[0001] The present invention relates to methods of cleaning oil/rock mixtures in oil drilling
operations and especially to cleaning of drilling oil from rock cuttings on offshore
drilling rigs, removal of oil from the face of newly drilled holes prior to reinforcement
with casing, and to the cleaning of oil muds from drilling rigs.
[0002] In the process of drilling for oil and gas, it is necessary for a number of reasons,
to use a drilling fluid or drilling mud. The types of drilling fluid or mud in common
use are:-
a) water based.
b) oil based.
c) water in oil emulsion based (invert).
[0003] Oil based drilling media (b) may also contain water in the form of water in oil emulsion.
It is. customary in the art to refer to a drilling medium containing up to about 15%
aqueous phase by volume as oil based. Those drilling media referred to as invert fluids
or muds, (c) generally contain between 15% and 55% water. This patent application
is particularly concerned with types (b and c) both of which are included in the term
"oil" as used herein, together with crude and refined mineral oils.
[0004] One of the functions of drilling fluid is to carry drill cuttings from the drill
bit to the surface, the cuttings are then removed by physical techniques, for example,
by using shale shakers, screens, cyclones, and centrifuges. After removal of the cuttings
the drilling fluid is re-used and the cuttings are disposed of. If the drilling is
offshore then the cuttings are disposed of into the sea, where in the case of aqueous
drilling fluids the cuttings disperse and settle without causing significant problems.
However, in the case of oil drilling fluids the cuttings are oil wet and settle rapidly
to the sea bed below the drilling rig and form an oily, sticky mass, which can interefere
with drilling operations, for example, by hindering the movement of divers involved
in sub-sea construction and maintenance work. It is thought that the swelling of clays
in the cuttings is responsible for the formation of this mass. In addition, the cuttings
cause oil pollution through gradual release of the oil.
[0005] One technique to remove oil from cuttings is to wash the cuttings with a solvent
such as diesal, this has the effect of removing most of the oil but still leaves the
surface contaminated with hydrocarbons, which can gradually be released to the environment.
Another way is to use a water miscible solvent, such as a glycol ether, but these
are expensive. Yet another way is to wash the cuttings in sea water using good agitation
to dislodge the oil from the surface of the cuttings. This process. can be used either
as the sole process for removing the drilling oil from the cuttings, or as a second
step to remove an oil solvent frcm cuttings previously washed with a hydrocarbon.
This process can be improved by adding a surfactant to the sea water, to lower the
oil/water interfacial tension. The cuttings may then be discharged to the sea where
they disperse and settle over a wide area of sea bed rather than accurate directly
in the area of the drilling operations. The oil in water emulsion which is forned
as a result of washing the cuttings may be discharged to the sea where fine dispersion
of the oil will facilitate its breakdown by micro-organisms.
[0006] A commonly used surfactant for the foregoing purposes is a C
9-11 alcohol six mole ethoxylate. An object of the present invention is to provide more
effective methods of cleaning oil frcm rock cuttings.
[0007] A further object of our invention is to provide a method whereby oil can be separated
from the emulsion resulting from cleaning of the cuttings.
[0008] We have discovered that a particular blend of an ethoxylated nonionic surfactant
with an alkanolamide exhibits a synergistic effect permitting the more efficient cleaning
of oil from rock cuttings. We have further discovered according to a preferred embodiment
of our invention that when the emulsions of oil in water formed by cleaning according
to our invention are heated, the emulsion is readily broken and the oil. may then
be recovered.
[0009] Accordingly, our invention provides a method of cleaning which comprises contacting
an oil coated rock with an aqueous solution containing an affective amount of a mixture
of (A) from 5 to 95% by weight of at least one alkoxylated alcohol, carboxylic acid,
alkylphenol, or nonionic phosphate ester, having in each case at least one alkyl group
with from 6 to 22 carbon atoms and from 1 to 20 ethyleneoxy groups, with (B) from
95 to 5% by weight of at least one alkanolamide of the formula:-

