Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD FOR THE FRACTt1RE STIMULATION OF A SUBTERRANEAN
FORMATION HAVING A WELLBORE BY liSING THERMOSET POLYMER
NANOCOiVIPOSITE PARTICLES AS PROPPANTS, Vi'HERE SAID PARTICLES
ARE PREPARED BY USING FORMULATIONS CONTAINING REACTIVE
INGREDIENTS OBTAINED OR DERIVFD FROM RENEWABLE FEEDSTOCKS
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Patent Application No. 11i740,389,
entitled "Method #'or the Fracture Stimulatioti of a Subterranean Formation
Iiaving a
Wellbore by Using Thermoset Polymer Nanocomposite Particles as Proppants,
where
Said Particles Are Prc.Ypared by Ylsing Formulations Containing Reactive
Ingredients
Obtained or Derived from Renewable Feedstocks", filed Aptil 26, 2007, which
application is a continuation-in-part of U.S. Patent Application No.
11/323,031 entitled
"Therrnoset Nanocomposite Particles, Processing For Their Production, And
Their Use
In Oil And Natural Gas Drilling Applications", filed December 30, 2005, which
claims
priority to U.S. Provisional Application No. 60/640,965 filed Deccmber 30,
2004. This
application is also a continuation-in-part of U.S_ Patent Application No.
11/451,697
entitled "Thetmoset Particles With Enhanced Crosslinking, Processing For Their
Production, And Their Use In Oil And Natural Gas Drilling Applications", filed
June 13,
2006. This application is also a continuation-in-part of U.S. Patent
Application No.
11/695,745 entitled "A Method For The Fracture Stimulation Of A Subterranean
Formation Having A Wellbore By Using Impact-Modified Thermoset Polvnier
Nanocomposite Particles As Proppants," filed April 3, 2007. The contents of
prior
application nos. 11/323,031, 11/451,697, 11/695,745, and 60/640,965 are fully
incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to a method for the fracture stimulation of a
subterranean formation having a wellbore by using ultralightweight thermoset
polymer
_1.
SUBSTITUTE SHEET (RULE 26)
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nanocomposite particles as proppants, where said particles are prepared bv
using
fotmulations containing reactive ingrcdicnts obtaincd or dcrivcd from
rencwable
fccdstocks. Without reducing thc genera{ity of the invention, in its currcntly
preferred
cmbodiments, the thermoset polymer matrix of said particles consists of a
copolymer of
styrenc, ethyvinylbenzcnc, divinylbcnzene and additional monomers obtained or
derived
froni plant oils; carbon black is used as the nanofiller, suspension
polymerization in the
rapid rate polyrnerization mode is pcrfonned to prepare said particles, and
post-
polymerization heat treatment is performed in an tutreactive gas environment
to further
advance ihe curing of the thermoset polymer matrix. The main benefit of the
use of
reactive ingredients obtained or derived from renewable feedstocks is that
doing so
reduces the reliance on petrochemical feedstocks and hence provides advantages
in terms
of sustainability. 1'he fracture stimulation method of the invention can be
implemented
by placing said particles in the fracture either as a packed mass or as a
panial monolayer.
Without reducing the generality of the invention, said panicles are placed as
a partial
monolayer in its preferred embodiinents.
I3ACKGROUND
1. Introduction
U.S. Patent No. 6,248,838, "Chain entanglement crosslinked proppants and
related uses"; the background section of U.S. patent Application No.
111323.031 entitlcd
"l'hermoset nanocomposite panicles, processing for their production, and their
usc in oil
and natural gas drilling applications"; the background section of U.S. Patent
Application
No. 11/451,697 entitled "Thermoset particles with enhanced crosslinking,
processing for
their production, and thcir use in oil and natural gas drilling applications";
and the
background section of U. S. Patent Application No. 11 /695,745 entitled "A
method for
the fracture stimulation of a subtrrranean formation having a wellbore by
using impact-
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modified thertnoset polymer nanocomposite particles as proppants", provide
background
infotmation rclated to the prescnt invention and are fully incorporated herein
by
reference. The background discussion presented below is intended to supplement
the
background discussions in these four prior filings, and focuses on additional
background
> information that is not found in these filings.
Applicant has found no prior art in the patent litcrature, and no publications
in the
general scientific literature, that disclose a method for the fracture
stimulation of a
subterrancan formation having a wellbore by using, as proppants,
ultralightweight
thcmloset polymcr nanocomposite partictes where the matrix polymer phase is
prepared
by the reaction of'cotnponents (monomers, oligomers and/or polytncrs
containing
reactive functionalities) obtained or derived trom renewable feedstocks. Thc
discussion
below is hence intended to he mainly of a pedagogical nature. It provides
background
information that will help those in the field understand the invention by
familiarizing
them with key information on the use of renewable feedstocks as components of
(a)
proppants in the fracture stimulation of a subterranean formation, and (b) the
reactive
mixture (monomers, oligomers and/or polymers containing reactive
functionalities) used
in the synthesis of the matrix polymers of thermoset composites. Since these
two types
of use of renewable feedstocks do not appear to have ever been pursued
simultaneously
in previous work, they will be discussed below in separate subsections.
Por the purposes of this disclosure, a"n:newable feedstock" is delined as a
feedstock obtained from a microorganism-based, plant-based, or aniinal-based
re-source
that, once used, can be renewed on the time scale of a hutnan life; in other
words, within
no more than one century. In practice, most of the typical renewable resources
(such as
soybean or com plants) that can serve as a source of useful renewable
feedstocks can be
renewed in much shorter periods, such as yearly. By contrast, while
pctrochemical
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(fossil fiiel) resources also have a biological ongin, they are not
"renewable" in the
practical sense captured by our definition since, once used, their rene.val
would requtre
the passage of geological time scales (thousands to millions of years).
2. Utilization of Renewable Fcedstocks as Components of Proppants
a. Fundamcntal Considcrations
The potcntial utilixation of rencwable feedstocks as ingredients of
lightwcight
and ultralightweight proppants of sufficient compressive strength to be useful
for
applications in fracture stimulation has been investigated for manv years.
1t is important, for the sake of clarity, to bcgin by distinguishing the
general
benefits that result from the ulttalightwcight characteristies (near neutral
buoyancy in
water) of such proppants from the benefits of using renewable f eedstocks as
ingredients
in their preparation.
The general benefits of using ultralightweight proppants of sufficient
compressive strength, regardless of the source of the feedstock used in their
preparation,
arise from their densities which are much lower than the densities of typical
sand-based
or ceramic-based liroppants. These gencral benefits are, hence, independent
of'the
inbredicnts used in the preparation of such ultralightweight proppants. These
benefits
include excellent ability to be transported (without requiring the use of very
high
pumping rates), without settling substantially during transport, in fraeturing
fluids of
210 very low viscosity such as "slickwater". The key benefit of efficient
proppant transport
is that ultralightweight proppants can be transported much further than heavy
proppants
into the formation by using such tluids so that rnuch greater effective
fracture lengths can
be attained. tilickwatcr is less damaging to the reservoir permeability than
the
crosslinked gelled fluids requircd to carry proppants of high density.
