Note: Descriptions are shown in the official language in which they were submitted.
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WELL BORE DRILLING DIRECTION ClIANGING METHOD
Thi~ is a continuation-in-part of copending application
Serial No. 07/638,~78, filed January 8, 1991.
Backqround of the Invention
1. Field of the Invention
This invention relates to wells used in the introduction
of fluids into and the recovery of fluids from subterranean
formations. It further relates to the use of hydraulic
cement compositions to construct and repair such wells.
This invention particularly relates to methods of using a
very finely divided hydraulic cement composition to con-
struct and repair such wells.
2. Problems Solved
In the drilling of a well bore, it is often desirable or
necessary to change the direction of the well bore. The
angle of the well bore from vertical can be increased or
decreased by adjusting drilling conditions, such as the
weight exerted on the drill bit or the rotary speed of the
drill bit; or special tools designed specifically to effect
a change in well bore direction can be used.
Certain formations cause the drill bit to drill in a
particular direction. If that direction is away from ver-
tical in a vertical well, undesirable well bore deviation
from vertical can result. In a directional well which is
purposely drilled at an angle after drilling an initial
portion of the well bore vertically, the direction induced
by the formation can make following the desired path
difficult. In those and other instances, special direc-
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tional drilling tools are often used such as a whipstock, abent sub-downhole motori2ed drill combination, and the like.
Generally, the directional drilling tool or tools used are
orientated so that a pilot hole is produced at the desired
angle to the previous well bore in a desired direction.
When the pilot hole has been drilled for a short distance,
the special tool or tools are removed, if required, and
drilling along the new path is resumed.
In order to insure that the subsequent drilling follows
the pilot hole, it is often necessary to drill the pilot
hole in a cement plug placed in the well bore. That is,
prior to drilling the pilot hole, a cement slurry is pumped
into the well bore and allowed to set therein. The pilot
hole is then drilled in the cement plug formed in the well
bore, and the high strength of the cement plug insures that
the subsequent drilling proceeds in the direction of the
pilot hole. While this procedure is generally successful in
insuring that the drilling follows the desired path, the
cement slurries heretofore used re~uire considerable waiting
time after placement for the development of sufficient com-
pressive strength to allow drilling of the pilot hole, et~.
The use of the finely divided hydraulic cement of this
invention significantly reduces such waiting time and
thereby significantly reduces the cost involved.
In the operation of wells used in the recovery of fluids
from or the introduction of fluids into subterranean forma-
tions problems relating to the unwanted passage of fluids
and/or fine solids into or from undesirable losations in the
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formation or wellbore sometlmes occur. This unwanted pas-
sage of fluids and/or fine solids can severely disrupt or in
fact terminate the desired operation o~ a well.
To be more specific, the problems involving unwanted
passage of fluids, referred to above, ordinarily involve the
movement of fluids, such as oil, gas or water throu~h very
small undesirable openings. These problems are not unique
and the solutions have traditionally involved apparatus,
methods and compositions adapted to cover, seal or to other-
wise plug the openings to thereby terminate the unwanted
passage of fluid through the openings. The openings
referred to above include: holes or cracks in well casing;
spaces such as holes, cracks, voids or channels in the
cement sheath deposited in the annular space between the
formation face and well casing; very small spaces - called
microannuli - between the cement sheath, referred to above,
and the exterior surface of the well casing or formation;
and permeable spaces in gravel packs and formations.
It is clear that holes or cracks in well casing and/or
cement sheath can permit the unwanted and therefore uncon-
trolled passage of fluid therethrough. Sometimes, of
course, holes are deliberately made in casing and sheath by
a known process called perforating in order to permit the
controlled recovery of fluid from a formation or to permit
the controlled introduction or injection of fluid into a
formation. The sealing or plugging of such holes or cracks,
whether or not made deliberately, has been conducted by
attempts to place or otherwise force a substance into the
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hole or crack and permitting it to remain therein to thereby
plug the opening. Naturally, the substance will not plug
the opening iE it will not enter the opening. I~ the sub-
stance does not fit then, at best, a bridge, patch, or skin
may be formed over the opening to produce, perhaps, a tempo-
rary termination of the unwanted flu:id flow.
Substances used in methods to terminate the unwanted
passage of fluids through holes or cracks in casing and/or
sheath have been compositions comprised of hydraulic
cement, wherein the methods employ hydraulic pressure to
force a water slurry of the cement into the cracks and holes
wherein the cement is permitted to harden. These methods
are variously referred to in the art as squeeze cementing,
squeezing or as squeeze jobs. The success of squeezing
hydraulic cement into such holes and cracks is among other
factors a function of the size of the hole relative to the
particle size of the cement as well as the properties of the
slurry. As mentioned earlier, if the particle size of the
cement is greater than the crack width, the cement will not
enter and at best a patch instead of a plug is the result.
A problem therefore is to substantially reduce cement parti-
cle size without reducing the hardening and strength charac-
teristics of hydraulic cement.
During the construction of a well it is known to plac~ a
volume of a water slurry of a hydraulic cement into the
annular space between the walls o~ the borehole and the
exterior of the casing wherein the cement is permitted to
solidi~y to thereby form an annular sheath of hardened
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cement. The objective of the sheath, the construction of
which is referred to as primary cementing, includes physical
support and positioning of the casing in the borehole and
prevention of unwanted fluid (liquid and gas) migration
between various formations penetrated by the wellbore. If,
for some reason, the hardened sheath contains spaces such as
voids, cracks or chann~ls due to problems involved in the
placement of the slurry it is clear that the sheath may not
be capable of providiny the desired objectives.
Accordingly, by employing known techniques to locate the
voids, channels or cracks, a perforation penetrating the ;
spaces can be made in the casing and sheath and cement then
squeezed into the spaces via the perforation so as to place
the sheath in a more desirable condition for protecting and
supporting the casing and providing fluid flow control. As
mentioned earlier, the success of the squeeze job is at
least a function of the size of the space or spaces to be
filled relative to the particle size of the cement.
Another problem incidental to the formation of the
cement sheath, referred to above, revolves about the occa-
sional failure of the sheath to tightly bond to the exterior
wall of the casing or the interior of the borehole. This
failure can produce a very thin annular space called a
microannulus between the exterior wall of the casing and the
sheath or the sheath and the borehole. For the reasons
already discussed, it is important to place a substance,
such as a hydraulic cement, in the microannulus to enable
the sheath to fully provide the intended benefits. Again,
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as stated above, ~he success of squeez ing cement into a
microannulus space is dependent upon the relative size of
the space and the particle size of the cement.
