TECHNICAL FIELD

This invention relates to hydrocarbon contaminated cuttings such as oily drill cuttings and processes for their treatment. More specifically, it relates to processes by which hydrocarbon contaminated cuttings can be freed from hydrocarbon contaminants to a sufficient extent to render them environmentally acceptable for disposal.

BACKGROUND ART

In the drilling of oil wells and gas wells, cuttings are formed by broken and displaced solids materials as the drilling bit penetrates into and passes through subterranean or subsea formations. The cuttings are collected into the drilling mud or fluid medium which surrounds the drill bit. Drilling mud is circulated into the borehole by downward injection through the drill stem that supports the drill bit. The mud then passes through holes in the bit and spreads over the cutting faces of the drill bit to act as a lubricant as the drill bit operates. Finally, the drilling mud rises back to the surface through the annular space surrounding the drill stem and drill bit along with cuttings from the drilling operation. The drilling mud needs to have an appropriate combination of rheological properties and lubricating properties to perform its drill bit lubricating function, to withstand the high pressures to which it is subjected during the drilling operation, without emulsion breakdown or excessive fluid loss into the formation, and to permit circulation even when it is loaded with cuttings.

Oily drill cuttings laden with hydrocarbon contaminants originate mainly from the use of oil. based

drilling muds. Such muds are especially useful in operations which involve drilling through or into water sensitive formations, or for directional drilling operations both onshore and offshore. Diesel oil is the commonly used oil in the formulation of oil based drilling muds, for economic reasons. However, a major disadvantage of most diesel oils is high toxicity. As a result, mineral oils which are substantially less toxic are also used in formulating oil based muds despite their higher cost. Mineral oils are low in aromatics content, have a room temperature viscosity of about 0.5- 50 centipoise and a boiling range 180-300°C. They are normally substantially free from carbon-carbon unsaturation, and consist largely of paraffinic and cycloparaffinic liquid hydrocarbons.

In either case, the drilling mud can consist of the liquid hydrocarbon as essentially the only liquid vehicle, or more commonly the drilling mud is formulated such that the liquid hydrocarbon forms the continuous phase of a water-in-oil emulsion. Suspended in the liquid medium of the drilling mud are various liquid additives and solid particles, functioning to impart various properties to the mud. In the cases where the liquid hydrocarbon oil is the only liquid vehicle of the mud, the solid particles . are normally solid polymer particles, for filtration and viscosity control, and for ease of cleaning. Clay solids can also be used therein. Where the liquid vehicle is a water-in-oil emulsion, the particles commonly include organically coated clays, optionally weighting agents and other solid additives, as required, to impart specific density, rheological properties and lubricating properties to the mud. The oil phase of muds of this type normally contains primary and secondary emulsifiers, to stabilize and promote the dispersion of the water phase into very small droplets,

and oil wetting agents to promote oil wettability of %he suspended solids. The emulsified water in muds of this type may contain dissolved salts, e.g. calcium chloride _r sodium chloride, potassium chloride or the like compounds, to draw connate or formation water present with the cuttings into the drilling mud water, phase by osmotic activity and to reduce clay swelling with the water. The drilling muds can have a highly variable specific gravity. The solids have a broad particle size distribution, usually in the range up to 250 microns.

Effectively, therefore, a typical, invert drilling mud is a complex fluid, comprised of a water- in-oil emulsion containing fine suspended so_Li|ls and having appropriate rheological properties such _^ as viscosity, gel strength, lubricity, , and .ottos r characteristics that render it suitable for downhole drilling use and circulation, especially for directional drilling applications.

The used drilling mud which is recirculated-to the surface of the borehole has drill cuttings mixed therein, and comprises an oily, gritty mixture of hydrocarbon, water, clay, sand, shale and drill residues from the formation being drilled. The particles of formation residue are of widely different sizes. Since the spent drilling mud still has most of the basic characteristics and properties of the original mud, its separation from the drill cuttings is desirable for re¬ use and the prior art describes various methods by which this may be accomplished. For instance, it is common practice to subject the used drilling mud containing cuttings to a screening process to separate out the coarsest particles, and to wash these to reclaim some Of the drilling mud. The material which passed through $#ιe screen is then subjected to additional solids

separations or liquid-solids separations involving centrifugation, hydrocycloning, etc. to reclaim additional drilling mud and hydrocarbon and to separate out the finer drill cuttings particles not removed by the screening process. The reclaimed drilling mud is then recycled and reused by the drilling operation, while the cuttings are rejected and temporarily stored prior to disposal.

