Note: Descriptions are shown in the official language in which they were submitted.
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1
CLEANING OF DRILL CUTTINGS AND APPARATUS THEREOF
The present invention comprises a process and an apparatus for removing non-
polar organic contaminants including oil from particulate solid wherein said
solids
s is brought in contact with an extracting agent. The use of natural gas as an
ex-
tracting agent is also described in the present invention.
Components from the drilling and well-operations represents 94% of total dis-
charge of chemicals from the offshore oil industry in the Norwegian sector
(Mil-
jresok report, 1996, OLF) . Oil-based drilling fluids have traditionally been
favoured
over aqueous based systems because they are more cost-efficient. The present
development in directional drilling techniques has further dictated the need
for
more efficient environmental friendly drilling fluids. Following the complete
ban
against the discharge of oil-based drill cuttings in the early 90's, a new
generation
,s of synthetic drilling fluids emerged. These fluids were based on alkyl-
ester or-
ethers and poly-alfa-olefines. They were classified as «non toxic» and were
per-
mitted to be discarded overboard. These synthetic drilling-fluids offers the
same
drilling performance as oil-based drilling-fluids, but at a significantly
higher cost.
Recent research indicates however that these synthetic fluids represent an
envi-
Zo ronmental hazard, and their use is expected to be restricted in the near
future
(Milja~sok report, 1996, OLF). It appears that the industry has no other
alternative
than using oil-based drilling fluids in the future. The drill cuttings will
either have to
be disposed on-shore or re-injected into the reservoir. Both alternatives are
ex-
tremely expensive. It appears however that re-injection is generally favoured
by
is both the legislators and the industry. According-to-the Norwegian Pollution
Control
Authority there are not yet any specific guidelines for the disposal of
produced
sand, and it is generally assumed that the current guidelines and legislation
for
disposal of «drill cuttings» might also apply for produced sand. The maximum
re-
sidual oil content for overboard disposal of drill cuttings is 1.0%. Sand or
drill cut-
so tings with higher oil contents is considered «toxic waste» and has to be
either re-
injected into the reservoir or brought on shore for processing.
The Norwegian patent application number 19953419 (PCT/N000060), Inge Brun
Henriksen et al, describes a method for NGL extraction-techniques for de-
oiling of o
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CA 02319016 2000-07-27
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produced water. The process does not include removal of organic contaminants
from solids.
The use of supercritical extraction techniques to remove and recover oil from
cut-
s tings was first proposed in 1981 by C.P.Eppig et al in US-patent no.
4.434.028.
US 4.434.028 relates to a method and apparatus for removing oil and other or-
ganic constituents from inorganic-rich mineral solids, particulate drill
cuttings. The
solids to be treated are transferred into pressure vessel means wherein they
are
contacted with an extracting agent which is normally a gas such as e.g.
dichloro-
io difluoromethane, propan, carbondioxide, ethane and ethylene. The gas is
under
condition of pressure and temperature to provide the extracting in a fluidic
solvent
state for the constituents to be removed. The extracting containing the
constituents
is withdrawn from the pressure vessel and depressurized and forms a two-phase
system. The two-phase system can be separated by distillation into a vapour
phase containing the extracting and a liquid phase containing oil and organic
con-
stituents. The method described in US 4.434.028 is a very expensive extraction
process comprising the use of pure gas components as an extracting agent fol-
lowed by compression- and to-steps distillation procedures to fully recover
the ex-
tracting agent which is pure gas components. In order for the process to be
eco-
zo nomic feasible, full recovery of the extracting agent (99.7%) is required.
The proc-
ess described in US 4.434.028 is based on using liquid gas (i.e.COz, Propane
or
Freon) to extract the oil and to fully recycle the gas (99.7%). The proposed
proc-
ess has apparently never been scaled up to an industrial plant .
25 US-A-4485079 discloses a process for remov+Rg-~onpolar organic contaminants
in
a three-step serial extraction process for separating residual heavy organic
con-
taminants from solids, where each step has the following main characteristics.
Step 1: Contacting the solids with a hydrocarbon fluid composed of 2 to 9
carbon
atoms.
so Step 2. Contacting the solids from Step1 with a second hydrocarbon fluid
that is
capable of dissolving part of the heavy contaminants from the solids.
Step 3: Contacting the solids from Step 2 with a third hydrocarbon fluid
composed
of 2 to 9 hydrocarbon atoms to extract part of the residual hydrocarbon
fluid from step 2.
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This process is distinct from the present invention in that the extraction is
con-
ducted in three steps where different solvents are used at each step. It
should be
stressed that the present invention is a one step extraction process for
removing
nonpolar organic contaminants in which only one extracting agent (NGL) is
added.
