Note: Descriptions are shown in the official language in which they were submitted.
71456-7g
BACKGROUND ~F THE INVENTI~ON
Field of the Invention:
This invention pertains to the manipulation of fer-
rofluids. More specifically, this invention is related to a
magnetic device for the manipulation of ~erro~luids in the
cementing of oil wells.
TechnoloqY Review
U.S.Patent 4,356,098 (Chagnon) describes certain stable
ferrofluid compositions ~nd ~ method of making same. Chagnon
indicates that ferrofluids are ferromagnetic liquids which
typically comprise a colloidal dispersion of finely-divided
magnetic particles, ~uch as iron, gamma-Fe203 (maghemite),
Fe304 (magnetite) and combinations thereof, of ~ubdomain
size, such as, for example, 10 to 800 Angstroms, and more
particularly 50 t~ 500 Angstr~ms, dispersed in a liquid
through the use of a surfactant-type material. Chagnon
states that typically ferrofluids are remarkably unaffected
by the presence of applied magnetic fields or by other force
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fields in that the magnetic particles remai~ uniformly
di~per~ed throughout the liquid carrier. Such ferrofluid
compositions are widely known, and typical ferrofluid
compositions are described, for example, in U.S.Patent
3,764,540 and a process for making such materials is des-
cribed in V.S.Patent 3,917,538 and U.S.Patent 4,019,9g4.
Chagnon and the reclted references therefore describe
ferrofluids in which the only suspe.nded particles are
magnetic particles and the liquid medium is generally
organic rather than aqueous.
The well cementing technology is replete with references
to hydraulic cements and methods of using such cements in
cementing wells. In this technology, cement slurries are
used to fill the void space between the casing or pipe and
the walls of the b~rehole penetrating a subtexranean forma-
tion; a process called "well cementing" in the industry. In
using such cement slurries, a line or string of pipe is
inserted into the borehole and a cement slurry is pumped
downwardly through the pipe into the bo~tom of the borehole
and then upwardly along the outside of the casing or pipe
displacing dxilling mud from the annular space. The cement
slurry is then displaced from the interior of the pipe before
it hardens; this is normally accomplished by injecting a
liquid medium behind the cement slurry and using it as a
a)~
"hydraulic fluid" to force the remaining cement out of the
pipe and into the annulus. In another but less common
technique, the boxehole is filled with the cement slurry and
the pipe or casing (normally wlth the end ~ealed~ is lowered
into the hole. Cementing techniques are more fully described
by D. K. Smith in "Cementing", Monograph Vol. IV, Henry L.
Doherty Series, Society of Petroleum Engineers of AIME, New
York (1976). A problem can occur if the c~ment slurry does
not form a good bond with the casing and the formation wall.
If drilling mud is not uniformly and completely displaced
from the annulus, a "microannulus" will ~orm around the
casing when the slurry fails to bond properly. Various
techniques have been used but the most common commercial
techniques used to combat this problem involve chemical
washes or spacers and/or expansive cements. See~ for
example, U.S. Patent 4,207,194 (Sharpe et al.) which il-
lustrates the use of chemical washes and spacers~ Such
chemical washes are injected as a preflush ahead of the
cement slurry and are thereby used to displace the drilling
mud and "wash" the walls of the formation and casing before
being contacted by the cement slurry. See also U.S. Patent
4,328,036 (Nelson et al.) which illustrates the use of
expansive cements. Another method utilizes sonic or energy-
carrying waves to displace the drilling mud from the walls of
the casing and formation. See U.S.Patent 4,093,028 (Bran-
don). These methods work to a greater or less degree, but a
need still exists for a method of removing the drilling mud
from the casing and formation walls so as to promote better
bonding of the cement slurry theret:o. The drilling muds and
cement slurries are typically incompatible, particularly when
the drilling mud is an oil-base drilling mud.