Some of the liquid hydrocarbon content of the rejected cuttings will separate as a supernatant layer on standing and can be skimmed off. The remaining solid or semi-solid portion still has an undesirably high hydrocarbon content, even after several days standing. It is most desirable to reduce the hydrocarbon content substantially before the solids are discarded. Indeed, environmental regulations for both land disposals and off-shore disposals often require such hydrocarbon reduction, and such regulations are becoming more and more stringent in this regard. Diesel oil, the commonest hydrocarbon used in drilling muds, is a particularly environmentally hazardous material.

There is, accordingly, a need for a relatively effective, simple, and economical process for reducing the hydrocarbon content of oil contaminated cuttings and drilling mud residues, prior to their disposal.

Considerable effort has been expended in the past on developing ways of recovering drilling muds for recirculation and reuse. For example, U.S.patent 2,919,898 Marwil et al discloses a process in which the drill cuttings are removed from the used drill mud by a process of screening out the coarse particles and then

subjecting the semisolids to hydraulic cyclone separation with discard of the resultant separated clay and sand fines. U.S. patent 3,899,414 Hansen discloses a particular form of vibratory screen separator used in conjunction with hydrocyclones for cleaning up drilling mud. U.S. patent 4,192,392 Messines et al discloses a centrifugal process for separating solids from the used drilling fluid.

The prior art also reveals several different approaches to the problem of cleaning up the oil contaminated cuttings recovered with the oil based drilling mud.

U.S. patent 3,693,733 Teague describes a process in which the effluent stream of drill cuttings, drilling mud and oil from an offshore well bore is washed with liquid detergent and then discharged into the body of water.

U.S. patent 4,040,866 Mondshine discloses a process in which the oil base mud adhering to solid cuttings is treated with a mixture of a polar solvent and a paraffin oil, to form a mixture of oil and solvent on the cuttings, which is readily removable by washing or centrifuging.

U.S. patent 4,181,494 Kimberley and U.S. patent 4,222,988 Barthel disclose processes in which the hydrocarbon contaminants on drill cuttings are heated to burn or vaporize them off the solids.

U.S. patent 4,482,459 Shiver discloses a process for treating a slurry of waste drilling mud fluids in which the slurry is acidified to coagulate it

and then flocculated by addition of an organic polymeric flocculant.

U.S. patent 4,599,117 Luxemburg discloses treating contaminated drill cuttings with an aqueous polymeric flocculant solution and a filter aid.

U.S. patent 4,645,608 Rayborn discloses washing oil contaminated cuttings with a detergent solution of a solvent and a selected surfactant to wash the oil into the detergent solution.

A technical advertising brochure published by Thomas Broadbent and Sons Limited proposes to wash oil contaminated cuttings from 'an offshore drilling operation with an oil wash solution, then to centrifuge the mixture and dump the resulting washed cuttings directly overboard. The oil wash is a mixture of the same oil as used in the drilling mud base, admixed with water.

U.S. patents 4,242,146 and 4,480,702 Kelly disclose a totally different approach, namely that of binding the oil more tightly to the solids so that the solids can be discarded and the oil will not thereafter migrate out of the solids to pose an environmental hazard.

None of the above prior art discloses a process whereby the residual hydrocarbon content of the cleaned drill cuttings, i.e. the total solids stream including the clay, sand, mud components, silt and all other down-hole produced mineral matter, etc., produced over a substantial period of continuous operation, is as low as 6 grams per 100 grams of dry cuttings, and wherein most of the residual hydrocarbon is present in a

form where it is unlikely to migrate out of the solids to harm the environment, under normally experienced conditions. ^Λ

DIS _C LOSURE OF INVENTION

It is an object of the present invention to provide a novel method for the cleanup of oily drill cuttings.

