Note: Descriptions are shown in the official language in which they were submitted.
~2~735~ GE TA: O 4 8
IIIGH TEMPERATllRE CHEMICAL CEMENT
This invention relates generally to cements capable
of use in oil and qas wells, and more particularly to high
temperature cements capable of use in treating high
temperature wells and other hiqh temperature subsurface
formations.
Cements used in oil and gas wells serve a variety of
; 20 functions. Typically, oil and gas wells are walled with
steel tubing called the casingO Cements are employed to
secure the cas;ng to the wall of the borehole usually by
pumping the cement down the inside and up the outside of
the casinq to the desired level. Once the cement sets,
the cement and casing provide a seal which protects
surrounding fresh water resevoirs and the like from
contamination by the formation fluids. Additionally, ~he
cemented casing aids in supporting unconsolidated rock
formations surrounding the borehole, and helps to prevent
blowouts and subsequent waste of the reservoir's
resources. Another important application of cement in oil
and ~as wells is its use in water-exclusion methods~ In
many oil and gas wells, the production of water makes the
well uneconomical to operate. This can be overcome by
placing a cement seal at the water-oil interface in a
borehole to exclude water from the oil production.
Typical cements used in the above applications are
cements of the portland and portland-pozzolarl tyPes.
These cements are ~enerally produced by burninq a mixture
of finely divided calcareous and argillaceous material and
grindinq the resultant residue to produce a fine powder.
The calcium silicates and calcium aluminates produced by
the calcining process react chemically with water to form
a stone-like mass.
However, these types of cement are often inadequate
~hen used in the high temperature, hi~h pressure, corro-
sive environment of many deep wells and subsurface forma-
tions such as oil wells, hydrothermal wells, and other
~eothermal formations. Portland and pozzolan type cements
tend to deteriorate under these conditions o~ten causinq
failure of the cemented well or formation.
Past methods of modifying portland type cements have
proved unsatisfactory for many applications. Magnesium or
ma~nesium containinq compounds have been added to ~ortland
cement to increase temperature resistance. ~nfortunately,
unpredictable swelling often occurs making the set of the
cement unsatisfactory. In addition, the high viscosity of
the ma~nesium containin~ slurry inhibits satisfactory
pumping in many instances. Addition of more water to
improve pumpability further decreases the settin~, curinq
and other physical qualities of the cement. Temperature
resistance is claimed to be improved by the use of
calcined serpentine, silica and a calcium silicate to form
a high temperature cement which is pumped into a well and
allowed to hydrothermally cure to form a crystallized
diopside and/or serpentine-containing phase. In addition,
asbestos fibers have heen added to portland type cements
to im~rove temperature resistance, but the requirement o~
a hiqh water to asbestos ratio permits only the use of
small amounts of asbestos fibers in order to maintain
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ade~uate pumpa~ility. In addition, too hiqh an asbestos
fiber content (generally qreater than 2~) in the cement
decreases the compressive strength of the cement.
In addition to difficulties with temperature resis-
tance, stability and pumpability, settinq time is a major
disadvanta~e of portland type cement. The hiqh tempera-
ture formations tend to decrease the set time siqnifi-
cantly and impair pumpability. Retarder additives such as
calcium lignosulfonate and carboxymethyl hydroxyethyl
cellulose have been added to portland cement to increase
the settin~ time. Unfortunately, the results are qener-
ally unpredictahle due to the absence of a homogeneous
mixture of the additive throu~hout the cement. Improve-
ments have been provided for this condition hy coatinq thecement qrains with crosslinked hydroxyalkyl cellulose in
an attempt to provide a uniform concentration of retarder
throuqhout the cement.
Althouah improved portland type cemsnts are
available, a hiah temperature cement havinq overall
qualities of hiqh temperature resistance, stability,
pumpability, chemical resistance and controllable settinq
time is desired.
The present invention comprises a unique foamed hiah
temperature chemical cement havinq the aualities of hiqh
st~en~th, chemical resistance, controllable settina time,
pumpability and stability.
More particularly, the invention in one as2ect
pertains to a high temperature chemical cement composition
comprising finely divided particulate cementing matter
capable of use under high temperature conditions, a
polymeri~able resin capable of coating the particulate
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matter and of setting and maintaining its set under
the high temperature conditions, a liquid carrier, and
a foaming agent capable of foaming the composition
comprising air and surfactant.
In its foamed condition, the composition is liquid
in form or liquescent in that it can act and perform as
a liquid, thus providing pumpability. At the subsurface
formation temperature, the resin will set and consolidate
the composition into a rigid dense mass.
