Note: Descriptions are shown in the official language in which they were submitted.
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ADDITIVE FOR REDUCING TORQUE ON A DRILL STRING
BACKGROUND OF THE INVENTION
When oil and gas wells are drilled, fluid formulations with a multitude of
properties,
including lubricity, are pumped down the well through the drill string and out
through
nozzles in the drill bit, so that the drilling fluid circulates upward through
the annular space
between the rotating drill string and the rock formation. The functions of
these drilling fluids
or "muds" are to cool and lubricate the bit and drill string, to cany the
cuttings from the
drilling process to the surface, to control and reduce fluid loss into the
rock formations, and
to support and protect the bore hole until the metal casing can be cemented in
place (i.e.,
create a stable hole).
Mud lubricity (to achieve minimum torque and drag) and mud toxicity (for wells
in
environmentally sensitive areas, such as offshore drilling) are major concerns
when selecting
a drilling fluid formulation. Most drilling fluids may be grouped into two
major categories:
water-based or oleaginous-based. The majority of drilling fluids used today
are water-based,
i.e., they contain water as the continuous external phase. Although oleaginous-
based drilling
fluids including the so-called synthetic-based fluids do have performance
advantages,
drawbacks are higher costs and difficult environmental compliance in specific
areas of the
world.
The lubricity of a drilling fluid is an important factor in the economics of
well drilling
and is measured by determining the effect of the fluid upon the coefficient of
friction between
a moving part, such as the drill string, and a surface in contact with the
moving part. The
lower the coefficient of friction, the greater the lubricity. The lubricity of
a drilling fluid
determines the fluid's ability to lower torque and drag forces during the
drilling operation.
The prior art is full of reports of various lubricants utilized to reduce the
torque of a
drill string. For example various types of hydrocarbons, synthetic oils,
esters, fatty acids,
natural oils, soaps, and other compounds have been added to drilling fluids to
help reduce
torque. Organic, oil-based lubricants are often added to water-based drilling
fluids to reduce
the coefficient of friction. Reduction of friction during drilling is
particularly important in
drilling operations where the well bore is not vertical. Emulsifiers or
surfactants are typically
added to drilling fluids to keep these oil-based, water-insoluble lubricant
components
suspended as droplets in the water-based fluids and to prevent their
separation and
coalescence. These lubricants can increase the toxicity and irritation level
of the fluids.
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In addition to liquid lubricants, micrometer-sized solid particles or beads
may also be
added to water-based drilling fluids to increase their lubricity. Some
representative examples
of this type of lubricant system are: (1) Abrasion- and fracture-resistant,
thermally stable and
chemically inert ceramic spheres; (2) Plastic beads, for example, those made
from a
copolymer of divinyl benzene and styrene; (3) Plastic-coated magnetic
particles in bead form,
to facilitate the removal and recycling of these bead compositions; (4)
Chemically-resistant,
lime-silica glass beads; (5) Resilient graphitic carbon particles; (6)
Cellulose, peat or bagasse,
containing absorbed oil-based liquid lubricants; (7) Mixtures of graphite,
silicate and silicone
materials. Common difficulties with the above solid lubricants have been the
environmental
concerns when aqueous based drilling fluids are being used and the loading up
of the drilling
fluid with solid materials. Further, it should be appreciated that the
addition of solid
materials that do not contribute to the weighting of the fluid may result in
an underweight
fluid raising concerns about blow-out or wall collapse. A further problem
encountered with
solid lubricating agents is small diameter apertures present in the valves and
other flow and
pressure control equipment used may prevent the use of solid particulate
lubricating agents
because these material block and plug the narrow restrictions. A more serious
concern is that
the solids might be difficult to remove from the well bore and thus cause
formation damage.
Despite the continued efforts in this area, there remains and exists an unmet
need for fluids
that reduce drill string torque and do not exhibit the problems of solids
settling, high
viscosity, toxicity and reduced total fluid weight.
SUMMARY OF THE INVENTION
The present invention is generally directed to fluids useful in reducing the
torque of
drill string, as well as methods for making and methods of using such fluids.
The fluids of the
present invention include a polymer coated colloidal solid material that has
been coated with
a polymer added during the cominution (i.e. grinding) process for preparing
the polymer
coated colloidal solid material.
One illustrative embodiment of the present invention includes a method of
reducing
the torque in a rotating drill string component. In such an illustrative
method, the method
includes, injecting into the drilling fluid a composition including a base
fluid, and a polymer
coated colloidal solid material. The polymer coated,colloidal solid material
includes: a solid
particle coated with a polymeric dispersing agent absorbed to the surface of
the solid particle.
The polymeric dispersing agent is absorbed to the surface of the solid
particle during the
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cominution (i.e. grinding) process utilized to make the polymer coated
colloidal solid
material. The base fluid utilized in the above illustrative embodiment can be
an aqueous
fluid or an oleaginous fluid and preferably is selected from: water, brine,
diesel oil, mineral
oil, white oil, n-alkanes, synthetic oils, saturated and unsaturated
poly(alpha-olefins), esters
of fatty acid carboxylic acids and combinations and mixtures of these and
similar fluids that
should be apparent to one of skill in the art. Suitable and illustrative
colloidal solids are
selected such that the solid particles are composed of a material of specific
gravity of at least
2.68 and preferably are selected from barium sulfate (barite), calcium
carbonate, dolomite,
ilmenite, hematite, olivine, siderite, strontium sulfate, combinations and
mixtures of these
and other suitable materials that should be well known to one of skill in the
art. In one
preferred and illustrative embodiment, the polymer coated colloidal solid
material has a
weight average particle diameter (d50) less than ten microns. Another
preferred and
illustrative embodiment is such that at least 50% of the solid particles have
a diameter less
than 2 microns and more preferably at least 80% of the solid particles have a
diameter less
than 5 microns. Alternatively, the particle diameter distribution in one
illustratvie
embodiment is such that greater than 25% of the solid particles have a
diameter of less than 2
microns and more preferably greater than 50% of the solid particle have a
diameter of less
than 2 microns. The polymeric dispersing agent utilized in one illustrative
and preferred
embodiment is a polymer of molecular weight of at least 2,000 Daltons. In
another more
preferred and illustrative embodiment, the polymeric dispersing agent is a
water soluble
polymer is a homopolymer or copolymer of monomers selected from the group
comprising:
acrylic acid, itaconic acid, maleic acid or anhydride, hydroxypropyl acrylate
vinylsulphonic
acid, acrylamido 2-propane sulphonic acid, acrylamide, styrene sulphonic acid,
acrylic
phosphate esters, methyl vinyl ether and vinyl acetate, and wherein the acid
monomers may
also be neutralized to a salt.
