Note: Descriptions are shown in the official language in which they were submitted.
1 3293 1 9
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
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.
.
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
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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
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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
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1 3293 1 9
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.
1 3293 1 9
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
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~ 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.
.. . .
1 3293 1 9
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
- 10 -
1329319
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
-- 11 --
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.
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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
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....
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
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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
- 15 -
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.
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,. ..
- -
1 32931 9
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.
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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:
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 whlch separated was
removed. The residual pasty material was homogenized
and analyzed. It gave an analysis of 88.1 part by
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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.
EXAMPLE 2
~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
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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.
EXAMPLE 3
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
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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.
EXAMPLE 4
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%
- 21 -
1329319
on a wet basis, or 4 g per 100 g on a dry basis.
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