Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED DRILLING FLUIDS
GROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
BACKGROUND OF THE INVENTION
[0002] The invention relates to improved drilling fluid additions which
comprise
fine particles of crosslinked elastomer. The elastomer acts as a plugging
agent thereby
preventing loss of the drilling fluid to a porous formation. A method for
preventing loss of
drilling fluids is also provided.
[0003] Drilling fluids, or drilling muds as they are sometimes called, are
slurries
used in the drilling of wells in the earth for the purpose of recovering
hydrocarbons and other
fluid materials. Drilling fluids have a number of functions, the most
important of which are:
lubricating the drilling tool and drill pipe which carries the tool, removing
formation cuttings
from the well, counterbalancing formation pressures to prevent the inflow of
gas, oil or water
from permeable rocks which may be encountered at various levels as drilling
continues, and
holding the cuttings in suspension in the event of a shutdown in the drilling
and pmnping of the
drilling fluid.
[0004] For a drilling fluid to perform these fwctions and allow drilling to
continue,
the drilling fluid must stay in the borehole. Frequently, undesirable
formation conditions are
encountered in which substantial amounts or, in some cases, practically all of
the drilling fluid
may be lost to the formation. Drilling fluid can leave the borehole through
large or small fissures
or fractures in the formation or through a highly porous rock matrix
surrounding the borehole.
[0005] Most wells are drilled with the intent of forming a filter cafe of
varying
tluckness on the sides of the borehole. The primary purpose of the filter cafe
is to reduce the
large losses of drilling fluid to the surrounding formation. Unfortunately,
formation conditions
are frequently encountered which may result in unacceptable losses of drilling
fluid to the
surrounding formation despite the type of drilling fluid employed and filter
calve created.
[0006] A variety of different substances are now pumped down well bores in
attempts to reduce the large losses of drilling fluid to fractures and the
like in the surrounding
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formation. Different forms of cellulose are the preferred materials employed.
Some substances
which have been pumped into well bores to control lost circulation are: almond
hulls, walnut
hulls, bagasse, dried tumbleweed, paper, coarse and fine mica, and even pieces
of rubber tires.
These and other prior ai-t additives are described in U.S. Pat. No. 4,498,995.
[0007] Another process that is employed to close off large lost circulation
problems
is referred to in the art as gunk squeeze. In the gunl~ squeeze process, a
quantity of a powdered
bentonite is mixed in diesel oil and pumped down the well bore. Water
injection follows the
bentoute and diesel oil. If mixed well, the water and bentonite will harden to
form a gunl~y semi-
solid mess, which . will reduce lost circulation. Problems frequently occur in
trying to adequately
mix the bentonite and water in the well. The bentonite must also be Dept dry
until it reaches the
desired point in the well. This method is disclosed in U.S. Pat. No.
3,082,823.
[0008] Many of the methods devised to control lost circulation involve the use
of a
water expandable clay such as bentonite which may be mixed with another
ingredient to form a
viscous paste or cement. U.S. Pat. No. 2,890,169 discloses a lost circulation
fluid made by
forming a slurry of bentoute and cement in oil. The slurry is mixed with a
surfactant and water
to form a composition comprising a water-in-oil emulsion having bentonite and
cement dispersed
in the continuous oil phase. As this composition is pumped down the well bore,
the oil expands
and flocculates the bentonite which, under the right conditions, forms a
filter cafe on the well
bore surface in the lost circulation area. Hopefully, the filter cafe will
brealc the emulsion
causing the emulsified water to react with the cement to form a solid coating
on the filter calve.
But such a complex process can easily go wrong.
[0009] U.S. Pat. No. 3,448,800 discloses another lost circulation method
wherein a
water soluble polymer is slurried in a nonaqueous medium and injected into a
well. An aqueous
slurry of a mineral material such as barite, cement or plaster of Paris is
subsequently inj ected into
the well to mix with the first slurry to form a cement-lilte plug in the well
bore.
[0010] U.S. Pat. No. 4,261,422 describes the use of an expandable clay such as
bentonite or montmorillonite which is dispersed in a liquid hydrocarbon for
injection into the
well. After injection, the bentonite or montmorillonite will expand upon
contact with water in the
formation. Thus, it is hoped that the expanding clay will close off water
producing intervals but
not harm oil producing intervals.