The present invention is also directed to a lubricating composition that
includes a base
fluid and a polymer coated colloidal solid material . The polymer coated
colloidal solid
material is formulated so as to include a solid particle coated with a
polymeric dispersing
agent absorbed to the surface of the colloidal solid particle.
These and other features of the present invention are more frilly set forth in
the
following description of preferred or illustrative embodiments of the
invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
The description is presented with reference to the accompanying drawing which
is a
graphical representation of the particle diameter distribution of the
colloidal barite of the
present invention compared to that of API barite.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
A new and novel aspect of the present invention is the dual role that the
colloidal
particles play in the drilling fluid. That is to say, the polymer coated
colloidal particles may
serve both as a weighting agent and lubricating agent. This dualistic view of
the material is
novel to the drilling industry because previously the functionality of
weighing agent and
lubricating agent were distinct.
One of skill in the art should appreciate that the solid lubricating agents
noted above
generally have a density less than conventionally used weighting agents. For
example,
mineral derived graphite has a specific gravity of about 2.09 to 2.25. In
contrast conventional
weiihting agents such as barite has a specific gravity of about 4.50, hematite
has a specific
gravity of about 5.3. According to one preferred embodiment of the present
invention, the
lubricating / weighting agent of the present invention is formed of particles
that are composed
of a material of specific gravity of at least 2.68. In this way the particles
can serve as , a
combination lubricating agent and weighting agent. Materials of specific
gravity greater than
2.68 from which colloidal solid particles that embody one aspect of the
present invention
include one or more materials selected from but not limited to barium sulfate
(barite),
calcium carbonate, dolomite, ilmenite, hematite or other iron ores, olivine,
siderie, strontium
sulfate. Normally the lowest well bore fluid viscosity at any particular
density is obtained by
using the highest density colloidal particles. However other considerations
may influence the
choice of product such as cost, local availability and the power required for
grinding.
One of skill in the art should also understand and appreciate that
conventional
weighting agents, such as powdered barium sulfate ("barite"), exhibit minimal
effects on
reducing drill string torque. Physically conventional weighting agents are
utilized for their
high density and exhibit an average particle diameter (d50) in the range of 10-
30 microns. It
should be well known to one of skill in the art that properties of
conventional weighting
agents, and barite in particular are subject to strict quality control
parameters established by
the American Petroleum Institute (API). To suspend these materials adequately
requires the
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addition of a gellant or viscosifier such as bentonite for water based fluids,
or organically
modified bentonite for oil based fluids. Polymeric viscosifiers such as
xanthan gum are
typically added to slow the rate of the sedimentation of the conventional
weighting agent. It
is therefore very surprising that the products of this invention, which
comprise solid colloidal
particles that are coated with a polymeric defloculating agent or dispersing
agent, provide
fluids that contain high density solids that also reduce the torque in the
rotating portions of
the drill string without increasing sedimentation or sag.
The additives of this invention comprise dispersed solid colloidal particles
that are
coated with a polymeric defloculating agent or dispersing agent. The fine
particle size will
generate suspensions or slurries that will show a reduced tendency to sediment
or sag, whilst
the polymeric dispersing agent on the surface of the particle control the
inter-particle
interactions. It is the combination of fine particle size and control of
colloidal interactions
that reconciles the two objectives of high density and increased lubricity.
According to the present invention, the polymeric dispersant is coated onto
the
surface of the particulate weighting during the grinding process utilized to
form the colloidal
particle. It is believed that during the course of the grinding process, newly
exposed particle
surfaces become polymer coated thus resulting in the properties exhibited by
the colloidal
solids of the present invention. Experimental data has shown that colloidal
solid material
created in the absence of the polymeric dispersant results in a concentrated
slurry of small
( particles that is an unpumpable paste or gel. According to the teachings
of the present
invention, a polymeric dispersant is added during the grinding process. It is
believed that this
difference provides an advantageous improvement in the state of dispersion of
the particles
compared to post addition of the polymeric dispersant to fine particles.
According to a
preferred embodiment, the polymeric dispersant is chosen so as it provides the
suitable
colloidal inter-particle interaction mechanism to make it tolerant to a range
of common well
bore contaminants, including salt saturated.
A method of grinding a solid material to obtain the solid colloidal particle
so of the
present invention is well known for example from British Patent Specification
No 1,472,701
or No 1,599,632. The mineral in an aqueous suspension is mixed with a
polymeric
dispersing agent and then ground within an agitated fluidized bed of a
particulate grinding
medium for a time sufficient to provide the required particle size
distribution. An important
preferred embodiment aspect of the present invention is the presence of the
dispersing agent
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in the step of "wet" grinding the mineral. This prevents new crystal surfaces
formed during
the grinding step from forming agglomerates which are not so readily broken
down if they are
subsequently treated with a dispersing agent.
A preferred embodiment of this invention is for the weight average particle
diameter
(d50) of the colloidal solid particles to be less than ten microns. Another
preferred and
illustrative embodiment is such that at least 50% of the solid particles have
a diameter less
than 2 microns and more preferably at least 80% of the solid particles have a
diameter less
than 2 microns. Alternatively, the particle diameter distribution in one
illustrative
embodiment is such that greater than 25% of the solid particles have a
diameter of less than 2
microns and more preferably greater than 50% of the solid particle have a
diameter of less
than 2 microns. This will enhance the suspension's characteristics in terms of
sedimentation
or sag stability without the viscosity of the fluid increasing so as to make
it unpumpable.
The polymer coated colloidal particles according the invention may be provided
as a
concentrated slurry either in an aqueous medium or an oleaginous liquid. In
the latter case,
the oleaginous liquid should have a kinematic viscosity of less than 10
centistokes (10
mm2/S) at 40 C and, for safety reasons, a flash point of greater than 60 C.
Suitable
oleaginous liquids are for example diesel oil, mineral or white oils, n-
alkanes or synthetic oils
such as alpha-olefin oils, ester oils or poly(alpha-olefins).
Where the polymer coated colloidal particles are provided in an aqueous
medium, the
dispersing agent may be, for example, a water-soluble polymer of molecular
weight of at least
2,000 Daltons. The polymer is a homopolymer or copolymer of any monomers
selected from
(but not limited to) the class comprising: acrylic acid, itaconic acid, maleic
acid or anhydride,
hydroxypropyl acrylate vinylsulphonic acid, acrylamido 2-propane sulphonic
acid,
acrylamide, styrene sulphonic acid, acrylic phosphate esters, methyl vinyl
ether and vinyl
acetate. The acid monomers may also be neutralized to a salt such as the
sodium salt.
