Note: Descriptions are shown in the official language in which they were submitted.
METHOD FOR TREATING OIL-CONTAMINATED DRILL CUTTINGS FROM A
WELL DRILLING OPERATION PARTICU A LY AT AN OFFSHORE LOCATION
F9961
The present invention relates to an method for
treating contaminated drill cuttings before disposal and
more particularly, relates to a method for treating oil-
contaminated drill cuttings at an offshore location so that
the treated cuttings can be disposed of without ecological
risk.
In a rotary drilling operation, a fluid co~monly
called "mud" is circulated from a storage area on the surface
downward through the drill pipe, out openings in the drill bit,
and upward within the borehole to the surface. This return
mud carries with it the drill cuttings from the bottom of the
borehole. The returning mud along with its entrained drill
cuttings is passed onto a "shale shaker" before it is returned
to the storage area. The shaker, which is normally above the
mud storage area, is essentially a screen that is used to
separate the drill cuttings and cavings from the mud. The
mud falls by gravity through the screen and the cuttings pass
over the end of the screen.
Disposal of these separated cuttings is sometimes a
problem, e.g. where the drilling operations are carried out
at an offshore location. In some instances, the cuttings are
merely passed from the shaker into the body of water and are
allowed to settle to the bottom. However, as is often the
case, when a drilling mud system such as an oil-base mud is
9961 used, the cuttings are usually coated with undesirable con-
taminants, e.g. oil. If these contaminated cuttings are dis-
posed of directly into the water, there is a risk that free
oil on the cuttings may wash off the cuttings and accumulate
on the surface of the water. Unless the cuttings can be
ecologically disposed of, governmental regulations mayS
because of this pollution threat, prevent the use of oil-base
muds in some drilling operations where the use of such muds is
highly beneficial, if not necessary.
There are at least two known general techniques for
treating these contaminated cuttings to make them ecologically
acceptable. Either they must be taken to disposal facilities
on shore or they must be treated on site to remove the con-
taminants before they are disposed of in the water. ~he added
expense involved the taking the cuttings ashore is substantial,
and, accordingly, detracts from widespread application of this
technique. Further, it may not be possible to take the cuttings
ashore in time of bad weather and rough seas. Therefore, for
obvious reasons, it is much preferred to treat and dispose of
the drill cuttings from offshore operations directly at the
drilling site.
Several methods have been proposed for treating contamin-
ated cuttings on site. One approach is to burn oil off the
cuttings with high intensity lamps. However, this approach
presents problems (i~e., possible fire hazards due to the lamps
and the difficulty of equally exposing all the cuttings to the
9961 lamps) which makes it unfeasible in most instances.
Another approach involved washing the cuttings with
a detergent to remove the contaminants, separating the washing
solution and contaminants, and dumping the cleaned cuttings
into the water. One example of this approach is disclosed in
U.S. Patent No.3,688,781. Other wash techniques are discussed
in the article "Cuttings Can Meet Offshore Environment
Specifications', OIL AND GAS JOURNAL, August 14, 1972, pp. 73-
76. While such techniques may be successful in cleaning the
/5 cuttings, the handling and disposal of large volumes of wash
solution and the equipment necessary for washing the cuttings
detract from the overall effectiveness of this method.
Therefore, a reliable method for treating oil-contaminated
cuttings onsite is needed to ensure that oil base muds can
be safely used in all instances where drilling conditions can
require their use.
The present invention provides a method for treating
oil contaminated drill cuttings at an onsite location so that
the treated cuttings can be disposed of without any pollution
r,~ risk.
The present invention involves separating the cuttinys
from the drilling fluid and then thoroughly mixing the oil-
contaminated cuttings with an oil absorbent material, e.g.
clay. The contaminated cuttings will normally have some oil
absorbed therein but will also have "free oil" on their sur-
faces. This free oil is what presents the threat of pollu-
tion when
l~V~Z3
the cuttings are disposed of directly into a body of water.
The ~ree oil on the cuttings will be aDsorbed by the oil
absorbent material as the mixing takes place. To aid in
binding the absorbed oil onto or into both the cuttings and
the oil absorbent material, a surfactant, e.g. calcium
dodecylbenzene sulfonate, may be added to the cuttings and
oil absorbent material prior to or during mixing.
The present invention, then, in one aspect, provides a method
of treating oil-contaminated drill cuttings from a well
drilling operation in which a drilling fluid is circulated
to remove drill cuttings from the well being drilled, said
method comprising: separating said cuttings from said
drilling fluid; mixing a solid, oil absorbent material
with said separated cuttings to absorb free oil from the
cuttings into said oil absorbent material; compacting said
cuttings and said oil absorbent material after mixing;
and disposing of said cuttings and sai.d solid, oil
absorbent material after they are compacted.