wherein R is a saturated or unsaturated alkyl group, having from 5 to 17 carbon atoms
and x and y are each chosen from 0 and integers from 1 to 12, such that x - y is from
1 to 12.
[0010] Preferably (A) is primary straight or branched chain alcohol having from. 6 to 18
carbon atoms and alkoxylated with from 1 to 10 ethylene-oxy groups.
(A) may alternatively be normal or branched chain alkanoic or alkenoic acid having
from 7 to 23 carbon atoms, alkoxylated with from 1 to 10 ethylene-oxy groups; straight
or branched chain alkyl phenol with from 6 to 12 aliphatic carbon atoms, alkoxylated
with from 1 to 12 ethylene-oxy groups; nonionic phosphoric acid ester having at least
one straight or branched chain alkyl group with from 6 to 22 carbon atoms, at least
one alkoxy or polyalkoxy group with from 1 to 20 ethylene-oxy units.
(B) typically has from 1 to 4 ethtleneoxy groups. While we have discovered that monoethanolamides
are particularly effective synergists, and may be preferred for use in warm climates,
concentrated mixture of monoethanolamide with component (A) tend to be insufficiently
fluid at low temperatures for convenient handling under the conditions which may be
encountered in, for example, North Sea operations. For such low temperatures we prefer
to use diethanolamides.
[0011] Typically, a mixture of (A) and (B) is supplied as a concentrate which is dissolved
in, or diluted with, water to provide the cleansing solution at the site of the rig.
Such concentrates optionally contain a solvent such as water or a water miscible alcohol,
glycol or glycol ether, e.g. isopropanol, ethylene glycol, propylene glycol, polyethylene
glycol, as required to provide a fluid, pourable composition under the conditions
likely to be encountered. The concentrate may, additionally, contain minor proportions
of hydrotropes, such as alkaline earth, sodium potassium mono- di- or tri- alkyl benzene
sulphonate salts having less than six aliphatic carbon atcms, e.g. toluene or xylene
sulphonates, phosphate esters salts, preservatives, such as formalin, dyes and/or
perfumes. Water may be present in any convenient proportion between zero and the final
working concentration of the cleaner. Generally, the lower the proportion of the water
the greater the convenience for transport and storage of the concentrate. These considerations
however must be balanced against the preference for a stable, pourable composition.
Organic solvents can add appreciably to the cost of the composition and are preferably,
therefore used sparingly e.g. less than 50% and preferably less than 20% of the weight
of the concentrate.
[0012] The concentrate may typically contain from 5 to 95% by weight of (A) and from 95
to 5% by weight of B. Preferably however (A) is present in concentrations greater
than 10% by weight, most preferably greater than 20% and usually greater than 30%.
(B) is also preferably present in concentrations of greater than 10% by weight, more
preferably greater than 20% and usually greater than 30%. A suitable mixture contains
from 40% to 60% of (A), from 60% to 40% of (B) and from 0 to 20% of solvent.
[0013] The concentrate is dissolved or dispersed in water at the site of application. When
used at offshore locations, the concentrate may conveniently be dissolved or dispersed
in sea water. Typically, the concentrate is diluted to from 0.5% to 10% active matter
by weight preferably from 1 to 5. We do not exclude higher concentrations, but they
are unlikely to prove cost effective. - Concentrations below 0.5% are not excluded
but are only marginally effective.
[0014] When used to clean rock cuttings, the cuttings are preferably agitated with the solution
of the concentrate in water or brine, for a sufficient time to emulsify a substantial
proportion of the oil. The emulsion may then be separated from the cuttings which,
when sufficiently clean, are dumped. The emulsion may be discharged. However, according
to a preferred embodiment of our invention the oil is recovered from the emulsion
by moderate heating. Typically temperatures in excess of 40°C e.g. 50 to 70°C are
sufficient to break the emulsion and permit recovery of the separated oil phase.
[0015] The cleaning solution according to our invention may also be injected into bore holes
to clean oil frcm the sides of the rock. This is necessary when a casing is to be
bonded with cement to the sides of the bore hole. The solution may also be used according
to our invention to clean oil mud from the rigs themselves and generally to remove
viscous hydrocaroon oils from hard surfaces.
[0016] The solution will be illustrated by the following examples:
The products were tested as follows:
Cuttings Wash Test Method
[0017]
a) 43 grams of oil mud cuttings obtained from a North Sea drilling operation were
added to 150g of X% active matter surfactant solution in synthetic sea water.
b) This was stirred for 5 minutes using a Janke4Kunkel stirrer at setting 2 at 800
rpm.
c) The mixture was allowed to stand for five minutes after which time the liquid was
decanted. This liquid contained the emulsified oil which could be separated by warming
to above 40°C.
d) The mixture was then made up to 150 ml with standard sea water and stirred for
a further minute as in b).
e) The mixture was then filtered through two layers of muslin.
f) 20g of washed cuttings were weighed accurately (W1) into a 250 ml round bottomed
flask and the water content was determined by the Dean and Stark method using 100-120
petroleum ether. The weight of water removed was determined as W2.
g) A further 10g of the washed cuttings were accurately weighed (W3) into an evaporating
dish and dried to constant weight (W4) at 110°C).
[0018] The weight of oil on the cuttings, W5 = W3 - W4 - (W2 x W3)
[0019] The weight of oil left on the cuttings expressed as a percentage of weight of dry
cuttings - weight of oil