It has been found that when the dispersing agent is added during the
cominution
process (i.e. grinding), intermediate molecular weight polymers (in the range
10,000 to
200,000 for example) may be used effectively. Intermediate molecular weight
dispersing
agents are advantageously less sensitive to contaminants such as salt, clays,
and therefore are
well adapted to well bore fluids.
Where the colloidal particles are provided in an oleaginous medium, the
dispersing
agent may be selected for example among carboxylic acids of molecular weight
of at least
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150 such as oleic acid and polybasic fatty acids, alkylbenzene sulphonic
acids, alkane
sulphonic acids, linear alpha-olefin sulphonic acid or the alkaline earth
metal salts of any of
the above acids, phospholipids such as lecithin, synthetic polymers such as
Hypermer 0M-1
(trademark of ICI).
While not intending to be bound by any specific theory of action, it is
believed that
the formation of the colloidal solid material by a high energy wet process, in
which API
Barite of median particle size of 25-30 micron is reduced to a median particle
size of less
than 2 microns, is more efficient when the milling is done at high density,
normally greater
than 2.1sg, preferably at 2.5sg. At these high densities, the volume or mass
fraction of barite
is very high. For example, at a specific gravity of 2.5, a 100kgs of the final
product contains
about 78kgs is barite. However, the resulting slurry still remains fluid. The
presence of the
surface active polymer during the course of the cominution process is an
important factor in
achieving the results of the present invention. Further, the surface active
polymer is designed
to adsorb onto surface sites of the barite particles. In the grinder, where
there is a very high
mass fraction of barite, the polymer easily finds it way onto the newly formed
particle
surfaces. Once the polymer 'finds' the barite ¨ and in the environment of the
grinder it has
every chance to do so ¨ a combination of the extremely high energy environment
in the wet
grinding mill (which can reach 85 to 90 C inside the mill), effectively
ensures that the
polymer is 'wrapped' around the colloidal size barite. As a result of this
process it is
speculated that no polymer 'loops' or 'tails' are hanging off the barite to
get attached,
snagged, or tangled up with adjacent particles. Thus it is speculated that the
high energy and
shear of the grinding process ensures the polymer remains on the barite
permanently and thus
the polymer doesn't desorb, or become detached.
This theory of action is supported by the observation that adding the same
polymer to
the same mass fraction of colloidal barite at room temperature and mixing with
the usual lab
equipment results provides very different results. Under such conditions it is
believed that
polymer doesn't attach itself to the surface properly. This may be due to
presence of a sphere
of hydration or other molecules occupying the surface binding sites. As a
result the polymeric
dispersant is not permanently 'annealed' to the surface, and thus, the
rheology of the
suspension is much higher. It has also been observed that the suspension is
not so resistant to
other contaminants possibly because the polymer wants to detach itself from
the barite and
onto these more reactive sites instead.
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The following examples are to illustrate the properties and perfolutance of
the well
bore fluids of the present invention though the invention is not limited to
the specific
embodiments showing these examples. All testing was conducted as per API RP 13
B where
TM TM
applicable. Mixing was performed on SiIverson L2R or Hamilton Beach Mixers.
The
viscosity at various shear rates (RPM's) and other theological properties were
obtained using
a Farm viscometer. Mud weights were checked using a standard mud scale or an
analytical
balance. Fluid loss was measured with a standard API fluid loss cell
In expressing a metric equivalent, the following U.S. to metric conversion
factors are
used : 1 gal = 3.785 litres; 1 lb. = 0.454 kg; 1 lb./gal (ppg)=0.1198 g/cm3 ;
1 bb1=42 gal;
1 lb./bbl (ppb)=2.835 kg/m3; 1 lb/100ft9-0,4788 Pa.
These tests have been carried out using different grades of ground barite: a
stnndard
grade of API barite, having a weight average particle diameter (D50) of about
20 microns ; a
untreated barite (M) having an average size of 3 -5 microns made by
milling/grinding barite
while in the dry state and in the absence of a dispersant, with and colloidal
barite according
the present invention with a polymeric dispersant included during a "wet"
grinding process.
It should be appreciated by one of skill in the art that other solid
particulate materials may be
used in the practice of the present invention.
A representative sample of particle size distributions are shown figure 1. As
shown in
figure 1, one of skill in the art should understand and appreciate that the
colloidal barite
particles of the present invention have a particle size distribution that is
very different from
that of API barite. Specifically one should be able to determine that greater
than about 90%
(by volume) of the colloidal barite of the present invention has a particle
diameter less than
about 5 microns. In contrast, less than 15 percent by volume of the particles
in API
specification barite have a particle diameter less than 5 microns.
The polymeric dispersant is IDSPERSETM XT an anionic acrylic ter-polymer of
molecular weight in the range 40,000-120,000 with carboxylate and other
fiinctional groups
commercially available from LLC. Houston, Texas. This preferred polymer is
advantageously stable at temperature up to 200 C, tolerant to a broad range
of contaminant,
gives good filtration properties and do not readily desorb off the particle
surface.
The following examples illustrate the dual use of the lubricating agent as
both
weighting agent and as a lubricating agent. (i.e. reducing torque)
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Example 1
22 ppg [2.63 gicm3] fluids based on barium sulfate and water were prepared
using
standard barite and colloidal barite according to the invention. The 22 ppg
slurry of API grade
barite and water was made with no gelling agent to control the inter-particle
interactions
(Fluid #1). Fluid #2 is also based on standard API barite but with a post-
addition of two
pounds per barrel (5,7 kilograms per cubic meter) IDSPERSE XT. Fluid #3 is
100% new
lubricating / weighting agent with 67% w/w of particles below 1 micron in size
and at least
90% less than 2 microns. The results are provided in table I.
Table I
Viscosity at various shear rates (rpm of agitation) : Plastic Yield
Dial reading or "Fann Units" for: Viscosity Point
600 rpm 300 rpm 200 rpm 100 rpm 6 rpm 3 rpm mPa.s
lb/100ft2
(Pascals)
1 250 160 124 92 25 16 90 70(34)
2 265 105 64 26 1 1 160 -55 (-
26)
3 65 38 27 17 3 2 27 11(5)
For Fluid #1 the viscosity is very high and the slurry was observed to filter
very
rapidly. (If further materials were added to reduce the fluid loss, the
viscosity would have
increased yet further). This system sags significantly over one hour giving
substantial free
water (ca. 10% of original volume).
