Note: Descriptions are shown in the official language in which they were submitted.
1C~855~8
Background of the Invention
In drilling oil and gas wells and the like by the
rotary drilling method, a string of drill pipe having a
drill bit mounted on the lower end thereof is rotated to
cause the cutting elements or "teeth" on the bit to drill
the hole. Drilling fluid is circulated through the drill
pipe emerging through openings in the drill bit returning to
the surface in the annular space between the drill pipe and
the walls of the borehole. Such circulation is substan-
tially continuous while drilling, being interrupted by
essential operations, such as adding an additional section
of drill pipe at the top of the drill string or when the
entire string of drill pipe is pulled from the wellbore to
replace a worn-out drill bit.
In addition to removing drill cuttings from the
hole the drilling fluid performs many functions vital to a
successful drilling operation. These functions have been
discussed by Rodgers ("Composition and Properties of Oil
Well Drilling Fluids", Water F. Rodgers, pps. 10-18, Gulf
Publishing Company, Houston, Texas, 1963).
In the drilling of wells sand contamination of
drill fluid results from the drilling of sandy shales and
sandstones. Sand is a highly undesirable mechanical con-
taminant because sand is considerably harder than most steels
and its abrasive qualities cause rapid and excessive wear of
pipe elbows and reciprocating and centrifugal pumps. Higher
sand contents in drilling fluids increase drill pipe fric-
tion resulting in increasing rotating torque and drag. The
rapid settling of sand may even stick drill pipe in the hole
or cause core barrels to fail to operate. Sand may also
~`~
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10~35S~8
bridge outside the casing and prevent a satisfactory cement-
ing operation. For these reasons, drilling operators make
every reasonable effort to keep sand out of drilling fluids;
sand contents of 2 or 3 percent can be tolerated but if the
percentage rises, steps must be taken to reduce the sand
content.
Crooked holes, including doglegs, corkscrews, and
boreholes deviating from the vertical are a primary cause of
excessive torque and drag.
It is important to recognize that ordinary crooked
holes can be significantly minimized by good drilling engi-
neering practice. However, current economic and environ-
mental considerations dictate that an increasing number of
wells, both on land and offshore, be deliberately deviated.
In such deviated holes where the borehole is at an angle
from the vertical, the drill string must rest against the
side of the wellbore. This lateral force significantly
increases normal rotating torque and drag over that of
vertical drilling, notwithstanding whether the drilling
fluid is oil base or water base. This frictional effect
becomes very important in current offshore drilling where 20
to 22 wells are drilled from a single platform and the
deviation of the wellbore from vertical is sixty degrees or
more.
The rate at which the hole can be made depends in
part upon the rate of rotation of the drill pipe and upon
the "weight on bottom" or force with which the drill bit
acts on the bottom of the hole. This force is controlled by
addition of drill collars which are pipes of larger diameter
and greater mass than drill pipe. It is, therefore, very
1~855~8
desirable to minimize friction upon the drill string and
maximize horsepower at the bit.
Clearly, high rotational friction or high drag
friction in removing a string of drill pipe miles in length
for the purpose of periodically changing bits can severely
limit the ability and efficiency of a given derrick to drill
deep wells and also increases the cost of drilling.
In present day offshore drilling there are areas
where basic rig overhead costs are $50,000 or more per day.
It is, therefore, economically desirable to drill as rapidly
as possible with minimum equipment and power.
Current drilling fluid technology predicated upon
maintaining low clay solids in aqueous drilling muds also
contributes to increasing rotating torque and pipe drag.
Traditional drilling muds contained an appreciable component
of hydrated bentonite which acted as a borehole lubricant.
With the advent of solids control equipment and the delib-
erate reduction in bentonite content for the purpose of
increasing penetration rate and minimizing formation damage,
this lubricating effect of bentonite has been greatly
reduced.
Even with traditional bentonitic drilling fluids
and techniques, the friction of running pipe into and out of
the hole, the increases in torque and power to rotate the
drill pipe, the wear and stress on drill pipe and danger of
twist offs of the drill pipe has caused numerous drilling
fluid lubricants to be investigated.
The prior art shows such lubricant drilling addi-
tives to be composed of saturated or unsaturated fatty acids,
mixtures of fatty acids and resin acids, naturally occurring
10855~8
triglycerides, stearates of aluminum and other metals, fatty
amides, sulfurized vegetable oils, sulfated fatty acids and
fatty alcohols and mixtures thereof and their solutions or
emulsions in water or primary alcohols of 12 to 15 carbon
atoms.