Finally, the use of
ultralight.veight proppants inakes it practical to placc the proppant in the
fracture as a
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"partial monolayer", a mode of proppant placement that was demonstrated by
Darin and
Huitt as far back as 1959 on theoretical grounds to be especially effective in
fracture
stimulation. In sumniarv, substantially smaller volumes and concentrations of
proppant
would be required to realize sufficient fracture width and conductivity when a
partial
monolayer can be emploved instead of a convcntional proppant pack. Contbined
with a
greater effective fracture length, the ability to place the proppant as a
partial monolayer
would result in the exposure of more of the reservoir to the conductive path
and thus lead
to greater hydrocarbon production over the long term.
lf renewable feedstocks are used in the preparation of uliralightweight
pruppants
ofsufficient coinpressive strength, then they offer tx.nefits in ternis
ofsustainability in
addition to ot7ering all of the general benefits of ultralightweight
proppants. Since
renewable feedstocks typically have much lower densities than materials such
as sand
and ceramics, it is thus natural to expect that their potential use in the
preparation of
ultralightweight proppants manifesting the additional advantages of
sustainability has
generated much interest.
b. Detailed Example of a General Approach
Typical of a general approach that is often used, but further along than
similar
technologies in its reduction to practice and hence especially useful as an
example, is the
technology taught in a scries of U.S. patcnts (No. 6,364,018, No. 6,749,025
and
6,772,838') and U.S. patent applications (No. 20060065398 atid No.
2006007398U). 'l'his
technology will be reviewed below.
The particulate material comprises a plant-based malerial selected from at
least
oae of ground or crushed nut (such as walnut, pecan, almond, ivory nut or
brazil nut)
shetts, ground or crushed secd shells of other plants (such as corn), ground
or crushed
fruit (such as plum. peach, cherry or apricot) pits, processed wood (for
examptc, from
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oak, hickory, walnut, poplar or mahogany), or a mixture thereof. A protective
and/or
hardening coatirtg is also used. Additional components are also incorporated
in somc
embodiments, for purposes such as tailoring the densily and/or providing
additional
hardness. In a preferred embodiment. ground or crushed walnut shell material
is coated
with a polyurethane resin for protection and waterproofing.
Applications of the resulting rclatively lightweight and/or substantially
neutrally
buoyant particles arc claimed as proppant material in hydraulic fracturing
treatments
(U.S. Patent No. 6,364,018 and U.S. Patent No. 6,772,838); as enhanccrs of
productivity
in hydraulic fracturing of subacrranean forntations having natural fractures
when used to
pre-Ireat the fonnation (U.S. Patent Application No. 20060065398); as proppant
material
in acid fracturing treatments ((U.S. Patent Application Nlo. 20060073980); and
as
particulate material for sand control niethods such as gravel packing and frac
packs (U.S.
Patent No. 6,749,025 and U.S. Patent No. 6,772,838).
The theoretical and practical advantages (as well as the technical challenges)
of
the use of ultralightweight proppants such as those taught by the cited U.S.
patcnts (No.
6,364,018, No. 6,749,025 and No. 6,772,838) and U.S. patettt applications (No.
20060065398 and No. 20060073980) are described further, and examples
(including
field testing results) are given of the utilization of such proppants, by
Rickards et al.
(2003). Wood et al. (2003), Brannon et al. (2004), Myers et al. (2004), Schein
et al.
(2004), Posey and Strickland (2005), Kendrick et al. (2005), and Ward et al.
(2006). It is
also worth noting that Kendrick et al. (2005) state that the ultralight,-
veight proppant used
in that study "consists of a cliemically hardened %i,alnut hult core with
multiple layers of
epoxy resin coating as the outer shelP'.
c. Other C:xaniples
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In addition to the technology reviewed in the subsection above which has been
fully reduced to practicc, many other patents and pateni applications also
mention (albeit
in a inore cursory inanner) the use of renewable ingredients in proppants.
Some of these
patent documents mention the use of rencwable ingredients only in the main
bndv of
their text, while others also mention them in the clainis.
One typical context is in patent documents teaching coated proppant
technologies. In some such technologies, the proppant particles that are being
coated
niay comprise renewable ingredients siniilar ro those discussed above, such as
grotmd or
crushed walnut shell material. ]n an alternative and less commonly proposed
coated
proppant approach, the coating that is placed on sand or ceramic proppant
panicles may
comprise renewable ingredients (such as plant oils).
The other typical context is in patent documents teaching various techniques
for
fracture stimulation, gravel pack completion and!or sand control; where
partictes
comprising renewable ingredients are often listed among the types of proppant
compositions that may be used in the implementation of the method that is
being taught.
Some examples of additional patent documents (beyond those that were
discussed in the previous subsection) that mention the possible use of
renewable
ingredients in proppants in one or both of tltese two typical contexts include
U.S.
4,585,064, U.S. 5,597,784, U.S. 7.021,379, U.S. 7,073,581, U.S. 7,128,158,
U.S.
7,160.844, U.S. 7,178,596, U.S. 20050194141. U.S. 20060048943, U.S.
20060048944,
U.S. 20060078682, U.S. 20060204756, U.S. 20060205605, U.S. 20060260811, U.S.
20060272816, U.S. 20070007010, U.S. 20070036977, W02005100007,
W02006034298, and W02006084236.
3. Utilization of Renewable Feedstocks as Components of Reactive Mixture Used
in
Syrtthesis of Vlatrix Polymcrs of Thermosel Composites
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a. Introduction
A background paper on biopolymcrs, publishcd by the U. S. Congress, Officc of
Technology Assessment (September 1993), suggcstcd that the usc of biologically
derived
polymers could emerge as an important component of a new paradigm of
sustainable
economic systems that rcly on renewable sources of energy and materials. This
concept
has, indeed, gained increasing acceptance in the years that followed the
publication of
the background paper. The utilization of monomers obtained or derived from
biological
starting materials (such as amino acids, nucleotides, sugars, phenols, natural
fats, oils,
and fatty acids) in the chemical synthesis of polvmers is an important
component of this
paradigm of sustainable development. This is an area of intense research and
development activity because of the global drive to reduce the dependence of
the world
economy on petrochemical feedstocks.
b. Some Promising Renewable Sources of Reactive Ingredients
Suitable renewable feedstocks can be obtained or derived from a wide variety
of
microorganism-based, plant-based, or animal-based resources. The utilization
of
monomers, oligomers and polymers obtaincd or derived from renewable resources
as
coinponents of polymer composites is, therefore, anticipated to continue to
increase in
the future.