Accordingly, the invention also comprehends a
method of cementing a subsurface zone comprising intro-
ducing the composition into a subsurface zone
and maintaining the composition in the subsurface area
until the resin has set. A polymer profile control
treatment would further include introducing a polymer
suitable for profile control into the fracture containing
the cement matrix.
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Advantaqeously, the permeability of the set composi-
tion can be adjusted so as to provide a maximum barrier to
the flow of oil, gas, steam, water and the like, or to
provide a more permeable partial barrier. Partial bar-
riers are desirable in forminq a matrix for later polymertreatment of naturally fractured reservoirs having
extremely high local permeability which qenerally prohibit
traditional polymer profile control treatments. The
permeability of the set composition can be adjusted by
varyinq the amount of air and surfactant incorporated into
the comPosition.
In addition, the setting time of the composition can
be predetermined by varyinq the pH of the composition.
Once se~, the composition is stable to at least tempera-
tures of about 400F. Further, the composition once set
is chemically resistant to hydrocarbons, acids, bases and
most other non-oxidizing chemicals.
The subject invention is a novel hi~h temperature
chemical cement. The composition of the chemical cement
comprises appropriate temperature resistant finely divided
particles combined with a polymerizable resin capable of
settin~ under formation conditions and maintaining its
set, a liquid carrier, and a foaming system comprisinq
surfactant and air. The foaming system provides a
pum~able mixture of uniform concentration~ Under
formation conditions the resin sets, consolidatinq the
composition into a riqid dense mass havinq high strenqth~
temperature and chemical resistance and stability.
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The Particulate Matter Component
The particulate matter component of the compositions
of this invention may be any suitable finely divided
particulate cementinq matter, such as powders, dusts, or
flours such as silica flour, capable of use under hiqh
temperature formation condtions which have the capability
of forming a hi~hly imper~eable mass in conjunction with a
set resin. In addition, the particulate matter i5 chosen
for its strength, economy, and compatibility with other
components of the composition and the formation fluids~
_he Thermosettin~ Resin
Various resins may be used in the present invention.
This includes true thermosetting resins, often referred to
as one-step resins because no curing agent is required,
and two-step thermosettinq resins which utilize a catalyst
for curing. An example of a true thermosetting resin
would be a phenolic, or phenol-formaldehyde, resin of the
resole type. An example of a two-step resin would be a
phenolic resin of the novolac type. Other thermosetting
resins of the aminoplast type may also be used, including
urea-formaldehyde and melamine-formaldehyde resins.
~lthough these resins may be used as one-step resins,
addition of acid catalysts will speed the curinq time.
Furan resins, including resins produced from the reaction
of furfuryl alcohol with urea, formaldehyde or phenols,
may also be used~ These resins are generally cured by
addition of mineral or organic acid catalysts, althou~h
occasionally alkaline catalysts are used for curing. In
addition, it is contemplated that epoxy type resins may
also be used.
In a preferred embodiment of the present invention,
an oil-soluble resin is desirable, for example a urea-
~ 2~7;~i2
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~ormaldehyde resin. This allows addition of substantial
amounts of water without affecting the polymerization of
the resin.
Of primary importance in choosing a resin is the
ability to control the settinq time. A sufficient amount
of time must be allowed for preparation of the composi-
tion, storaqe, and introduction of the mixture into the
subsurface formation before setting. In this respect, an
oliqomer type resin is preferred to a ~onomer type resin
because of the increased settin~ time for the oligomer.
If the thermosetting resin is of the two-step vari-
ety, a catalyst is qenerally required. Acid catalysts are
usually employed, althouqh base catalysis is qenerally
employed in limestone formations. Generally as the pH of
the composition is decreased by addition of the acid
catalyst, a corresponding decrease in resin setting time
results. Ir, a preferred embodiment of the invention, a
buf~ered acid catalyst is u~sed to raise the pH of the
composition, thereby increasing the setting time of the
resin while leaving the total acid quantity nearly the
same.
If desired, the resin may be pre-coated on the parti-
culate matter before combining it with the other compo-
nents of the composition. Methods for making resin coated
particles are well known in the art, as typi~ied by Nesbit
et al., U.S. Patent No. 2,986,538. Pre-coating is deemed
especially desirable in those instances where the resin-
forminq material is soluble in water and the liquid car-
rier is water.
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The Liquid Carrier
.
