CA1329319C - Oil removal from hydrocarbon contaminated cuttings - Google Patents

Abstract

ABSTRACT

Drill cuttings contaminated with hydrocarbon, such as diesel oil, kerosene or mineral oil, from residual drilling mud are cleaned up to a solid particulate form containing very low amounts of residual hydrocarbon by means of an integrated four-step treatment process. In the first step, the cuttings are conditioned to destroy the complex fluid structure of the material and to break up agglomerations and clumps of solid particles into individual particles.
Preferably this is accomplished by addition of a compatible hydrocarbon diluent under shearing agitation.
Secondly, the destabilized contaminated cuttings are subjected to centrifugation to separate excess liquid.
Thirdly, the residual solids are treated, preferably under shearing agitation, with water and an appropriate wetting agent at low concentration to displace residual surface hydrocarbon contamination. Fourthly, the treated cuttings are subjected to a final phase separation step, eg. by centrifugation of the total stream, or by screening and washing the coarse fraction followed by washing and filtration of the fines fraction. The resultant solid material has a residual hydrocarbon content of less than about 6 grams per 100 grams of dry cuttings, largely in a form where it is unlikely to migrate out of the solids to harm the environment, under normal environmentally experienced conditions.

Description

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.

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 in~ection through the drill stem that supports the drill blt. The mud then passes through holes in the blt and spreads over the cuttlng faces o$ the drill bit to act as a lubrlcant 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 wlth cuttlngs from the drllllng operatlon. The drilllng mud needs to have an appropriate combination of rheological properties and lubrlcatlng propertles to perform lts drill blt lubrlcatlng functlon, to withstand the high pressures to which it is subJected during the drilllng operatlon, wlthout emulslon breakdown or excesslve fluld 1088 lnto the formation, and to permit clrculatlon even when it is loaded with cuttings.
Oily drlll cuttlngs laden wlth hydrocarbon cont2mlnants orlglnate malnly from the use of oll based drllllng muds. Such muds are especlally useful ln operatlons which involve drllling through or into water sensitive formations, or for directional drilllng operations both onshore and offshore. Dlesel oll is the .

.

132q319 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 180-300C. 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 liquld hydrocarbon forms the continuous phase of a water-ln-oil emulsion. Suspended in the liquid medium of the drilling mud are varlous 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 particle~, for filtration and viscosity control, and for ease of cleaning. Clay sollds can also be used therein.
Where the liquid vehicle is a water-in-oil emulslon, the particles commonly include organically coated clays, optionally weighting agent~ 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 the suspended ~ollds. The emulslfled water ln muds of this type may contain dissolved salts, e.g. calcium chloride, sodlum chloride, potas81um chlorlde or the like 132931q 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 solids and having appropriate rheological properties such as viscosity, gel strength, lubricity, and other 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 bcrehole 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 wldely 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 prlor art describes varlous methods by which this may be accomplished. For instance, it ls 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 drllling mud. The material whlch passed through the screen is then sub~ected to additlonal solids separatlons or llquld-sollds separations involving centrifugation, hydrocycloning, etc. to reclaim additional drilling mud and hydrocarbon and to separate out the finer drill cuttings particles not removed by 1 3293 1 q the screening process. The reclaimed drilling mud is then recycled and reused by the drilling operation, while the cuttings are re~ected and temporarily stored prior to disposal.

Some of the llquid hydrocarbon content of the re~ected 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, slmple, and economlcal process for reducing the hydrocarbon content of oil contaminated cuttings and drllling mud resldues, prlor to thelr dlsposal.

Considerable effort has been expended ln the past on developing ways of recovering drilling muds for recirculatlon and reuse. For example, U.S.patent 2,919,898 Marwll et al dlscloses a process in which the drlll cuttlngs are removed from the used drlll mud by a process of screenlng out the coarse partlcles and then sub~ectlng the semisolids to hydraulic cyclone separation wlth discard of the resultant separated clay and 8and fines. U.S. patent 3,899,414 Hansen discloses a partlcular form of vibratory screen separator used in conJunction wlth hydrocyclones for cleanlng up drllling mud. U.S. patent 4,192,392 Messlnes et al dlscloses 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, whlch is readlly removable by washing or centrlfuging.

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

U.S. patent 4,482,459 Shlver discloses a process for treating a slurry of waste drilling mud flulds 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 dlscloses treating contamlnated drill cuttings with an aqueous polymerlc flocculant solutlon and a filter aid.

