Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a new and :improved
method for reducing torque, drag, and wear on casing and
drill string~ used in the drilling of an oil well.
There are other important features relating thereto,
some of which are set forth more fully hereinbelow in
the specification.
It is suggested in U. S. Patent 3,216,933,
issued November 9, 1956 to Park et al, that hard particu- -
late materials be employed in drilling fluid to prevent
sticking of drill pipe. ~he examples given of such mat- -
erials are steel shot, aluminum shot, sand, walnut shells, ~-
plastic and the like. Steel and aluminum shot have rela-
tively high specific gravities and will tend to settle
ou-t in muds of normal weight. This can be particularly
troublesome when circulation ceases for one reason or
another because there is then the possibility that the
shot will settle out of the mud in the drill string into
the bit. In certain cases, this can result in plugging of
the bit. U. S. Patent 2,943,679, issued July 5, 1960 to
Scott, Jr. et al, suggests the use of walnut shells and hard
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pla~tic~ in a drilling fluic~-~or decrea~ing the frictional drag
on a drilling string. However, in both patents, these particu-
late materials are descrlbed a.~ being ~ground~ and hence are
necessarily irregular in shape.
sriefly~ the present invention relate~ to a new and
improved method in the use o~ plastic beads or spheres in a well
to reduce the friction in th0 well bore occurring between the
rotating drill string and dri~f bit and the sides of the well
bore and/or well bore casing adjacent thereto.
In accordance with a broad aspect of the invention,
~here is provided the method of drilling a well comprising
rotating a drill string to cut a bore hold in the earth;
circulatin~ a drilling mud down through the drill string ~ ;
and thence up to the annulu~ between the drill string and the
wall of the hole.
adding solid pla~tic beads to the drilling mud to prevent
torque from elevating to an undesirably high level
said beads being smooth-surface spheres with a screen si.ze
within the range of 10 to 100 mesh;
said spheres being made of a plastic material (i) having
a specific gravity within the range of about 1.1 to about l~S,
(ii) being solid, insoluble in oil and water and stable under
well condition~ both chemically and physically and (iii) hav-
ing phy~ical properties such that there i9 no substantial
crushing of the beads during the drilling operation~
A drilling mud is a mixture of water, clays and
various treating agenks which control the physical or rheo~
logical properties of the drilling mud in a well bore.
In the ~rilling of a well, the obvious objective is
to normally produce hydrocarbons, water, or the like and the
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drilling mud ~erves the function o~ removing the chip~ or
cuttings, which are produced by the rotatîng drill bit, rom
the well bore by circulating drilling mud down from the
surface of the well through the drill string and out through
openings in the drill bit such that the drilling mud iB then
circulated upwardly in the annulus between the side of the
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well bore and the rotating drill strincJ.
One of the objectives of a drilling mud 1~
to reduce friction or provide a lubricating medium for
the drill hit and the drill pipe to work in while
drillin~ the well bore.
Friction is normally defined as a relative
r~sistance to motion of touching suraces. In the
~rilling of well ~ores, friction must be overc~me by
lubricating and thus enabling the surfaces which are
creating undesirable friction to appropriately move or
glide over one another. Some materials which are
presently being considered as lubricating materials
for use with drilling mud to help in reducing friction
are water, diesel oil, vegetable oil, detergents,
bentonite clays, alcohols, gilsonite, a~phaltice
materials, cellulose materials, polymers, dextrose
materials, glycerins and amines.
Applicant has found that the addition of
plastice beads~ of the character more fully described
below, to a drilling mud substantially reduces the
friction between tha drill bit, drill string and the
well bore. Thus, according to applicant's method, the
drill string is rotated to cut a bore hole into the
earth while circulating a drilling fluid down through
the drill string and thence up to the annulus between
the drill string and the wall of the hole. While this
is occurring, the torque required to rotate the drill
string is observed and when the torque becomes
undesirably high, sufficient of the plastic beads are
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added to reduce the torque.