Post addition of two pounds per barrel [5.7 kg/cm3] of IDSPERSE XT to
conventional
API barite (Fluid #2) reduces the low shear rate viscosity by controlling the
inter-particle
interactions. However due to the particle concentration and average particle
size the fluid
exhibits dilatency, which is indicated by the high plastic viscosity and
negative yield point.
This has considerable consequences on the pressure drops for these fluids
while pumping.
That is to say the ability to pump this fluid is substantially reduced due to
the high viscosity.
The fluid #2 sags immediately on standing.
By contrast, Fluid #3 exhibits an excellent, low, plastic viscosity. The
presence of the
dispersing polymer controls the inter-particle interactions, so making fluid
#3 pumpable and
not a gel. Also the much lower average particle size has stabilized the flow
regime and is now
laminar at 1000 s4 demonstrated by the low plastic viscosity and positive
yield point.
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Example 2
Experiments were conducted to examine the effect of the post addition of the
chosen
polymer dispersant to a slurry comprising weighting agents of the same
colloidal particle
size. A milled barite ( D50 4um) and a milled calcium carbonate (70% by weight
of the
particles of less than 2pm) were selected, both of which are of similar
particle size to the
invention rOated herein. The slurries were prepared at an equivalent particle
volume fraction
of 0.282 and compared to the product of the present invention (new barite).
See table II.
The rheologies were measured at 120 F (49 C), thereafter an addition of 6ppb
(17.2 kg/m3) IDSPERSE XT was made. The rheologies of the subsequent slurries
were
finally measured at 120 F (see table III) with additional API fluid loss test.
Table II
# Material Dispersant Density (ppg) Volume wt/wt
Fraction
4 New barite while grinding 16.0 [1.92 g/cm3]
0.282 0.625
Milled barite none 16.0 [1.92 g/cm3 1 0.282 0.625
6 Milled barite post-addition 16.0 [1.92 g/cm3] 0.282
0.625
7 Calcium Carbonate none 12.4 [1.48 g/cm3] 0.282
0.518
8 Calcium Carbonate post-addition 12.4 [1.48 g/cm3]
0.282 0.518
Table III
Viscosity at various shear rates (rpm of agitation) : Plastic Yield API
Dial reading or "Fann Units" for: Viscosity Point
Fluid
Loss
600 rpm 300 rpm 200 rpm 100 rpm 6 rpm 3 rpm mPa.s lb/l00&
4 12 6 4 2 6 0 11
5 os OS OS OS OS OS
6 12 6 4 2 6 0 total!
7 os os 260 221 88 78
8 12 6 4 3 1 1 6 0 total2
1 - total fluid loss in 26 minutes; 2 - total fluid loss in 20 minutes
No filtration control is gained from post addition of the polymer as revealed
by the
total fluid loss in the API test.
One of skill in the art should appreciate and know that the performance
parameters of
major importance are: low theology, including plastic viscosity (PV), yield
point (YP), gel
strengths; minimal rheology variation between initial and heat aged
properties; minimal fluid
loss and minimal sag or settlement. Sag is quantified in the following
examples by separately
CA 02598123 2013-05-28
measuring the density of the top half and bottom half of an aged fluid sample,
and a
dimensionless factor calculated using the following equation:
Sag Factor = (density of the top half)/(density of the top half + density of
the bottom
half)
A factor of 0.50 indicates zero solids separation and a no density variation
throughout
the fluid sample. A sag factor greater than 0.52 is normally considered
unacceptable solids
separation.
Example 3
In the following example, two 13.0 ppg fluid formulations are compared, one
weighted with conventional API barite and the second weighted with polymer
coated
colloidal barite (PCC barite) made in accordance with the teachings of the
present invention,
as a 2.2sg liquid slurry. Other additives in the formulation are included to
provide additional
control of pH, fluid loss, rheology, inhibition to reactive shale and
claystones. These
additives are available from M-I Drilling Fluids.
PRODUCT Fluid A Fluid B
PCC barite lbs/bbl 320.0
API barite lbs/bbl 238.1
Freshwater lbs/bbl 175.0 264.2
Soda Ash lbs/bbl 0.4 0.4
= Celpol ESL lbs/bbl 3.5 4.2
= Flotrol lbs/bbl 3.5 0
* Defoam NS lbs/bbl 0.4 0
KC' lbs/bbl 32.9 36.1
* Glydril; MC lbs/bbl 10.5 10.5
% DuoteeNS lbs/bbl 0.1 1.4
* Trademark
The fluids were heat aged statically for 48 hrs at 104 F with the following
exemplary
results.
FANN 35 Reading (120 F) . Fluid A Fluid B
Initial Aged Initial Aged
600 rpm 56 62 73 65
300 rpm 36 41 52 47
200 rpm 28 33 42 39
100 rpm 19 23 31 29
6 rpm 5 7 11 10
3 rpm 4 6 9 8
PV (cps) 20 21 21 18
YIP (lbs/100sq.ft) 16 20 31 29
sec gel (lbs/100sq.ft) 1 5 7 10 9
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min gel (lbs/100sq.ft) 8 8 12
Sag Factor 0.50 0.58
One of skill in the art should appreciate upon review of the above results
that Fluid A,
formulated with the polymer coated colloidal barite, had no solids separation
with a sag
factor of zero with a theological profile much lower than a fluid weighted
with conventional
API barite.
Example 4
In the following example, a 14.0ppg Freshwater fluid was chosen to compare the
properties of fluids formulated with a polymer coated colloidal barite; an
uncoated colloidal
barite and a conventional API barite. Fluid A was formulated with the polymer
coated
colloidal barite of this invention. Fluid B was formulated with conventional
API barite. Fluid
C was formulated with a commercial grade of non coated colloidal barite, of
median particle
size of 1.6 microns available from Highwood Resources Ltd., Canada. Post
grinding addition
of the coating polymer of the invention are included in the formulation of
Fluids B and C to
maintain the fluid in a deflocallated condition.
PRODUCT Fluid A Fluid B Fluid C
PCC barite lbs/bbl 407
API barite lbs/bbl 300
Sparwite W-51-LB lbs/bbl 310
Freshwater lbs/bbl 182 276 274
Idsperse XT 6.0 6.2
XCD Polymer lbs/bbl 0.5 0.6 0.5
* DUAL-FLO lbs/bbl 7 5 7
Bentonite 10 10 10
* Trademark
Samples of fluid A, B and C were purposely contaminated with bentonite to
simulate
the inclusion of naturally drilled solids in the formulation. The samples were
heat aged
dynamically at 150 F for 16 his. Exemplary and representative results after
aging are shown
below.