In another aspect, the present invention resic,es in a
method of treating oil contaminated drill cuttings from a well
drilling operation in which a drilling fluid is circulated to
remove drill cuttinys from the well being drilled, said
method comprising:
separating said cuttings from said drllling fluid,
increasing the surface area of said cuttings,
mixing said cuttings to enhance the absorption of free oil
on the cuttings by the additional solid, oil absorbent material
exposed to said free oil through the increased surface area of
said cuttings, and
compacting said cuttings after mixing.
4a
According to a further aspect of this invention
there is provided a system for treating oil-contaminated
drill cuttings from a well drilling operation in which a
drilling fluid is circulated to remove drill cuttings from
the well being drilled, comprising:
a shaker for separating the drill cuttings from the
drilling mud,
a muller for increasing the surfaee area of said
cuttings to thereby expose additional solid, oil absorbent
material,
a holding tank for collecting the mulled cuttings,
a mixer for enhancing the absorption of free oil into
the additional solid, oil absorbent material exposed through
the increased surface area of said euttings, and
means for metering the flow of said mulled cuttings
from said holding tank into said mixer to insure that all the
free oil on the mulled cuttings is absorbed into the additional
solid, oil absorbent material.
Where the cuttings are originally of a relatively large
size, it ls preferable to mull or grind the cuttings before
mixing the cuttings with the oil absorbent material. This
reduces the size of the cuttings, which aids in mixing, and
also increases the surface area of the cuttings themselves
which now becomes available for absorbing scme of the free
oil.
4b
After the cuttingsand oil absorbent material are
thoroughly mixed, substantially all of the free oil will be
bound by the cuttings and the oil absorbent material. This
mixture can now be safely disposed of directly into a body
of water without the risk of any signiicant amount of free
oil being washed out. However, where the mixture contains
extremely s~all or dustlike particles, these particles,
themselves, may float on the water surface thereby creat-
ing an undesirable condition. In these instances, the
present invention provides for compacting the mixture before
disposal into pellets, briquettes, or the like which are of
a sufficient density to ensure that they will safely sink to
the bottom of the body of water.
Z3
9961 The actual construction, operation, and the apparent
advantages of the invention will be better understood by re-
ferring to the accompanying drawings in which:
FIG. 1 is a perspective view, partly in section,of
an offshore drilling platform incorporating a treatment system
for cuttings;
FIG. 2 is a schematical, elevational view, partl~ in
section, of a treating unit in accordance with the present
invention; and
FIG. 3 is a cross-sectional view taken along line 3-3 of
FIG. 2.
Referring to the drawings, the offshore drilling rig 10
shown in FIG. 1 has a platform 11 supported on marine bottcm
12 of the body of water 13 by means of legs 14. A derrick 15
is mounted on platform 11 which is used to carry out normal
rotary drilling operations. Although a fixed platform is
shown for illustrative purposes, it should be realized that
the present invention can be used equally as well with other
offshore drilling apparatus, e.g., floating drilling vessels,
submergible barge platforms, etc. or it can be used at onshore
locations.
99~1 A mud circulation system 20 for rotary drilling is
partly illustrated in FIG. 1. A conductor pipe 21 extends
from platform 11 into marine bottom 12. ~ud is circulated
down a drill string (not shown) which extends through cond-
uctor pipe 21. The mud leaves the drill pipe through openings
in a drill bit ( not shown) on the lower end of the drill pipe
and flows upward through conductor pipe 21 to mud return line
24, carrying the drill cuttings with it. The mud leaves mud
return line 24 and flows through shale shakers, desanders, de-
silters, hydrocyclones, centrifuges, other devices (shown coll-
ectively as 26a in FIG. 1) to separate the cuttings from the
mud. The mud is then returned to a storage area (not shown)
for reuse.
9961 As shown in FIGS. 2 and 3, contaminated cuttings ~5,
after being separated from the mud, washed with diesel or
other suitable oil or both, pass through holding bin 30 into
inlet hopper 31 or treating unit 27. A second holding bin
32 positioned over inlet hopper 31 can receive a dry, solid
oil absorbent matexial, (e.g. clay material such as atta-
pulgite, kaolinite, montmorillonite, vermiculite) through
chute 33. For simplicity, both holding bins 30, 32, as illus-
trated, feed directly into inlet hopper 31 of treating unit
27. However, separate feed means (not shown) may be used in
conjunction with the holding bins to meter the cuttings and
absorbent material into inlet hopper 31 at a controlled rate.