In many instances, the optimum amount o~
plastic beads will be determined in the field on a
well to well basis. Thus, if a clriller observes
that the torque is increasiny to an undesirably high
level, he can begin adding heads until the torque is
reduced to a level which is accep-table to him. Normally,
a minimum addition and maintenance of four pound per
barrel (1.5 percent by volume) of the beads in the mud
will he required to cause a substantial reduction in
torque. Adding and maintaining amounts greater than
four pounds yer barrel will, in many cases, affect a
further reduction in torque. The maximum amount which
can be added or maintained is dependent upon economics
in that, for any given well, the cost of adding addi-
tional beads is not justified by the further reduction
in torque.
It will be appreciated that the concentration
of beads in the mud cake may be higher ~han that added
to or maintained in the mud inasmuch as the beads tend
to concentrate in the mud cake. One la~oratory test
has indicated that effective torque reduction is
accomplished only after a bead concentration in the mud
cake has exceeded an equivalent of 30 pounds per barrel.
Also, in this particular in~tance, additions beyond an
equivalent of 40 pounds per barrel does not materially
reduce the torque. When a well being drilled without
the beads being present encounters excessive torque~
the well can be "slug" treated, as by adding 10 pounds
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per harrel o~ the beads, to rapidly reduce the torque
and then the lowered torque can be maintained by main-
taininy about 4 ~ounds per barrel of l)eads in thc mud
whlle drilling ahead.
The size of the beads can vary over a .sub-
stantial ranye such as from 10 to 100 mesh (Tyler
standard screen size). A ~referred range is 40 to 60
rnesh. The preferred bead is one that is available
commercially and consists of a copolymer of divinyl
benzene and styrene. These beads exist in the size
range of 10 to 100 mesh. The maximum size of the bead
should be such that the beads will pass through the
shale shaker. The particle size distribution within
these ranges is not usually of sufficient significance
to warrant any particular attention.
The chemical composition and polymeric
structure of the beads should be such that they will
not crush in actual operation in tha well. They must
be solid; insoluble in oil and water; be stable at
bottom hole temperatures ranging up to, for example,
250 degrees F.; be inert, both chemically and phy~ically,
to well fluids; and should have a specific ~ravity
within the range of 1.1 to l.S. In this latter aonnection,
beads having a specific gravity substantially greater
than l.S may tend to settle out in the lighter weight
drilling muds in the event that circulation ceasesO
The heavier beads will also tend to settle out in the
mud pits. ~ ;
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The plastic beads should be in the sh~pe of
subst~ntially perect spheres. It is believed that the
spherical shape is important in providing the torque
reducing properties of the beads, thus when two metal
surfaces tend to rub against each other, as a ~rill
pipe against a casing or against a hard shale, the
round spheres existing between such surfaces are
thought to act in the nature of ball bearings to reduce
the contact between the hard surfaces. Examination of
returned mud cake particles under magnification has
shown that the beads appear to be partially imbe~ded
in the surface of the mud cake leaving exposed a semi-
spherical surface for contact with the drill string~
Obsexvation of this type of filter cake would lead one
to believe that there exists many hundreds of these
tiny protuberances of beads for each foot of bore hole.
Examination of "gumbo" shale returns has -~
revealed the cuttings to be partially coated with beads.
This leads one ~o believe, and evidence has been noted,
that the beads tend to prevent such shale from balling
up bits and stabilizers.
It has also been found that the use o the
new and improved method using beads as aforesaid
reduces drill pipe and casing wear especially in high
angle directional wells by preventing metal to metal
contact by the spherical beads. Such beads form a
layer or sheath between such metals to thereby reduce
~riction.
In this latter connection, one directional
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~ell was being drilled with a dowllhole turbo-drill,
and, in normal operation, it took two days to make
fifteen feet of hole. }lowever, when four pounds per
barrel of these plastic beads were added, the drillin~
rate increased to 15 feet per hourO
In like manner, it has been found that the
addition of such plastic beads, which will not melt
under high temperatures, is useful in improving wir~line
operations which must be performed downhole, such as
well logging, by enabling the logging tool to slide on
the surfaces, provided by the various plastic spheres.