Among renewable feedstocks for the synthesis of polymeric products, natur,il
fats
and oils extracted from some cornnton types of plants [such as soybcan,
sunflowcr,
canola, castor, olive, peanut, cashew nut, punipkin seed, rapeseed, corn,
rice, sesanie.
cottonseed, palm, coconut, safllower, linseed (also kno%vn as flaxseed), hemp,
tall oil,
and similar natural fats and oils; and especially soybean, sunflower, canola
and Iinseed
oils] appear to be very proinising as potential sources of inexpcnsivc
monomers. Some
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animal-based natural fats and oils, such as fish oil, lard, neatsfoot oil and
tallow oil, may
also hold promisc as potcntiai sourccs ofincxpcnsive monomers.
c. Gcneral Classes of'lltcrmoset Cornpositcs Using [ngrcdients Obtaiited or
Derived from Rencwable Feedstocks
Fibrous and/or particulate components extracted from plants have been used for
decades as fillers in composites where the matrix polymer is prepared by using
inonomers obtained or derived from petrochemical fecdstocks. For exarnple,
U.S. Patent
No. 5,834,105 teaches siructural polyinerie composites consisting of a
polymeric matrix
and intact corn husks, and hence provides an example of this general type of
approach.
Another well-established type of technology is the use of a polymeric resin
based
on petrochemical feedstock as a binder and/or coating for fibrous andlor
paniculate
components that have been extracted from plants and then pressed and/or
agglomerated.
For cxample, in the fabrication of panicleboard, a plant-hased cellulosic
inaterial (such
as wood chips, sawmill shavings, straw, or sawdust) is combined with a
synthetic resin
(binder) by using a process in which the interparticle bond is created by the
synthetic
resin under heat and pressure.
'1'he development of thermosel composites where reactive components extracted
from renewablc fcedstocks are used as building blocks for the matrix polymer
is a much
newer area of research and development that is gaining momentuni. This
research area is
of interest in the context of the present invention. It will hence be the
focus of'the
remainder of this section.
As a practical maUer, a proppant must be able to retain good performance for
prolonged periods in a wide rangc ofharsh cm=ironments in order to find
widespead
utility. Conscquently. while therc are many potenlial applications for
composites
2.5 (prepared from renewable feedstocks) where biodegradability and/or other
types of
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envirottmental deeradability are among the key target properties, such
composites are not
optimal for use as proppants in implcmenting thc fracture stimulation mcthod
of the
invcntion, and will hcnce not be discussed further.
d. Chemical Modification for Derivation of Optimal Reactive Ingredients for
Use in Polymer Synthesis
It is possible to use the triglycerides obtained from plant oils directly as
monomcrs in the preparation of thermoset polymers and composites. It is,
however,
usually preferable to modifv these triglycerides cheniically to obtain
inonomers which
have more attractive reactivity profiles and contribtuions to the properties
of the final
tbermoset system afler incorporation.
fvtany chemical modifications can be made readily to tailor the reactivity
profile
and the Gnal propenies. Different plant oils provide significantly different
mixtures of
staning triglyceride molecular structures for use in the possible chemical
modifications,
thus providing a vast range of possibilities for new monomers. The development
and
new and improved monomers by chemical modification is an area of inteiise
research.
The use of genetic engineering to develop plants yielding oils containing
monomers with especially desirable molecular structures is also an important
area of
research and developmenl.
The developinent of processes for the utilization of reactive components
obtained
or derived froni natural fats and oils extracted from plant-based sources as
building
blocks for polymers and the matrix polymers of polymer composites is,
therefore, an area
of intense research activity. Plant-based liquids are typically mixtures of
molecules with
various chemical structures and various types of active sites. Consequently,
the
extraction of diffcrent reactive components, and the modification of these
components by
breaking thetn down into snialler monomers and/or derivatizing thcm, is a
crucial part of
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rescarch aimed towards the utilization of such reactive components as building
blocks in
the preparation of polymer composites.
For exarnple, U.S. Patent Application No. 20050154221 teaches intcgrated
chemical processes for the indttstrial utilization ofseed oil feedstoek
compositions.
Pillai (2000) discusses the wealth of high value polymers that can be produced
by
usino constituents cxtractcd from cashcw nut shell liquid.
Additional examples will bc provided bclow in the context of specific types of
polynters and composites prepared by using reactive components obtained or
derived
from tiatural fats and oils extracted from plant-based sources.
c. Various Polymers and Polvmer Coniposiles Synthesized By Using
Formulations Containing Reactive Ingredients Obtained or Derived from
Renewable Feedstocks
U.S. Patent No. 6,682,673 teaches a process for making a composite where a
natural fiber is used as the reinforcing agent, and the niixture of reacrants
from which the
matrix potytner is synthesized via free radical copolymerization comprises a
ring
opening product of epoxidized fatty conipounds with olefinically unsaturated
tatty acids
such as acrylic acid or merhacrytic acid. The initial fatty compounds are
obtained from
sources such as soybean oil.
Methods arc taught for the production of radically postcured polyurethanes by
reacting acrylic or methacrylic acid derivadves based on natural oils
(epoxidized faity
acid esters and/or epoxidized triglycerides) with aromatic and/or aliphatic
isocyanates
(U.S. Yatent Application No. 20030134928). In similar approaches, reactive
anhydrides
(U.S. I'atent Application No. 20030134927), structural coinponents such as
acrolein,
acrylamide, vinyl acetate and styrene (U.S. Patent Application No.
20030139489), or
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diallyl phthalates (U.S. Patent Application No. 20040097655) are included in
the second
stage of the preparation of the polymers.
I-lusic et al. (2005) rcported that they prcpared and compared two series of
glass
fiber reinforced composites, one using a polyol based on soybean oil and one
using a
petrochcmical polyol in the prcparation of the polyurethane matrbi. llte
mechanical
properties (such as tensile and Ilexural ntodulus, and tensile and flexural
strength) of the
two series of coniposites were comparable. It was stated that soybean oil-
based
composites are likely to find increasing applications beeause of tfieir
superior oxidative,
themial and hydrolytic stabilities.
Mosiewicki et a1. (2003) and Aranguren et al. (2005) developed composite
materials forrnulated by using a natural polyphenolic matrix (a commercial
tannin
adhesive) with pine woodflour as the reinforcing agent. These composites had
attractive
mechanical properties when they were dry. However, they were highly
susceptible to
water absorption in humid environments. Water absorption caused their
mechanical
properties to deteriorate significantly. Thc cured tannin matrix was found to
be even
niore hygroscopic than woodtlour.
Belcher et al. (2002) investigated the properties of biofiber-reinforced
biobascd
epoxy resins for automotive exterior applications. '1'hey considered the use
of both
epoxidized linseed oil and epoxidized soybean oil as nioditicrs of
conventional epoxy
resin compositions bascd on pctrochemical prccursors. They showed that the
blending of
functionalized soybean oil with petrochetnical-based resins can incrcase the
toughncss of
a petroleum-based thermoset resin without compromising stiffness, whilc also
improving
its environmctttal friendliness.
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1: Various Polymers and Polymer Composites Synthesized By Using
Formulations Containing Petrochemical Comononiers Along With Reactive
ingredicnis Obtained or Derived from Renewable Feedstocks
The most extensive amount ofwrork appears to have been done on the use of
monomers extractcd from plant oils (and then optimized via chemical
modification in
most cases), as copolymerized with petrochemical comonomers. to prepare
unsaturated
liquid polyester resins, vinyl ester resins and epoxy resins that are capable
of curing into
thermoset polymers; and on the development of themioset composites using such
thermoset matrix polymers. This work will be summarized below.