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FANN 35 Fluid A Fluid B Fluid C
Reading (100 F)
No With No With No With
Bentonite Bentonite Bentonite Bentonite Bentonite Bentonite
600 rpm 74 76 78 205 94 off scale
300 rpm 48 49 51 129 58 off scale
200 rpm 38 39 39 100 45
100 rpm 27 27 27 67 29
6 rpm 8 8 8 20 7
3 rpm 6 6 6 19 6
PV (cps) 26 27 27 76 36
YP (lbs/100sq.ft) _ 22 22 24 53 22
sec gel 7 6 6 17 6
(lbs/100sq.ft)
10 min gel 9 9 7 20 7
(lbs/100sq.ft)
API Fluid Loss 3.5 3.0 4 3.9
(m1/30min)
Upon review of the above data, one of skill in the art should appreciate that
the
properties of Fluid A remain essentially unchanged, while the Fluid B became
very viscous,
whereas, the rheology of Fluid C formulated with non coated colloidal barite
after aging was
too viscous to measure.
Example 5
A further comparison between a polymer coated colloidal barite of this
invention and
conventional API barite was made in a 14ppg fluid, in which the yield point of
the fluid has
been adjusted such that it is the same between the two fluids before ageing.
PRODUCT Fluid A Fluid B
PCC barite (2.4sg) lbs/bbl 265
API barite lbs/bbl 265
Freshwater lbs/bbl 238 293
Soda Ash lbs/bbl 0.5 0.5
KOH lbs/bbl 0.5 0.5
PolyPlus RD lbs/bbl 0.5 0.5
PolyPac UL 2.0 2.0
Duovis lbs/bbl 1.0 0.75
KC1 lbs/bbl 8.0 8.0 .
The fluids were heat aged dynamically for 16 hrs at 150 F. The following table
presented exemplary results.
FANN 35 Reading Fluid A Fluid B
(120 F)
Initial Aged Initial Aged
600 rpm 64 61 80 72
,
300 rpm 42 39 50 43
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WO 2006/091562 PCT/US2006/006030
200 rpm 32 32 33 32
100 rpm 22 21 24 21
6 rpm 6 5 6 6
3 rpm 4 4 4 4
PV (cps) 22 22 30 29
YP (lbs/100sq.ft) 20 17 20 14
sec gel 5 5 5 5
(lbs/100sq.ft)
10 min gel 17 11 6 6
(lbs/100sq.ft)
API Fluid Loss 2.8 4.7
(m1/30min)
VST ppg 0.21 1.33
Upon review of the above, one of skill in the art should understand that the
plastic
viscosity for the polymer coated colloidal barite fluids were lower and thus
more desirable.
The Viscometer Sag Test (VST) is an alternative method for determining 'sag;
in drilling
fluids and is described in American Society of Mechanical Engineers Magazine
(1991) by
D.Jefferson. As indicated above, the VST values for Fluid A, containing the
polymer coated
colloidal barite of this invention is lower than that of Fluid B formulated
with untreated, API
barite.
Example 6
The long term thermal stability of the colloidal barite fluids of the present
invention
are shown in the following example at 17.34ppg. ECF-614 additive is an
organophilic clay
additive available from M-I Drilling Fluids.
PRODUCT Fluid A
PCC barite (2.4sg) lbs/bbl 682
Freshwater lbs/bbl 53.5
ECF-614 lbs/bbl 2.0
The fluid was heat aged statically for 4 days at 350 F. The following table
provides
exemplary results.
FANN 35 Reading (120 F) Fluid A
Initial Aged
600 rpm 107 45
300 rpm 64 28
6 rpm 7 3
3 rpm 5 2
PV (cps) 43 17
YP (lbs/100sq.ft) 21 11
10 sec gel (lbs/100sq.ft) 6 4
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WO 2006/091562 PCT/US2006/006030
min gel (lbs/100sq.ft) 10 11
Sag Factor 0.503
Upon review of the above data one of skill in the art should understand and
appreciate
the long term thermal stability of the colloidal barite fluids of the present
invention
Example 7
This test was carried out to show the feasibility of 24 ppg [2.87 g/cm3]
slurries (0.577
Volume fraction). Each fluid contained the following components: fresh water
135.4 g, barite
861.0g, IDSPERSE XT 18.0 g. The barite component was varied in composition
according
to the following table.
Table IV
# API grade Colloidal
barite (%) barite (%)
9 100 0
10 90 10
11 80 20 _
12 75 25
13 60 40
14 0 100
Table V
# Viscosity at various shear
rates (rpm of agitation) : Dial Plastic Yield
reading or "Fann Units" for: Viscosity
Point
600 300 200 117 100 59 30 6 3 mPa.s lb/100ft2
(Pascals)
9 *os 285 157 66 56 26 10 3 2
245 109 67 35 16 13 7 3 2 136 -27(-13)
11
171 78 50 28 23 10 7 3 2 93 -15(-7)
12
115 55 36 19 17 8 5 3 2 60 -5(-2)
13
98 49 34 21 20 14 10 4 3 49 0
14
165 84 58 37 32 22 18 5 3 81 3(-1.5)
* os = off-scale
The results provided table V show that API grade barite due to its particle
size and the
high volume fraction required to achieve high mud weights exhibit dilatancy
i.e. high plastic
and apparent viscosity and negative yield values.
Introduction of fine grade materials tends to stabilize the flow regime keep
it laminar
at higher shear rates: plastic viscosity decreases markedly and yield point
changes from
CA 02598123 2007-08-16
WO 2006/091562 PCT/US2006/006030
negative to positive. No significant increase in low-shear rate viscosity (@ 3
rpm) is caused
by the colloidal barite.
These results show that the colloidal material of this invention may
advantageously be
used in conjunction with conventional API barite.