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[0011] A similar method is disclosed in U.S. Pat. No. 3,078,920 which uses a
solution of polymerized methacrylate dissolved in a nonaqueous solvent such as
acetic acid,
acetic anhydride, propionic acid and liquid aliphatic lcetones such as acetone
and methyl-ethyl
ketone. The methacrylate will expand upon contact with formation water in the
water-producing
intervals of the well.
[0012] It has also been proposed to mix bentonite with water in the presence
of a
water-soluble polymer which will flocculate and congeal the clay to form a
much stronger and
stiffer cement-life plug than will form if bentonite is mixed with water. U.S.
Pat. No. 3,909,421
discloses such a fluid made by blending a dry powdered polyacrylamide with
bentonite followed
by mixing the powder blend with water. U.S. Pat. No. 4,128,528 claims a
powdered
bentonite/polyacrylamide thickening composition prepared by mixing a water-in-
oil emulsion
with bentonite to form a powdered composition which rapidly becomes a viscous
stiff material
when mixed with water. U.S. Pat. Nos. 4,503,170; 4,475,594; 4,445,576;
4,442,241 and
4,391,925 teach the use of a water expandable clay dispersed in the oily phase
of a water-in-oil
emulsion containing a surfactant to stabilize the emulsion and a polymer
dispersed in the
aqueous phase. When the emulsion is sheared, it breaks and a bentonite paste
is formed which
hardens into a cement-like plug. The patent discloses the use of such polymers
as
polyacrylamide, polyethylene oxide and copolymers of acrylamide and acrylic or
methacrylic
acid.
[0013] A group of oil absorbent polymers is disclosed in U.S. Pat. Nos.
4,191,813;
4,263,407; 4,384,095 and 4,427,793. U.S. Pat. No. 4,191,813 discloses lightly
crosslinked
copolymers containing at least 40% by weight of vinylbenzyl chloride, the
balance of monomers,
if any, comprising a major portion of aromatic monomers, with the copolymer
being crosslinked
in a swollen state by a Lewis acid catalyst. The preferred comonomers are one
or more of
styrene, divinylbenzene and acrylonitrile. U.S. Pat. No. 4,263,407 discloses
similar copolyners
wherein the copolymer is post-crosslinked in a swollen state in the presence
of a Friedel-Crafts
catalyst with a crossliucer selected from a polyfunctional alkylating or
acylating agent and a
sulfur halide.
[0014] Another group of highly hydrocarbon absorbent copolymers is disclosed
in
U.S. Pat. Nos. 4,384,095 a~zd 4,427,793. They describe a crosslinlced linear
addition copolymer
which contains repeating units of vinylbenzyl alcohol and at least one other
alpha, beta-
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monoethylenically unsaturated monomer different from vinylbenzyl alcohol,
wherein the
vinylbenzyl alcohol units comprise about 0.5% to about 20% by weight of the
linear polymer.
The preferred comonomers are styrene, methylmethacrylate, vinyltoluene and
vinylpyridine. The
copolymers disclosed in all four of these patents absorb from two to ten times
their weight in
hydrocarbons and may swell up to ten times their original volume.
[0015] Oleophilic polymers for separating oil from water which show
significant
swelling in volume upon absorption of oil are described in U.S. Pat. No.
4,172,031. These
polymers include polymers of styrenes and substituted styrenes, polyvinyl
chloride copolymers
of vinylchloride such as a copolymer of 60 wt % vinylchloride and 40 wt %
vinylacetate,
polymers and copolymers of vinylidene chloride and acrylonitrile, and acrylic
polymers such as
polymers of methylmethacrylate and ethylacrylate, styrene and divinylbenzene
copolymers and
alkyl styrene polymers and copolymers. The reference discloses that these
polymers show
significant swelling in volume upon absorption of oil.
[0016] U.S. Pat. No. 4,633,950 discloses the use of oil swelling polymers to
reduce
lost circulation in drilling fluids. In this patent, the polymers are
introduced in an aqueous
solution to prevent absorption of the hydrocarbon fluid until the polymers
reach the well head.
[0017] While the above inventions purport to be effective in reducing loss of
drilling fluids, there continues to be a need for effective and inexpensive
additives for well bore
fluids which can prevent or stop the loss of the fluids into the subterranean
formation.
