked cuttings may not be indiscriminately dumped at any randomly selected onshore location. A pressing need therefore exists for a mechanically reliable, relatively simple, and relatively economical arrangement for processing such cuttings at the offshore drilling location in such a manner that they can be readily disposed of without causing the formation of an oil slick.

principal components of the apparatus in an offshore drilling installation.

FIG. 3 is a plan view of the cuttings separation and washing portions of our inventive apparatus.

FIG. 4 is an elevation partly in section of the cuttings .washer shown in FIG. 3.

' Generally speaking, and in accordance with an illustrative embodiment of our invention, at an offshore drilling location we provide a partially submerged down pipe extending both above the surface of the 'water and below the surface of the water; a cuttings spraying device receiving cuttings which have been separated from the drilling mud, spraying them with a cleaning liquid and discharging them into a flume which conveys them to the down pipe and discharges them interiorly of the down pipe and below the surface of the water; means for collecting the wash or cleaning liquid when located with silt and for pumping it into a desilting means such as a cyclone and returning the desilted liquid to the cuttings washer; a submersible pump within the down pipe and at the water level therein or adjacent said water level which serves to pump oil released from the cuttings and which has risen to the level of the top of the liquid in the down pipe; an oil-water separator receiving the mixture of oil and water pumped out by the pump from within the down pipe; and a discharge receiver for the oil emerging from the oil-water separator.

The arrangement and function of our inventive apparatus will be more readily understood by reference to the drawings.

In FIG. 2, 10 indicates a portion of the platform of an offshore drilling location, which is supported by a number of vertical supports of which one, 11, is indicated in the figure. 12 indicates the down pipe, which is conveniently welded or otherwise attached to the support leg 11. The down pipe is conveniently of 20-inch diameter steel pipe and should extend about 30 feet below the normal water level, provided of course that the water depth at the drilling locality permits this. Otherwise, it should extend to within not closer than about 10 feet of the ocean or lake bottom. The down pipe 12 should also extend sufficiently above the normal water level so as to be above the water regardless of tidal and normal wave action, for which 8 or 10 feet normally suffices. Of course, in estuarine and like locations where large tidal action occurs suitable allowance should be made therefor. The encased drilling string 13 is shown diagrammatically, with the flow line 14 indicating the conduit in which the drilling fluid with its burden of cuttings is conducted to vibrating

screens

15 and 16, which shakes a substantial portion of the oily mud from the cuttings, from which the cuttings are discharged into a cuttings Washer 17, which conveniently takes the form of a relatively small vibrating screen 18 over the top of which is arranged a series of

spray nozzles

19, 20, 21, etc., supplied with wash liquid from a header 22, also shown in FIG. 4. The cuttings are thus washed with the wash liquid, a large proportion of which falls through the screen carrying with it a portion of the oily mud from the cuttings. However, even with the spray action and vibratory screen action to which the cuttings are subjected in the cuttings washer 17, not all of the oily drilling fluid is necessarily removed from the cuttings. In any case, some of the wash liquid, to be described in detail hereinbelow, amalgamates with the residual oil on the cuttings and renders it more readily susceptible to eventual dislodgement when immersed in the water, generally sea water, in the down pipe 12. The cuttings are simultaneously washed and propelled to the discharge end 23 of the cuttings washer, whence they fall into flume 24 and are conveyed by the action of gravity into the down pipe 12. Water from the body of water surrounding the platform 10 or from the separator 29 may be pumped to the flume 24 to assist in conveying the washed cuttings to the down-pipe 12. The flume 24 terminates and discharges the cuttings below the water level and below the pickup level of the submersible pump 25, as may be seen from FIG. 2. The cuttings fall through thedown pipe 12, and eventually accumulate on the sea bed or'lake bed 26 as a tailings pile 27. In their passage through the down pipe 12, however, and in view of the fact that the cuttings are essentially water wettable, and more particularly aided by the amalgamated wash liquid carried by the cuttings, the oil together with wash liquid is displaced from the cuttings by the water and rises upwardly within the down pipe 12 to form an oil layer adjacent to the pump 25. The latter pumps the top layer of liquid within the down pipe, which as a practical matter includes both oil and water, and pumps it through conduit 28 to the oil water separator 29. The oil freed of any water is then pumped from the separator 29 through conduit 30 to the oil receiving tank 31.