The solid portions of some produc:ing formations are not
sufficiently stable and therefore tend to break down into
small pieces under the influence of t:he pressure differen~e
between the formation and the wellbor~. When fluid, such as
oil or water, flows under the influence o~ the pressure dif-
ference from the formation to the wellbore the small pieces
referred to above can be carried with the fluid into the
wellbore. Over a period of time, these pieces can build up
and eventually damage the well and associated equipment and
terminate production. The art has solved this problem by
placing in the wellbore a production aid which is referred
to in the art as a gravel pack. A gravel pack is usually
comprised of a mass of sand within the interior of a well.
The sand bed completely surrounds a length of tubular goods
containing very narrow slots or small holes; such yoods are
sometimes referred to as slotted liners or sand screens~
The slots or holes permit the flow of fluid therethrough but
are too narrow to permit the passage of the sand. The slot- -
ted liner or sand screen can be connected through a packer
situated up-hole of the gravel pack to production tubing
extended from the wellhead. The gravel pack ordinarily con-
sists of siliceous material having sand grains in the range
of from about 10 to about 100 mesh.
The gravel pack, which can be situated in the casing in
the perforated interval, traps the small pieces of formation
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material, for convenience herein referred to as formation
fines or sand, which flows from the formation with the fluid
through the perforations and into the gravel pack. Accord-
ingly, neither formation sand nor gravel pack sand pene-
trates the slotted tubing and only fluid is permitted to
pass into the tubular goods.
The above expedient performs nicely until undesired
fluid begins to penetrate the gravel pack from the forma-
tion. At that point the flow of undesired fluid, such as
water, must be terminated preferably in a way which will not
necessitate removal of the gravel pack. This invention per-
mits such an objective.
The problems referred to above uniformly deal with the
unwanted passage of materials into or from very small unde-
sirable openings in a well, including the cement sheath con-
structed during a primary cementing procedure. Solution of
these problems, according to this invention, all involve a
remedial or repair operation featuring the use of a very
finely divided hydraulic cement. Still another problem
involved in the construction and repair of wells involves
the primary cementing procedure itself.
Primary cementing, as was described above, is conducted
during the construction of a well and involves the placement
of a volume of a slurry of a hydraulic cement in water into
the annular space between the walls of the borehole and the
exterior of primary casings such as conductor pipe, surface
casing, and intermediate and production strings. The slurry
is permitted to solidify in the annulus to form a sheath of
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hardened cement the purpose of which is to provide physical
support and positioning of the casing in the borehole and to
isolate various formations penetrated by the borehole one
from another.
A problem encountered during primary cementing is cen-
tered upon the weight (that is the density) of the slurry
itself. In certain circumstances the hydrostatic pressure
developed by a column of slurry overcomes the resistance
offered by a formation in which case the formation fractures
or otherwise breaks down with the result that a portion o~
the slurry enters the formation and the desired sheath is
not formed. The formation breakdown thus occurs prior in
time to development of sufficient rigidity or hardening of
the cement to enable it to be self-supporting.
One solution has been to reduce the density of the ~-~
slurry so that the pressure developed by the required slurry
height will not exceed the ability of the formation to
resist breakdown. This expedient can result in sheaths hav-
ing physical deficiencies such as reduced strength or
increased permeability or both. Another solution has been
to reduce the weight of the slurry while maintaining density
by reducing the quantity of slurry pumped in a single lift
or stage to thus reduce the height of slurry. This expedi-
ent requires several separate stages in order to produce the
required sheath length. Time must pass between stages in
order to permit previous stages to develop strength suffi-
cient to support the weight of succeeding stages. The time
expended waiting on cement to set is lost time in the proc-
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ess of constructing the well.
The use of the finely divlded hyd~aulic cement of this
invention solves the primary cementing problems referred to
above.
Still another problem involved in the operation of wells
which are the subject of this invention, revolves about the
unwanted movement of water via crack; and fractures in the
subterranean formation - whether naturally occurring or
deliberately produced - from the formation into the well-
bore. Terminating this water movement may require remedial
efforts other than those referred to previously which fea-
ture plugging perforations, holes, cracks and the like in
casing, cement sheath and gravel packs - all of which occur
within the confines of the well borehole itself.
The unwanted movement of water from cracks and fractures
in the formation outside of the well borehole itself may be
prevented by use of the hydraulic cement composition of this
invention.
Disclosure of the Invention
The solutions to the problems discussed above broadly
relate: to remedial cementing operations conducted inside a
wellbore; to remedial cementing operations conducted outside
a wellbore in a subterranean formation; and to primary
cementing operations conducted during construction of a
well. The solutions to these problems, according to this
invention, basically feature the practice of well cementing
methods long accepted for confronting and solving these
problems with one substantial change. The substantial
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chany~ in the methods comprises the uniform use in the
accepted methods of a hydraulic cement, as defined below,
consisting of discrete particles of cementitious material
having diameters no larger than about 30 microns, preferably
no larger than about 17 micxons, and still more preferably
no larger than about 11 microns. The distribution of vari-
ous sized particles within the cementitious material, i.e.,
the particle size distribution, features 90 percent of them
having a diameter not greater than about 25 microns, prefer-
ably about lo microns and still more preferably about 7
microns, 50 percent having a diameter not greater than about
10 microns, preferably about 6 microns and still more pref-
erably about 4 microns and 20 percent of the particles hav-
ing a diameter not greater than about 5 microns, preferably
about 3 microns and still more preferably about 2 microns.
The particle size of hydraulic cement can also be indi-
rectly expressed in terms of the surface area per unit
weight of a given sample of material~ This value, sometimes
referred to as Blaine Fineness or as specific surface area,
can be expressed in the units square centimeters per gram
(cm2/gram~ and is an indication of the ability of a cementi-
tious material to chemically interact with other materials.
Reactivity is believed to increase with increase in Blaine
Fineness. The Blaine Fineness of the hydraulic cement used
in the cementing methods of this invention is no less than
about 6000 cm2/gram. The value is preferably greater than
about 7000, more preferably about 10,000, and still more
preferably greater than about 13,000 cm2/gram.
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Cementitious materials of particle size and fineness as
set out above are disclosed in various prior u.s. Patents
including U.s. 4,761,183 to Clark, which is drawn to slag,
as defined herein, and mixtures thereof with Portland
cement, and U.S. 4,160,67~ to Sawyer, which is drawn to
Portland cement. The cementitious materials preferred for
use in this invention are Portland cement and combinations
thereof with slag wherein the quantily of Portland cement
included in any mixture of Portland cement and slag used in
the methods of this invention can be as low as 10 percent
but is preferably no less than about 40 percent, more pref-
erably about 60 percent, still more preferably about 80 per-
cent and most preferably no less than about 100~ Portland
cement by weight of mixture.