BRIEF SUMMARY OF THE INVENTION
[0018] The present invention is directed to a system and method which «<begin
typing here»>
[0019] The invention relates to an improved additive for a drilling fluid
which
significantly reduces the loss of fluid to the surrounding subteiTanean
structure while maintaining
the lubricity of the drilling fluid. The novel additive comprises finely
ground elastomer particles.
[0020] Loss of drilling fluid occurs when drilling fluid seeps into the
subterranean
formation through holes, fractures or fissures in the formation. The region in
the well where this
occurs is referred to as the lost circulation zone. When elastomer particles
are added to a drilling
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fluid, they form a seal in the lost circulation zone by expanding in size to
seal the fractures or
fissures. This prevents further loss of drilling fluid into the formation.
[0021] In contrast to other elastomer based additives discussed above, the
present
system uses fme elastomer particles which are easily pumped into the well but
are capable of
swelling to about 40% to about 140% more than their original size when exposed
to hydrocarbon
fluids. Their ability to swell males the elastomer particles extremely
effective at preventing loss
of drilling fluid into the subterranean formation. When the elastomer
particles are used with
hydrocarbon-based drilling fluids or with a hydrocarbon additive, particles
gradually expand,
allowing the material to be easily pumped before significant expansion of the
particles occurs.
That most of the swelling occurs after the elastomer particles are in the
desired location in the
well eliminates the need for protective coatings or an aqueous pill to prevent
swelling of the
polymer until it has reached the desired region in the well.
[0022] Another advantage of the elastomer particles is their very low density
as
compared to conventional materials used to prevent fluid loss. The low density
of the elastomer
particles allows them to be used in higher amounts than conventional fluid
loss materials.
[0023] The fluid loss prevention system of the invention require no additional
additives other than those nornally encountered in drilling fluid such as
diesel, oil, other
hydrocarbon fluid and water. The elastomer particles are easily handled and
present little if any
industrial hazards. Moreover, since the preferred source of the fluid loss
agents of the invention
are prepared from recycled tires, the invention presents a way to effective
use the old tire
materials rather than allowing them to collect to form hazardous waste sites.
[0024] The invention also relates to a method for reducing drilling fluid loss
by
adding finely ground elastomer particles to a drilling fluid in an amount
sufficient to bloclc the
flow of fluid into the subterranean formation.
[0025] The foregoing has outlined rather broadly the features and technical
advantages of the present invention in order that the detailed description of
the invention that
follows may be better understood. Additional features and advantages of the
invention will be
described hereinafter which form the subject of the claims of the invention.
It should be
appreciated that the conception and specific embodiment disclosed may be
readily utilized as a
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basis for modifying or designing other structures for carrying out the same
purposes of the
present invention. It should also be realized that such equivalent
constructions do not depart
from the invention as set forth in the appended claims. The novel features
which are believed to
be characteristic of the invention, both as to its organization and method of
operation, together
with further objects and adva~ltages will be better understood from the
following description
when considered in comlection with the accompanying figures. It is to be
expressly understood,
however, that each of the figures is provided for the purpose of illustration
and description only
and is not intended as a definition of the limits of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The drilling fluid additive of the present invention comprise particles
of
elastomers which exhibit swelling when contacted with hydrocarbon fluids, yet
do not dissolve
in hydrocarbon fluids. This can be achieved by using crossliu~ed elastomers
which swell but do
not dissolve in the presence of a hydrocarbon fluid. The swelling elastomers
are such that little,
if any, swelling occurs until the polymer has reached the lost circulation
zone in the well to be
sealed. This is accomplished without resort to coatings on the polyner or
suspending the
polymer with aqueous pill.
[0027] The preferred elastomer used in the practice of this invention is cnamb
rubber. Crumb rubber generally comprises rubber derived from recycled tires or
scrap material
from the manufacture of tires. Crumb rubber particles are generally of about
3/8-inch or less in
size. In the practice of the invention, the crumb rubber should have a mixture
of particle sizes
ranging of from about 1 to about 400 microns, preferably about 20 to about 400
microns. In the
preferred embodiment, the material should include particles of varying
diameters within the
range stated above.