In some cases silt is produced by the washing action in washer 17. In that event, we prefer to collect the wash liquid at the bottom of 17 through exit pipe 35, pump it by means of pump 32 to a desilting cyclone 33 and back to header 22, the silt solids being discharged from the cyclone at 34. Cyclones are well-known in the art. See, for example, the book Cyclones in Industry, K. Rietema et al., Ed., Elsevier, Amsterdam and New York, 1961.

As suggested earlier, since the oil removed from the cuttings was derived from drilling fluid in the first instance, and since the wash fluid is compatible with the drilling fluid, it is convenient and practical to utilize the oil accumulating in the oil receiving tank 31 for the oil make-up requirements of the drilling fluid.

FIG. 1 shows a flow diagram of the cuttings washing and disposal system, in which the contaminated cuttings as discharged from

screens

15 and 16 are fed to the cuttings washer 17 where they are sprayed with wash liquid through header 22 and thence conveyed through flume 24 into down pipe 12 which functions as a liquid-solid separator, from which the discarded solids accumulate on the sea bed and the oil with some water from down pipe or separator 12 is pumped to the oil-water separator 29, from which the water is discarded and oil is returned eventually to the well fluid. FIG. 1 also shows the optional desilting means 33 and pump 32, as already described.

The vibrating

screens

15 and 16 as well as the vibrating screen portion 18 of the cuttings washer 17 are conventional vibrating screens, typical examples of which may be seen in the book by A. M. Gaudin entitled Principles of Mineral Dressing, McGraw-Hill, New York 1939, pages 157l61. The oil-water separator 29 is of the common industrial type frequently used in oil field practice.

Coming now to the wash liquid, this should comprise at least about 10% by volume of an organic solvent which is miscible with crude oil and also has substantial water solubility. While low boiling solvents such as acetone, methyl-ethyl ketone and dioxane meet these requirements, they are less desireable than higher boiling solvents because of the fire hazard associated with their high volatility. A large number of suitable solvents having the properties just mentioned are commercially available at reasonable cost. We prefer such higher boiling mutual solvents for oil and water as ethylene glycol monoisobutyl ether, commercially available under the registered trademark of Isobutyl Cellosolve. Other mutual solvents which are suitable include diethylene glycol monobutyl acetate, ethylene glycol ether, ethylene glycol monomethyl ether acetate, diethylene glycol diethyl ether, and diethylene glycol mono-nhexyl ether. These form the subject matter of a patent application of Thomas C. Mondshine assigned to the assignee of the instant application, and filed concurrently with this application, and entitled Laundering of Oil Base Mud Cuttings.

The wash liquid, as mentioned, should include at least 10% by volume of the mutual solvent for petroleum oil and water such as has been described, and may comprise as much as 100% of such a solvent or a mixture of several such solvents. However, we find that results are almost equally good by using as little as 10% of the mutual solvent in a carrier of petroleum oil, preferably diesel oil. By the term mutual solvent, specific examples of which have been given, we mean an organic solvent having substantial solubility in both petroleum oil, such as diesel oil, and water.

In a field trial of our inventive system, an offshore ocean drilling locality was equipped with the apparatus shown and described herein. Drilling was carried out commencing at a depth of 10,500 feet using an oil-base mud having a continuous phase of from about to by volume of oil and a dispersed phase of from about 20 to 25% by volume of water containing from 30 to 40% by weight of calcium chloride. The vibrating screen portion of the cuttings washer was about 2 feet wide by 6 feet long, with a l00-mesh screen. The cuttings took about 1 minute to traverse the screen during which time they were sprayed with a mixture of 4 parts by volume of diesel oil and 1 part by volume of Isobutyl Cellosolve. The installation operated to a high degree of satisfaction and the cuttings drilled up in the interval drilled with the oil base mud were discharged to the sea bottom with no production of an oil slick at the surface.