U.S. Patent 4,691,774 ~Nelson~ discloses a novel stable
cementitious ferrofluid suitable for use in cementing wells,
and a process for its use. The present invention provides a
device for manipulating cementitious or non-cementitious
ferrofluids used in a process for cementing wells.
SUMMARY OF THE INV~NTION
A novel device has been discovered which can be used for
manipulating cementitious or non-cementitious ferrofluids
outside a pipe or casing in a process for cementing wells or
preparing a well for cementing. This device comprises:
(a) means for generating at least one magnetic field
which extends from the casing into a ferrofluid in the
wellbore annulus separating the casing and the walls of a
subterranean formation; and
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(b) means for moving the ma~netic ~ield or fields
relative to the ferrofluid to cause movement of the fer-
rofluid.
A novel process for cementing wells has also been
discovered which comprises the steps of:
(a) injecting the stable cementitious ferrofluid
defined above into the wellbore annulus separating a casing
and the walls of a subterranean foxmation, and
(b) applying an alternating magnetic field to cause a
mechanical response (e.g., movement) of said fçrrofluid in
the annulus before the cement sets.
While we do not wish to be bound by any specific theory,
it is believed that the mechanical response of the ferrofluid
can (a) help hold the cement slurry in place, (b) dislodge
and displace any residual drilling fluid on the walls in the
casing or formation, (c~ "stir" the cement mass in situ in
the wellbore and thereby disperse and incorporate residual
drilling mud and other contaminates into the cement slurry ~o
form a more homogeneous mass and continuous hydraulic seal,
and/or (d) "stir" the cement mass in situ in the wellbore to
thereby minimize the static gel strength o~ the slurry which
allows the cement column to continue to exert a hydrostatic
pressure against formation fluids and prevent channeling by
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such fluids; this, in turn, leads to be~ter cement bondlng
and more effective hydraulic seal.
The magnetic field can be generated by permanent magne-
tics, electromagnets, or superconducting electromagnets. If
the pipe or casing is composed of a ferromagnetic material,
such as steel, the pipe or casing :Ltself may be permanently
magnetized Regardless of the cas:ing material, a device
containing permanent, electromagnets, or supercondu~ting
electromagnets can be lowered into or attached inside or
outside the casing to produce the magnetic field. A fer-
romagnetic casing may require a device generating a relative-
ly stronger field when inside the casing than a nonferromag-
netic casing would, due to the magnetic shi~lding effect of a
ferromagnetic casing. Thereore, attaching permanent magnets
to the outside of a ferromagnetic casing would be preferred.
If the casing consists of a nonferromagnetic substance, such
as a composite material, the preferred method would be to
lower a magnetic device into the casing, ince the device
could afterward be recovered by raising it out of the casing.
An array of magnetic fields which extend in a radial
direction from the casing is preferred. Motion of the
magnetic field relative to the ferrofluid can be achieved by
rotating or axially displacing the device containing per-
manent magnets, or rotating or axially displacing the casing
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if the device is attached to the casing; or if the device
contains electromagnets, alternating the magnetic fields by
electronic means while the device is inside the casing. If
the casing itself is magnetized, motion of the magnetic field
can be accomplished by rotating or axially displacing the
casing. Axial rotation of radially alternating poles
efficiently produces motion of the ~errofluid.
Additionally, if the casing is composed of ferromagnetic
material, a first magnetic field can be generated in, for
example, an axial direction along the casing by winding wire
around the casing and applying direct current through the
resulting solenoid. Then a second magnetic field at an
obligue angle or perpendicular to the first magnetic field,
for example in a radial direction through the pipe, can be
generated by a permanent magnet, electromagnet, or supercon-
ducting electromagnet. The result of this arrangement is
that the first magnetic field creates a degree of magnetic
saturation of the ferromagnetic casing, thus overcoming the
tendency of the casing to shield the second magnetic field
from the ferrofluid outside the casing and allowing the
second magnetic field to penetrate more deeply into the
ferrofluid than would otherwise be possible without the first
magnetic field. The magnet or arrangement of magnets or
electromagnets generating the ~econd magnetic field aan be
moved or rotated as described above.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a drawing of a section of pipe or casing
showing the magnetic fields. A section of casing with
magnets is shown in Fig. 2. Fig. 3 illustrate another
possible arrangement of magnetic fi~elds, and Fig. 4 shows a
ferromagnetic casi~g with solenoid windings and a magnet
inside. Fig. 5 is a drawing of an electromagnetic device
which can be lowered into and raised out of the casing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
.