For example, individual screw conveyors or belt conveyors can
be positioned below bins 30 and 32, respectively, to receive
material from their respective hopper and then move the res-
pective material into inlet hopper 31 to ensure that a proper
ratio between the cuttings and the oil absorbent material is
maintained for example, as shown in U.S. Pat. No.4,116,681.
A conduit 34 is provided to supply a liquid surfactant into
inlet hopper 31 for a purpose to be described later.
3Z3
9961 Treating unit 27 includes a mixer 35 which receives the
cuttings and the oil absorbent material from inlet hopper 31.
Mixer 35 may be of any known type that is capable of adequate-
ly mixing the cuttings and oil absorbent material into a uni~
formly dispersed mixture. Examples of such mixers are Readco's
Continuous Processor, sold by Readco of York, Pa., and Twin
Screw Continuous Mixer, Model MPCV-160, sold by Baker-Perkins,
Inc. of Houston, Texas.
In some instances where the cuttings include relatively
large cuttings, a muller or grinder 36 may be positioned bet-
ween chute 26 and holding bin 30 to mull the cuttings before
mixing.
The cuttings and oil absorbent material are thoroughly
mixed in mi~er 35 and are fed to a compactor 38 through con-
duit 37. Compactor 38 can be of any known type which compacts
the mixture of cuttings and oil absorbent material into a solid
form, e.g. any of many known, commercially available "pellet-
izers" which compact a solid mixture and extrude the mixture
as pellets or briquettes, e.g. K-G Briquetting System sold by
Komarek-Greaves and Co., Rosemont, Ill. The
V~Z3
9961 pelletized mixture 40 is conveyed from compactor 38 to chute
51 through cnnduit 41. Chute 51 conveys pelletized mixture
40 to a disposal area, e.g. water 13, as shown in FIG. 1.
Cuttings are separated from the drilling mud by process-
ing equipment 26a. The cuttings may be washed with diesel or
other oil to remove "whole mud" and other chemical
contaminants that may be present on the cuttings, The oil-
contaminated cuttings 25 are then passed through chute 26 into
holding bin 30 from where they are fed into inlet hopper 31 of
treating unit 27. At the same time, the dry, solid oil
absorbent material is fed from bin 32 into inlet hopper 31.
The rates at which the cuttings and the oil absorbent material
are fed into inlet hopper 31 are determined experimentally
based on the a~ount of oil present on the cuttings, the
absorbency of the oil absorbent material, etc. Preferably,
an excess of oil absorbent material will be supplied to inlet
hopper 31 to ensure that all of the free oil present on the
cuttings will be absorbed.
Most oil-base mud systems utilize a surfactant in the mud
to make the solids wettable by oil. The oil becomes chemi-
cally adsorbed on the surfaces of the solids and prevents the
solids from becoming wet with water. The chemically adsorbed
oil is not removed or displaced when the oil-wet solids are
placed in water. In many
9961 operations, there will be a substantial amount of this surf-
actant present on the contaminated cuttings 25 along with the
oil. Where no or insufficient surfactant is present on the
cuttings, a s~rfactant capable of making the surfaces of the
solids oil wettable, e.g. calcium dodecylbenzene sulfonate, is
added to the cuttings and oil absorbent material through con-
duit 34. In some instances, the oil absorbent material may
be pretreated to include the surfactant before mi~ing.
The cuttings, oil absorbent material, and surfactant are
thoroughly mixed in mixer 35. All free oil on the cuttings
will be absorbed by the oil absorbent material. The surfactant,
either present or added will aid in chemically binding the oil
to the cuttings and to the oil absorbent material. As mentioned
above, if the cuttings are relatively large, it is preferred that
the cuttings be mulled or ground before they are finally mixed with
the oil absorbent material. This exposes additional absorbent surface
area on the cuttings which will also be available for the absorption
of free oil, and the small cutting size also pr~vides for better
mixing with the oil absorbent material.
After the mixture exits mixer 35, substantially all the oil
will be adequately bound in the mixture so that no significant amount
of oil, if any, will wash free once the mixture is disposed of in
a body of water. However, if the mixture contains extremely small
or dust like particles, these
A
3 2
9961 particles, themselves, may float on the water and cause an
undesirable condition around an offshore location. In these
instances, the mixture from mixer 35 is fed to compactor 38
wherein the mixture is c~pacted into pellets 40, briquettes,
or the like, which are of sufficient density to insure they
will sink in the water.
As can be seen from the above description, the
present invention provides a safe, reliable method for
the onsite treatment of oil-contaminated drill cuttings
to be disposed of without the risk of pollution.