In general all sorts of soft solids including
graphite, blown asphalts, gilsonite, soaps, plastics (such
as polyethylene or teflon particle dispersions), have been
proposed as drilling fluid lubricants. A wide variety of
such substances that have a known performance history as
boundary or hydrodynamic lubricants in industry have been
introduced as drilling fluid lubricant additives, as for
example in United States Patents 2,773,030; 2,773,031;
3,014,862; 3,027,324; 3,047,493; 3,047,494; 3,048,538;
3,214,374; 3,242,160; 3,275,551; 3,340,188; 3,372,112;
3,377,276; and 3,761,410.
Ground walnut hulls are commonly used in drilling
fluids for lost circulation control. It is, however, a
matter of common knowledge that when angular walnut hull
fragments are introduced into a circulating drilling fluid
that some reduction in rotating torque occurs and that
sticking tendencies of the drill pipe are reduced. It is
further known that this lubricating effect decreases with
time, presumably because of chemical disintegration of the
nut hulls in the circulating drilling fluid. It has been
further shown in the prior art, specifically U. S. Patent
2,943,679, Table V, that the lubricity effect of walnut
shells is maximum in the 4 to 10 mesh size range and dimin-
ishes rapidly in sizes below 80 mesh.
Unfortunately, the use of ground walnut hulls
necessitates the by-passing of the mud screens resulting in
1~85598
an undesirable build-up of clay solids in the drilling fluid.
Furthermore, the incorporation of walnut hulls in the drill-
ing fluid results in an increase in pump pressure, sometimes
to such an extent that formations may be fractured thus
inducing lost circulation. Both high clay solids and walnut
hulls act to decrease penetration rate.
The 1977-78 Guide to Drilling, Workover and Comple-
tion Fluids, Gulf Publishing Company, Houston, Texas, lists
some sixty-two proprietary drilling fluid lubricant additives
offered by various drilling fluid additive suppliers. All
of these compounds, composed of the above cited oils and
soft solids lubricating materials, attest to the interest
in, and need for, practical and effective means of reducing
drag and rotating tor~ue in the rotary drilling of wells.
The design and formulation of lubricant additives
is made difficult by the fact that there are no standard
methods of evaluating the effectiveness of such additives by
laboratory tests.
Such testing was recently studied by a task group
of the Committee on Standardization of Drilling Fluid Mate-
rials of the American Petroleum Institute. The variables
involved, it was found, made such tests of little value in
predicting the actual field performance of a given additive.
Thus, despite of the obvious desirability of meaningful
testing of lubricant additives, the task group was disbanded.
Regardless of the effectiveness of a drilling
fluid lubricant in reducing friction in a laboratory fric-
tion test or in the field, the additive can be useful only
if it meets criteria of practicality. It must not impair
necessary drilling fluid properties of chemical or physical
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nature. It is recognized in the prior art that a lubricant
may have limitations which seriously effect its usefulness.
For example, a lubricant additive must have tolerance to the
variation in pH and electrolytes normally encountered while
drilling. Some additives curdle and ball up in the presence
of calcium and are removed on the shale shaker screens.
Other additives will cause oil wetting of barite in water
base fluids or water wetting of barite in oil base fluids.
In either case, the barite may objectionably settle out in
low weight fluids or cause objectionably high viscosities in
high weight fluids. Some additives cause foaming with the
result that the mud becomes gas cut and unpumpable in the
reciprocating mud pumps. Other additives resist wetting out
and dispersion in the drilling fluid and float on the mud
pits or are removed and discarded by the screens. Some
additives fluoresce in ultraviolet light and thus interfere
with certain well logging operations. Some of the proposed
additives are effective only in uneconomical concentrations.
Other additives may be potentially toxic, carcinogenic or
environmentally undesirable.
Description of the Preferred Embodiment
Contrary to expectations based upon prior art con-
siderations, I have found that when hard, non-softening
minute solid glass spheres (beads) are introduced into a
drilling fluid that a surprising reduction in rotating
torque and drag occurs in rotary drilling of oil and gas
wells. Considering the a priori unpredictable properties of
drilling fluid additives it would not be anticipated that
such glass beads would in fact function as a friction
reducer in drilling fluids.
1(~855~8
The glass beads of my inVentiQn are essentially
spherical, devoid of gas inclusions, composed of chemically
resistant lime-silica glass having a hardness of 5.5 on the
Moh's scale and a particle size of 88 to 44 microns (through
170 mesh on 325 mesh screens). If such beads are added to a
circulating drilling fluid through the chemical hopper or
otherwise in amounts ranging from 2 pounds to 8 pounds per
barrel of oil base or water base drilling fluid, a signifi-
cant reduction in rotating torque and drag results.