The stable cementitious ferrofluids utilized herein
comprise:
(a~ a hydraulic cement,
(b) finely divided magnetic particles,
~ c) a binding agent or a surfactant, and
(d) a liguid medium.
The hydraulic cements comprise ~ known class of materi-
als, any member of which can be used herein. However,
Portland cements are preferred and the Class A, Class B,
Class G and Class H Portland cements (as classified by the
American Petroleum Institute (API)) are most preferred
because of price and commercial availability. Other hydrau-
1 ~ ~3(~3
lic cements include calcium aluminate cements (e.g. t sold asLumnite or Ciment Fondu), epoxy cements, silicone cements
(geothermal cements), and the like.
The finely divided magnetic particles used in the
present invention can be selected from the known class o
magnetic materials, any member of which can be used so long
as the material is essentially chemically inert in the stable
ferrofluid composition. Such materials include, for example,
magnetite, ~amma-Fe203, chromium dioxide, cobalt-treated iron
oxides, samarium cobalt alloys, and the like~ Of these,
magnetite and gamma-Fe2O3 are preferred based upon cost and
commercial availability. The particle size of the magnetic
particle can be varied to convenience so long as the formu-
lated ferrofluid is stable (i.e., the magnetic particles
remain uniformly suspended throughout the ferrofluid composi-
tion under conditions of use in well cementing and in the
presence of a magnetic field). Magnetic materials with
particle sizes of up to about 4000 Angstroms are presently
preferred~ based on commercial availability of such
materials. Larger particle sizes and mixtures of particle
sizes can also be used. The amount of magnetic material
included in the ferrofluids can be varied, but generally
amount of up to about 20 weight percent are used, total
weight basis.
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A binding agent or surfactant is also used in the stable
ierrofluid composition. The binding agent is preferably a
synthetic polymer latex, and a styrene-butadiene polymer
latex is most preferred. If a surEactant is chosen, any
surfactant may be used which will keep the magnetic particles
uniformly suspended in he cementitious ferrofluid composi-
tion and which does not adversely react with the hydraulic
cement component. Normally, a non-ionic or anionic surfac-
tant is used. Examples of such surfactants include:
sulfonated aromatic polymers (e.g., naphthalene sulfonates,
sulfonated polystyrenes, sulfonated polyvinyltoluenes,
lignosulfonates, etc.); polyamines (e.g., polyalkylenepolya-
mines, etc.), polyvinylalcohols, and the like. The polymeric
latex binding agents are presently preferred over the
surfactants in formulating the cementitious ferrofluids.
Additives conventionally used in well cements can also
be included in th~ present cementitious ferrofluids in
conventional amounts so long as such additives do not affe~t
the stability and performance of the cement slurry.
The liquid medium in ~he cementitious ferrofluids is
normally an aqueous liquid. When Portland cement is util-
ized, water or water-alcohol solution are used and water is
the preferred medium. The lower alkanols (e.g., methanol,
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ethanol, isopropanol, etc.) are occasionally used to enhance
the solubility of organic additives in the cement slurry.
As noted above, conventional oilfield cement additi~es
~an be used herein. Such additives include: for example,
fluid-loss additives, retardexs, accelerators, extenders,
lost circula~ion ma~erials, weighting agents, gases, expan-
sive agents, dispersants, sur$actants, and the like, all of
which are known classes of materials.