The present invention provides a multistage clean up process for decontaminating hydrocarbon contaminated cuttings, such as oily drill cuttings, particularly those cuttings which are rejected for disposal following mud recovery operations, to produce over a substantial period of continuous operation, total solids low in residual hydrocarbon content, down to 6% by weight, water-free basis, or less. Not only are the solids resulting from the process of the present invention low in total residual hydrocarbon, but also,

** _* . what residual hydrocarbon they do contain is, in most cases, present in a form or location from which it does not easily separate from the solids under normal environmentally encountered conditions. It is not ¹ easily separable or leachable from the solids, under normal environmental conditions. Accordingly, it is expected that it will hazard over the long t

The invention derives from the discovery that oil contaminated drill cuttings are in the fbrm of a complex fluid containing in large part climps or agglomerations of individual particles which are firmly held together by surface layers of residual drilling mud. Also dispersed in the residual ^" drilling mud re fine cutting particles. Microphotographs indicate that

most of the contaminating oil deriving from the drilling mud is disposed on the surface of individual particles in the complex fluid, or as a binder between individual members of a clump of particles. Very little oil penetrates into the particle core. Many of the larger particle clumps are obtained from the initial coarse screening of the spent mud and the return of the large particles therefrom to the semisolid material after washing to reclaim drilling mud.

Accordingly, deriving from this discovery of the nature of the location and distribution of the contaminating oil in and on the residual solids, the invention provides a process in which, in the first stage, the contaminated solids are conditioned to break up the clumps or aggregates of solid particles and break up the structure of any mud associated with the cuttings. As a result of this conditioning, the solids settle out or behave substantially completely in the form of individual particles. Now, in a subsequent second stage, the conditioned material can be subjected to primary centrifugation to separate off the bulk of the liquid, and leave discrete solid particles with residual hydrocarbon contaminations. As a result of the conditioning step, therefore, these solid particles have greatly increased accessible surface hydrocarbon contamination, and very little residual inaccessible interparticulate hydrocarbon contamination. In the third stage, therefore, the hydrocarbon is displaced therefrom by addition of an aqueous solution of an appropriate wetting agent. Finally, the treated cuttings are subjected to a phase separation step, e.g. by centrifugation of the total stream, or by screening and washing the coarse fraction followed by washing and filtration of the fines fraction.

By operating according to the present invention, one can obtain treated cuttings containing residual hydrocarbon contents of less than about 6 grams per 100 grams of dry cuttings.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is an illustration of the particle deagglomeration process which takes place during the con _d itioning step of the process of the invention;

Figure 2 is a diagrammatic process flowsheet of one preferred scheme for putting the present invention into practice;

Figure 3 is a similar diagrammatic proceiss f _l owsheet of an alternative embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

In the first step of the process of the present invention, the oily cuttings are conditioned, to _b reak the structure of any residual drilling mud.and to break up clumps and agglomerations of particles. This may be accomplished by subjecting the cuttings/mud system, after any appropriate adjustment of the li Sid consistency thereof by addition of hydrocarbon thereto, to shearing agitation, preferably vigorous shearing agitation, optionally in the presence of appropriate chemicals. - ^ji -

In order to achieve appropriate conditioning, the cuttings/mud system should contain sufficient liquid hydrocarbon, in relation to the solids present, for the shearing agitation to be effective. In some instances, the cuttings/mud system delivered to the reclamation and storage facility is already sufficiently diluted with residua _l or added oil such as diesel oil or the ^l ike

that no further dilution is necessary prior to shearing agitation. In most instances, however, addition of liquid hydrocarbon diluent to the cuttings/mud system for conditioning purposes is necessary. Such dilution is effected with a liquid solvent which is compatible with the contaminating hydrocarbon. Preferably the diluent is kerosene, mineral oil, or diesel oil, or whatever hydrocarbon was used as the base hydrocarbon of the drilling mud. Such hydrocarbons are normally available at most drilling sites. Kerosene is particularly preferred when the contaminating hydrocarbon is diesel oil. Kerosene effects a better and more efficient conditioning of diesel oil contaminated cuttings than diesel oil itself. When the contaminating hydrocarbon is mineral oil, dilution with the same oil is preferred over the use of kerosene or diesel, both for environmental reasons and for reuse of the hydrocarbon in drilling mud formulation. Addition of an amount of diluent to give a liquid hydrocarbon content in the mixture of from about 3 to about 6 times the volume of the contaminated cuttings being treated, i.e. at least 15-30 times dilution of the oil present, is most preferred. Temperature adjustment to the approximate range 40°C-80°C is beneficial. Agitation suitably continues for a period of 2-15 minutes.