Example 8
An eighteen (18) pound per gallon [2.15 g/cml slurry of lubricating /
weighting agent
according the present invention was formulated and subsequently contaminated
with a range
of common contaminants and hot rolled at 300 F (148.9 C). The rheological
results of
before (BHR) and after hot rolling (AHR) are presented below. The system shows
excellent
resistance to contaminants, low, controllable rheology and gives fluid loss
control under a
standard API mud test as shown in following table VI: An equivalent set of
fluids were
prepared using API conventional barite without the polymer coating as a
'direct comparison of
the two particle types. (Table VII)
Table VI (New barite)
Viscosity (Fann Units) at various shear rates PV YP Fluid
(rpm of agitation: loss
600 300 200 100 6 3 mPa.s lb/100& ml
(Pascals)
no contaminant BHR 21 11 8 4 1 1 10 1(0.5)
no contaminant AHR 18 10 7 4 1 1 8 2(1) 5.0
+80ppb NaC1BHR 41_ 23 16 10 2 1 18 5(2.5)
+80ppb NaC1 AHR 26 14 10 6 1 1 12 2(1) 16
+30ppb OCMA1BHR 38 , 22 15 9 2 1 16 6(3)
+30ppb OCMA AHR 26 14 10 6 1 1 12 2(1) 6.8
+5p_pb Lime BHR 15 7 5 3 1 1 8 -1(-0.5)
+5ppb Lime AHR 10 5 4 2 1 1 5 0 6.4
1 OCMA = Ocma clay, a fine particle ball clay commonly used to replicate
drilled solids contamination acquired
from shale sediments during drilling
Table VII( Conventional API baritel
Viscosity (Faun Units) at various shear rates PV YP Fluid
(rpm of agitation: loss
600 300 200 100 6 3 mPa. s
lb/100112 ml
_ (Pascals)
no contaminant BHR 22 10 6 3 1 1 12 -2
_ _ _
no contaminant AHR 40 24 19 11 5 4 16 8 Total'
- _ _ _
+80ppb NaC1BHR 27 13 10 6 2 1 14 -1
_ -
+80ppb NaCl AHR 25 16 9 8 1 1 9 7 Total'
16
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CA 02598123 2012-10-23
+30ppb OCMA BHR 69 55 49 43 - 31 26 14 31
+30ppb OCMA AHR 51 36 31 25 18 16 15 21 Total2
+5ppb Lime BHR
26 14 10 6 2 1 12 2
+5ppb Lime AHR 26 14 10 6 1 1 12 2 Total
I - Total fluid loss within 30 seconds
2 - Total fluid loss within 5 minutes.
A comparison of the two sets of data show that the lubricating / weighting
agent
according the present invention (new barite) has considerable fluid loss
control properties
when compared to the API barite. The API barite also shows sensitivity to
drilled solids
contamination whereas the new barite system is more tolerant.
Example 9
An experiment was conducted to demonstrate the ability of the new lubricating
/
weighting agent to formulate drilling muds with densities above 20 pound per
gallon [2.39
g/cm3].
Two twenty two pound per gallon [2.63 g/cm3].mud systems were formulated, the
weighting agents comprised a blend of 35% w/w new barite lubricating /
weighting agent
with 65% w/w API grade barite (Fluid #1) weighting agent and 100% API grade
barite (fluid
TM
#2), both with 11.5 pound per barrel [32.8 kg/m3] STAPLEX 500 (mark of
Schlumberger,
TM
shale stabilizer), 2 pound per barrel [5.7 kg/m3] IDCAP (mark of Schlumberger,
shale
inhibitor), and 3.5 pound per barrel [10 kg/m3] potassium chloride. The other
additives
provide inhibition to the drilling fluid, but here demonstrate the capacity of
the new
formulation to cope with any subsequent polymer additions. The fluid was hot
rolled to 200
F (93.3 C). Results are provided in table VIII.
Table VIII
Viscosity (Fann Units) at various shear rates PV Yield Fluid
(rpm of agitation: ' Point loss
600 300 200 100 6 3 mPa.s lb/100& ml
(Pascals)
Before Hot Rolling (#1) 110 58 46 30 9 _ 8 52 6 (2.9)
After Hot Rolling(#1) 123 70 52 30 9 8 53 17 (8.1)
8.0
Before Hot Rolling (#2) 270 103 55 23 3 2 167 -64 (-32)
After Hot rolling(#2) os 177 110 , 47 7 5 12.0
os : off-scale
The 100% API grade barite has very high plastic viscosity and is in fact
turbulent as
demonstrated by the negative yield point. After hot rolling the theology is so
high that it is
off scale.
17
CA 02598123 2012-10-23
Example 10
This experiment demonstrates the ability of the new lubricating / weighting
agent of
the present invention to lower the viscosity of fluids. The lubricating /
weighting agent is
100% colloidal barite according the present invention. Fluid #15 is based on
synthetic oil
TM
(Ultidrill, Mark of Schlumberger, a linear alpha-olefin having 14 to 16 carbon
atoms). Fluid
TM
#16 is a water-based mud and includes a viscosifier (0.5 ppb IDVIS, Mark of
Schlumberger,
-1-711
a pure xanthan gum polymer) and a fluid loss control agent (6.6 ppb IDFLO Mark
of
Schlumberger). Fluid #15 was hot rolled at 200 F (93.3 C), fluid #16 at 250
F (121.1 C).
After hot rolling results are shown table IX.
Table IX
Viscosity (Faun Units) at various shear rates PV Gels' Yield
(rpm of agitation: Point
600 300 200 100 6 3 inPa.s lbs/100112 lbs/100112
__________________________________________________ (Pascals) (Pascals)
#15 : 13.6 ppg 39 27 23 17 6 5 12 7/11 15
[1.63 g/cm3]
#16 : 14 ppg 53 36 27 17 6 5 17 5/- 19
[1.67 g/cm31
1A measure of the gelling and suspending characteristics of the fluid,
determined at 10 sec/10 min using a Farm
viscosimeter.
Even though the formulation was not optimized, this test makes clear that the
new
lubricating/ weighting agent provides a way to formulate brine analogues
fluids useful for
slimhole applications or coiled tubing drilling fluids. The rheology profile
is improved by the
addition of colloidal particles.
Example 11
An experiment was conducted to demonstrate the ability of the new lubricating
/
weighting agent to formulate completion fluids, were density control and hence
sedimentation stability is a prime factor. The lubricating / weighting agent
is composed of the
new colloidal barite according to the present invention with 50 pound per
barrel [142.65
kg/m3] standard API grade calcium carbonate, which acts as bridging solids.
The 18.6ppg
[2.23 g/cm3] fluid was formulated with 2 pound per barrel [5.7 kg/m3] PTS 200
(mark of
Schlumberger, pH buffer) The static aging tests were carried out at 400 F
(204.4 C) for 72
hours. The results shown in the table below, before (BSA) and after (ASA)
static aging reveal
good stability to sedimentation and theological profile.
