SALT FREE INVERT DRILLING MUD

BOUE DE FORAGE INVERTIE SANS SEL

English Abstract

A fluid is provided for the drilling, workover and completion of a
subterranean well
comprising of an oil emulsion invert, containing an emulsifier, lime, clay
and/or polymer
and a aqueous internal phase consisting of molasses which is a solution of
sucrose, plus
some glucose, fructose and other organic and inorganic matter in water.
Further the vapor
activity of the internal phase can be adjusted with the use of desiccants to
provide increased
shale stability while drilling. Desiccants comprised of anhydrous salts are
preferred, such as
trisodium phosphate and zinc sulfate.

Claims

5

What is claimed is:

1. A method for drilling a well comprising:
rotating a drill string to cut a borehole into the earth; and
circulating invert oil emulsion drilling fluid through the drill string and
through the
annulus between the drill string and the wall of the borehole, the drilling
fluid comprising
oil, emulsifier and carbohydrate, the invert oil emulsion drilling fluid
having an internal
phase and the carbohydrate being at least about 30% by weight of the internal
phase.

2. The method of claim 1 in which the carbohydrate comprises simple and
complex
carbohydrates.

3. The method of claim 1 in which the carbohydrate is carried in an aqueous
medium
that forms part or all of the internal phase of the emulsion.

4. The method of claim 1 in which the carbohydrate is any one or more of
molasses,
fructose, glucose, sucrose, corn syrup and starch.

5. The method of claim 1 in which the carbohydrate is at least about 50% by
weight of
the internal phase.

6. The method of claim 1 in which the carbohydrate is at least about 90% by
weight of
the internal phase.

7. The method of claim 1 in which the carbohydrate is substantially water
free.

8. The method of claim 7 further comprising the step of adding a desiccant to
the invert
oil emulsion drilling fluid to remove water from the internal phase before
circulating the
invert oil emulsion drilling fluid in the borehole.





6

9. The method of claim 8 wherein the desiccant is anhydrous salt.

10. The method of claim 9 wherein the anhydrous salt is selected from the
group
consisting of zinc sulfate, lithium chloride, silica gel, and trisodium
phosphate.

11. An invert oil emulsion drilling fluid, comprising oil, carbohydrate and
sufficient
emulsifier to render the carbohydrate as an internal phase in the oil.

12. The invert oil emulsion drilling fluid of claim 11 in which the
carbohydrate
comprises simple and complex carbohydrates.

13. The invert oil emulsion drilling fluid of claim 11 in which the
carbohydrate is carried
in an aqueous medium that forms part or all of the internal phase of the
emulsion.

14. The invert oil emulsion drilling fluid of claim 11 in which the
carbohydrate is any
one or more of molasses, fructose, glucose, sucrose, corn syrup and starch.

15. The invert oil emulsion drilling fluid of claim 11 in which the
carbohydrate is at least
about 50% by weight of the internal phase.

16. The invert oil emulsion drilling fluid of claim 11 in which the
carbohydrate is at least
about 90% by weight of the internal phase.

17. The invert oil emulsion drilling fluid of claim1 1 in which the
carbohydrate is
substantially water free.

18. The invert oil emulsion drilling fluid of claim 17 further comprising the
step of
adding a desiccant to the invert oil emulsion drilling fluid to remove water
from the internal
phase before circulating the invert oil emulsion drilling fluid in the
borehole.




7

19. The invert oil emulsion drilling fluid of claim 18 wherein the desiccant
is anhydrous
salt.

20. The invert oil emulsion drilling fluid of claim 19 wherein the anhydrous
salt is
selected from the group consisting of zinc sulfate, lithium chloride, silica
gel, and trisodium
phosphate.

Description

CA 02451926 2003-12-23
SALT FREE INVERT DRILLING MUD
BACKGROUND OF THE INVENTION
O1 Drilling muds are used for various purposes, including powering downhole
motors,
cleaning drill bits of debris and returning cuttings to surface. It is
important that drilling
muds not interfere with hydrocarbon production, and that they be non-toxic.
There have
therefore been disclosed a variety of drilling muds some of which are
disclosed in US patent
nos. 5085282, 6251288, 6518223, H1611, 5072794 and 5110484. While these fluids
may
achieve their objectives, there is a need for an improved invert drilling mud,
particularly a
salt free invert drilling mud.
SUMMARY OF THE INVENTION
02 There is therefore provided an invert oil emulsion drilling fluid,
comprising oil,
carbohydrate and sufficient emulsifier to render the carbohydrate as an
internal phase in the
oil. In another aspect of the invention, there is provided a method for
drilling a well
comprising rotating a drill string to cut a borehole into the earth; and
circulating invert oil
emulsion drilling fluid through the drill string and through the annulus
between the drill
string and the wall of the borehole, the drilling fluid comprising oil,
emulsifier and
carbohydrate, the carbohydrate being at least about 30% by weight of the
internal phase of
the emulsion. By using carbohydrate, this invention avoids using calcium
chloride or other
salts, which is difficult to dispose of. Further details of aspects of the
invention are found in
the claims.
DETAILED DESCRIPTION OF THE INVENTION
03 A fluid is provided for the drilling, workover and completion of a
subterranean well
comprising of an oil emulsion invert, containing an emulsifier, lime, clay
and/or polymer
and an aqueous internal phase comprising a carbohydrate such as molasses.
Molasses is a
solution of sucrose, plus some glucose, fructose and other organic and
inorganic matter in
water. Molasses is an inexpensive source of simple and complex carbohydrates,
but other
carbohydrates such as starch, fructose, corn syrup, sucrose and glucose may be
used.