[0020] The test was performed in duplicate. It should be noted that we have found that the
amount of oil removed from the surface of cuttings by any given surfactant or blend
of surfactants is dependent on the age of the cuttings, more oil being removed from
fresh cuttings than fran aged cuttings.
Example 1
[0021] Using the test method above, the following results were obtained using oil mud cuttings
from the North Sea.

Example 2
[0022]

Example 3
[0023]

Example 4
[0024]

In addition the emulsion decanted in step c) and obtained using A (1.5%) = B (3.75%)
was heated to 40°C and separated into distinct oil and aqueous phases.
Example 5
[0025]

Example 6
[0026]

The emulsion decanted in step c) and obtained using A (3.75%) +B (1.25%) was heated
to 40°C and seperated into distinct oil and aqueous phases.
Example 7
[0027] A concentrate was prepared for use according to the invention consisting of 45% by
weight of C10 C12 fatty alcohol 5 mole ethoxylate, 45% by weight coconut diethanolamide,
5% by weight propylene glycol, 5% by weight water. The product was fluid and stable
at temperatures between -5°C and 35°C and readily dispersed in sea water. When evaluated
in the above cuttings cleaning test the results were as follows.

[0028] The emulsion decanted in step c) of the method and obtained using the formulation
of Example 7, was heated to 50°C and separated into distinct oil and aqueous phases.
Example 8
[0029] . The following test was used to show the effectiveness of the blend of nonionic
surfactants of types A and B as defined above, for removing oil from metal surfaces.
a) A mild steel plate was washed thoroughly in household detergent solution followed
by rinsing under the tap and then with acetone.
b) One surface of the plate was coated evenly with 0.4g of hydrocarbon oil, e.g. crude
oil.
c) 0.6g of test solution was then mixed intimately with the surface oil, and the plate
was allowed to rest horizontally with the coated face uppermost for 15 minutes.
d) The surface was then washed with 200 cm of synthetic sea water from a laboratory
wash bottle.
e) The amount of oil remaining on the plate was assessed visually.
[0030] In this test, the test solution used contained 7.5% of a C10 C12 fatty alcohol 5
mole ethoxylate, 7.5% coconut diethanolamide and 85% water. The oil was substantially
removed from the surface of the mild steel leaving a clean non-oily surface.
[0031] In a further test, the test solution was a commercial hydrocarbon solvent based degreaser
believed to contain emulsifiers. The mild steel was less thoroughly cleaned and the
surface was oily.
Example 9
[0032] The test method described above (examples 1-7) was used, but the concentration of
ssrfactant (X%) was changed..