WO-A-9108375 concerns an extraction method and apparatus which uses organic
solvent, i.e. toluene or stabilised gasoline. WO-A-9108375 requires
regeneration
of solvent and a dryer to remove residual solvent from the cleaned cuttings.
This is
distinct from the present invention in that said invention uses pressurised
natural
,o gas liquid which is volatile at ambient conditions and which is available
from a pro-
duction flow-line and requires no regeneration.
As the oilfields matures and the water-cut increases, more sand from the
reservoir
formation tends to follow the production stream in some oilfields. The sand
settles
~5 in the separators and are periodically washed out and disposed by re-
injection or
brought ashore for disposal or processing. One object is therefore to provide
an
inventive and cost-effective process for cleaning of oily-drill cuttings and
sand to
allow overboard discard of the cuttings.
zo The present invention concerning a method of extracting oil from drill
cuttings and
sand offshore. The method is based upon using natural gas liquid (NGL) as a
sol-
vent to extract the oil from the soilds. The process has been successfully
tested in
lab-scale and the results shows less than 1.0% by weight of the maximum
residual
oil content for overboard disposal of drill cuttings. Further, the present
invention
z5 reduces the investment and operation costs to-a~-fraction of that which was
pro-
posed in US 4.434.028 since NGL is available from the production flw-lines at
most oil and gas production facilities. Further, the present process is
considerably
distinct from other extraction processes in that it is carried out with no
«solvent-
recovery. One further object with the present invention is a significant
saving in
so chemical costs and utility requirement compared to re-injection or on-shore
dis-
posal of drill cuttings.
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The present invention comprises a process for removing nonpolar organic con-
taminants including oil from particulate solids, wherein said solids are
brought in
contact with an extracting agent in which:
a) the particulate solids are conveyed into a pressure vessel to which an
extracting
s agent is added in the form of natural gas liquids (NGL), whereby the organic
contaminants from the particulate solids are dissolved in the extraction agent
to
form a single phase solution;
b) whereafter said solution containing the extraction agent and nonpolar
organic
contaminants without any separation is added to a production flow;
,o c) and the clean particulate solids are discarded.
It is an object of the present invention that the extracting agent is a
condensate
collected from a production flow in the form of natural gas liquid. The
cleaned par-
ticulate solids contains less than 1 % by weight of organic nonpolar
contaminants,
,s more preferably less than 0.5% by weight . The particulate solids comprise
drill
cuttings and sand in the present invention. An apparatus for removing nonpolar
organic contaminants from drill cuttings is also described in this invention
where
said contaminated drill cuttings are contacted with an extractant to form a
solution
of said extractant and said contaminants, comprising:
20 - means for discarding clean drill cuttings after said contacting;
- means for conveying said solution to a production flow. A scope of the inven-
tion is also the use of natural gas liquid as an extracting agent for removing
or-
ganic nonpolar contaminants including oil from particulate solids.
is The present process comprises the use of condeflsate (NGL) as a solvent to
clean
the drill cuttings and sand. Use of natural gas liquid according obtained from
the
production flow-line of oil and gas producing facilities is also object of the
present
invention.The NGL is conveyed from one of the production condensate flows at
e.g. an oil drilling platform and used as a solvent and subsequently added
back to
so the production mainstream. A preliminary evaluation of the gas-condensate
streams at several North Sea oilfields (Statfiord, Sleipner, Valhall, Ekofisk,
Forties,
Andrew) indicates that condensates (NGL) with the right thermodynamic proper-
ty
ties to act as a solvent are available in sufficient quantifies at these
production fa-
CA 02319016 2000-07-27
cilities. It is most likely that most oil and gas production facilities in the
North Sea
have access to such condensates.
The use of a NGL flow for extracting and subsequently adding the extract into
the
main production flow is a novel and cost-effective process. The process is
carried
out without «solvent-recovery» and with minimum utility requirement.
Figure 1 shows the experimental set-up for the extraction of drill cuttings
with NGL.
NGL is conveyed from e.g. a NGL container (1) through a valve (2) and a pump
(3), and further trough the pipe 4. The NGL is conveyed through a valve 5 and
io further pumped to an extracting cell (6) in which the drill cuttings are
cleaned. The
flow (7) containing NGL and the organic contaminants may optionally be con-
veyed to a production flow-line. The Figure 2 shows a phase diagram of the
avail-
able NGL, and figure 3 showes the residual oil versus void volumes of NGL.
CA 02319016 2000-07-27
WO 99/40292 PCT/N099/00037
~ The NGL has to be in liquid state at the pressure and temperature of
extraction.