The friction reducing effect of the glass beads
may be utilized in fresh water, calcium inhibited, salt or
sea water aqueous drilling fluid at all suitable pH ranges.
These glass beads have a softening point of 1,346F. (730C)
and a melting point of 1,600F. (871C). Inasmuch as drill-
ing fluids infrequently attain a temperature of 500F.
(260C), no melting or softening of the glass beads would be
expected in drilling operations.
The hardness of the glass beads is considerably -
less than drilling rig steels (530 knoop for the beads, 800
to 1,670 knoop for the steels). The degree of hardness of
the beads is such that it is not abrasive to drilling equip-
ment but it is distinctly not a soft solid, such as are con-
ventionally used as lubricants. Materials with a hardness
less than 3.0 tend to abrade too rapidly in a circulating
drilling fluid. The established industrial use of the
subject glass beads in plastic injection molding composi-
tions in 40% loadings without causing extrusion die erosion
is a further indication of the non-abrasive nature of the
glass beads of my invention.
The solid nature of the subject beads and absence
of gas inclusions contributes to the resistance of the beads
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1(~855~3
to comminution by the shear forces present in the drilling
operation.
The nature of the glass beads facilitates their
incorporation into drilling fluids resulting in a non-
flocculant dispersion.
The particle size distribution of the sub~ect
beads (170-325 mesh) enables them to be recirculated without
removal by 80 mesh mud screens. Minus 200 mesh beads may be
used if desired.
Neither laboratory or field use has found the
incorporation of the non-toxic subject glass beads to cause
any adverse side effects on drilling fluid properties.
It is not fully understood how the method of this
invention accomplishes friction reducing results by materi-
als so strickingly different from the prior art of drilling
fluid lubricant additives. However, although it is not
intended that this invention be bound by any speculations or
theoretical explanations, certain characteristics relevant
to the physical-chemical properties of glass beads should be
noted.
The glass beads of my invention do not qualify as
surface active agents and do not lower surface or interfacial
tensions of liquids or act as wetting agents. Neither are
they classifiable as soft solids capable of reducing fric-
tion by full fluid flow or hydrostatic mechanisms. It may
be, nevertheless, that the micro glass beads function as a
mechanical analog of chemical E.P. lubricants (Browning,
W. C., in "Composition and Properties of Oil Well Drilling
Fluids", Walter F. Rodgers, pps. 627-630, Gulf Publishing
Company, Houston, Texas, 1963).
1~85598
The unexpected lubricating effect of glass micro-
spheres in drilling fluids, however, may be a surface area
related effect in which the "ice" structure of bound water
at the glass surface produces a result somewhat similar to
metal stearates in ordinary grease compositions ("Water --
A Comprehensive Treatise", Felix Frank, Ed. Vol. 5, Plenum
Press, New York, 1975; Williams, P. S., Jour. Applied Chem-
istry [London] 3, 120 ~1953]; Sweeny, K. H. and Geckler,
R. D., Jour. Applied Phys. 25, 1135 ~1935]).
Material
The preferred glass beads of my invention are
Ballontoni Impact Beads manufactured under U. S. Patents
2,334,578; 2,619,776; 2,945,326; and 2,947,115.
To function as a practical and useful additive to
reduce rotating torque and pipe drag in rotary drilling, it
is essential that the solid glass beads be as nearly 100%
spherical as possible. Roundness is controlled during manu-
facture according to ASTM 1155-53.
The preferred size range of the glass beads of my
invention is 170 to 325 U. S. Standard Sieve. Size is deter-
mined according to Mil Spc G-9954 A. The maximum allowable
broken or angular particles are 3% by count. The beads are
solid without gas inclusions. The amount of accidental gas
inclusion is microscopically determined and limited during
manufacture according to Mil G-9954 using a 1.50 refractive
index fluid. The true density of the beads is maintained
within 2.45-2.55 gm/cc3, and the hardness is 5.5 on the
Moh's scale (530 knoop).
To assure low chemical reactivity of the silica
lime glass used in bead manufacture, the silica content is
maintained above 67% as determined by ASTM C-169-57T.
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The chemical durability of the subject glass beads
has been reported by Keppel and Walker (Ind. Eng. Chem.
Product Research, _, 132 [1962]).
The preferred glass beads of my invention are
non-toxic chemically and physically, and meet all non-
hazardous industrial use requirements including U. S. mili-
tary specifications.
Most particularly, the subject solid glass micro-
spheres have been found to be compatible with the chemistry
of water base and oil base drilling fluids and to cause no
undesirable chemical or physical side effects on drilling
fluid properties.