Further details (beyond the summary that will be provided below) can be found
in
the following references: U.S. Patent No. 6.121,398, Warth et al. (1997),
Willianis and
Wool (2000), Khot et al. (2001), Can et al. (2001), Can ct al. (2002), La
Scala and Wool
(2002), Belcher et al. (2002) which was bric(ly discussed above, I..u et al.
(2004),
O'Donnell et at. (2004), La Scala and Wool (2005), Hong and Wool (2005),
Mosiewicki
et al. (two publications in 2005), Aranguren et al. (2006), and Lu and Larock
(2006).
Soybean oil and linseed oil have been used most often in such work. Rapeseed
oil, corn oil, olive oil, cottonseed oil, safflower seed oil, sunflower oil,
palm oil, canola
oil and genetically engineered high oleic oil have also been used in some
work. Most of
the polymer and composite synthesis has been performed by using monomers which
wcre dcrived by chemical modirication from the plant oils, rather than using
the plant
oils thentselves or the niononters extracted 1rorn llte plant oils directly.
In fact, research
on the developinent ofclieinically modified monomers has paralleled thermoset
polymcr
and composite synthcsis in many rescarch groups.
Styrenc is the most comnionly ttsed petrochemical comonomer in such thermoset
polymers and composites. Divinylbcnzene is also sometimcs used as a comonomer,
to
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provide additional crosslinking sites beyond those that are present in the
monomers
originating from plant oils. 'fhe plant oil based monomers can readily undergo
free
radical copolymerization over a very broad range of amount of coinonomer with
styrene
andJor divinylbenzene in the presence of suitable initiators and/or catalysts.
The ntost
extensively investigated composition region is front a total of 33% (a
fraction of 113) to
40% (a fraction of 215) by weight of comonomers such as styrene and
divinylbenzene.
't'his composition range corresponds to a common amount of such comonomers
used in
typical petrochemical-based resins such as epoxy vinyl esters.
Plant oil based niunumers can cause both plasticization (because of their
flexibility) and an increase in the glass transition temperature (because of
their ability to
introduce crosslinks). The glass transition typically becomes very broad
because of these
two competing ct'f'ects. The higher the level of unsaturation in the plant oil
based
monomer (andlor the more its functionality has been increased via chemical
modification), the more its use results in an increase in the glass iransition
teniperature
and the less its use causes plasticization.
l'he use of styrene and/or divinylbcn=r_enc in the I'ormulation enhances the
rigidity
of the resulting thermoset polymer since these aromatic monomers introduce
rigid
moieties into the thermoset network. In particular, the use of the rigid
crosslinker
divinylbenzene increases the glass transition temperature without any
competing
plasticization ctlect.
If there is a significant reactivity difference between the monomers obtained
or
derived from a particular plant oil and the styrenic mononiers which tend to
react fast,
then there is a tendency towards the formation of a heterogeneous morphology.
In such
a morphology, one finds domains that are. rich in styrcnic polymer and domains
that are
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rich in the product of the polytneriaation of monomers obtained or derived
from the plant
oil.
Thermoset composites whose properties are comparable with those where the
matrix polymer is obtained entirely from monomers originating from
petrochemical
feedstocks have been prepared with niany of the matrices described above
(based on thc
use of monomers obtained or derived from plant oils, as copolymerized with
petrochemical comonomers) as reinforced by various natural or synthetic fibers
or by
layered silicate nanoGllcr. Whenever such composites can be prepared at
comparabie
cost so that economic factors do not discouragc their potential manufacturers
and users,
they can provide signiticant sustainability advantages.
SUMMARY OF T'ME INVENTION
1. Introduction
The present invention relates to a method for the fracture stimulation of a
subtcrranean l'ormation ltavinl; a wellbore by using ultralit;hhweight
thermoset polymer
nanocomposite particles as proppants, where the particles are prepared by
using
formulations containing reactive ingredients obtained or derived trom
renewablc
feed stocks.
The niain coniponents of the particles are a rigid themloset polymer matrix
(Section 2) and a nanofiller which provides reinforeentent (Section 3).
Optionally, an itnpact modif.ier (Section 4) may also be present.
Additional formulation ingredient(s) may also be used during the preparation
of
the particles; such as, but not limited to, initiators, catalysts,
inliibitots, dispersants,
stabilizers, rheology modifiers, buffers, antioxidants, defoamers,
plasticizers, pigments,
flame retardants, smoke retardants, or mixtures thereof. Some of these
additional
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ingredient(s) may also become either partially or completely incorporated into
the
particles.
1'he particles may be manufactured by any suitable polymerization process.
They
are preferentially manufactured by suspension polymerization (Section 5).
Optionally, the particles may be postcurcd (Scetion 6) by any suitable
process.
They are preferentially postcured by heat treatment after polymerization.
Optionally, the particles may be coated (Section 7) by any suitable process.
They
are preferentially coated by using a fluidized bed process after
polymerization.
The particles formulated and manufactured as sununarized above are used in
fracture stimulation (Section 8).
2. Matrix Polymer
a. General Nature of Matrix Polymer
Anv rigid thennoset polymer may be used as the matrix polymer of the
nanocomposite particies utili-r.,cd as proppants in implementing the fracture
stimulation
method of the invention, subject solely to the limitation that the formulation
from witich
it is synthesized comprises a renewable feedstock cotnponent.
Rigid thermoset polymers are, in general, amorphous polymers where covalent
crosslinks provide a three:-dimcnsional network. However, unlike thennoset
elastomers
(often referred to as "rubbers") which also possess a three-dimensional
network of
covalent crosslinks, the rigid thennosets are. by definition, `stiff'. In
other words, they
have high elastic tnoduli at "room temperature" (25 C), and often up to much
higher
temperatures, because their cotnbinations of chain segment stiffness and
crosslink
density result in a high glass transition temperature.
For the purposes of this disclosure, a rigid thetmoset polynter is defined as
a
thermoset polymer whose glass transition temperature, as measured by
difterential
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scanning calorimetry at a heatittg rate of 10 CJminute. equals or exceeds 45
T. Thc
gradual softening of an amorphous polymcr with incrcasing tcmpcraturc
accclcratcs as
the tempcrature approaches the glass transition tcmperature. As discussed by
Bicerano
(2002), the rapid decline of the stiffness of an amorphous polymer (as
quantified bv its
elastic moduli) with a further increase in temperaturc normally begins at
roughly 20 C
below its glass transition teinperature. Consequently, at 25 C, an amorphous
polymer
whose glass transition teinperarature equals or excceds 45 C will be below
the
temperature range at which it.s elastic ntoduli begin a rapid decline with a
further increase
in temperature, so that it will be rigid.
Some exaniples of rigid thermosct polymers that can be used as ntatrix
materials
in the nanocomposite panicies utilized as proppants in implementing the
fracture
stimulation method of the invention will be provided below. It is to be
understood that
these examples are provided without reducing the gencrality of the invention,
to facilitate
the teaching of the invention.