~ The NGL has to be in gaseous state at atmospheric pressure at the extraction
temperature.
It is apparent from the phase diagram of the available NGL (Figure 2) that at
60°C,
s the minimum extraction pressure is aproximatly 20 bar.
The extraction cell was always first completely filled with the drill cuttings
(about
630-660 g) and then completely flooded with NGL (about 600 ml) at a pressure
of
30 bar, agitation was applied by turning the extraction cell up side down
twice.
Table 3 shows the results. The "void volume = 694 ml" is defined as the volume
of
NGL which can be added to the extraction cell containing the drill cuttings
plus the
volume of the tube connecting the cell to the choke valve.
Table 2: Molar compositions of NGL
Methane 0.0336 Butane 0.1848
Ethane 0.1272 (pentane 0.1102
Propane 0.1984 Pentane 0.1620
(butane 0.0754 Hexane 0.1074
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WO 99/40292 PCT/N099/OOb37
Table 3: Extraction of 623.7 g drill cuttings (34/10-D4H) with NGL at 30bar,
60°C
V(liquid gas)void moil) removed [wt
[ml] volumescollected oil %]
[g] [wt %] Wet
basis
694 1 0 0 7.20
932 1.3 4.9 10.9 6.46
1156 1.7 16.4 36.5 4.69
1268 1.8 21.3 47.4 3.92
1550 2.2 27.4 60.9 2.94
2060 3.0 33.3 74.1 1.97
2550 3.7 39.5 87.9 0.93
2920 4.2 41.4 92.1 0.61
3278 4.7 42.4 94.3 0.44
3914 5.6 43.2 96.1 0.30
4280 6.2 43.3 96.3 0.28
Figure 3 shows the residual oil content (related to the wet sample) on the
drill cut-
s tings versus the void volume of NGL injected. It is apparent from Figure 3
that the
initial oil concentration of 7.2 wt % remains in the cell until it is flooded
with the
first void volume of NGL. Upon additional injection of NGL, a reduction of the
oil
content is evident. It is apparent that each time one void-volume is injected,
the
concentration is reduced by approximately 50%. The experimental data were con-
~o sequently compared with the relationship expected from a pure dilution
process.
The following genera! equation were used for the dilution-model:
C=Co*0.5~"-~~
~s wherein:
C°= Initial oil concentration
C= Residual oil concentration
n= number of void volumes injected
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Table 3: Extraction of 623.7 g drill cuttings (34/10-D4H) with NGL at 30bar,
60°C
V(liquid void moil) removed [wt
gas) volumes collected oil %]
[ml] [g] [wt %] Wet
basis
694 1 0 0 7.20
932 1.3 4.9 10.9 6.46
1156 1.7 16.4 36.5 4.69
1268 1.8 21.3 47.4 3.92
1550 2.2 27.4 60.9 2.94
2060 3.0 33.3 74.1 1.97
2550 3.7 39.5 87.9 0.93
2920 4.2 41.4 92.1 0.61
3278 4.7 42.4 94.3 0.44
3914 5.6 43.2 96.1 0.30
4280 6.2 43.3 96.3 0.28
Figure 3 shows the residual oil content (related to the wet sample) on the
drill cut-
s tings versus the void volume of NGL injected. It is apparent from Figure 3
that the
initial oil concentration of 7.2 wt % remains in the cell until it is flooded
with the
first void volume of NGL. Upon additional injection of NGL, a reduction of the
oil
content is evident. It is apparent that each time one void-volume is injected,
the
concentration is reduced by approximately 50%. The experimental data were con-
,o sequently compared with the relationship expected from a pure dilution
process.
The following general equation were used for the dilution-model:
C=Co*0.5~"'~~ _
wherein:
C°= Initial oil concentration
C= Residual oil concentration
n= number of void volumes injected
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The experimental data correspond very well with the graph for the dilution
model
as illustrated in Figure 3. It is apparent that the NGL-extraction of the oil
from cut-
tings obeys the rules for dilution. Which indicates that the oil is already
completely
dissolved in the NGL at the first void volume. It is therefor reasonable to
assume
s that the extraction process is fast and exhibits no significant mass-
transfer restric-
tions.
All drill cuttings which were tested, exhibited the same behaviour as
presented in
Figure 3 and the results are summarised in Table 4.
Table 4:Oil concentration (weight %) before and after extraction with NGL
Drill cuttings 34/10-D4H 34/10-G-2T2H 30/3-A9A
(Gullfaks) (Gullfaks) (Veslefrikk)
Initial concentration7,2 9.0 18,6
Residual concentra-0.28 0.37 0.22
tion (wet basis)
Residual concentra-0.26 0.34 0.20
tion (dry basis)
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