18
CA 02598123 2012-10-23
Viscosity (Faun Units) at various shear rates PV YP Free
(rpm of agitation : water *
600 300 200 100 6 3 mPa.s lb/100ft2 ml
(Pascals) ______________________________________________
18.6ppg BSA 37 21 15 11 2 1 16 5(2.5) -
18.6ppg ASA _ 27 14 11 6 1 1 13 1(0.5) 6
*free water is the volume of clear water that appears on top of the fluid. The
remainder of the
fluid has uniform density.
Example 12
This experiment demonstrates the ability of the new lubricating / weighting
agent to
formulate low viscosity fluids and show it's tolerance to pH variations. The
lubricating /
weighting agent is composed of the new colloidal barite according to the
present invention.
The 16ppg [1.91 g/cm3] fluid was formulated with caustic soda to adjust the pH
to the
required level, with the subsequent fluid Theology and API filtration tested.
The results shown
in the table below reveal good stability to pH variation and Theological
profile.
Viscosity (Faun Units) at various shear rates PV Yield Fluid
(rpm of agitation: Point Loss
PH 600 300 200 100 6 3 mPa.s lbs/100ft2 ml
(Pascals)
8.01 14 7 5 3 7 0(0) 8.4
9.03 14 8 5 3 6 2 (1) 8.5
10.04 _ 11 9
7 _9 6 3 8 1(0.5) 7.9
7
10.97 6 3 8 1(0.5) 7.9
12.04 19 10 7 4 1 1 9 1(0.5) 8.1
Example 13
This experiment demonstrates the ability of the new lubricating / weighting
agent to
formulate low rheology HMI' water base fluids. The lubricating / weighting
agent is
composed of the new colloidal barite according to the present invention, with
10 pounds per
TM
barrel [28.53 kg/m3] CALOTEMP (mark of Schlumberger, fluid loss additive) and
1 pound
TM
per barrel [2.85 kg/m3] PTS 200 (mark of Schlumberger, pH buffer). The 17ppg
[2.04 g/m3]
and 18ppg [2.16 gicm3] fluids were static aged for 72 hours at 250 F (121 C).
The results
shown in the table below reveal good stability to sedimentation and low
rheological profile
with the subsequent filtration tested.
19
CA 02598123 2013-05-28
Density PH Viscosity (Farm Units) at various shear rates PV Yield
Free Fluid
(rpm of agitation : Point Water Loss
PPg 600 300 200 100 6 3 mPa.s lbs/100ft2 ml ml
(Pascals)
17 7.4 28 16 11 6 1 1 12 4(2) 10 3.1
18 7.5 42 23 16 10 1 1 19 4(2) , 6 3.4
Example 14
The following examples illustrate the ability of the fluids formulated
utilizing the
polymer coated colloidal solid materials of the present invention to reduce
the drill string
torque and thus act as a lubricating agent.
Field test 1) A 311-nun section of a high temperature, high pressure well was
drilled
at a 60 degree inclination to 5,121 in using a 1.8 kg/L (15 lb/gal) invert oil
(paraffin) based
drilling fluid incorporating the polymer coated, colloidal solids of the
present invention. The
fluid was formulated as an 80:20 oil: water ratio drilling fluid with the
following additional
= components: Emul HT (27.0 lb/bbl); Lime 8.1 lb/bbl; EMI-783 (3.2 lb/bbl);
EMI-603 (3.5
lb/bbl); VG Supreme (1.8 lb/bbl). the fluid exhibited the following
properties:
Fluid Properties
Fluid weight (1b/gal) 14.58¨ 15.08
Viscosity at 100 rpm (lbs/100ft2) 11-17
Viscosity at 3 rpm (lbs/100ft2) 2-3
Electrical Stability (Volts) 555-898
HTIIP fluid loss (cc/30 min) 2.0-3.4
LOS (lbs/bbl) 10-70
The following observations regarding the fluid were made: the fluid system
proved
stable to maximum downhole temperature of 166 . C; in long static periods up
to 82 hours
duration no evidence of cutting fill or mud weight variation; Plastic
Viscosity was 25 cps
initially and gradually increased to 41 cps by the end of the section as both
mud weight and
low gravity solids increased; yield point remained unchanged through the
section varying
between 3 and 4 1 lbs/100112. Surprisingly, when compared with a
conventionally formulated
fluid used to drill offset wells, the torque required to rotate the drilling
string components was
reduced by 22% over the entire interval and up to 25% in the deviated section.
CA 02598123 2013-05-28
Field test 2) An extended reach 215.9 ram-section was drilled offshore in the
North
Sea in the reservoir using a 1.6 kg/L (13 lb / gal) oil-based drilling fluid
incorporating the
polymer coated, colloidal solids of the present invention and having the
following
formulation:
PRODUCT Fluid
PCC barite lbs/bbl 175.0
Freshwater bbl 0.18
EDC99DW Base bbl 0.5
oil
Lime lbs/bbl 7
* Versatro I lbs/bbl 2.8
* Bentone 128 lbs/bbl 4.6
* Emul HT lbs/bbl 17.5
* Trademark
The fluid exhibited the following properties:
Viscosity (Fann Units) at various shear rates PV Yield Fluid
(rpm of agitation: Point loss
600 300 200 100 6 3 cps lb/100ft2 ml
(Pascals)
62 36 26 16 4 3 26 10 2.1
The section was drilled with a mud weight of 13.2 lb/gal and an oil:water
ratio of
between 72:28 and 84:16. Water activity varied between 0.89 and 0.82 with the
electrical
stability controlled between 675 and 706 Volts. The observations were: no sag
or settlement
or change in the mud weight occurred; an aggressive (i.e. finer screen) solids
separation
program could be used; no differential sticking with 2,321 psi overbalance
pressure in the
lower part of the reservoir. The fluid system reduced the torque in the open
hole by about
28% when compared to the offsets drilled with convention drilling fluids.
One of ordinary skill in the art should understand and appreciate in view of
the above
data that fluids including the polymer dispersant coated colloidal barite of
the present
invention reduced the torque required to rotate the drilling string when
compared to
conventionally formulated fluids.