Commonly ttsed: rigid thermoset polymers include, but are not limited to,
crosslinked epoxies, epoxy vinyl esters, polyesters, phenolics, melamine-based
resins,
polyurcthancs, and polyureas. Rigid thermoset polymers that are used less
oftcn because
of their high cost despite thcir cxceptional performance include, but are not
limited to,
crosslinl:ed polyiniides. For use in proppant particles suitable for different
embodiments
2U of the fracture stitnulation method of the invention, these various types
of polymers can
bc prepared by starting froin their monomers, from oligomers that are often
referred to as
"prepolvmers", or from conibinations thereot:
Many additional types of rigid ihermoset polymers can also be used. Such
polymers include, but arc not limited to, various families of crosslinked
copolymers
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prepared most often by the polymcrization of vinvlic monomcrs, of vinylidene
monontcrs, or ofmixtures thcrcol:
The "vinyl fragment" is commonly dcfined as the CH:=<: H- hagmcnt. So a
"vinylic inonomer" is a monomer of the general structure C1=12=C1-IR where R
can be any
one of a vast variety of molecular fragments or atoms (other than hydrogen).
When a
vinylic nionomer CH2=CHR reacts. it is incorporated into thc polymer as the -
CH2-CHR-
repeat unit. Among rigid thetmosets built from vinylic monomers, the
crosslinked
styrcnics and crosslinked acrylics are especially familiar to workers in the
field. Some
other familiar types of vinylic monomers (antong others) include the olefins,
vinyl
alcohols, vinyl esters, and vinyl halides.
The "vinylidene fragment" is commonly deGned as the. CH2=CR"- fragment. So
a"vinylidene monomer" is a niononier of the general strticture CH2=CR'R" where
R'
and R" can each be any one of a vast varicty of molecular fragments or atoms
(other than
hydrogen). When a vinylidene monomer C1-IZ=CR'R" reacts, it is incorporated
into a
polymer as the -CH2-CR'R"- repeat unit. Among rigid thermosets built [Tom
vinylidene
polvmers, the crosslinked alkyl acrylics [such as crosstink.ed poly(methyl
methacryiate)]
are especially familiar to workers in the field. However, vinylidene monomers
similar to
cach type of vinyl monomer (such as the styrenics, acrylates, olelins, vinyl
alcohols,
vinyl esters and vinyl halides, among others) can be prepared, One example of
particular
interest in the contcxt of styrenic monomcrs is alpha-methyl styrene, a
vinylidene-type
monomer that difTers froni styrene (a vinyl-type monomer) by having a inethyl
(-CH3)
group serving as the R" fragment replacing the hydrogen atom attached to the
alpha-
carbon.
rhermasets based on vinylic monomers, vinylidene monomers, or ntixtures
thereof, are typically prepared by the reaction of a mixturc containing one or
more non-
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crosslinking (difunctional) monomer(s) and one or more crosslinking (three or
higher
functional) monomer(s).
'fhe follovving are some specific bul non-limitink examples of crosslinking
monomers that can be used: Divinylbenzene, trimethylolpropane
t.tintethacrytote,
triniethylolpropane triacrylate, trimethylolpropane dimethacrylate,
trimethyloipropane
diacrylatc. pcntacrythritol tetramethacrylate, pentaerylhritol
trimethacrylate,
pentaerythritoi diFnethacrylate, pentaerythritol tetraacrylate,
pentaerythritol triacq=late,
pcntacrythritol diacrylate, bisphenol-A diglycidyl methacrylate,
ethylcneglycol
dimethacrylate, ethyleFteglycol diacrylato, diethyleneglycol dimethacrylate,
diethvlcneglycol diacrylate, triethyleneglycol dimethacrylate, and
triethyleneglycol
diacrylate, a bis(Fnethacrylaniide) having the formula:
0 0
a bis(acrylamide) having the formula:
11, R=
CU =Clt-~--t-(G1{~,-A'-~`.^-C1PC1l.
~O pU
a polyolern having the f=ormula CI-1Z=CH-(Cl-h),;-CI-1=C1-l. (wherein x ranges
tiom 0 to
100, inclusive), a polyethyleneglycol dimethylacrylate having the formula:
Q
IF,~c;---r-ci-,~II:-CIF_C1-f~FF:-ial;~ Ci-CI!=-c:'I!;-~CY--<1---(:--C'Ii=
U iII;
a polyethyleneelycol diacrylatc having the formula:
CF
u
<'11 =('Fi-I' t~-c II;-l FI.-:o-<N:-Ctl: t---cfF=rl17
ci
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a molecule or a macromolecule containing at least thrcc isocyanatc (-N=C=O)
groups, a
molecule or a macrotnolecule containing at least thrce alcohol (-OH) groups, a
moiccule
or a macromolecule containing at least three reactive amine functionalities
where a
primary amine (-NH2) contributes nvo to the total number of reactire
functionalities
while a secondary aniine (-NI-IR-, wherc R can be any aliphatic or aromatic
organic
fragment) contributes one to the total number of reactivc functionalities: and
a molecule
or a macromolecule wherc the total number of reactive functionalities arising
from any
combination of isocyanate (-N=C=0), alcohol (-01-1), primary amine (-NH2) and
secondary amine (-N1-YR-, where R can be any aliphatic or aromatic organic
fragment)
adds up to at least three, 1,4-divinyloxybutane, divinylsulfone, diallyl
phthalate, diallyl
acrylamide, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate
or mixtures
thereof.
The following are some specific but non-limiting examples of non-crosslinking
monomers that can be used: Slyrenic monomers, styrene, methylstyrcnc,
ethylstyrcne
(ethylvinylbenzenc), chlorostyrcnc, chloromcthvlsryrene, styrenesulfonic acid,
t-
butoxystyrene, t-butylstyrenc, pentylstyrenc, alpha-methylstyrene, alpha-
methyl-p-
pentylstvrene; acrylie and methacrylic monomers, methyl acrylate, methyl
methacrylate,
ethyl acrylatc, ethyl mcthacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl
methacrvlate,
lauryl acrylate, lauryl methacrylate, glycidyl acrylate, glycidyl
methacrylate,
dimethylarninoethyl acrylatc, dimethvlaminocthyl methaerylate, hydroxyethyl
acrylate,
hydroxycthyl niethacrylate, diethylene glycol acrylate, diethylene glycol
mcthacrylate,
glycerol monoacrvlate, glycerol monomethacrylate, polyethylene glycol
monoacrylate,
polyethylene blycol monomethacrylate, butanediol monoacrylate, butanediol
monomethacrylate; unsaturated carboxylic acid monomers, acrylic acid,
methacrvlic
acid; alkyl vinyl ether ntonomers, methvl vinvl ether, ethyl vinyl ether;
vinyl ester
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monomcrs, vinyl acctate, vinyl propionatc, vinyl butyrate; N-alkyl substituted
acrylamidcs and mcthactylamides, N-methylacrylamide, N-ntethylmcthacrylamide,
i\-
ethyl acrylamide. N-ethyl methacrylamide; nitrile monomers, acrylonitrile.
methacr-ylonitrile: olefinic monomers, ethylene (H2C=CI-I2) and the alpha-
olefins
~ (I-hC=CI=IR) wltere R is any saturated hydrocarbon fragment; vinylic
alcohols, vinyl
alcohol; vinyl halides, vinyl chloride; vinylidene halides, vinylidene
chloride, or
mixtures thereof.
b. Rcnewable Feedstack Component of Matrix Polynier Fomtulatian
A key aspect of the present invention is the utilization of reactive entities
(monomers, oligomers and/or polymers wntaining reactive functionalities)
obtained or
derived from rencwable resources as components of the fonnulations from which
the
polymeric matrix of the thermoset nanocomposite proppant particles used in
implementing the fracture stimulation method of the invention is prepared.