Some of the problems solved by this invention require
the use of a cementitious material of very small particle
size to enable passage thereof through very narrow openings
and penetration thereof into low permeability gravel packs
and formations. To solve other problems described above,
the material when slurried in water must exhibit a suffi-
ciently low slurry density to enable use in situations
requiring a light-weight cement which nevertheless develops
satisfactory high compressive strength. In this regard the
large surface area of the cement of this invention, i.e.,
the Blaine Fineness, renders it more reactive than cements
of lower Blaine Fineness; accordingly, quantities of water
greater than quantities usually employed in well cementing
operations may be employed to thereby enable the formulation
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of slurries of l~w density and low viscosity without unsat-
isfactory loss in strength.
Thus, slurries useful herein can be formlllated utilizing
ratios of the weight of water per Ullit weight of cementi-
tious material in the range of from about 0.5 to about 5.0,
preferably from about 1.0 to about 1.75 and still more pref-
erably from about 1.00 to about 1.5 pounds water per pound
of cementitious material. Water to cement ratios in excess
of about 1.75 and up to about 5.0 can be formulated for
highly specialized applications requiring slurries of very
low density and very low viscosity. It is noted, however,
that slurries haviny such high water ratios tend to exhibit
free water separation and excessive solids settling. Addi-
tives can be utilized to control free water separation and
solids settling.
The slurry densities of the fine, i.e., low particle
size, cements of this invention are lower than cements hav-
ing usual particle sizes because of the high water ratios
required to wet all of the surface area of the fine cement.
The compressive strengths, however, of the set lower density
slurries are satisfactory for both primary cementing and
penetration cementing purposes especially in view of the
greater reactivity of the fine cements. Also, and particu-
larly in the case of slurries formulated at high water
ratios, where penetration into very small holes, cracks and ;
openings is the goal, water may indeed be eventually forced
out of the fine penetrating particles to thereby deposit in
the target crack, opening or porosity a dense, high-strength ~
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and highly water impermeable mass of set cement.
Consideriny the range of water-to-cement ratios dis-
closed above the slurries which can be formulated utilizing
the fine cement of this invention is in the range from about
9.4 to about 14.9, preferably from a]bout 11.0 to about 12.5
and still more preferably in the range of from about 11.5 to
12.5 pounds per gallon of slurry.
One particular advantage, in addition to the low slurry
densities available herein, is that the high water ratios
produce low heats of hydration. Thus, the fine particle
size hydraulic cement of this invention is quite useful when
conducting cementing operations, and particularly primary
cementing operations, adjacent to structures which may
undergo undesired physical breakdown in the presence of pro-
duced heat. Examples of such structures include permafrost
and gas hydrate zones.
Still another particular advantage accruing from using
the fine particle size Portland cement of this invention is
the observed unexpected expansion of the cement duriny
setting. This expansion property can help prevent the for-
mation of microannuli - when the cement i.s used in primary
cementing operations - and can help the formation of very
tightly fitting plugs - when the cement is used in squeeze
cementing.
It is believed that this desirable expansive feature of
the fine particle size Portland cement is due to the chemi-
cal content thereof and particularly to the high concentra-
tion of crystalline tricalcium aluminate (C3A~ and sulfates
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present therein. See, for example, Table VII. It is
thought that a Portland cement having a maximum particle
size of about 11 ~icr~ns, a slaine Fineness of preferably
greater than about 10,000 cm2/gram, a C3A cry.stalline con-
tent of preferably about 3.0 percent or more and a sulfat~
content of preferably about 1.0 percent or more will exhibit
expansive characteristics desirable in an oil field cement.
Slurries of water and the fine particle size cement o~
this invention, as previously mentioned, are very useful to
penetrate, fill and harden in fine holes, cracks and spaces
such as might be expected to be found in well casing, cement
sheaths, gravel packs and subterranean formations in the
vicinity of a well bore. By way of example, it is believed
that such slurries are useful to penetrate subterranean for-
mations having effective permeabilities as low as about 3000
to about 5000 millidarcies. Accordingly, a condition known
as water coning, in which water from a subterranean forma-
tion enters the wellbore in a rising or coning fashion, can
be terminated by squeezing a slurry of fine particle size
cement of this invention into formations producing such ~ -
water, wherein the formations to be penetrated can have
effective permeabilities as low as 3000 to 5000
millidarcies.
In addition, a water slurry of the fine particle size
cement of this invention can be utilized to terminate the
unwanted flow of water through a zone in a gravel pack. In
this regard such a slurry can be formulated to permeate and
set in a gravel pack consisting of a packed sand bed wherein
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the san~ in the pack has a particle size as low as 100 mesh
(about 150 ~icron). Such a procedure can be utilized to
plug channels in gravel packs created by flowing steam as
well as by flowing water.
Still further, a water slurry of the fine particle size
cement of this invention can be formulated to penetrate,
plug and set in fine cracks in well pipe and in channels and
microannulus spaces in and around the cement sheath wherein
such fine cracks can be as narrow as about 0.05 millimeters
(0.002 inches).
With regard to the above uses - but without being bound
by the following slurry design aid - it is considered for
commercial design purposes that a particle of given size in
a suitable slurry as described herein can penetrate, fill
and set in a crack, hole or void having a size of approxi-
mately 5 times greater than the size of the particle~ Thus
the 0.05 millimeter (50 micron) crack referred to above can
be penetrated by a slurry of particles having a size of
about 10 microns which is within the scope of the cement of
this invention.
It was mentioned previously that the rate of hardening
of the fine cement of this invention is related to the
Blaine Fineness wherein the hardening rate increases as
Blaine Fineness increases. In addition, the hardening rate
is also related to the specific cementitious material being
used and the temperature of the environment wherein the
hardening reaction is proceeding. Thus fine particle size
Portland cement, as hereinafter defined, hardens more rap-
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idly in low temperature environ~ents in the range of from
ab~ut 30F to about lOO~F than does fine particle size slag
cement, also as hereinafter defined. Also Portland cement
hardens more rapidly at elevated temperatures than does slag
cement.
Accordingly, to adjust to specific environments, spe-
cific slurries of fine cement can include mixtures of
Portland cement and slag consistent with the concentrations
previously disclosed. In general, longer set times can be
achieved by increasing slag content with accompanying
decrease in compressive strength and/or increasing slurry
density or both.
In the application of forming a cement plug in a well
bore to facilitate and insure desired drilliny direction,
the fine cement used in accordance with this invention can
be slag cement, Portland cement or a mixture of the two.