We wish it to be understood that we do not desire to be limited to the exact details of construction and operation shown and described, for obvious modifications will occur to a person skilled in the art.

Having described the invention, we claim:

1. Apparatus for removing oil from drill cuttings at an offshore drilling location above the surface of a body of water comprising in combination a platform; a partially submerged down pipe extending both above the surface of the water and below the surface of the water; means on said platform for shaking oily mud from said cuttings by vibratory screening action; means on said platform for discharging said shaken cuttings onto cuttings washer means; means on said platform and associated with said cuttings washer means for spraying said cuttings with a wash liquid; pump means on said platform for collecting said wash liquid subsequent to its contact with said cuttings and for pumping it to desilting means located on said platform; return flow means for recirculating said desilted wash liquid to said cuttings washer means; means for conveying said washed cuttings from said platform to a point within said down pipe and below the surface of said water; pump means for pumping oil dislodged from said cuttings in said down pipe and present within said down pipe adjacent the surface level of said water to oil-water separating means; means for receiving oil discharged from said oilwater separating means.

2. Apparatus in accordance with claim 1 wherein said detergent wash liquid comprises at least 10% of its volume of a mutual solvent for petroleum oil and water.

3. Apparatus in accordance with claim 1 wherein said desilting means comprises a cyclone.

4. Apparatus in accordance with claim 3 wherein said detergent wash liquid comprises at least 10% of its volume of a mutual solvent for petroleum oil and water.

5. Apparatus for removing oil from drill cuttings at an offshore drilling location above the surface of a body of water comprising in combination a platform; a par tially submerged down pipe extending both above the surface of the water and below the surface of the water; means on said platform for shaking oily mud from said cuttings by vibratory screening action; means on said platform for discharging said shaken cuttings onb cuttings washer means located on said platform; means located on said platform associated with said cuttings washer means for spraying said cuttings. with a wash liqcharged from said oil-water separating means.

Claims

1. Apparatus for removing oil from drill cuttings at an offshore drilling location above the surface of a body of water comprising in combination a platform; a partially submerged down pipe extending both above the surface of the water and below the surface of the water; means on said platform for shaking oily mud from said cuttings by vibratory screening action; means on said platform for discharging said shaken cuttings onto cuttings washer means; means on said platform and associated with said cuttings washer means for spraying said cuttings with a wash liquid; pump means on said platform for collecting said wash liquid subsequent to its contact with said cuttings and for pumping it to desilting means located on said platform; return flow means for recirculating said desilted wash liquid to said cuttings washer means; means for conveying said washed cuttings from said platform to a point within said down pipe and below the surface of said water; pump means for pumping oil dislodged from said cuttings in said down pipe and present within said down pipe adjacent the surface level of said water to oil-water separating means; means for receiving oil discharged from said oil-water separating means.

5. Apparatus for removing oil from drill cuttings at an offshore drilling location above the surface of a body of water comprising in combination a platform; a partially submerged down pipe extending both above the surface of the water and below the surface of the water; means on said platform for shaking oily mud from said cuttings by vibratory screening action; means on said platform for discharging said shaken cuttings onto cuttings washer means located on said platform; means located on said platform associated with said cuttings Washer means for spraying said cuttings with a wash liquid which comprises at least 10% of its volume of a mutual solvent for petroleum oil and water; means for conveying said washed cuttings from said platform to a point within said down pipe and below the surface of said water pump means for pumping oil dislodged from said cuttings in said down pipe and present within said down pipe adjacent the surface level of said water to oil-water separating means; means for receiving oil discharged from said oil-water separating means.