[0033] This is the surfactant most commonly used for cleaning oil mud cuttings and over
the wide concentration range studied was clearly less effective.
ALKYL DISTRIBUTION OF ALCOHOLS USED IN THE EXAMPLES
[0034] The following are typical distributions.
Example
[0035]

1. A method for the removal of oil from solid surfaces which comprises contacting
the surfaces with aqueous solution containing an effective amount of a mixture of
(A) from 5 to 95% by weight of at least one alkoxylated alcohol, carboxylic acid,
alkyl phenol, or nomionic phosphate ester, having in each case an alkyl or alkenyl
group with from 6 to 22 carbon atoms and from 1 to 20 ethylene oxide groups with (3)
from 95 to 5% by wt. of at least one ethylolamide of the formula

wherein R is a saturated alkyl group having from 5 to 17 carbon atoms and x and y
are each chosen from 0 and integers from 1 to 12, such that the average value of (x
and y) is from 1 to 12.
2. A method according to claim 1 wherein (A) is a primary, straight or branched chain
alcohol having from 6 to 18 carbon atoms ethoxylated with from 1 to 10 ethylene oxide
groups.
3. A composition according to claim 1 wherein (A) is a normal or branched chain alkanoic
or alkenoic acid having from 3 to 20 carbon atoms alkoxylated with from 1 to 10 ethyleneoxy
groups.
4. A method according to claim 1 wherein (A) is a straight or branched chain alkyl
phenol having from 5 to 12 aliphatic carbon atoms alkoxylated with from 1 to 12 ethylene
oxide groups.
5. A method according to claim 1 wherein (A) is a nonoinc phosphoric acid aster having
at least one straicht or branched chain alkyl group having from 6 to 22 carbon atoms
and at least one ethylene group or polyalkoxy group having up to 20 ethyleneoxy units.
6. A method according to any foregoing claims wherein (B) has from 1 to 4 ethyleneoxy
groups.
7. A method according to claim 6 wherein (b) is an alkyl monoethanolamide.
8. A method according to claim 6 wherein (3) is an alkyl diethanolamide.
9. A method according to any foregoing claim wherein (A) and (B) are each present
in a proportion of more than 20% of the total active weight of the mixture.
10. A method according to any foregoing claim wherein the aqueous solution is sea
water.
11. A method according to any foregoing claim wherein the mixture is present in the
aqueous solution in a concentration of from 0.5% to 10%.
12. A method according to any foregoing claim for washing oil rig cuttings.
13. A method according to any foregoing claims for washing structures.
14. A method according to claim 13 for cleaning surfaces of oil rigs.
15. A method according to any foregoing claim substantially as described herein with
reference to any one of the examples.
16. A concentrate for use in the preparation of aqueous solutions for use according
to the method of any foregoing claim, consisting essentially of from 20% to 60% by
wt. of (A), from 20% to 60% by wt. of (B), up to 10% by wt. of water and up to 10%
by wt. of a water miscible, hydroxyl containing organic solvent.
17. A concentrate according to claim 16 wherein (A) is an ethoxylated alcohol having
from 8 to 14 carbon atoms and from 2 to 7 ethylenoxy groups.
18. A concentrate according to either of claims 16 and 17 wherein (B) is an alkyl
diethanolamide.
19. A concentrate according to any of claims 16 to 18 wherein the solvent is a water
miscible mono di- or tri-hydroxy alcohol or alcohol ether having from 2 to 8 carbon
atoms.
20. Aqueous solutions formed by dilution of a concentrate according to any of claims
1 to 19 with water, and containing at least 0.5% surface active matter.
21. Sea water having dissolved therein a concentrate according to any of claims 1
to 19 and containing at least 0.5% surface active matter.