Preferably, however, 100% Portland cement is used in that
Portland cement sets and develops high compressive strength
the most rapidly. After placement in the well bore, the
fine cement slurry develops high strength in a short time
whereby the waiting time is reduced. More specifically, the
waiting on cement (WOC) time is significantly reduced as
compared to the hereto~ore used conventional Portland cement
slurries whereby drilling costs are also substantially
reduced. In low temperature environments, the waiting time
can be reduced by as much as fifty percent (50%).
The usual well cementing additives can be combined with
the cem~ntitious materials of this invention to achieve the
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usual results. For example, to assist in the dispersion of
individual cementitious particles in a slurry and thus to
help prevent the formation of large particles by agglomera
tion or lumping a dispersing agent may be adcled to a water
slurry of the cement of this invention in an amount effec-
tive to produce adequate dispersion. Such an effective
amount is considered to include amounts up to about 1.5
parts by weight dispersant per 100 parts by weight of
cementitious material. One such dispersant is identified by
the name CFR-3 and another by the name Halad-322 each of
which is disclosed and claimed in U.S. Patent 4,557,763 to
George, et al., the disclosure of which is incorporated
herein by reference. In view of a principle object of this
invention to provide a slurry of particles which will enter
very small openings and still develop adequate compressive
strength the use of a material to help assure particle dis-
persion is considered to be an important aspect of the
invention.
Other additives commonly used in well cementing which
may be utilized herein include defoaming agents, fluid loss
additives, lost circulation additives, expansion additives,
hardening accelerators (although, not normally required) and
hardening retarders which may be particularly useful when
high temperature environments are encounteredO Portland
cements having the small particle sizes required in this
invention may require retardation of set time at elevated
temperatures. Accordingly, conventional lignosulfonates are
considered to be useful to achieve sufficient retardation.
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Still other additives may be utilized to still further
decrease the slurry density of the cement composition of
this invention. Such lightweight additives include
nitrogen, perlite, fly ash, silica fume, microspheres and
the like. It is believed that a combination of fine parti-
cle size cement, water and additives can produce a competent
slurry having a density of as low as about 9 pounds per gal-
lon which will achieve compressive strength sufficient for
oil field operations.
When well cementing environments exhibit high tempera-
tures, e.g. about 230F or more, it may be necessary to com-
bine with the slurry a material which will help prevent the
loss of compressive strength of set cement over time - a
condition referred to as compressive strength retrogression.
In one specific embodiment, a cement placed in a cased hole
adjacent a geothermal formation or a formation into which
steam will be introduced can be subjected to temperatures of
up to about 600F. Such extremely high temperatures can
produce a loss in compressive strength of set cement;
however, by using the fine particle size, preferably
Portland cement of this invention in combination with Silica
Flour, a crystalline form of silicon dioxide ~SiO2), com
pressive strength retrogression can be prevented or at least
reduced in magnitude. This material is added to the slurry
in an amount effective to react with the hydraulic cement to
help prevent the development of compressive strength
retrogression. It is believed that such an effective amount
is in the range of from about 0.15 to about 1.0 and prefera-
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bly about 0.35 pounds silica flour per pound of hydraulic
cement.
Still another advantage of this invention in addition ko
light weight slurries, low viscosity, good compressive
strength, and small particle size are the thixotropic prop-
erties displayed by the slurry. Accordingly, with a slurry
preferably consisting solely of smal]. particle size Portland
cement used in primary cementing operations the thixotropic
properties help prevent unwanted fluid migrati.on, especially
unwanted gas migration, during the time when the cement is
in an unset plastic condition.
Subterranean formations sometimes produce unwanted water
from natural fractures as well as from fractures produced by
forces applied deliberately or accidentally during produc-
tion operations. It is known that such fractures provide a
path of least resistance to the flow of fluid from a forma-
tion to a wellbore. When the fluid flowing in a fracture is
primarily oil, the fracture is considered to be beneficial
and thus desirable; however, when the fluid flowing in the -
fracture from the formation to the wellbore is primarily
water the fracture is considered to be a problem and thus
undesirable. By the method of this invention the undesira-
ble fracture can be filled with fine cement to plug it and
thereby terminate the flow of fluid therein.
The fine particle size cement of this invention can be
placed in a subterranean fracture as well as in a high
permeability zone of the formation by the application of
conventional procedures, but the cement itself, being highly
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reactive due to its small parti.cle size, must: be rendered
temporarily non-reactive by preventing contact between it
and water prior in time to actual placement of the cement
into the fracture. Accordingly the fine cement of this
invention is dispersed in a relatively low viscosity, rela-
tively non-volatile liquid hydrocarbon, such as diesel oil,
to form a pumpable slurry of cement in oil. (See U.S.
Patent 4,126,003 to Tomic) The slurry is then introduced
into the fracture. After the slurry of cement and oil is in
the fracture, water flowing in the fracture slowly contacts
the cement to thereby render the cement reactive so as to
initiate hydration, hardening and ultimate formation of a
permanent plug in the fracture. By this technique the
cement in the hydrocarbon slurry will only set when con-
tacted by water in the fracture and thus will not set if the
slurry enters a fracture containing oil. Accordingly oil
producing portions of a reservoir will remain relati~ely
damage free after water flow is terminated.
Successful formulation of a cement in hydrocarbon oil -
slurry to obtain the goals set out above depends to a large
extent upon sufficient dispersion of the cement in the oil.
In this regard such a dispersion can be obtained by combin-
ing a hydrocarbon liquid such as diesel oil, a liquid sur-
factant soluble in the hydrocarbon, as hereinafter defined,
and the fine particle size cement of this invention. The
preferred order of blending of the ingredients involves add-
ing the correct quantity of surfactant to the diesel oil
with thorough mixing and then slowly adding the cement to
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the oil/surfactant hlend with continued mi.xing to obtain khe
desired slurry of uniform consistency.
The surfactant useful herein, an organic acid or salt
thereof dissolved in a low molecular weight alcohol, is
mixed with a hydrocarbon liquid, such as diesel oil, in an
amount in the range of from about 10 to about 25 and prPfer-
ably about 20 gallons of surfactant per 1000 gallons of
hydrocarbon liquid. The quantity of hydrocarbon liquid to
be utilized is dependent upon the quantity of cement
employed and is in the range of from about 6 to about 10
gallons of hydrocarbon liquid per 100 pounds of fine cement.
The amount of hydrocarbon liquid and surfactant utilized,
within the scope of the above proportions, will determine
the density of the resulting slurry wh~rein the slurry den-
sity is inversely proportional to the quantity of liquid.
Accordingly, 4400 pounds of fine cement, 5.5 gallons of sur-
factant and 275 gallons of diesel will produce a slurry hav-
ing a density of about 14.1 pounds per gallon while 4400
pounds of fine cement, 8.0 gallons of surfactant and 400
gallons of diesel will produce a slurry having a density of
about 12.5 pounds per gallon.