1 32q31 9 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 dlscarded and the oil will not thereafter migrate out of the sollds to pose an environmental hazard.

None of the above prlor art discloses a process whereby the residual hydrocarbon content of the cleaned drlll 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 operatlon, is as low as 6 grams per 100 grams of dry cuttings, and whereln most of the resldual hydrocarbon 18 present ln a form where it is unlikely to migrate out of the solidQ
to harm the environment, under normally experienced condltlons.

It is an ob~ect of the present invention to provide a novel method for the cleanup of olly 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 lt does not easily separate from the solids under normal environmentally encountered conditions. It is not easily separable or leachable from the solids, under normal environmental conditions. Accordlngly, it is expected that it will pose no slgnificant environmental hazard over the long term.

The invention derives from the discovery that oll contaminated drill cuttings are in the form of a complex fluld contalning in large part clumps or agglomeration~ of individual particle~ which are firmly held together by surface layers of residual drilling mud. Also dispersed in the residual drilling mud are flne cutting particles. Microphotographs indicate that most of the contaminating oil deriving from the drilling mud 18 disposed on the surface of individual particles ln the complex fluld, or as a binder between individual members of a clump of particles. Very llttle oil penetrate8 lnto the partlcle core. Many of the larger partlcle clumps are obtalned from the lnltlal coarse ~ 32q31 9 screening of the spent mud and the return of the large particles therefrom to the semisolid material after washin~ 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 sub~ected 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 contamlnatlon. In the thlrd stage, therefore, the hydrocarbon 18 dlsplaced therefrom by addition of an aqueous solutlon of an appropriate wetting agent. Finally, the treated cuttings are subJected to a phase separatlon step, e.g.
by centrlfugatlon of the total stream, or by screening and washlng the coarse fractlon followed by washlng and filtration of the flnes fraction.
8y operating according to the present invention, one can obtaln treated cuttlngs containing resldual hydrocarbon contents of less than about 6 grams per 100 grams of dry cuttings.

.. . .

Figure 1 is an illustration of the particle deagglomeration process which takes place during the conditioning 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 process flowsheet of an alternative embodiment.

In the first step of the process of the present invention, the oily cuttings are conditioned, to break the structure of any residual drilling mud and to break up clumps and agglomerations of particles. This may be accomplished by sub;ecting the cuttings/mud system, after any appropriate ad~ustment of the liquid consistency thereof by addition of hydrocarbon thereto, to shearing agitation, preferably vigorous shearing agitation, optionally in the presence of appropr$ate chemicals.
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 residual or added oil such as diesel oil or the like that no further dilution is necessary prior to shearlng 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 contaminatlng hydrocarbon. Preferably the diluent i8 ~erosene, mineral oil, or diesel oil, or whatever hydrocarbon was used as the base hydrocarbon of the drllllng mud. Such hydrocarbons are normally _ g _ , .. . .
.

1 32q3 1 q available at most drill$ng sites. Kerosene ls 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, l.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 dlagrammatically the conditioning effect belng accomplished. In the upper part of Figure l, 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 indivldual 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 by 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 will not break this structure to cause particle settling and separation. After conditioning by dilution with diluent under vigorous agitation, this structure breaks down, and leaves the fine particle 6 in a settled condition but each having a contaminating surface layer 8 of 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 observlng the particles in the sample. Achievement of appropriate conditioning is thus signalled when addltion 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 ls achleved is not especlally important, so long as it is relatlvely quick, efficient, economical and yields a suitably conditioned product. As noted, dilution with sultable llguld hydrocarbon under vlgorous agltation is most preferred. Alternatively, however, dilution with liquld hydrocarbons together wlth the addltlon of approprlate chemlcal agents such as surfactants, wettlng 1 32q3 1 9 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-breaklng 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, indivldually or as agglomeratlons of partlcles present ln the system, are settled out by the a¢tion of sald chemlcals or in con~unction wlth dllutlon, is a sultable condltionlng chemlcal. Many of these chemicals, whether present as emulsion breakers, as rheology modifiers, as wetting agents or comblnations thereof will be apparent to those skllled ln the art. A speclflc example of a sultable such chemlcal 18 that marketed under the trade mark LOSURF OT M . Thls 18 a surfactant, proprletary product of Hallburton Servlces. As ln the case of condltloning by dllutlon in the absence of chemlcals, a temperature of 40-80C is preferred for condltlonlng by dllutlon wlth chemlcal addltlon. Surfactants are used ln small amounts, e.g. up to 1.0% by volume.