Figure 1 of the accompanying drawings illustrates diagrammatically the conditioning effect being accomplished. In the upper part of Figure 1, there is illustrated a coarse clump or agglomeration 1 of four individual particles, bound together by an envelope of residual drilling mud and contaminating hydrocarbon 2 which extends around and between the individual particles. This clump may be obtained from the screening and washing process for mud recovery described above, or directly from the downhole

operation. In regions such as 3, between the individual particles, the contaminating mud and hydrocarbon is not readily accessible to chemical or solvent treatment, so that this part of the contamination is not simply removable by washing. Nor is it easily removable »όy conventional centrifugation. On conditioning ^by dilution with a suitable diluent, under vigorous agitation, the clump 1 breaks up into constituent particles such as 4, each carrying its own individual envelope 5 of contamination. This contaminant is much more accessible. The lower part of Figure 1 shows diagrammatically fine solid particle 6 which originally passed the screening process and is suspended in residual mud medium 7. Conventional centrifugation wfϊl not break this structure to cause particle settling and separation. After conditioning by dilution with diluent under vigorous agitation, this structure breaks dowm, and leaves the fine particle 6 in a settled condition but each having a contaminating surface layer 8 o "Mud residue. Fine particles 4 deriving from break-up of clumps 1 also settle out. Very little contaminating diesel oil from the mud penetrates the interior of particles 4 or particles 6. *■

Conditioning according to the first stage of the process of this invention is achieved when substantially all of the clumps or agglomerations of particles have been broken up and the individual particles can settle out. This can be determined' by sampling and visually observing the particles in the sample. Achievement of appropriate conditioning is thus signalled when addition of further conditioning material under agitation fails to accomplish any further significant amount of particle settling or any further significant reduction in particle size of the settled particles.

The precise method by which such conditioning is achieved is not especially important, so long as it is relatively quick, efficient, economical and yields a suitably conditioned product. As noted, dilution with suitable liquid hydrocarbon under vigorous agitation is most preferred. Alternatively, however, dilution with liquid hydrocarbons together with the addition of appropriate chemical agents such as surfactants, wetting agents or de-emulsifiers, under vigorous agitation, can also be used to achieve conditioning. The need for chemicals addition is dependent upon the morphology and nature of the drilling mud used as well as on the amounts of residual drilling mud present with the cuttings. The above types of chemicals can assist in the attainment of conditioning by their effects on the emulsification, rheological characteristics and wettability characteristics of the cuttings/mud system. When the drilling mud is a water-in-oil emulsion, the use of emulsion-breaking chemicals is commonly indicated. Substantially any chemical which will act as an emulsion breaking agent to render the droplets of the dispersed water phase of the mud/cuttings system amenable to coalescence, so as to effect a separation of said water from the continuous hydrocarbon phase is a suitable conditioning, chemical. Furthermore, substantially any chemical which will act to modify the rheological characteristics and wettability of the cuttings/mud system so that suspended solids, whether fine or coarse particles, individually or as agglomerations of particles present in the system, are settled out by the action of said chemicals or in conjunction with dilution, is a suitable conditioning chemical. Many of these chemicals, whether present as emulsion breakers, as rheology modifiers, as wetting agents or combinations thereof will be apparent to those

skilled in the art. A specific example of a suitable such chemical is that marketed under the trade mark LOSURF 0™ . This is a surfactant, proprietary product of Haliburton Services. As in the case of conditioning by dilution in the absence of chemicals, a temperature of 40-80°C is preferred for conditioning by dilution with chemical addition. Surfactants are used in small amounts, e.g. up to 1.0% by volume.

The next step in the process of the present invention is the subjection of the conditioned mixture to centrifugation. This takes place prior to subsequent chemical treatment with wetting agents and final phase separation. It is accordingly appropriately termed "first stage centrifugation". By this means, excess liquid is removed from the cuttings. Substantial amounts of liquid hydrocarbon are thereby removed as liquid centrate, leaving a solid waste, still contaminated but with the contaminant disposed on the solid surfaces in an accessible manner as a result of the previous conditioning step. It has been found that,

. '< * if this first stage centrifugation is omitted, subsequent chemical treatment of the solids is ineffective in reducing the residual hydrocarbon content of the final solid waste to less than about 6 grams per

100 grams of dry cuttings.