The cementitious ferrofluids are formulated by blending
the components in appropriate amounts in any convenient
manner. Normally, the magnetic particles are blended with
the drv hydraulic cement and the dry blend is then added to
the li~uid medium containing the binding agent or surfactant
with stirring or other mechanical means of agitation. If
other additives are used, they are added to the cement slurry
via conventional techniques. In well cementing, the cemen-
titious ferrofluid will normally be prepared at the well site
using conventional blending equipment to blend the solids and
liquids together.
The spacer or chemical wash ~errofluids which are used
herein are prepared by blending the magnetic particles, a
stabilizing agent (binding agent or surfactant) and the
spacer or chemical wash formation.
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The cementitious ferrofluid can be injected l~to the
annulus by any convenient technique, but most commonly the
cementitious fluid will be pumped through the piping or
casing to the bottom of the wellbore and then upwardly
through the annulus separating the casing and the walls of
the formation until the desired zone has been filled with
cement ~lurry.
Alternatively, the spacer or chemical wash ferrofluid
is injected through the casing to the bottom of the wellbore
and upwardly through the annulus separating the casing and
the walls of the formation to the zone to be treated, and the
spacer or chemical wash ferrofluid is thereafter displaced by
a conventional well cement or by the cementitious ~errofluid
of the present invention.
In each instance, an alternating magnetic field is
applied to the spacer or chemical wash ferrofluid and/or the
cementitious ferrofluid while it is in the zone to be
cemented. The magnetic field applied may be a continuous or
intermittent magnetic field strong enough to cause a mechani-
cal response (e.g., movement) from the ferrofluid in situ.
The response of the ferrofluid will thereby dislodge and
displace residual drilling mud on the walls of the casing
and/or the formation. Cement bonding to the casing and
formation is thereby enhanced.
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Experimental
All of the experimental slurries described below were
prepared according to cement slurry preparation procedures
recommended by the API in API Spec 10, "API Specification
for Materials and Testing for Well Cementing Second Edition,
Section 5, pp. 16-17.
1. Class H Portland Cement (500 g), Dow Magnetic Latex
#181 tmagnetization: 130 gauss; 90 mL) and fresh water (110
mL) were blended together to form a homogeneous cement
slurry. Upon placing a bar magnet made of samarium cobalt
next to the glass beaker containing the slurry, the slurry
moved as a unit toward the magnet. Upon continuous exposure
to the magnetic field, no segration of the magnetic latex
from the cement matrix occurred. Therefore, the slurry is a
stable cementitious ferrofluid which can be used in cementing
wells, per the present invention.
2. Class H Portland Cement (400 g), gamma-Fe203
Pfizer No. MO-2228; 40 g), polynapthalene sulfonate -
formaldehyde condensate (Dowell Schlumberger D65; 4 g~,
styrene-butadiene latex (Dowell Schlumberger D600; 20 mL),
and fresh water (300 mL~ were blended together to form a
homogeneous cement slurry. Upon placing a samarium cobalt
bar magnet next to the glass beaker containing the slurry,
the slurry moved as a unit toward the magnet. Upon con-
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tinuous exposure to the magnetic field, the ~amma-Fe203
particles did not separate from the cement matrix. This
system is also a stable cementitious ferrofluid useful in the
present invention.
3. Class ~ Portland Cement 1~400 y), CaSO4.1/2 H2O (40
g), silica flour (140 g), polynapthalene sulfonate - formal-
dehyde condensate (Dowell Schlumberger D65; 2 g), styrene-
butadience latex (Dowell Schlumber~er D600; 8 mL), and water
(309 mL) were blended together to :Eorm a homogeneous cement
slurry. Upon placing ~ samarium cobalt bar magnet next to
the glass beaker containing the slurry, the slurry moved as a
unit toward the magnet. Upon continuous exposure to the
magnetic field, the gamma-Fe203 particles did not separate
from the cement matrix. This system is also a stable
cementitious ferrofluid useful in the present invention.