1 3293 1 q The next step in the process of the present invention is the sub;ection 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 cuttlngs.

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 mlneral surfaces, to render these surfaces water wettable lnstead 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 o--TM, HYFLO IVTM
and NOWFLUSH 5T M . The wetting agent is suitably added ln dllute aqueous solutlon, to form a water/cuttlngs ratio (v/v) of from about 3: 1 to 6:1, and at a pH of 2.0-11Ø A sultable concentration of wetting agent is from about 0.001-10.0 volume %, preferably 0.01-2.0 volume %. The wetting agent ln agueous solutlon is ....

1 3293 1 q suitably added under conditions of agitation, e.g. in a blender or mixer. Use of alkyl aryl sulfonate surfactants such as HYFL0 IV may result in reagent losses in conditions whsre high concentrations of magnesium and calcium will be encountered.

In cases where the drilling mud is a water-in-oil emulsion using as primary emulsif$er 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 wlll 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 partiale 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 oll/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 lnventlon 18 a phase 8eparatlon step, ln whlch the free hydrocarbons and dlsplacement water are removed from the treated cutting8. Sultably thl8 18 done by mechanical 132931~

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 sub~ected to filtration to obtain a solid filter cake.
The residual solid fractions so obtained are very low in residual hydrocarbon, and in an acceptable condition for discard to the environment.

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 fractlons may then be recovered therefrom, for reuse as dlluent and ln the drllling mud preparatlon, by thermal means such as distillation, or by physlco-chemlcal means.

Referrlng now to Flgure 2 of the accompanying drawings, this preferred embodiment of the present lnventlon lllustrates the operation of a process where a condltloning hydrocarbon compatible with but different from the contaminating hydrocarbon 18 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 lO includes a mixing vessel 18 having a heater 20 and a stlrrer 22. Three 1 32~3 1 9 inlet lines feed into mixing vessel 18, namely a diluent line 24, ~ 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 32r 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 mlxing tank 38, equipped with an agitator 40 and a heater 42 is disposed in hydrocarbon dlsplacement zone 14, and the solids via line 36 are fed into the top of the mlxing tank. The mixing tank is also provided with a wetting agent inlet llne 44 and a water inlet line 45. Appropriate amounts of wetting agent and water are added to the sollds in the mixlng tank 38 under agitatlon, with the effect of displacing residual hydrocarbon from surface contamlnatlon. After appropriate treatment therein, the mlxture is lead via lower outlet line 46 to phase separation zone 16, containlng a solld bowl type centrlfuge 48. The centrifuge efficiently separates the mix~ure lnto a liquld centrate whlch exits vla centre llne 50, whllst the solid waste exits the centrifuge by a side llne 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 llne 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 b~ttom line 70 to the water recycle line 72 where it mixe8 with water from separator 58, for recycle to water inlet line 45 to mixing tank 38 in hydrocarbon displacement zone 14, or to dlscard. The upper hydrocarbon layer from separator 68 is fed to separator 58 to mix with the kerosehe thereln.

132q31q The diagrammatic process flowsheet of Figure 3 is partlcularly 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 lnto hydrocarbon and agueous 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 llne 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 ln the conditioning zone 10. Some or all of the hydrocarbon and water that 18 recovered may be discarded or fed to other uses as indicated, via lines 20 and 82, respectively.
The invention 18 further illustrated in the following non-llmiting examples:

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 whlch separated was removed. The residual pasty material was homogenized and analyzed. It gave an analysis of 88.1 part by 132q319 weight (8.8~) diesel oil, 37.1 parts by weight (3.7~) water and 874.8 parts by weight (87.5%) solids. To th~s 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 40C.

Then the mixture was sub;ected 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 9%, 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 sub~ected to a wetting agent action for hydrocarbon displacement purposes. For this, the pH of the mixture was ad~usted to pH 2 by addition of 9.1 parts hydrochlorlc acld in 1878.6 parts of water and there was added 9.1 parts (0.5 volume %) of wetting agent LOSURF 0. The mixture was agitated for 5 minutes on a shaker at about 230 strokes per minute.

Then the mixture was centrlfuged 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 basls, or 5.8 grams per 100 grams dry cuttings.

~he startlng material, after removal of the supernatant dlesel layer, was of essentlally the same composltlon as that reported ln Example 1. To 1,000 parts by welght of thls pasty materlal, after homogenlzatlon, was added 2,204.4 parts by welght of 132931~

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 80C for 10 minutes.