The solid waste product obtained from the centrifuging step is accordingly next treated with an aqueous solution of wetting agent or surfactant, to cause hydrocarbon displacement therefrom. The wetting agent reverses the wetting nature of the mineral surfaces, to render these surfaces water wettable instead of hydrocarbon wettable. Substantially any harmless wetting agent which will effect this can be used in the process of the invention, many of which will

be apparent to those skilled in the art. Specific examples of suitable such wetting agents are those marketed under the tradenames "LOSURF 0 ^M ™ , HYFLO IV™ and NOWFLUSH 5 ^TM . The wetting agent is suitably added in dilute aqueous solution, to form a water/cuttings ratio (v/v) of from about 3:1 to 6:1, and at a pH of 2.0-11.0. A suitable concentration of wetting agent is from about 0.001-10 volume %, and preferably 0.01-2.0 volume %. The wetting agent in aqueous solution is suitably added under conditions of agitation, e.g. in a blender or mixer. Use of alkyl aryl sulfonate surfactants such as HYFLO IV may result in reagent losses in conditions where high concentrations of magnesium and calcium will be encountered.

In cases where the drilling mud is a water-in- oil emulsion using as primary emulsifier a calcium salt of a fatty acid such as that produced by the reaction of tall oil and lime, it is advantageous to add to the aqueous solution cations which form water insoluble hydroxides. This will serve to break the emulsion, by precipitating the hydroxyl ions from the lime. The preferred such hydroxyl precipitating ions are magnesium and aluminum, with magnesium being most preferred. Magnesium salt solutions are preferably added at substantially neutral pH conditions, and at amounts from about 1-10% by weight, based on the hydroxyl ion content of the water present in the solid waste product.

By means of the wetting agent addition, residual superficial hydrocarbon is displaced from the solid particle surfaces with water. Because of the conditioning step described above, substantially all of the residual hydrocarbon contaminant derived from the mud and added for conditioning purposes is surface disposed and accessible for displacement. Now the

solids can be separated from the residual oil/water liquids, and obtained in a water-wet but substantially hydrocarbon-free condition suitable for environmental disposal.

Thus, the final step of the process of the invention is a phase separation step, in which the free hydrocarbons and displacement water are removed from the treated cuttings. Suitably this is done by mechanical means such as centrifugation, or by screening, and filtering. One such method is a process whereby the mixture, after blending with the wetting agent solution as described, is washed with water as required then screened to obtain a coarse solids-containing fraction, and a fine solids-containing stream. Then the latter is subjected to filtration to obtain a solid filter cake. The residual solid fractions so obtained are very low in residual hydrocarbon, and in an acceptable conditiqn for discard to the environment. i

The process of the invention yields a mixed liquid phase or phases of water and hydrocarbon from the phase separation step. Preferably, therefore, the process of the present invention includes the additional steps of water treatment and hydrocarbon recovery from the mixed liquids so obtained. Fines and hydrocarbon removal from the liquid mixture may be conducted by physico-chemical means or mechanical means, to obtain a separate hydrocarbon phase and sufficiently hydrocarbon- free water for reuse or disposal. The individual hydrocarbon fractions may then be recovered therefrom, for reuse as diluent and in the drilling mud preparation, by thermal means such as distillation,, or by physico-chemical means.

Referring now to Figure 2 of the accompanying drawings, this preferred embodiment of the present invention illustrates the operation of a process where a conditioning hydrocarbon compatible with but different from the contaminating hydrocarbon is used. It includes a conditioning zone 10, a primary centrifugation zone 12, a hydrocarbon displacement zone 14 and a phase separation zone 16 interconnected in series with one another. The conditioning zone 10 includes a mixing vessel 18 having a heater 20 and a stirrer 22. Three inlet lines feed into mixing vessel 18, namely a diluent line 24, a chemicals inlet line 26 and an oil contaminated cuttings inlet line 28. Conditioning of the cuttings takes place in mixing vessel 18, by dilution with hydrocarbon from line 24 and optionally by action of chemicals from line 26 under relatively vigorous agitation from stirrer 22 at controlled temperatures. Outlet line 30 from the bottom of mixing vessel 18 feeds the conditioned cuttings mixture as a liquid slurry to primary centrifugation zone 12 in which is a solid bowl type centrifuge 32. Primary separation of solids component from liquid centrate occurs due to operation of centrifuge 32, and the liquid centrate therefrom is fed via centre outlet 34 for recovery of liquid components therefrom, while solids material, still contaminated by hydrocarbons, is fed via side outlet 36 out of primary centrifugation zone 12 into hydrocarbon displacement zone 14.