Note that this cement system is an "expanding cement" which
expands after setting.
The following "washes" or "spacer fluids" are non-cemen-
titious ferrofluids, in a well cementing context. The API
slurry preparation procedure applies for these fluids.
4. A commercial silicate-gel spacer concentrate
(Spacer 1000 from Dowell Schlumberger; 64 g) was blended with
gamma-Fe2O3 (61 g), and diluted with water (475 mL) to form
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an aqueous slurry. Upon placing a samarium cobalt bar magnet
next to the glass beaker containing the slurry, the slurry
moved as a unit toward the magnet. Upon continuous exposure
to the magnetic field, the gamma-Fe203 particles did not
separate from the matrix, This ~ystem is a stable ferrofluid
and can be used as a spacer or wash in cementing wells.
5. A commercial cellulose-gel spacer concentrate
(Spacer 3000 from Dowell Schlumberger; 50 g) was blended with
barite (76 g), gamma-Fe2O3 (50 g), styrene-butadiene latex
(Dowell Schlumberger D600; 4 mL) and 380 mL water to form a
slurry. Upon placing a samarium cobalt bar magnet next to
the glass beaker containing the slurry~ the slurry will move
as a unit toward the magnet. Upon continuous exposure t~ the
magnetic field, the gamma-Fe2O3 partioles did not separate
from the matrix. This system is a stable ferrofluid and can
be used as a spacer or wash in cementing wells.
The following is an illustration o~ one embodiment of
the invention.
6. A cementitious ferrofluid with the composition
given in Example 2 was placed in the annulus of a laboratory-
scale wellbore model. A magnetic device, with samarium/co-
balt magnets arranged radially, was placed inside the model's
casing. Upon rotation of the magnetic device inside the
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o~
casing, the cementitious ferrofluid was observed to ~pin
around the casing.
one embodiment of the invention is shown in Fig. 1, in
which a casing 2 is provided with magnetic fields having
north and south poles 4 and 6, respectively. The magnetic
fields could be generated as shown in Fig. 2, or the casing
itself could be magnetized, or the fields could be generated
by an axially displaceable device containing permanent
magnets or electromagnets. The magnetic fields are then
caused to move around axis 8, ~or example by rotating the
casing if the casing is magnetized, or by rotating a device
containing permanent magnets or electromagnets, or, in the
case of electromagnets, by electronic means. In Fig. 2,
magnets 10 are attached on the outside of casing 2 by straps
12. Other ways of attaching the magnets to the casing, such
as by welding or glue, are also suitable.
Fig. 3 shows a casing 2 provided with magnetic fields
consisting of north and south poles 22 and 24, respectively,
in an alternative configuration. Movement of a ~errofluid
outside the casing is caused by moving the magnetic fields up
and down axis 26, in ways analogous to those discussed for
Fig. 2.
Fig. 4 is a cut-away view of a ferromagnetic casing 3
furnished with solenoid windings 14 and a magnet 16 inside
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o~
magnetized in the direction shown by arrow 17. Flux line 18
of magnet 16 shows the shielding effect of the ferromagnetic
casiny when no current is supplied to the solenoid, compared
to the enhanced flux line 20 illustrating the increased
~mount of flux manifested by magnet 16 when current is
supplied to the solenoid. The magnet1c field represented by
flux lines 18 or 20 can be rotated with respect to a fer-
rofluid surrounding the casing by rotating magnet 16 around
the axis 19.
Fig. 5 shows an electromagnetic device 30 in a casing 2.
The device can be moved vertically along the suspending means
32. Coils 34 produce magnetic fields 36 which can be moved
with respect to a ferrofluid outside the casing by moving
the device along the vertical axis of the casing, and/or by
electronic means resulting in changing the polzrity of the
coils.
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