Further, the addition of these spheres reduces "wireline
drag" both in cased well bores and open well bores.
Applicant further discovered that the use
of such beads in a well bore may he further aided with
other mud lubricants, such as vegetable oil, such that
the beads are suspended in vegetable oil and circulated
in the well bore mixed with the drilling mud to further
provide the improved properties stated hereinabove.
As a further example of applicant's use, the
following examples have been disclosed by applicant as
showing the new, use~ul and unobvious properties of
applicant's invention.
Example One
A drilling operator who was drilling an oil
well, had "high torque and drag problems" on an off-
shore well and called for assistance.
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The well being drilled was a 37~ directional
well h~ving several offsets or doglegs. The ~7ell was
a 9 7/8" hole being drillcd at 11,200 feet with 4,000
feet of 10 3/4" surface casing set. The measured total
depth of the well was to be 13,400 feet and the tor~ue
had already reached 850 amps on a conventional torque
gauge. The torque was such that the operator was
~arely turning or rotating the drill pipe. Plastic
beads were added to the mud which was pumped through
the drill pipe and reached the casing whereupon the ;~
torque immediately dropped to 600-650 amps and the
rotary speed increased 20 revolutions per minute. The
well was drilled the remaining 2,000 feet to completion
using the plastic beads.
Example Two
The same drilling operator in another well
had approximately 13,000 feet of casing set and arrange-
ments had already been made to displace the present mud
with an oil base mud hecause the torque and drag con-
ditions were thought to be too severe for t.he subject
plastice beads to provide the needed reduction in torque.
The system was "slug" treated with five percent by
volume of the drilling mud with plastic beads and 300
barrels of mud. As soon as the bead laden mud reached ~ ?
the annulus of the well bore, the torque began to drop
and the penetration rate of the drilling string increased
by fift~ percent. The well was treated to completion
at 18,000 feet with the subject beads and upon completion,
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t}le m~ld system contained 1 3/4percent by volum~ of the
beads in relation to the drilling mud.
x~ Three
The same drillin~ operator was drilling a
well in South Louisiana with an excessive torque pro-
blem rela~ive to rota~ion of the drill string downholeO
This was a directional well which demanded a high
rotary revolution per minu~e (rpm) in order to maintain
the direction desired. The tor~ue was being indicated
as 650-750 amps on the torque gauge with 180 rpm rotary
speed. The depth of the well at that time was 8,000
feet and the casing was set for 3,300 feet. Plastic
beads were added at 1 1/2 percent by volume of the mud
system and the tor~ue dropped immediately to 550-600
amps. In this well, excessive "balling" or build up
of shales and clays on the stabilizers and drill collars
was also eliminated by the subject beads and the well
was successfully completed.
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An oil company had a well being drilled in
South Louisiana, with extreme torque and drag problems
relative to the drill string and drill bit. In this
instance, the rotary table would actually stop turning
while in high gear. In addition, the drill pipe rubbers
would also have to be replaced after each "trip" with the
drill bit. An 'lintermediate" string of casing was set
to 9,000 feet to attempt to help to eliminate the torque
problem~ The drilling operator went in the hole with
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4 ~/4" drill pipe and could not turn the pipe. The
operator pulled out of the hole and replaced the 4 l/A"
pipe with 3 1/2" pipe ~ut the torque was 750 amps and
was twisting the drill p~pe and the possibility of
twistiny the drill in two existed. Dicsel, graphite
and other popular ~orque reducers had been added with
no improvement or with no reduction of torque and drag
on the drill string. Plastice beads were ad~ed ~t two
percent per volume of the drilling mud and the torque
dropped to 600-625 amps as indicated on the torque
indicator and the well was drilled to completion.
In the foregoing examples, tha plastic
beads were a copolyer of divinyl benzene and styrene,
were of a mesh ranging from 10 to 100 and were spherical
in shape throughout.
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