It is most desirable, from the viewpoint of sustainability, to maximize the
proportion of renewable fcedstock that is being used. In practice, however,
this desired
outcome inust be balanced with the performancc requirements and the economic
constraints of the application. Consequently, the renewable feedstock content
may be,
and in most embodinients is, less than 100%. The total quantity of the
componcnt(s)
obtained or derived trom renewable feedstocks can range from 1% up to 100% bv
weight
of the constituents of the formulation of the thermoset matrix polymcr. If it
is less than
100%, the remainder can coinprisc any suitable petrochemical ingredients, such
as but
not limited to those sunuttarized in the preceding subsection.
Any type of biological starting material (such as, but not limited to, amino
acids,
nucleotides, sugars, phenols, natural fats, oils, and fatty acids) can be used
as the
renewable resource in implenienting the invention. Such renewable feedstocks
can be
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obtained or derived from a widc varicty of microorganism-bascd, plant-bascd,
or animal-
bascd resourccs.
Without reducing the gcnerality of the invention, among renewable tcedstocks
that can be used for the synthesis of the matrix polymer of the nanocomposite
particles,
natural fats and oils cxtracted from some comnion types of plants [such as
soybean,
sunflower, canola, castor, olive, peanut, cashew nut, pumpkin seed, rapcserd,
corn, rice,
sesame, cottonseed, palm, coconut, safflower, linseed (also known as
flaxseed), hemp,
tall oil, and similar natural fats and oils; and especially soybcan,
sunflower, canola and
linseed oils] appear to be- very promising as potential suurces of inexpensive
mononiers.
Again without reducing ttte generality of the invention, some animal-based
natural fats and oils, such as fish oil, lard, neatsfoot oil and tallow oil,
may also hold
promise as potential sources of inexpensive monomers.
3. Nanofiller
By definition, a nanofiller possesses at least one principal axis diniension
whose
length is less than 0.5 microns (500 nanometers). Some nanofillers possess
only one
principal axis dimension whose length is less than 0.5 microns. Other
nanofillers possess
two principal axis dimensions whose lengths are less than 0.5 microns. Yet
other
nanotillers possess all three principal axis dimensions whose lengths arc less
than 0.5
microns. Any reinforcing material possessing one nanoscale dimension, two
nanoscale
dimcnsions, or thmc nanoscale dimensions. can bc used as the nanofiller. Anv
mixture
of hvo or more diff'erent types of such reinfore.ittg materials can also be
used as the
nanofiller. The nanoliller is present in an amotint ranging from 0.001 to 60
percent of
the total particle by volume.
Without redticing the generality of the invention, to facilitate the teaching
of the
invention, we note that nanoscale carbon black, fumed silica, fumed alumina,
carbon
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nanotubcs, carbon nanofibcrs, ccllulosic nanofibcrs, natural and synthetic
nanoclays,
vcry finely dividcd gradcs of 11y ash, the polyhcdral oligomeric
silscsquioxancs; and
clttstcrs of different types of mctals, metal alloys, and metal oxid'es, are
some examples
of nanofillers that can be incorporated into the nanocomposite partictes used
as
proppants in implementing the fracture stimulation metltod of the invention.
Since the
development of nanofillers is an area that is at the frontiers of materials
research and
development, the future emergence of yet additional types of nanotillers that
are not
currently known inay also be readily anticipated.
4. Impact Modifier
Optionally, the thermoset nanocomposite particles used as proppants in
implementing the fracture stimulation method of the invention may contain an
impact
modificr.
If its t~5e is desired, an impact modifier is sclccted and incorporated into
the
particles as described in the SUMMARY OF THE iNVr~ITiON and the
DESCRIPTIO-NI OF "I'HE PREFERRED EMBODIMENTS sections of U.S. Patent
Application No. 11/695,745 entitled "A method for the fracture stimulation of
a
subterranean formation having a wellbore by using impact-modified thermoset
polymer
nanocomposite particles as proppants", which are fully incorporated herein by
reference.
5. Suspension Polymerization
Any method lor lhe fabrication of thermoset polymer nanocomposite particles
known to those skilled in the art may be used to preparc the themtoset
nanocompositc
particlcs which are utilized as proppants in implementing the fracture
stimulation method
of the invention.
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Without reducing the generality of the invention, it is especially practical
to use
methods that can prodttce ilte panicles directly in the desired (usually
substantially
spherical) shape during polymerization from the starting monomers.
A substantially spherical particle is defined as a pariicle having a roundness
of at
least 0.7 and a sphericity of at least 0.7, as measured by the use of a
Krumbien/Sloss
chart using the experimental procedure recommended in fnternational Standard
ISO
13503-2, "Petroleum and natural gas industries - Completion fluids and
materials - Part
2: Mcasurcmcnt of properties of proppants used in hydraulic fracturing and
gravel-
packing operations" (first cdition, 2006), Section 7, for the purposes of this
disclosure.
Without reducing the generality of the invention, it is cspecially useful to
produce
the substantially spherical particles discussed in the paragraph above with an
average
diamcter that ranges 1rom 0.1 mm to 4 nim for use in fracture stimulation
applications.
Without reducing the generality of the invetttion, in a tnost preferred
embodiment, at least 90% of the substantially spherical particles are produced
with
diameters tanging from 0.42 mm (40 U.S. mesh size) to 1.41 mm (14 U.S. mesh
size).
Ntfithout reducing the generality of the invention, suspension (droplet)
polymerization, where the polymer precursor mixture is dispersed in a suitable
liquid
tnediutn prior to being polymerized, is currently the most powerful
manufacturing
method available for producing the particles directly in a substantially
spherical shape
during polvnieriz.ation front the starting monomers. In pursuing this
approach, it is
especially inlportant for the nanofiller particles to be well-dispersed within
the liquid
medium so that they can becotne intimately incorporated into the thermoset
rianocomposite particles that will be forttted upon polymerization.
6. !-leat Treatment
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Optionallv, the thetYrtoset nanocomposite particles used in implementing the
ti-acture stimulation mcthud of the invention may be subjected to suituble
post-
polymerization process steps intended mainly to advartce the curing of the
thermoset
polymer matrix.
If a suitablc post-polymcri=ration process stcp is applicd to the thermoset
polymer
nanocomposite particles, in many cases the curing reaction will be driven
funher to%vards
completion so that the maximum possible temperature at which the fracture
stimulation
method of tfie invention can be applied by using these particles will
increase.
In soine instances, there may also bc further benefits of a post-
polymeri2ation
process step. One such possible additional henefit is an enhancement in the
flow of the
gascs, fluids, or mixtures thereof, produced by the subterranean formation,
towards the
wellborc, even at temperatures that are far below the niaximuin possible
application
temperature ot'thc fracture stimulation method. Another such possible
additional bcneCit
is an increase of such magnitude in the resistance of the particles to
aggressivc
environments as to enhance significantly the potential range of applications
of the
fracture stimulation method utilizing the particles.