The low viscosity, non-volatile hydrocarbon liquid use-
ful herein can be an aliphatic compound, such as hexane,
heptane or octane, an aromatic compound such as benzene,
toluene or xylene and mixture thereof such as kerosene, die-
sel oil, mineral oil and lubricating oil.
The organic acid component of the surfactant is selected
from dodecylbenzenesulfonic acid and the alkali and alkaline
.: : .
, ., ,' ., ~ .,
8 2
-22-
earth metal salts thereof. Calcium dodecylbenzenesulfonate
is preferred. The low molecular weight alcohol solv~nt for
the organic acid component is selected from aliphatic alco-
hols having in the range of from 1 to 5 carbon atoms wherein
isopropanol is preferred. The organic acid component is
present in the surfactant in the range of from about 60 to
about 80 and preferably about 75 parts acid per 100 parts by
volume surfactant. The alcohol is present in the surfactant
in the range of from about 20 to about 40 and preferably
about 25 parts alcohol per 100 parts by volume surfactant.
The tables which follow provide information and data
concerning the chemical, physical and performance properties
of four hydraulic cements. Three of the cements are
Portland cements and the fourth is a slag cement. One of
the cements, identified as API Class A, due to particle size
only, is not within the scope of this invention. The
remaining three cements are within the scope of this
invention.
Tables I and II provide physical data including specific
surface, specific gravity, blending, and particle size
analysis.
Tables III and IV provide performance data including
compressive strength developed by stated slurries and pene-
tration by stated slurries.
Tables V, VI, VII and VIII provide chemical content as
determined by various different analysis techniques.
Table IX provides a chemical analysis of Portland type
III cement as disclosed in U.S. Patent 4,160,674 to Sawyer.
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V
X-ray Fluc~rescen~e Analysi~ of
Hydraulic Cement Material
Oxlde Hydraulic Ceme~nt Name
Components _ Percent
API
MC-500Ultra FineCla~s A White
Na2O 0 . 30 0 . 17 0 . 37 0 . 37
MgO 3 . 40 1.10 1. 30 2 . a,o
Al2O3 11. 29 4 . 26 4. 32 4 . 01
SiO2 29 . 54 17 . 80 20 . 8$ 21 . 08
S03 2.157.85 2.98 3.40
~C2O 0 . ~ 10 . 95 0 . 93 0 . 27
CaO 50 . 79 62 .12 65 . 29 65 . 64
TiO2 0 . 490 .18 0. 23 0 .12
Cr203 0.0 o.o o.o o.o
MnO O . 38 0 . 03 0 . 03 0 . 02
Fe2O3 1.16 2.30 2.35 0.29
Zno 0.010.01 o.a2 0.01
SrO 0 . 08 0 . ll 0 . 07 0 . 04
Lo~s On 0.03.12 1.25 2.35
Igniti~n
: . . :. .: ,
: . : : -.
2 ~
, . --2~--
T~E! VI
Cement Compound Concentration, Perccnt
Compound By Bogue Calculation
From Oxide Components in Table V
API
MC-500 Ultra Fi.ne Class A ~hite
Free Lime 0.4 0.7 0O58 3.67
C3S * 62.56 ~4.89 55.58
C2S * 5.47 11.6 19.96
C3A * 7.63 7.57 10.39
C~AF ~ 7.22 l.23 0.89
CaSO~ (CS) ~ 13.78 5~12 S.92
*Cannot Calculate due to excess of Al and Si
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-31-
Referriny lloW to Tables I, II, III, IV, V, VI, 'JI~, and
VIII set out above, there is presented, in convenient tabu-
lar form, a comparison of various properties of four differ-
ent cementitious materials each of which exhibit hydrhulic
activity. "Hydraulic activity" and "reactivity" as used
herein mean the chemical nature of a material to set and
harden, upon being mixed with water, without contact with
the atmosphere (e.g. the ability to harden under water) due
to the interaction of the constituents of the material
rather than by evaporation of the water. The term
"hydraulic cement" as used herein means all inorganic
cementitious materials of known type which compri~e com-
pounds of calcium, aluminum, silicon, oxygen and/or sulfur
which exhibit "hydraulic activity", that is, which set solid
and harden in the presence of water. Cements of this type
include common Portland cements, fast setting or extra fast
setting, sulfate resistant cements, modified cements, alu-
mina cements, high alumina cements, calcium aluminate
cements, and cements which contain secondary components such
as fly ash, pozzalona and the like. See for example Roca,
et al., U.S. 4,681,634. There are in existence inorganic
camentitious materials other than those exemplified in
Tables I - VIII which exhibit hydraulic activity, but this
invention is preferably limited to the types included in
Tables I - VIII.
Accordingly, Portland cement, one of the materials
listed in the Tables is made by sintering (thermally
treating) a ground mixture of raw materials one of which is
:
; :
-32- ~ 3~
usually composed main:Ly of calcium carbonate (as limestone)
and another of which ls usually composed mainly of aluminum
silicates (as clay or shale) to obtain a mixture of lime, -~
aluminum oxide, silicon dioxide and ferric oxide. During
the sintering process chemical reactions occur which produce
nodules, called clinkers, which are primarily composed of
mixed calcium silicates (C2S and C3S), calcium aluminates
(C3A) and calcium aluminoferrites (C~AF) all of which com-
pounds contribute to the hydraulic activity of Portland
cement. See for example Braunauer, U.S. 3,689,294; Buchet,
et al., U.5. 4,054,460; and Gartner, U.S. 4,619,702. An
example of a chemical analysis of Portland cement clinker is
provided by Skvàra, U.S. 4,551,176 as follows:
Component Wei~ht Percent
sio2 20 - 21.9
CaO 62.2 - 67.3
Al2O3 4.7 - 6.3
Fe23 2.4 - 4.5
MgO 1.3 - 3.3
so3 0.16 - 1.05
Na2O + K2O 0.81 - 0.95
After sintering, the clinkers are ground together with
additives, including for example a quantity of calcium sul-
fate dihydrate (gypsum) to control set time, to a specific
surface area, sometimes called Blaine Fineness, of as high
as 10,000 cm2~gram or more, but ordinarily the grinding is
sufficient to produce a specific surface area in the range
of from about 2500 to 5000 cm2/gram With 3000 to 4500
.. . . .
- 2 ~
-33-
cm2/gram being the usual Blaine Fineness range for Portland
cement. See for example Gartner, U.S. 4,619,702; Miyoshi,
et al., U.S. 4,443,260; Buchet, et al., U.S. 4,054,460; and
Braunauer, U.S. 3,689,294.