Any suitable liquid may be used in practicinq the
present invention. In general, the liquid is chosen on
the basis of its economy, fluidity, and chemical compati-
bility with the rock formation and the reservoir fluids.
Water, brine and like liquids are generally preferred
because they are economical.
The Foaming System
The components required to produce a foamed fluid in
accor~ance with the present invention will normally in-
clude a surfactant and air foaming agent. The foaming
agent helps maintain the liquidity of the overall composi-
tion. The surfactant may be cationic, anionic or non-
ionic, but it must be capable of qeneratinq a foam with a
liquid carrier and air at ambient temperatures. Examples
of surfactants which may be used are soaps, synthetic
detergents, and proteins. Desirable surfactants can be
selected from the many alkyl aromatic sulfonic acids. A
principal purpose of the surfactant is to control bubble
life in the foam. Buhble strenqth can be increased by
addinq minute amounts of polyvalent cations which further
stabilizes the foam.
.
The foaminq system can be adapted to give a set
cement with minimal permeability, such as desired for
plugging a well or sealing a porous formation, or to give
a set cement havin~ more than minimal permeability, such
as desired for providing a matrix for polymer profile
control treatments. Generally, the fractures of naturally
fractured resevoirs have extremely high local perme-
ability, and as a result typical polymer profile control
has limited success. By regulating the foaming system to
ProVide a more permeable cement, an effective cement
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matrix can be provided in the fracture so that a Polymer
will hold.
Generally, the foaming system can be adapted to
provide a cement with more than minimal Permeability by
(1) incorporating more air into the composition, ~2) in-
creasinq the concentration of surfactant in the composi~
tion, or both. Cements of minimal permeability are pro-
vided by incorporatinq as little air as possible into the
composition and decreasing surfactant compositon.
EXAMPLES
The following examples describe the invention in more
detail. Such examples are for the purpose of illustrating
the invention and do not limit the scope of the invention.
Example 1
A chemical cement for use under conditions where
minimal permeability is desired was constructed from the
components listed in Table 1.
~2 ?~7 3 ~
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TABLE 1
Equivalent Laboratory
Material Field Units W4iqht Comments
-
Silica Flour 208 lb.500 g 400 mesh
Resin I 1.70 qal. 40 a Urea/for?Taldehyde type
*
Resin II 1.76 qal. 40 q ?~uacorr 1300: Butyl
Acetate (80:20 by wt.)
Catalyst 2.10 gal.50 g 39.2% Phosphoric Acid
15 Component t85%), 4.4~ Fluos il ic i c
Acid (40%), 20.0~ Toluene
Sulfonic Acid, 36.4
Water
20Surfactant- 3.80 qal. l00 g 35.3% Phosphoric Acid,
Catalyst 3.9~ Fluosilicic Acid,
Co~ponent 18~ Toluene Sulfonic
Acid, 10% Dodecyl
Benezene Sulfonic Acid,
32.8% Water
Water/A~monium 10.00 qal. 200 ?~ Enough Amm~nium Hydroxide
Hydroxide to bring the mixture's pH
^ to 6
The Quacorr 1300 referred to in Table 1 is a partially
polymerized furfuryl alcohol resin supplied by the Quaker Oats
Ch?emical Company (the butylacetate serves as a solvent for the resin)
35 as ~?ell as a water scaven~er for the polymerization reaction.)
Example 2
The components of Example 1 were mixed in a Kitchen
Aide mixer at the lowest speed settinq so as to incorpo-
rate as little air as possible. The silica flour was
mixed with resins I and II until coated. The catalyst and
surfactant comPOnents and the water/ammonium hydroxide
solution were then added. (These may be premixed before
adding). Mixing was continued until the silica flour
* Trademarks
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mixture was liquidized. Further mixina will not damage
the results.
Example 3
A six inch pipe nipple was packed with solvent
stripped formation material and equipped with fittin~s.
An initial permeability to water was measured and found to
be 3.49 darcies. A liquidi~ed silica flour mixture pre-
pared according to Example 2 was injectsd into the pipeni~ple under 5 psi and allowed to set. The core was then
uncapped and visually inspected. The silica flour was
well dispersed in the core as evidenced by the uniform
consolidation of the core material at both injection and
production ends of the core. The core was recapped ~ith
clean end caps and the permeability was remeasured. The
core was found to be plu~ed. The core was thsn placed in
an oven at 392bF for 96 hours to see if the heat would
deqrade the polymerized resinO After the 96 hours, the
permeability was remeasured and the core was found to
still be plua~ed. Visual examination revealed no damaqe
as well.