Processes that may be used to enhance the degree of curing of a thermoset
polymer include, but are not limited to, heat treatnient (which may be
combined with
stirring, flow and/or sonication to enhance its effectiveness), electron beam
irradiation,
and ultraviolet irradiation.
Without reducing the generality of the invention, we focused mainly on the use
of
heal treatment as a post-polymerization process step during the manufacturing,
of the
particles. Such heai treatment can be performed in manv types of rnedia;
including a
vacuum, a non-oxidizinS gas, a mixturc ot'non-oxidizino gases, a liquid, or a
niixture of
liquids.
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It is possible, in some instances, to postcure the "as polymerized" particles
adequately as a resutt of the etevat.ed temperature of a downhole environment
of a
hydrocarbon rescrvoir during the application of the fracture stimulation
method of the
invention. However, since it does not allow nearly the same level of
consistency and
control of particle quality, this "in situ" approach to heat trcatmcnt is
gencrally less
prcferred than the application of heat treatment as a manufacturing process
stcp bcfore
using the particles in fracture stiniulation.
7. Coating
Optionally, the thermoset nanocomposite particles used in iinplenienting the
fracture stimulation method of the invention may be coated; to achieve
benefits such as
proteetion &om chemicals, waterproofing, hardening, and combinations thereof.
It is preferable, in most cases, to use matrix polymer cotnpositions that can
withstand the downholc environment without requiring a coating on the
particles. A
coating may, however, sonietimes be needed, to make it possible to use
particles that
have very attractive performance attributes, but that if left uncoated would=
suffer from
some deficiency which can be remedied by the application of a coating.
Any available method may be used to place a coating around the particles. A
coating may be placed during polymerization, after polvmerization, or a
conibination
thereof
Without reducing the generality of the invention, for example, monomers and/or
reactive oligomers having the tendency to undergo phase segregation from the
bulk of
the matrix polymer and migrate to the surfaces of the particles niay be
included in the
polymer prectirsor rnixture to place a coating during polymerization. With
this approach,
there is also a likelihood of some pcnctration of the coating ntaterial to the
interior of the
particles and/or the interpenttration of the coating phase and the matrix
phase and/or the
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development of an "interphase" region ovcr which thc composition changes
gradually
from that of the matrix polymer to that of the coating.
Again uithout rcducing the gcncrality of the invcntion, various types of
fluidized
bed processes provide familiar examples of methods for placing a coating
around the
particles after polyntcrization.
It should also be obvious that the approaches summarized in the two paragraphs
above can be combined so that a coating may comprise both components that have
been
placed during polymerization and components that have been placed afier
polymerization.
Witliout reducing the generality of the invention, the use of a fluidized bed
process as a post-polyme=rization step is a preferred method for the placement
of a
coating if needed, but it is most preferred to select a matrix polymer
cotnposition such
that a coating will not lx needed.
Any suitable coating niaterial may be used if a coating is needed. Without
reducing the generality of the invention, epoxies, epoxy vinyl esters,
polyesters, acrylics,
phenolics, alkyd resins, rnelamine-based resins, furfuryl alcohol resins,
polvacetals,
polyurethancs, polyureas, polyimides, polyxylylencs, silicones,
fluoropolyniers,
copolymers therc:ol; and mixtures thereof; arc some examples of coating
niaterials that
tnay be used.
8. Fracture Stimulation
Ute fracture stimulation method of the invention is implemented by using
stitt;
strong, tough, heal resistanl, and anvironment:ally resistant
ultrtrlightweight thermoset
polymer nanocompositc particles. Such particles may be placed cither as a
proppant
partial inonolayer or as a conventionat proppant pack (packed mass) in
implementations
of the invention.
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The optimum mode of panicle placement is determined by thc details of the
specific fracture that needs to bc propped. In practice, the use of
ultralightwcight
particles as proppant particles in implementing the fracture stimulation
method of the
invention provides its greatcst advantages in situations where a proppant
partial
monolayer is the optimum mode of placcment. Curthermore, the development of
the
fracture stimulation method of the invention has resulted in partial
monolayers becoming
the optimum proppant placentcnt method in ntany situations where the use of
panial
monolavers was either impossible or impractical with previous technologies.
In any case, the inethod 1'or fracture stiniulation comprises (a) forming a
slurry
comprising a fluid and a proppant, (b) injecting this slurry into the wellbore
at
sufficiently high rates and pressures such that the formation fails and
fractures to accept
the sluny, and (c) thus etnplacing the proppant in the fomiation so that it
can prop open
the fracturc network (thereby allowing pmduced gases, fluids, or mixtures
thereof, to
tlow towards the wellbore).
The most comnionly used measure of proppant performance is the conductivity
of liquids andior gases (depending on the type of hydrocarbon reservoir)
through
packings of the particles. A minimum liquid conductivity of 100 mllft is often
considered as a practical threshold lor considering a packing to be useful in
propping a
fracture that possesses a given closure stress at a given tempcrature. In
order for a
fracture stimulation niethod to have significant practical utility, a static
conductivity of at
least 100 mDll ntust be retained for at least 200 hours at a temperature
greater than 80
oP
It is a common practice in the industry to use the simulated environment ot' a
hydrocarbon reservoir in evaluating the conductivities of packings of
partic{es. The API
RP 61 niethod, described by a publication of the American Petroleum Institute
titled
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"Recommended Practices for Evaluating Short Term Proppant Pack Conductivity"
(first
edition, Octobcr 1. 1989), is currcntly the commonly acccpted testing standard
for
conductivity tcsting in the simulated cnvironment of a hydrocarbon reservoir.
As of the
date of this filing, hoa-ever, work is underuay to develop alternative testing
standards,
3 such as International Standard [SO 13503-5, "Petrolcum and natural gas
industries -
Completion fluids and materials - Part 5: Procedures for measuring the long-
term
conductivity of proppants" (final draft, 2006).
DE'SCRIP'I'ION OF THE PRFFER.RED 6M.BODIMENTS
Details will now be provided on the currently preferred embodiments of the
invention. These details will be provided without reducing the generality of
the
invention. Persons skilled in the an can readily imabine niany additional
embodimcnts
that fall within the full scope of the invention as taught in Ihe SUMMARY OF
THE
II~TVENTION section.
The fracture stimulation method of the invention is preferably implemented by
placing the uitralibhteveight thermoset polymer nanocomposite particles in the
fracture as
a panial monolayer. We have found, under standard laboratory test conditions,
that the
use of particles of narrow size distribution such as 14/16 U.S. mesb size
(diameters in the
range of 1.19 to 1.41 millimeters) is more effective than the use of broad
particle size
distributions. We have also found, under standard laboratory test conditions,
that 0.02
lb/ItZ is an cspccially preferred lcvcl ot'covcrage of the liacturc arca with
a partial
monotayer of therinoset nanocomposite particles of sutficient siiffiness and
strength that
possess an absolute density of 1.054. I-Iowever, real-life dommhole conditions
in an
oilfield may differ significantly fronl those used under laboratory test
conditions.