Portland cements are classified ~y the ~merican Society
of Testing Materials (ASTM) into five major types identified
by Roman Numerals I, II, III, IV and V and by the American
Petroleum Institute into at least 9 categories identified by
the letters A, B, C, D, E, F, G, H and J. The classiPica
tions are based on chemical composition and physical
properties.
Sawyer in u.S. 4,160,674 specifically discloses a Type
III Portland cement exhibiting high early compressive
strength wherein: substantially all particles in the cement
are of a size of about 20 microns and smaller; the Blaine
Fineness is about 8990 cm2/gram; and the specific gravity is
3.00. Sawyer provides an analysis of the Type III material,
which is referred to as the "fine product". The analysis is
set out in Table IX below.
::~ ~, : . . . . .
2~g~
-34-
Table IX
Chemical Analysis-Fine Product _ompound Composition
sio2 l9.G1 ~3S 46.58
Al2O3 4-93 C2S 21.10
Fe23 2.50 C3A 8.83
CaO 61.26 C4AF 7.61
MgO 1.42 CaS04 10.18
SO3 5.99
Loss 3.12
Total g B . 83
Lime Factor 2.45 .,.
Silica Ratio 2.64
A/F 1.97
Insol Residue 0.53
Free CaO 1.26
Na20 O. 11
K2O 1.06
Total alk. 0.81
Galer, et al., in U.S~ 4,350,533 provides abbreviations
for chemical formulas of cement compounds in accordance with
general practice in the cement industry as follows:
C represents calcium oxide (CaO)
A represents aluminum oxide (Al2O3)
F represents ferric oxide (Fe203)
M represents magnesium oxide (MgO)
S represents silicon dioxide (SiO2)
R represents potassium oxide (K2O)
N represents sodium oxide (Na~0)
~', ' : ` `
~35~ ~6i~
H represents water (H20)
S represents sulfur trioxide (SO3)
C represents carbon dioxide (CO2)
Accordinyly, based upon the above abbreviations the
chemical composition of the Type III Portland cement dis
closed by Sawyer (Table IX above) is:
C3S : 3CaO sio2 46.58
C2S : 2CaO Si02 21.10
C3A : 3CaO Al203 8.83
C4AF : 4CaO A1~03 Fe203 7 . 61
CS : CaSO~ 10.18
Tables I - VIII also include a hydraulic cement material
identified as I~SLAG/Portland~ which is a combination of
Portland cement and slag.
"Slag", a~ used herein, means a gr~nulated, blast-
furnace, by-product formed in the production of cast iron
and is broadly comprised of the oxidized impurities found in
iron ore.
During the operation of a blast furnace to remove iron
from iron ore a molten waste product i5 formed. By prevent-
ing this molten product from crystallizing, and thereby los-
ing its energy of crystallization, a super-cooled liquid or
non-crystalline glassy materlal can be formed thus retaining
the energy of crystallization. This non-crystalline, glassy
material, which has also been described as a vitreous sub-
stance free from crystalline substances as determined by X-
ray diffraction analysis, is said to be capable of
exhibiting hydraulic activity upon being reduced in size by
.. . . .
-36- ~ 6~
grinding from a particle size of 1 to 5 millimeters to a
fine particle size in the range of from about: 1 to about 100
microns. Many commentators, including Clarke in U.S.
4,761,183 and Forss in U.s. 4,30G,912, state that the glass
content of the material, in order to exhibit latent hydrau-
lic activity, must be high and preferably above about 95
percent.
Crystallization of the molten blast furnace waste prod-
uct can be prevented and the super cooled liquid or glass
can be formed by rapidly chilling the molten waste. This
rapid chilling can be effected by spraying the molten uaste
with streams of water which operation causes rapid solidifi-
cation and formati~n of a water slurry of small, glassy,
sand-like particles. The slurry is then thermally dried to
remove substantially all moisture to thereby produce a dry
blend of coarse particles. This dry blend of particles,
having a particle size in the range of 1 to 5 millimeters,
is then ground to reduce particle size to values in the
range of from 1 to about 100 microns and preferably less
than about 325 mesh (45 microns) to produce the granulated,
blast-furnace by-product herein defined as "Slag". See, for
example, Miyoshi, et al., U.S. 4,443,260; Allemand, et al.,
U.S. 3,809,665, Buchet, et al., U.S. 4,054,460; Gee, et al.,
U.S. 4,242,142; Clarke, U.S. 4,761,183; and Forss, U.S.
4,306,912.
Clarke '183 and Miyoshi, et al., in U.S. 4,306,910 dis-
close the following analysis, said by them to be representa-
tive of the usual ranges of chemical content of slag.
. , . . , : .
. ~ , . - ~ :
.
,' : '. - - . ' ~ ' ': '
.
: . , .
,
-
2~6~4~
-37-
Weiqht Per Cent
Component Clarke Miyoshi
Sio2 30~0 ~.o -
3 8-18 13 - 18
Fe2O3 - 0.5 - 1.0
CaO 35
MgO 0-15 3 - 6
S03
FeO 0-1 -
0-2 0.5 - 1.0
Mn203 0-2
MnO - 0.5 - 1.5
Tio2 o 0.5 - 1.0
Clarke further states that the density of slag is con-
sidered to be 2.92 grams per cubic centimeter.
Another analysis of slag is provided by Yamaguchi, et
al., in U.S. 3,904,568 as follows: ~
Component Weiaht Per Cent ~:
Si2 34.9
Al2O3 ~ Fe2O3 16.8
CaO 41.1
MgO 5.5
Miyoshi, et al., '910 state that the hydraulic activity
of slag is low if the particle size of the slag is in the
range of 1 to 5 millimeters and accordingly, suggest that i
the particle size of slag should be reduced by grinding to a ~-
value of at least about 5 microns or less; and still further
state that the slag, by itself, even after grinding has no
;, , , ~ - - .
. . : ~ - .; .. . ,.. ., :, , . : :
~6~2
-3~-
or very low hydraulic activity and thus requires activation
or stimulation such as by the addition thereto of slaked
lime (CaO H20). Other additives to stimulate or activate
the hydraulic activity of Slag inclucle sodium hydroxide,
sodium sulfate sodium carbonate, sodium silicate, potassium
sulfate and Portland cement. See for example Clarke, U.S.
4,761,183 and Clarke, U.S. 4,897,119.
According to Forss in U.S~ 4,306,912 grinding slag to a
high specific surface, e.g. in the range of from about 4000
to about 8000 cm2/gram, can increase the hydraulic activity
and hardening rate of the material. Forss also states that
it is known that grinding cement clinker beyond a certain
limit is not beneficial because additional fineness hardly
improves the properties of hardening and strength. On the
other hand Birchall, et al., in U.S. 4,353,747 state that
the strength of Portland cement can be improved by reducing
the weight average mean particle size of Portland cement to
a value of less than 20 microns.