A mixing tank 38, equipped with an agitator 40 and a heater 42 is disposed in hydrocarbon displacement zone 14, and the solids via line 36 are fed into the top of the mixing tank. The mixing tank is also provided with a wetting agent inlet line 44 and a water inlet

- -

line 45. Appropriate amounts of wetting agent and wat 4er are added to the solids in the mixing tank 38 under agitation, with the effect of displacing residual hydrocarbon from surface contamination. After appropriate treatment therein, the mixture is lead via lower outlet line 46 to phase separation zone 16, containing a solid bowl type centrifuge 48. The centrifuge efficiently separates the mixture into a liquid centrate which exits via centre line 50, whilst the solid waste exits the centrifuge by a side line 52, to waste.

The centrate issuing from the primary centrifuge 32 via centre outlet 34 consists essentially of hydrocarbon diluent, hydrocarbon oil contaminant, salty water and residues of other added chemicals.. These may be aqueous and/or organic in nature. Accordingly, the centrate is treated to recover diluent,, hydrocarbon oil contaminant and water. It is first fed to an evaporator 54 equipped with a heating means 56, in which the lower boiling hydrocarbon, e.g. kerosene used as hydrocarbon diluent, and any water present are evaporated off and fed via condenser 57 to a separator 58, in which they are allowed to phase separate. The hydrocarbon diluent thus separated can be recycled via recycle line 60 to the diluent inlet line 24 into mixing vessel 18, or alternatively, removed from the process through outlet line 62. Higher boiling hydrocarbons, namely the hydrocarbon oil contaminant, are recovered from the bottom of the evaporator 54 via line 64 for discard or alternate use. The water recovered, from the separator 58 is fed via water line 66 to mix with water recovered from the centrate from the phase separation zone, for discard or recycle, as described below.

The centrate exiting phase separation zone 16 via centre line 50 consists essentially of residual wetting agent, wash water and hydrocarbon recovered from the solid drill cuttings residue. This is fed to a phase separator 68 where it separates into water and hydrocarbon phases. The water is fed out of separator 68 via bottom line 70 to the water recycle line 72 where it mixes with water from separator 58, for recycle to water inlet line 45 to mixing tank 38 in hydrocarbon displacement zone 14, or to discard. The upper hydrocarbon layer from separator 68 is fed to separator 58 to mix with the kerosene therein.

The diagrammatic process flowsheet of Figure 3 is particularly for use when the same hydrocarbon is used as the diluent in the conditioning step as that used to make the drilling mud, e.g. diesel oil in both cases. The arrangement similarly comprises conditioning zone 10, primary centrifugation zone 12, hydrocarbon displacement zone 14 and phase separation zone 16, all containing the same components and treatment and flow sequences as described in connection with Figure 2. In this case, however, the centrates from both the primary centrifuge 32 and the phase separation zone centrifuge 48 are fed to a common phase separation vessel 74 where separation into hydrocarbon and aqueous phases takes place. No evaporator is needed, since only one type of liquid hydrocarbon is present. The aqueous phase is fed from the bottom of separator 74 through water outlet line 76 for recycle to the mixing tank 38 in the hydrocarbon displacement zone 14. The hydrocarbon phase is pumped from separator vessel 74, through recycle line 78 to diluent inlet line 24 to the mixing vessel 20 in the conditioning zone 10. Some or all of the hydrocarbon and water that is recovered may be discarded

or fed to other uses as indicated, via lines 20 and 82, respectively.

The invention is further illustrated in the following non-limiting examples:

EXAMPLE 1

A five-gallon pail of diesel oil contaminated drill cuttings and spent drilling mud was obtained and allowed to stand and settle for several days. The supernatant layer of diesel oil which separated was removed. The residual pasty material was homogenized and analyzed. It gave an analysis of 88.1 part by weight (8.8%) diesel oil, 37.1 parts by weight (3.7%) water and 874.8 parts by weight (87.5%) solids. To this was added, 2,129.9 parts by weight kerosene (six times the volume of the total mixture being treated) and 3.1 parts by weight (0.1% volume) of surfactant HYFLO IV. The mixture was prepared in a shaker and agitated at 130 strokes per minutes for 5 minutes at 40°C.