In view of the above disclosure, one of ordinary skill in the art should
understand and
appreciate that one illustrative embodiment of the present invention includes
a method of
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WO 2006/091562 PCT/US2006/006030
reducing the torque of a drill string utilized to drill subterranean wells. In
one such illustrative
method, the method includes, injecting into the drilling fluid a composition
including a base
fluid, and a polymer coated colloidal solid material. The polymer coated
colloidal solid
material includes: a solid particle having an weight average particle diameter
(d50) of less
than ten microns, and a polymeric dispersing agent absorbed to the surface of
the solid
particle during the course of the cominution process. The base fluid utilized
in the above
illustrative embodiment can be an aqueous fluid or an oleaginous fluid and
preferably is
selected from: water, brine, diesel oil, mineral oil, white oil, n-alkanes,
synthetic oils,
saturated and unsaturated poly(alpha-olefins), esters of fatty acid carboxylic
acids and
combinations and mixtures of these and similar fluids that should be apparent
to one of skill
in the art. Suitable and illustrative colloidal solids are selected such that
the solid particles are
composed of a material of specific gravity of at least 2.68 and preferably are
selected from
barium sulfate (barite), calcium carbonate, dolomite, ilmenite, hematite,
olivine, siderite,
strontium sulfate, combinations and mixtures of these and other suitable
materials that should
be well known to one of skill in the art. In one preferred and illustrative
embodiment, the
polymer coated colloidal solid material has a weight average particle diameter
(d50) less than
2.0 microns. Another illustrative embodiment contains at least 60% of the
solid particles have
a diameter less than 2 microns or alternatively more than 25% of the solid
particles have a
diameter less than 2 microns. The polymeric dispersing agent utilized in one
illustrative and
preferred embodiment is a polymer of molecular weight of at least 2,000
Daltons. In another
more preferred and illustrative embodiment, the polymeric dispersing agent is
a water soluble
polymer is a homopolymer or copolymer of monomers selected from the group
comprising:
acrylic acid, itaconic acid, maleic acid or anhydride, hydroxypropyl acrylate
vinylsulphonic
acid, acrylamido 2-propane sulphonic acid, acrylamide, styrene sulphonic acid,
acrylic
phosphate esters, methyl vinyl ether and vinyl acetate, and wherein the acid
monomers may
also be neutralized to a salt.
In addition to the above illustrative method, the present invention is also
directed to a
lubricating composition that includes a base fluid and a polymer coated
colloidal solid
material . The polymer coated colloidal solid material is formulated so as to
include a solid
particle having an weight average particle diameter (d50) of less than ten
microns; and a
polymeric dispersing agent coated onto the surface of the solid particle. One
illustrative
embodiment includes a base fluid that is either an aqueous fluid or an
oleaginous fluid and
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CA 02598123 2007-08-16
WO 2006/091562 PCT/US2006/006030
preferably is selected from, water, brine, diesel oil, mineral oil, white oil,
n-alkanes, synthetic
oils, saturated and unsaturated poly(alpha-olefins), esters of fatty acid
carboxylic acids,
combinations and mixtures of these and other similar fluids that should be
apparent to one of
skill in the art. It is preferred in one illustrative embodiment that the
solid particles are
composed of a material of specific gravity of at least 2.68 and more
preferably that the
colloidal solid is selected from barium sulfate (barite), calcium carbonate,
dolomite, ilmenite,
hematite, olivine, siderite, strontium sulfate and combinations and mixtures
of these and
other similar solids that should be apparent to one of skill in the art. The
polymer coated
colloidal solid material utilized in one illustrative and preferred embodiment
has a weight
average particle diameter (d50) less than 2.0 microns. Another illustrative
embodiment
contains at least 60% of the solid particles have a diameter less than 2
microns or
alternatively more than 25% of the solid particles have a diameter less than 2
microns. A
polymeric dispersing agent is utilized in a preferred and illustrative
embodiment, and is
selected such that the polymer preferably has a molecular weight of at least
2,000 Daltons.
Alternatively the illustrative polymeric dispersing agent may be a water
soluble polymer is a
homopolymer or copolymer of monomers selected from the group comprising:
acrylic acid,
itaconic acid, maleic acid or anhydride, hydroxypropyl acrylate vinylsulphonic
acid,
acrylamido 2-propane sulphonic acid, acrylamide, styrene sulphonic acid,
acrylic phosphate
esters, methyl vinyl ether and vinyl acetate, and wherein the acid monomers
may also be
neutralized to a salt.
One of skill in the art should understand and appreciate that the present
invention
further includes a method of making the polymer coated colloidal solid
material described
above. Such an illustrative method includes grinding a solid particulate
material and a
polymeric dispersing agent for a sufficient time to achieve an weight average
particle
diameter (d50) of less than ten microns; and so that the polymeric dispersing
agent is absorbed
to the surface of the solid particle. Preferably the illustrative grinding
process is carried out
in the presence of a base fluid. The base fluid utilized in one illustrative
embodiment is
either an aqueous fluid or an oleaginous fluid and preferably is selected
from, water, brine,
diesel oil, mineral oil, white oil, n-alkanes, synthetic oils, saturated and
unsaturated
poly(alpha-olefins), esters of fatty acid carboxylic acids and combinations
thereof. In one
illustrative embodiment the solid particulate material is selected from
materials having of
specific gravity of at least 2.68 and preferably the solid particulate
material is selected from
23
CA 02598123 2012-10-23
barium sulfate (barite), calcium carbonate, dolOmite, ilmenite, hematite,
olivine, siderite,
strontium sulfate, combinations and mixtures of these and other similar solids
that should be
apparent to one of skill in the art. The method of the present invention
involves the grinding
the solid in the presence of a polymeric dispersing agent. Preferably this
polymeric
dispersing agent is a polymer of molecular weight of at least 2,000 Daltons.
The polymeric
dispersing agent in one preferred and illustrative agent is a water soluble
polymer that is a
homopolymer or copolymer of monomers selected from the group comprising:
acrylic acid,
itaconic acid, maleic acid or anhydride, hydroxypropyl aerylate vinylsulphonic
acid,
acrylamido 2-propane sulphonic acid, acrylamide, styrene sulphonic acid,
acrylic phosphate
esters, methyl vinyl ether and vinyl acetate, and wherein the acid monomers
may also be
neutralised to a salt.
It should also be appreciated by one of skill in the art that the product of
the above
illustrative process is considered part of the present invention. As such one
such preferred
embodiment includes the product of the above illustrative process in which the
polymer
coated colloidal solid material has a weight average particle diameter (d50)
less than 2.0
microns. Another illustrative embodiment contains at least 60% of the solid
particles have a
diameter less than 2 microns or alternatively more than 25% of the solid
particles have a
diameter less than 2 microns.
The scope of the claims should not be limited by the preferred embodiments set
forth in the description, but should be given the broadest interpretation
consistent with
the description as a whole.
24