The various methods for conducting cementing operations
normally associated with wells in subterranean hydrocarbon
producing formations are generally known. These basic tech-
niques with changes, as required, can be employed to place
the fine particle size cement of this invention in position
to solve the various problems addressed herein.
The techniques which can be used herein are set out
below in outline f~rmat.
Procedure I, "Method for Placing Cement in a Micro-
annulus",
.. .. , ; :, - ~ , ,
- .:: . .
,:
2 ~ 2
-39-
Procedure II, "Method for Placing Cement in Voids,
Cracks and Channels in the Cement Sheath",
Procedure III, "Method for Plugc3ing Cracks and Perfora~
tions in Casing",
Procedure IV, "Alternate Method for Repair of Cracks in
Casing",
Procedure V, "Method for Terminating Water Flow Through
a Gravel Pack and the Matrix of a Subterranean Formation"
can be employed to perform remedial cementing operations
within a wellbore,
Procedure VI, "Method for Terminating the Flow of Water
from a Zone in a Subterranean Formation" can be employed to
perform remedial cementing operations outside of a wellbore
in the formation,
Procedure VII, "Method f or using Ultra Fine cement in
Primary Cementing Operations," can be employed to perform
primary cementing, and
Procedure VIII, "Method of Changing the Direction of a
Well-Bore Being Drilled Wherein a Cement Plug is Formed in
the Well Bore".
Procedure I
Method For Placing Cement in a Microannulus
1. Determine the location, size and upper and lower-
most linear limits of the microannulus relative to the axis
of the wellbore. This determination may be accomplished by
use of a conventional cement bond log procedure.
2. BLOCX SQUEEZE TECHNIQUE
a. Perforate the well casing so as to inter- -
~ , ~
. , , . ., :~ ........................ ~ . - : ,
. - ~. , ~ - ~ :. ,
~o -
sect the micro~nnulus at its lowest point relative
to the wellhead.
h. Isolate the perforation by placing a
bridge plug in the casing below the perforation and
a packer in the casing above the perforation to
thereby define a space within the casing between
the bridge plug and packer which is in communica-
tion with the microannulus via the perforation;
establish communication with the wellhead via tub-
ing from the wellhead to the packer.
c. Introduce an acld solution into the
microannulus via tubing from the wellhead to the
packer, the defined space and the perforation. The
purpose of the acid, which can be a 15%
hydrochloric acid solution, is to prepare the per-
foration and microannulus for cementing.
d. Introduce water into the microannulus via
the tubing and perforation to establish an injec-
tion rate.
e. Introduce a water slurry of the cement
composition of the invention into the microannulus.
The slurry must be of sufficient volume to form a
plug in the entire lower portion of the micro-
annulus to prevent passage of fluid therethrough.
Introduction of the slurry must be effected at a
pressure less than the pressure required to
fracture the formation.
f. Remove excess slurry from tubular yoods
.- , .
and casing.
g. Shut well in, preferably under pressure,
to permit the cement to harden.
h. Remove the tubing, the packer and the
bridge plug from the well and perforate the well
casing so as to intersect the microannulus at its
uppermost point xelative to the wellhead.
i. Repeat steps "b" through "g" with re~pect
to the perforation made in step "h".
The block squeeze method described in steps 2a - 2i thus
produces water blocks at the extreme linear limits of a
microannulus but does not completely ~ill the microannulus
with cement.
The use of acid, as described in Step 2c, may be elimi-
nated in the performance of the procedure when the cement of
this invention is employed.
3. ROLLOVER TECHNIQUE
a. Perforate the well casing in two
locations, so as to intersect the microannulus at
its uppermost point and its lowermost point rela-
tive to the wellhead.
b. Isolate the zones below the perforated
interval by placing a bridge plug in the casing
below the perforation in the lowermost point of the
microannulus.
c. Place a drillable packer in the casing ~ ;
between the uppermost perforation and the lowermost
perforation to thus establish a space within the
8 ~
-42-
casing between the bridge plug and clrillable
packer.
d. Establish communication between the
wellhead and the defined space via tubular goods
from the wellhead to the packer.
e. Establish communication hetween the per~o-
rations by introducing an acid solution into the
microannulus via the tubing, the defined space and
the lowermost perfo,ation and permi~ting the solu-
tion to exit the microannulus via the uppermost
perforation.
f. Fill the microannulus with a water slurry
of the cement composition of this in~ention by
introducing the slurry into the microannulus via
the tubing, the defined space, and the lowermost
perforation and maintaining such introduction until
the slurry exits the microannulus via the uppermost
perforation.
g . ~emove excess slurry from the def ined
space by backwashing.
h. Shut well in, preferably under pressure,
to permit the cement to harden.
i. Dxill set ¢ement above drillable packer
and drill through packer and remove bridge plug.
The rollover squeeze method described in steps 3a - 3i
results in a microannulus completely filled with the cement
composition of this invention.
The use of acid, as described in S~ep 3e, may be elimi- -
: - ..
- .
. . .
,. ,. . ., ~ ~ ;
~: ..
2 ~
-- 3--
nated in the performance of the procedure when the cement of
this invention ls employed.
Procedurs II
Method For Placing cement in Voids, Cracks and
Channels in the Cement: Sheath
Utilize the procedure described }n Procedure I for plac-
ing t:he cement composition of this invention in microannuli,
however, as an additional step, a chemical flush preceding
introduction of the cement slurry maybe employed. The pur-
pose of the flush, which is not essential to the procedure,
is to condition the hardened cement in the sheath for
bonding. An example of a suitable such reactive chemical
pre-flush is sodium silicate.
Procadure III
Method For Plugging Cracks and Perforations in Casing
1. Locate the casing hole by conventional means.
2. Isolate the hole by placing a bridge plug in the
casing below the hole and a packer in the casing above the
hole to thereby define a space within the casing between the
bridge plug and packer; establish communication with the
wellhead via tubing from the wellhead to the packer.
3. Introduce an acid solution into the hole via tubing
from the wellhead to the packer and the defined space. The
acid, which can be a 15~ hydrochloric acid solution, will
prepare the hole for cementing.
4. Introduce water into the hole via the tubing to
establish an injection rate.
5. Introduce a water slurry of the cement composition
~ - ~-^ - - - - . . .. .. .