Then the mixture was subjected to primary centrifugation to remove the liquid bulk. The solid cake resulting from this centrifugation had a liquid hydrocarbon content (kerosene and/or diesel) of 9Ϊ, a water content of 2.8% and a solids content of 88.2%.

Next, the contaminated and wet solids (907.8 parts by weight) were subjected to a wetting agent action for hydrocarbon displacement purposes. For this, the pH of the mixture was adjusted to pH 2 by addition of 9.1 parts hydrochloric acid in 1878.6 parts of water and there was added 9.1 parts (0.5 volume %) of we^ting, agent LOSURF 0. The mixture was agitated for 5 minutes on a shaker at about 230 strokes per minute.

Then the mixture was centrifuged to effect phase separation. The solids waste material thus recovered was analyzed and found to have a hydrocarbon (kerosene and/or diesel) content of only 3.8% on a wet basis, or 5.8 grams per 100 grams dry cuttings.

EXAMPLE 2

The starting material, after removal of the supernatant diesel layer, was of essentially the same composition as that reported in Example 1. To 1,000 parts by weight of this pasty material, after homogenization, was added 2,204.4 parts by weight of kerosene and 3.1 parts by weight of surfactant HYFLO 4. The mixture was prepared in a shaker and agitated at 210 strokes per minute at 80°C for 10 minutes.

Then the mixture was subjected to primary centrifugation, to leave a solid cake having a liquid hydrocarbon content (kerosene and/or diesel) of 23.9 weight %, a water content of 2 weight % and a solids content of 70.9 weight %.

To this cake was added an aqueous solution of LOSURF 0 surfactant, 0.5% by volume in an amount of water corresponding to six times the volume of solids. The mixture was agitated on a shaker for 10 minutes at 80°C at 210 strokes per minute. The pH was adjusted to pH 9 by addition of caustic soda, prior to shaking.

Then this mixture was centrifuged. The solid waste material thus recovered was analyzed and found to have a hydrocarbon content of 4.4% on a wet basis, or 5.8 grams per 100 grams dry cuttings.

EXAMPLE 3

Following the procedure of Example 1 using an essentially similar starting material and the same amounts of additives and treatment conditions, there was obtained from the displacement stage (third zone) a slurry of drill cutting solids, water and residual hydrocarbon. The slurry was subjected to a phase separation process involving washing, screening and filtration.

Thus the slurry was washed three times with water at pH 2.0 containing LOSURF 0 (0.5% by volume) using a blender on the high agitation setting, each time for 1 minute. After washing, the product was screened using a 40 mesh Tyler screen and separated to a coarse fraction stream (+40 mesh) and a fines fraction screen (-40 mesh). The coarse fraction was subjected to fresh water wash on the screen. The cuttings retained 0.8 weight % hydrocarbon and about 20 weight % water. This rraction comprised about 20 weight % of the total solids. The fines fraction was vacuum filtered using a fine filter. Good filtration characteristics were observed. The solids retained 2.9 weight % hydrocarbon and 12 weight % water.

EXAMPLE 4

In this example, conditioning a ^s achieved by dilution and shearing agitation only, without addition of any chemicals to the conditioning medium.

The same starting material as described in Example 1 was used, and conditioned by addition thereto of three times its volume of kerosene (i.e. 1036.8 parts by weight of kerosene). The mixture was prepared by

shearing agitation in a blender for 2 minutes at 80°C. The mixture was then subjected to primary centrifugation, giving a solid cake of hydrocarbon content 11.6%, water content 1.9% and solids content 86.5%. The total weight of the cake was 1011.3 g.

To this cake was added 1% by volume of wetting agent NOWFLUSH 5 and 1% by weight of Mg** ion equivalent as sulphate hydrate. This was blended for 2 minutes at 40°C. Then the mixture was centrifuged to effect phase separation.

The solids waste material thus recovered was analysed and found to have a hydrocarbon content of 3.4% on a wet basis, or 4 g per 100 g on a dry basis.