The usefulness and practicality of my invention is
illustrated in the following examples of actual field tests
wherein the method of my invention was used to reduce
rotating torque and drag during the rotary drilling of oil
wells.
EXAMPLE I
A well drilled in Harris County, Texas, with a
projected depth of 9,471 feet deviated at 3,000 feet to an
angle of 19-1/2 degrees. The well was corrected back to
vertical at 8,356 feet resulting in a borehole with an "S"
shaped double curve. The glass beads of my invention were
added at 8,800 feet. The drag on pipe being pulled from the
hole before adding the beads was 37,000 pounds. After add-
ing 4 pounds of beads per barrel of water base drilling mud,
the drag was reduced to 25,000 pounds, a reduction of 32.4%
in drag. Rotating torque was also reduced by 6.25%.
The drilling fluid before adding the beads had a
viscosity of 52 centipoise and an API fluid loss of 6.2 ml.
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1~855~8
After adding the beads the viscosity was 52 centipoise and
the water loss was 6.0 ml. The addition of the beads,
therefore, was essentially without effect upon the viscosity
and filtration rate of the drilling fluid.
EXAMPLE II
A well was drilled offshore Louisiana with an oil
base drilling fluid. At 16,143 feet of depth, 4 pounds per
barrel of the glass beads of my invention were added to the
oil base drilling fluid. The rotating torque before adding
the beads was recorded as 560 amperes, after adding the
beads a rotating torque of 490 amperes was recorded, a
reduction of 12.5~.
The oil base fluid before addition of the glass
beads had a viscosity of 61 cp, after addition of the beads
the viscosity was 61 cp. Thus in contrast to chemical drill-
ing fluid lubricants, the glass beads of my invention have a
demonstrable effectiveness in both water base and oil base
drilling fluids.
EXAMPLE III
A well projected to 10,000 feet in the North
Dryersdale Field in Harris County, Texas deviated at 2,000
feet to an angle of 28 degrees and was corrected back to
vertical at 8,643 feet. This reverse curvature caused
excessive drag and rotating torque problems. Four pounds
per barrel of the glass beads of my invention were added to
the water base drilling fluid at 7,253 feet. After addition
of the glass beads the upward drag was reduced from 50,000
pounds to 35,000 pounds, a reduction of 30%. Rotating
torque was reduced 50% to 66%. No significant change in mud
properties was noted.
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EXAMPLE IV
A 9,600 foot well drilled in the Texas Gulf region
with a Lignosulfonate-Lignite treated drilling fluid, devi-
ated at 4,000 feet attaining a 17 degree angle and was then
corrected back to vertical at 8,122 feet. The drilling
fluid was treated with 4 pounds per barrel of the glass
beads of my invention at a depth of 8,200 feet. Before
addition of the glass beads the indicated torque ranged from
125 to 130 and the upward drag ranged from 15,000 pounds to
20,000 pounds. After addition of the glass beads the indi-
cated torque was reduced to 90 and the upward drag was
reduced to a range of 8,000 pounds to 10,000 pounds. The
torque and drag reduction thus effected by addition of 4
pounds of the glass beads of my invention per barrel of
water base drilling fluid in this instance amounted to 29.5%
for torque and 46.5% to 50~ for drag.
Drilling fluid viscosity remained unchanged and
API filtration rate was 6.4 ml before addition of the beads
and 6.0 ml after addition of the glass beads of my invention.
By the preceding examples and additional field
usage, it has been demonstrated that the Ballontoni glass
beads of my invention, which are essentially spherical,
chemically resistant lime-silica glass beads having a hard-
ness of 5.5 on the Moh's scale and a particle size range of
88 microns to 44 microns, when used in amounts ranging from
2 pounds to 8 pounds per barrel of water base or oil base
drilling fluids, will effectively reduce rotating torque and
drag in the rotary drilling of oil and gas wells.
The glass beads of my invention have been shown to
be chemically and physically compatible with oil well
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drilling fluids causing no deleterious effects on drilling
fluid properties.
The compatibility of the glass beads of my inven-
tion with oil or water base drilling fluids means that they
may be compounded as an additive blend, or used in conjunc-
tion with surface active and soft solid types of drilling
fluid lubricant additives. These micro-spherical glass
beads may also be blended in obvious ways with other drill-
ing fluid additives, such as thinners (dispersing agents),
viscosifiers, bentonite, fluid loss control additives and
lost circulation control materials to effect reduction in
torque and drag.
Thus, while certain embodiments of my invention
have been described for illustrative purposes, various other
modifications will be apparent to those skilled in the art
in view of the disclosure. Such modifications are within
the spirit and scope of the invention.