CA 02451926 2003-12-23
2
Further, the vapor activity of the internal phase can be adjusted with the use
of desiccants to
provide increased shale stability while drilling. Desiccants comprised of
anhydrous salts are
preferred, such as sodium phosphate and zinc sulfate.
04 Preferably, the carbohydrate is at least about 50% by weight of the
internal phase of
the emulsion, and even more preferably is at least about 90% by weight of the
internal phase
of the emulsion. Apart from the addition of the carbohydrate in the internal
phase of the
drilling fluid, the drilling fluid may be made according to conventional
procedures in which
emulsifier, lime, clay and/or polymer are used to obtain desirable properties.
OS The internal phase of the emulsion and hence the carbohydrate is also
preferably
substantially water free. This may be achieved by forming the drilling fluid
with an
aqueous internal phase and then adding a desiccant to the drilling fluid prior
to circulating
the drilling fluid in the well. The desiccant may be anhydrous salt such zinc
sulfate, lithium
chloride, silica gel, and sodium phosphate.
06 Example:
An exemplary formulation for a drilling fluid according to the invention
comprises:
907 ml Oil ~ Alpha Olefin C 12 supplier for example BP
81/m3 Primary emulsifier -~ fatty acid such as palm oil available from various
sources
121/m3Secondary emulsifier ~ conventional secondary emulsifier from various
sources
41/m3Wetter ~ reactive amine available from various sources
49 ml Carbohydrate brine ~ Molasses supplier for example Montaro
20 kg/m3 Lime ~ Supplier for example Camamara United
15 kg/m3 Clay ~ as a viscosifier, various sources
15 kg/m3 Gilsonite ~ for borehole stability, supplier for example Camamara
United
Desiccant -~ TSP anhydrous granular supplier for example Canada Colors
07 In the examples that follow, the properties are from API standards. The
indication
600, 300 etc is an rpm test, n indicates power law test, PV is the plastic
viscosity, YP is the
yield point, AV is the apparent viscosity and Gel 0/10 is a gel strength test.

CA 02451926 2003-12-23
3
Properties of 95/5 invert made
from the formulation above


600 18.5


300 10


200 7


100 4


6 1


3 0.5


PV 8.5


YP 0.8


AV 9.3


Gel 0/10 0.5/1.5


High Temperature High Pressure8.4 ml / 30 minutes
fluid loss
at 200oF, and 500 psi.


Electrical stability 2000 volts


Density 843 kg/m3


08 Any suitable oil may be used as the oil phase. Such oils are well known and
should
be chosen so as not to be incompatible with the environment. The emulsifiers
are also
conventional. The emulsifiers are provided in an amount sufficient to render
the
carbohydrate as an internal phase in the oil. Fatty acids such as palm oil are
inexpensive and
readily available. The wetter is also conventional and may be for example a
reactive amine,
for example a cyclic amine used as a corrosion inhibitor for steel. The brine
is a mixture of
water and carbohydrate, and should be free of calcium chloride or other salts.
Molasses is
an inexpensive source of carbohydrate. Lime is added to activate the primary
emulsifier in
conventional fashion. Clay is a conventional viscosifier. Gilsonite is added
in conventional
fashion for fluid loss control or borehole stability. The gilsonite plates out
on the wall of the
borehole to protect against formation contamination. Trisodium phosphate (TSP)
is

CA 02451926 2003-12-23
4
preferably used for the desiccant since it is inexpensive, readily available,
and acts as a
fertilizer when disposed of by spreading.
09 The drilling fluid is made in accordance with conventional procedures, then
used in
drilling a well in conventional manner where a drill string is rotated to cut
a borehole into
the earth. The drilling fluid may be circulated through the drill string and
through the
annulus between the drill string and the wall of the borehole. The drilling
fluid may be
disposed of by spreading on fields since the components degrade within a
reasonable period
of time.
Immaterial modifications may be made to the embodiment of the invention
described
here without departing from the invention.