Example 4
A chemical cement for use under conditions where more
than minimal permeability is desired was constructed from
the components listed in Table 2.
TABLE 2
Equivalent Laboratory
Materi0 Field Units Weiaht G~,ents
Silica Flour 208 lb. 500 a 400 mesh
Resin I 1.70 aal. 40 9 Urea/formaldehyde t~pe
Resin II 1~76 gal. 40 q Quacorr 1300: Butyl
Acetate (80:20 by wt.)
Catalyst None
Ccmponent
Surfactant- 5.7 qal. 150 g Increased amount of the
Catalyst surfactant component as
Component ~escribed in Table l.
Ihis c ~ onent contains
0.5% Aluminum cation
based on the D~decyl
Benzene Sulfonic Acid
wei~ht.
~ater/A~moniu~ lO.0 qal. 200 9 Enouqh Ammonium to
Hydroxide brin~ the pH to 6.
Example 5
The components of Example 4 were mixed as in Example
2 with the exception that more air was incorporated into
the mixture to produce a more hiqhly foamed composition.
As evidenced in Table 2, foaminq was further increased by
addinq more surfactant. The soap bubbles of the foam were
strengthened by use of an aluminium cation as a foam
stabilizer.
Example 6
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A fracture-like environment was created for testing
the compositions of Examples 1 and 4 in the followin~
manner. Two Berea cores, 2x2x12 inches were cut in half
and two qrooves were placed on each of the newly formed
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faces. The cores were then fitted back together according
to their original orientation with the sides of the cores
sealed with epoxyO The grooves served to insure a
fracture-like environment within the cores. The cores
were then equipped with fittings at each end to facilitate
the introduction of fluids and cast in epoxy resin. After
the epoxy resin had set, the cores were ready for
treatment.
Example 7
An initial permeability to water was run on one of
the cores prepared accordin~ to Example 6 and found to be
14.67 darcies. Liquidized silica flour constructed
accordinq to Example 2 was ~ravity flowed into the core
and allowed sufficient time to set. The permeability was
remeasured and found to be 0~ The fittinqs were removed
and found to be plugqed. The core was fitted with new
fittings and the permeability was found to be 0.822
darcies. This corresponds to a 94.4% reduction in perme-
ability.
Example 8
An initial permeability to water was run on the other
core prepared in accordance with example 6 and was found
to be 21.7 darcies. Liquidized silica flour prepared
accordinq to Example 5 was ~ravity flowed into the core.
After the silica flour had set and the fittin~s were
replaced, the permeability was remeasured and found to be
1.64 darcies. This corresponds to a 92.4% reduction in
permeability. A summary of the results are listed below
in Table 3.
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TABLE: 3
FRACTURE RESULTS
5 ~ Initial K _ Final K ~ Reduction
714.67 darcies 0.82 darcies 94.4
821.70 darcies 1.64 darcies 92.4
Because the mixture is non-viscous and the aggregate
used, the silica flour, is very fine ~400 mesh), the mix-
ture will penetrate high permeability formations easily.
In the practice of the invention, the rate of poly-
merization of the resin material qenerally increases alonq
with increasing temperature. In addition, polymerization
rate is varied by the type of resin used. A monomer-type
resin will polymerize faster than an oligomer-type resin,
qiven the same monomer chemistry. The Quacorr 1300
referred to in the above examples is water-insoluble.
Since Quacorr 1300 is an oligomer, it polymerizes slowly,
and since it is oil-soluble, it permits substantial
amounts of water to be added to the mixture thereby
increasing liquidity but not suppressing the setting
polymerization reaction.
In the compositions describe above, changing the
quantity of acid downward to extend setting time could
prevent polymerization entirely. Adding 6N ammonium
hydroxide to the acid mixture to raise the pH had the
effect of leaving the total acid quantity nearly the same
while providing hydrogen ions more slowly. The hiqher the
pH, the longer the set time for a given temperature. Con-
sequently, higher temperature mixtures require a higher pl~
to achieve the same set time as lower temperature mix-
tures. Very hiqh temperatures may require reduction of
total acidity.
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The foregoing description has been directed to a
particular embodiment of the invention for the purposes of
illustration and explanation. Those skilled in the art
will readily appreciate modifications and changes in the
procedures and components set forth without departin~ from
the scope and spirit of the invention. Applicant's intsnt
is that the folowin~ claims be interpreted to embrace all
such modifications and variations.