Cottst:quently, in the practical application of the 1racture stimulation
method of the
invention, the use of other panicle size distributions, other coverage levels,
or
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combinations thereof, mav be more appropriate, depending on the conditions
prevailing
in the specific downhole environment wbere the fracture stimulation methnd of
the
invention will be applied.
T'hc thermoset polynier matrix comprises a cnpolymeriiation product of
mnnnmers derived froni soybean oil (a renewable resource), with three vinylic
petrochemical monomers [styrene (S), divinylbenzene (DVB) and
ethylvinylbenzene
(EVB)]. The current preference for the use of soybean oil as a renewable
resource is a
result of its widespread availability and low cost, along with the fact that
the derivation
of uscful monomers from soybean oil is at a morc advanced stage than the
derivation of
nionomers from other suitable renewable feedstocks. The current preference for
the use
of all three of S, DVB and CVI3, instead of just using S and DVB, is a result
of economic
considerations related to monomer costs. The performance attributes of the
particles can
be tailored over broad ranges by niodifying (a) the proportion of the matrix
poly-ner
originating from tnonomers derived from soybean oil over the range of t% to
100 !o by
weight, (b) the mixture of nionomers derived froin sovbean oil, and (c) the
relative
amounts of the three vinylic monomers (S, DVB and EVB).
Carbon black, possessing a length that is less than 0.5 niicrons in at least
one
prittcipal axis direction, is used as the nanofillcr at an amount ranging from
0.1% to 15%
of the total particle by voluntc.
Suspension polymerization, preferably in its "rapid rate polymcrization" modc,
is
pcrformcd to synthesize the particics. The most important additional
formulation
ingredient (besides the reactive monomers) that is used during polymerization
is the
initiator. 'rhe initiator may consist of one type molecule or a niixture of
two or more
t,vpes of niolecules that each have the ability to function as initiators. We
have found,
with experiem;e, that ttte "dual initiator" approach, involving the use of
thvo initiators
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WO 2009/005880 PCTIUS2008/061520
which begin to manitcst significant activity at different temperatures, often
providcs the
best results.
Additional formulation ingrcdicnts, such as impact modifiers, catalysts,
inhibitors, dispersants, stabilizers, rheology modifiers, buffers,
antioxidants, defoamers,
plasticizers, pigments, 8anie retardants, smoke retardants, or mixtures
thercof, may also
bc used when needed. Some of the additional formulation ingredient(s) may
become
either partially or completely incorporated into the particles in some
embodiments of the
invention. An example of an additional fonnu{ation ingredient which becomes
incorporated in the particles is the optional impact mudilier, when it is used
in a
partictilar embodimerit,
'fhe suspension polymerization conditions are selected such that the particles
to
be used in the fracture stimulation method of the invention are selectively
manufactured
to have the vast majority of them fall within the 14/40 U.S. niesh size range
(diameters in
the ratige of 0.42 to 1.41 millimeters). The panicles are sometimes separated
into
Iractions having narrower diameter ranges for use in an optimal matuter in
proppant
partial monolavers.
Post-polymerization heat treatment in an unreactive gas environment is
performed as a manufacturing process step to further advance the curing of the
thermosct
polymer nlatrix. "fhis approach works especially well (vrithout adverse
effects such as
dcbradation that could occur if an oxidative gaseous environment such as air
were used
and/or sweiling that could occur if a liquid environmcnt wcre used) in
enhancing the
curing of the particles. The particles undergo a total exposure to
teniperatures in the
range of 130 C to 210 C for a duration of 5 minutes to 90 minutes,
inclusive, in an
unreactivc gas envirortment. The specific selection of an optimum temperaturc
(or
?5 optimuni temperaturc range) and optimuni duration of heat treatment within
these ranges
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WO 2009/005880 PCT/US20081061520
depends on the formulation fmm which the particles were prepared. Nitrogen is
used as
the unreactive gas environment.
Finally, it .vill be appreciated by those skilled in the art that changes
could be
niade to the embodimcnts described above without departing from the broad
inventive
3 concept thcrcof It is understood, lhcrefore, that this invention is not
limited to thc
particular cmboditnents disclosed, but is iatended to cover modifications
within thc spirit
and scope of the present invention as defined in the appended claims.
EXAMPLES
Sorne eheoretical examples of preferred embodiments of the fracture
stimulation
niethod of the invention will now be given, without reducing the generality of
the
invention, to provide a better understanding of some of the ways in which the
invention
may be practiced. Workers skilled in the art can readily imagine many other
embodiments of the invention with the benefit of this disclosure.
F:xample t
The fracture stiniulation method ol'the invention is applied in a situation
where it
will provide the maximum possible benefit as compared with prior i'racture
stimulation
methods. The downhole environment is one where the use of a proppant partial
monolayer would be very effeclive in the extraction of hydrocarbons from a
reservoir but
has not been practical previously because of the unavailability of proppant
particles of
near neutral buoyancy in water along with sufficient stiffness, strength and
environntental resistance. The ultralightweight thermoset polymer
nanocotnposite
particles used in iinplcmenting lhe fracture stintulation rnethod of the
invention
overconle this difficulty. Uetailed consideration of the downhole environment
results in
the dctcrmination that 14!16 U.S. ntcsh sizE: particles would be optintal.
Panicies in this
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WO 2009/005880 PCT/US2008/061520
size range are placed into the fracture as a partial monolayer bv using
slickwater as the
carrier fluid.
The thermoset polymer inatrix of the nanocomposite particles used in this
examp{c consists of a copolymer of styrene (S), ethyvinylbenzene (EVB),
divinylbenzcnc (DVB), and acrylated epoxidized soybean oil (AESO). The
quantities oi'
these ingredients in the reactive mixture are 51.55% S. 8.45% EVB. 15% DVB and
25%
AESO by wcibht. In addition, the particles contain 0.5% by volume of carbon
black as a
nanofiller.
The particles are prepared in the 14140 U.S. mesh size range by rapid rate
suspension polymeriiation. 'fhey are then postcured in a nitrogen environment
for 20
minutes at a temperature of 185 T. Particles faliing ti=ithin the 14/16 U.S.
mesh size
range arc separated from the broader distribution of 14/40 U.S. mesh size
range by
standard sieving techniques.
Example 2
As in Example 1, but the quantities of the ingredients in the reactive
tnixture are
61.86% S, 10.14% EVB, 18% DV13 and 10% AESO by weight.
Example 3
As in Example 1, but the quantities of the ingredients in the reactive mixture
are
41.24% S. 6.76% EVB, 12% llVB and 40% AESO by weight.
Example 4
As in Example 1, bui maleinized acrvlated epoxidized soybean oil (M.AESO) is
used instead of AESO as the formulation ingredient originating from a
renewable
n;sotirce.
Example 5
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The sanie types of paniclcs arc used as in Example I. 1-lowever, detailcd
considcration of the downhole cnvironment shows that the use of the full
available 14,140
U.S. mesh size range of the particles will be optimal. Particles in this size
range are
placed into the fracture by using slickwater as the carrier fluid.
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