[0028] W an alternative embodiment, the elastomer can be slightly larger, in
the
range of from greater than or about 400 to about 4000 microns. In a preferred
embodiment, the
additive can include particles of up to about 2000 microns (10 mesh) and more
preferably up to
about 1000 (18 mesh) microns. Mixtures of particle sizes within the ranges can
also be used. For
example, the additive can include particles of about 425 microns, (48 mesh),
about 1000
microns, (18 mesh) and about 2000 microns (10 mesh).
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[0029] Crumb rubber can be prepared several different ways. hl the first
method,
whole tires are cryogenically frozen and then shattered in a hammer mill to
break down the tire
into the desired particle sizes and to remove the steel and fibers from the
tire. A second method
involves physically tearing the tire apart and removing the unwanted steel and
fibers. In this
process, the tire is continuously milled until the desired particle sizes are
obtained. Another
source of crumb rubber is the bushings that remain as the tire is manufactured
or remanufactured.
[0030] One key feature of crumb rubber that males it useful in the practice of
the
invention is its ability to expand up to about 140% of its original size when
exposed to
hydrocarbon fluids and temperatures. As shown in the examples below, when the
elastomer
particles are exposed to hydrocarbon fluids and temperatures typically
encountered in a well
(200° F to 300° F) the particles expand to over 140% of their
original size. The amount of
expansion is dependent upon the hydrocarbon used and the temperature in the
well.
[0031] The expansion of the elastomer is not immediate, often taking several
hours
before a significant increase is seen. The delay in expansion of the crumb
rubber means that the
crumb rubber can be easily pumped down a well bore without resort to coatings
or the use of an
aqueous pill. The crumb rubber can then flow into the pores and cracks. Once
in the cracks and
pores, the crumb rubber will expand to fill the cracks and pores without
dissolving into the
drilling fluid. Thus, while cnunb rubber is the preferred elastomer in the
practice of the '
invention, any elastomer which exhibits the same swelling and solubility
characteristics as crumb
rubber may be used.
[0032] Another feature of the present invention is the relatively low density
of the
elastomer particles, relative to the fluid. This allows a higher additive
loading without adversely
affecting the properties of the drilling fluid. For example, the elastomers of
the invention can be
used in amounts up to about 100 lbs. per barrel (ppb)whereas conventional
fluid loss additives
can be used in amounts ranging from about 5 to about 20 lbs. per barrel. The
ability to use
higher additive loadings means that more of the elastomer particles are
present in the fluid to fill
and plug the openings into the subterranean formation.
[0033] This last feature is particularly important in deepwater operations
where the
drilling fluids used require a narrow density range. Typically the fluids used
in these
applications have a density of from about 9.5 to about 10.5 pounds per gallon
(ppg). The
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elastomer particles of the invention have a density of from about 8.5 to about
10.5 ppg. Thus,
the addition of the additives of the invention do not adversely affect the
density drilling muds.
[0034] Illustrative hydrocarbon fluids useful in this invention include cmde
oil,
diesel oil, lcerosene, mineral oil, gasoline, naptha, toluene,
ethylenedichloride and mixtures
thereof. In addition, synthetic oils such as those derived from olefins,
linear a-olefins, poly a-
olefins, internal esters and ethers may be used. Because of economics,
availability at any drilling
site and perfornaance, diesel oil is most preferred. Synthetic oils, however,
are preferred where
environmental impact is a concenl.
[0035] The drilling fluid additives of the present invention case be used in
both
hydrocarbon based and aqueous or water based drilling fluids. If polymer
expansion is needed in
an aqueous system, a hydrocarbon fluid must be added to the elastomer
particles to aclueve the
desired expansion. It has been observed, however, that improved fluid loss can
be achieved in
aqueous drilling fluids without adding a hydrocarbon fluid. The improved fluid
loss reduction is
achieved by the ability to use higher amounts of particles
[0036] One method for practicing this invention involves the injection of a
discrete
pill of drilling fluid containing the drilling fluid additives of the
invention in a sufficient amount
to seal off the lost circulation zone. This pill is then forced down to the
lost circulation zone.
The elastomer particles then fill the holes and fractures preventing loss of
the fluid. Depending
upon the polymer and the composition of the drilling fluid, about two to about
250 pounds of
polymer per barrel of fluid can be placed in the pill. Methods for introducing
the pill containing
the drilling fluid additive of the invention are well l~nown to those in the
art.