Then the mixture was sub~ected 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 O 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 80C at 210 strokes per minute. The pH was ad~usted 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 8 hydrocarbon ¢ontent of 4.4% on a wet basis, or 5.8 grams per 100 grams dry cuttings.

Following the procedure of Example 1 using an essentially simllar 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 sub~ected to a phase separation process involvlng washing, screening and filtration.

Thus the slurry was washed three times with water at pH 2.0 containing LOSU~F O (0.5% by volume) uslng a blender on the hlgh agltatlon setting, each time 1 32q31 q 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 sub~ected to fresh water wash on the screen. The cuttings retained 0.8 weight % hydrocarbon and about 20 weight % water. This fraction 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.

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

The same starting material as descrlbed 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 80C.
The mixture was then sub~ected 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~ lon equlvalent as sulphate hydrate. Thls was blended for 2 minutes at 40C. Then the mixture was centrlfuged to effect phase separatlon.

The sollds waste materlal 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.

,~

~'; ' -

Claims (20)

1. A process for reducing the hydrocarbon oil content of oil contaminated drilling cuttings associated with oil based drilling mud residues, which comprises the sequential steps of:

(1) conditioning the oil contaminated drill cuttings to obtain settled solid particles having surface oil contamination but being substantially free from particle agglomerations;

(2) centrifuging the conditioned mixture obtained from step 1 to obtain oil contaminated solids therefrom;

(3) treating the oil contaminated solids obtained from step 2 with water and a wetting agent, to displace hydrocarbon from the solid particle surfaces thereof; and (4) subjecting the treated mixture obtained from step 3 to phase separation processes to recover therefrom a solid particulate material having a residual hydrocarbon of less than about 6 grams per 100 grams of dry cuttings.

2. The process of claim 1 wherein the contaminating hydrocarbon oil is diesel oil, kerosene or mineral oil.

3. The process of claim 2 wherein the conditioning step 18 accomplished by subjecting a mixture of oil contaminated cuttings and liquid hydrocarbon of appropriate consistency to shearing agitation.

4. The process of claim 3 wherein the appropriate consistency of the mixture for conditioning by shearing agitation is achieved by diluting the mixture with liquid which is compatible with the contaminating hydrocarbon oil.

5. The process of claim 4 wherein the contaminating hydrocarbon oil is diesel oil and said liquid is selected from diesel oil and kerosene.

6. The process of claim 5 wherein said liquid is kerosene.

7. The process of claim 4 wherein the liquid solvent is added in an amount suitable to give a mixture having a liquid volume of from about 3 to about 6 times the volume of cuttings being treated.

8. The process of claim 5 including the step of adding a small amount of chemical surfactant to the mixture to be conditioned.

9. The process of claim 5 wherein said conditioning takes place at a temperature of from about 40-80°C.

10. The process of claim 4 wherein the contaminating hydrocarbon oil and the diluting liquid are both mineral oil.

11. The process of claim 1 wherein, in the third step, the conditioned oil contaminated solids from step 2 are treated with an aqueous solution of wetting agent, to alter the surface characteristics of the solid particles to render them preferentially water wettable.

12. The process of claim 11 wherein the wetting agent comprises 0.001-10 volume % of said aqueous solution.

13. The process of claim 12 wherein the wetting agent comprises from 0.01-2 volume % of said aqueous solution.

14. The process of claim 12 wherein the aqueous solution is added in an amount of from about 3 to about 6 times the volume of the solids to be treated.

15. The process of claim 12 wherein the treatment with the aqueous solution takes place under condition of shearing agitation, and at a pH in the range 2-11.

16. The process of claim 11 wherein an aqueous solution of a water insoluble hydroxide-forming cation is added to break the residual emulsion.

17. The process of claim 16 wherein said cation is Mg++.

18. The process of claim 1 wherein the fourth step, of phase separation, is accomplished by centrifugation.

19. The process of claim 1 wherein the fourth step, of phase separation, is accomplished by washing the mixture resulting from stage three with water, screening to obtain a coarse solids-containing fraction and a fine solids-containing stream, and subjecting the fine solids-containing stream to vacuum filtration to obtain a solids filter cake.

20. The process of claim 5 including the additional subsequent step of hydrocarbon recovery from process liquids, and at least partial recycle of the hydrocarbon as diluent to the conditioning step.