Method of reducing drag and rotating torque in the rotary drilling of oil and gas wells

A method of reducing drag and rotating torque in the rotary drilling of oil and gas wells comprising the incorporation of quantities of minute spherical glass beads in a liquid drilling fluid.

CROSS-REFERENCE TO RELATED APPLICATION 
Cross-reference is hereby made to application Ser. No. 739,657 filed Nov. 
8, 1976, and now abandoned, entitled "Drilling Mud Additive." 
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 substantially 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 contaminant 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 friction 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 
bridge outside the casing and prevent a satisfactory cementing 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 engineering practice. However, 
current economic and environmental 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 to drill collars which are pipes of larger diameter 
and greater mass than drill pipe. It is, therefore, very 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 deliberate 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 additives to be composed of 
saturated or unsaturated fatty acids, mixtures of fatty acids and resin 
acids, naturally occurring 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 U.S. Pat. Nos. 
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. Pat. 
No. 2,943,679, Table V, that the lubricity effect of walnut shells is 
maximum in the 4 to 10 mesh size range and diminishes rapidly in sizes 
below 80 mesh. 
Unfortunately, the use of ground walnut hulls necessitates the by-passing 
of the mud screens resulting in an undesirable build-up of clay solids in 
the drilling fluid. Furthermore, the incorporation of walnut hulls in the 
drilling 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 Completion Fluids, Gulf 
Publishing Company, Houston, Texas, lists some 62 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 torque 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 Materials 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 friction 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 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 considerations, 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. 
The glass beads of my invention 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 significant 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 
1,346.degree. F. (730.degree. C.) and a melting point of 1,600.degree. F. 
(871.degree. C.). Inasmuch as drilling fluids infrequently attain a 
temperature of 500.degree. F. (260.degree. C.), 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 equipment but it is distinctly not a soft solid, such as are 
conventionally 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 compositions 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 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 subject 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 materials so strinkingly 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 
friction 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). 
The unexpected lubricating effect of glass microspheres 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 Chemistry (London) 3, 120 (1953); Sweeny, 
K. H. and Geckler, R. D., Jour. Applied Phys. 25, 1135 (1954). 
MATERIAL 
The preferred glass beads of my invention are Ballontoni Impact Beads 
manufactured under U.S. Pat. Nos. 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 manufacture 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 determined 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/cc.sup.3, 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. 
The chemical durability of the subject glass beads has been reported by 
Keppel and Walker (Ind. Eng. Chem. Product Research, 1, 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. military 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.degree.. The well was 
corrected back to vertical at 8,356 feet resulting in a borehole with an 
"S" shape 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 adding 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. 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 drilling 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 
Country, Texas deviated at 2,000 feet to an angle of 28.degree. and was 
corrected back to vertical at 8,643 feet. This reverse curvature caused 
excessive drag and rotating torque problems. 4 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. 
EXAMPLE IV 
A 9,600 foot well drilled in the Texas Gulf region with a 
Lignosulfonate-Lignite treated drilling fluid, deviated at 4,000 feet 
attaining at 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 indicated 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 hardness 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 drilling fluids causing no deleterious 
effects on drilling fluid properties. 
The compatibility of the glass beads of my invention with oil or water base 
drilling fluids means that they may be compounded as an additive blend, or 
used in conjunction 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 drilling 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.