[0037] Other matter may be added to the pill to enhance the sealing properties
of
the fluid. For example, cellulose fiber from plant matter such as peanut
shells, sugar caale husl~s
or bagasse, almond shells, walnut shells, dried tumbleweed and paper, may be
added to the pill.
Bridging materials such as calcium carbonate may also be added. Coarse and
fine mica can also
be used.
[0038] To help maintain the seal established by the polyner containing pill
and to
prevent loss to new fractures, the polymer of the invention can be
continuously added~to the
drilling fluid. In these cases, the polymer should be added at a rate of 100
to 250 pounds per
hour to the drilling fluid.
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EXAlVE'LES
Example 1
[0039] In this example, samples of crumb rubber were exposed to various
hydrocarbon fluids to measure the degree of expansion over time. In each
experiment, 20 mls of
the base fluid were added to a 150 mm test tube. To this was added 2.29 gins
of cnunb rubber.
The tube was then shalcen to set the cnunb rubber. The total height of the
fluid and crumb rubber
was measured at 108 mm. The height of the rubber in each sample was 33 mm. The
hydrocarbon fluids used in these tests were two commercial internal olefin
fluids, a linear a-
olefin fluid and #2 diesel.
[0040] The test tube was then placed in a Baroid 500 ml static-aging cell
which
was then pressurized to 300 psi with nitrogen. The cell was then placed in an
oven at the
temperatures noted in the tables and static-aged for three days. A duplicate
sample was static-
aged for seven days.
[0041] After static-aging, the test tubes were removed from the test cells and
the
height of the rubber was measured. The amount of expansion was calculated
using the formula
("height after aging / 33) -1." The results are reported in Tables 1 and 2.
Table 1- Solubility and Percent Exaansion of NER PineRubber after three day
tests
Tem erature IO Base #1 LAO Base IO Base #2 #2 Diesel
200F 103% 97% 127% 158%
250F 109% 109% 97% 152%
300F 112%* ~ 112%* 97% 158%*
* Denotes partial solubility of PipeRubber in Base Fluid.
Table 2 - Solubility and Percent Expansion of NER PineRubber after seven day
tests
Tem erature IO Base #1 LAO Base IO Base #2 #2 Diesel
200F 82% 97% 103% 106%
_ -
X50F 112% 118% 118% 158%
-- - -
300F I 127% I 97%~, I 103%'~
112%x
* Denotes partial solubility of PipeRubber in Base Fluid.
Example 2
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[0042] In this example, a well was experiencing significant loss of drilling
fluid.
Traditional loss prevention treatments with agents such as calcium carbonate,
fiber and graphite
materials proved ineffective in reducing or stopping the loss. .
[0043] A combination of 30 pound per barrel of cnunb rubber with 20 pounds per
barrel of fiber were added to the drilling fluid. After the intial loading of
crumb rubber and
fiber, a maintenance load of 250 pounds of crumb rubber and 150 pounds of
fiber per hour of
pumping were used . The result was little or no additional loss of drilling
fluid during the rest of
the drilling process.
Example 3
[0044] W this example, a deepwater drilling rig was experiencing fluid losses
of
from 50 to 60 barrels an hour. Attempts to use conventional fluid loss control
agents proved
unsuccessful.
[0045] Two 50-barrel pills of fluid were prepared, each containing 15 pounds
per
barrel of crumb rubber were pumped into the well. After these pills were
pumped into the well,
the rate of fluid loss dropped to between 10 and 20 barrels an hour.
[0046] Although the present invention and its advantages have been described
in
detail, it should be understood that various changes, substitutions and
alterations can be made
herein without departing from the invention as defined by the appended claims.
Moreover, the
scope of the present application is not intended to be limited to the
particular embodiments of the
process, machine, manufacture, composition of matter, means, methods and steps
described in
the specification. As one will readily appreciate from the disclosure,
processes, machines,
manufacture, compositions of matter, means, methods, or steps, presently
existing or later to be
developed that perform substantially the same function or achieve
substantially the same result
as the corresponding embodiments described herein may be utilized.
Accordingly, the appended
claims are intended to include within their scope such processes, machines,
manufacture,
compositions of matter, means, methods, or steps.