':,, ' '' ~ : '
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: ~'' ; ~ ., : , ' ` ' , , :
,,
_4~_ 2~6~2
of the invention into the hole via tubing -from the wellhead
to the packer and the defined space. The slurry must be of
sufficient volume to form a plug in the hole to prevenk pas-
sage of fluid therethrcugh. Introduction of the slurry must
be effected at a pressure less than the pressure required to
fracture the formation.
6. Remove excess slurry from the defined space by
backwashing.
7. Shut well in preferably under pressure to permit the
cement to harden.
The use of acid as described in Step 3 may be eliminated
in the performance of the procedure when the cement of this
invention is employed.
Procedure IV
Alternate Method For Repair of Cracks in Casing
1. Locate crack in casing by conventional means~
2. Place a bridge plug in the casing below the crack to
thereby isolate the crack from portions of the casing below
the crack.
3. Introduce tubing into the casing from the wellhead
to a location in the approximate vicinity of the crack.
4. Remove any debris from the portion of the casing
above the bridge plug by introducing therein water via the
tubing and circulating the same out the casing.
5. Introduce a water slurry of the cement composition
of this invention via the tubing into the casing above the
bridge plug in amount sufficient to cover the crack.
6. Increase the pressure in the casing above the slurry
:: . . .
~':
2 ~ 8 ~2
--~5-
to force the slurry to slow:Ly penetrate intG the crack and
continue to increase c~sing pressure to assure such
penetration.
7. Shut well in under pressure and do not release the
pressure for a period of time, preferably about 24 hours, to
permit the cement to harden in the crack.
8. Remove set cement from casing by drilling.
9. Pressure casing with water to determine whether
repaired crack prevents loss of water.
Procedure V
Method For Terminating Water Flow Through A Gravel Pack
and the Matrix of a Subterranean Formation
1. Place a volume of a slurry of hydraulic cement in
water within the slotted liner. The volume of slurry placed
should be in an amount at least sufficient to saturate the
portion of the gravel pack throllgh which the unwanted water ~
is flowing. The slurry may be spotted by permitting it to ~ -
~low from the wellhead via tubing extended therefrom to the
liner or by lowering it to the liner in a section of pipe
having a valve in the bottom portion thereof and thereafter
opening the valve and literally dumping the slurry in the
liner. The section of pipe and valve is referred to as a
dump bailer.
2. Apply pressure against the slurry in an amount suf-
ficient to force the slurry from the liner and into and
through the gravel pack and at least partially into the por-
tion of the formation from which undesirable water is being
produced. The pressure applied to the slurry should not be
. ~
.
:
:: . - , . . .
. - .
-: - :
'
2~S46~2
-46-
of sufficient intensity to make a fracture in the
formation.
3. Maintain applied pressure for a time sufficiant to
permit the cement to harden before the well is returned to
production.
Procedure VI
Method for Terminating the Flow of Water
From a Zone in a Subterranean Formation
1. Locate the zone within the subterranean format~on
from which water i5 being produced. This task may be per-
formed by using known methods of identifying casing per~ora-
tions through which water is flowing. The water may be
flowing from a fracture or from a high permeability portion
in the zone.
2. Isolate the identified perforations by placing a
bridge plug in the casing, a bridge plug below the perfora-
tions, and a packer in the casing above the perforations to
thereby define a space within the casing between the bridge
plug and packer which is in communication with the zone via
the perforations; establish communication with the wellhead
via tubing from the wellhead to the packer.
3. Introduce a spacer fluid such as diesel oil into the
zone via the tubing and perforations.
4. Introduce a slurry of the cement composition of the
invention in a hydrocarbon liquid into the zone. The cement
must be of sufficient volume to form a plug in the zone to
prevent passage of fluid therethrough. Introduction of the
cement is preferably effected at a pressure less than the
,;
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pressure required to ~racture the zone.
5. Introduce an overf lush fluid such as diesel oil into
the zone via the tubing and perforations t~ help in the
introduction of the hydrocarbon-cement slurry into the zone.
6. Shut well in for 24 hours, preferably under
pressure, to permit the cement to hydrate with formation
water in zone and harden. Remove the tubing, the packer and
th~ bridge plug from the well.
Procedure VII
Method for Using Ultra Fine Cement in Primary
Cementing Operations
The method of cementing primary oil field casings using
ultra fine cement slurries include conductor pipe, surface
casin~, intermediate casing~ production casing, drilling
liner, production liner, scab liner, and tieback casing.
1. Pump the slurry or any preceding or following fluid
down the casing (tubing or drill pipe) and back up the annu-
lar space between the casing and the drilled hole.
2. (optional) Precede all fluids With a "bottom" wiper
plug to clean drilling fluid from the casing.
3. (optional) Pump a preflush chemical wash or
"spacer" to serve as a drilling fluid removal agent and as a
compatible spacer between the drilling fluid and the cement
slurry.
4. Pump the cement slurry.
5. toptional) Follow the cement slurry with a conven-
tional cement slurry.
6. Follow the cement slurry with a "top" wiper plug.
' .
-~3-
7. Pump a commonly used displacement fluid (water,
drilling fluid, e.g.) to force the cement slurry down the
casing and up into the annulus. Pump enough fluid to dis-
place the required amount of casing volume. The "top" plug
should land on a baffle or "float collar", closing of~ the
flow of fluid to the annulus.
8. Pressure up to ensure that the top plug has landed.
9. Release pressure on casing to test if the "float" is
holding to keep the cement in the annulus.
10. Terminate any operation in the wellbore for a time
sufficient to permit the cement to set (WOC).
Procedure VIII
Method of Changing the Direction of a Well Bore Being
Drilled Wherein a Cement Plug is Formed in the Well Bore
1. Pump the ultra fine cement slurry down the well bore
(generally via the drill pipe) to the bottom and/or other
location therein where the direction of the well hore is to ~ -
be changed.
2. (optional) Pump a preflush chemical wash or
"spacer" to serve as a drilling fluid removal agent and as a
compatible spacer between the drilling fluid and the cement
slurry.
3. Follow the cement slurry with a displacement fluid
(e.g., water or drilIing fluid) to force the cement slurry
through the drill pipe into the desired location in the well
bore. ~-
4. Terminate operations in the well bore for a time
sufficient to permit the cement slurry to set and develop ;
:.:
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: : :
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_~9_
sufficient compressive strength (WoC time).
5. (optional) Place and orient a special directional
drilling tool on top of the cement plug formed in the well
bore.
6. Drill a pilot hole through the cement plug in the
desired direction.
7. (optional) Remove the special directional drilling
tool.
8. Resume normal drilling operations whereby the well
bore is drilled in a direction following the direction of
the pilot hole through the cement plug.
The methods used to determine volumes, yrouting
patterns, mixing and injecting equipment and procedures will
be well known to one skilled in the art.
