A METHOD OF COATING A POROUS SUBSTRATE WITH A THERMOPLASTIC
MATERIAL FROM THE OUTSIDE OF THE SUBSTRATE
Technical Field
[0001] A method of coating a first porous substrate
with a thermoplastic material comprises the steps of: rotating
the substrate about an axis of the substrate; and applying the
material in a liquefied state onto the substrate, wherein the
step of applying is performed from the outside of the substrate.
In some embodiments, the method includes coating a second porous
substrate with the thermoplastic material . The method of
coating can include coating the substrate with a desired
quantity of material per a given length of the substrate.
Summary
[0002] According to an embodiment, a method of
coating a first porous substrate with a thermoplastic material
comprises the steps of: rotating the substrate about an axis of
the substrate; and applying the material in a liquefied state
onto the substrate, wherein the step of applying is performed
from the outside of the substrate.
[0003] According to another embodiment, a method of
coating a porous substrate with a thermoplastic material
comprises the steps of: connecting a first porous substrate to a
rotator; rotating the substrate about an axis of the substrate;
pumping the material in a liquefied state from a receptacle to
an application head; and applying the material in a liquefied
state onto the substrate, wherein the step of applying is
performed from the outside of the substrate.
Brief Description of the Figures
[0004] The features and advantages of certain
embodiments will be more readily appreciated when considered in
conjunction with the accompanying figures. The figures are not
to be construed as limiting any of the preferred embodiments .
[0005] Fig. 1 is a diagram of an apparatus,
according to certain embodiments, for coating a first porous
substrate with a thermoplastic material.
[0006] Fig. 2 is a diagram of some of the
components of the apparatus according to other embodiments.
[0007] Fig. 3 is a cross-sectional view of a first
and second porous substrate and an application head according to
an embodiment .
[0008] Fig. 4 is a plan view of Fig. 3 taken along
line 4 .
Detailed Description
[0009] As used herein, the words "comprise, "
"have," "include," and all grammatical variations thereof are
each intended to have an open, non-limiting meaning that does
not exclude additional elements or steps.
[0010] It should be understood that, as used
herein, "first," "second," "third," etc., are arbitrarily
assigned and are merely intended to differentiate between two or
more porous substrates, holding devices, etc., as the case may
be, and does not indicate any particular orientation or
sequence. Furthermore, it is to be understood that the mere use
of the term "first" does not require that there be any "second,"
and the mere use of the term "second" does not require that
there be any "third," etc.
[0011] A s used herein, a "fluid" is a substance
having a continuous phase that tends to flow and to conform to
the outline o f its container when the substance is tested at a
temperature of 7 1 °F (22 °C) and a pressure of one atmosphere
"atm" (0.1 megapascals "MPa") . A fluid can be a liquid or gas.
[0012] Oil and gas hydrocarbons are naturally
occurring in some subterranean formations . A subterranean
formation containing oil or gas is sometimes referred to as a
reservoir. A reservoir may be located under land or off shore.
Reservoirs are typically located in the range o f a few hundred
feet (shallow reservoirs) to a few tens o f thousands o f feet
(ultra-deep reservoirs) . In order to produce oil or gas, a
wellbore is drilled into a reservoir or adjacent to a reservoir.
[0013] A well can include, without limitation, an
oil, gas, water, or injection well. A well used to produce oil
or gas is generally referred to as a production well. A s used
herein, a "well" includes at least one wellbore. A wellbore can
include vertical, angled, and horizontal portions, and it can be
straight, curved, or branched. A s used herein, the term
"wellbore" includes any cased, and any uncased, open-hole
portion of the wellbore. A near-wellbore region is the
subterranean material and rock of the subterranean formation
surrounding the wellbore. A s used herein, a "well" also
includes the near-wellbore region. The near-wellbore region is
generally considered to be the region within about 100 feet of
the wellbore. A s used herein, "into a well" means and includes
into any portion o f the well, including into the wellbore or
into the near-wellbore region via the wellbore.
[0014] A portion of a wellbore may be an open hole
or cased hole. In an open-hole wellbore portion, a tubing
string can be placed into the wellbore. The tubing string
allows fluids to be introduced into or flowed from a remote
portion of the wellbore. In a cased-hole wellbore portion, a
casing is placed into the wellbore which can also contain a
tubing string. A wellbore can contain an annulus . Examples of
an annulus include, but are not limited to: the space between
the wall of the wellbore and the outside of a tubing string in
an open-hole wellbore; the space between the wall of the
wellbore and the outside of a casing in a cased-hole wellbore;
and the space between the inside of a casing and the outside of
a tubing string in a cased-hole wellbore.
[0015] In unconsolidated or loosely consolidated
subterranean formations (known as soft formations) , fines, such
as sediment and sand, can enter the tubing string during the
production of oil or gas. When this occurs, several problems
can arise, for example, erosion of production equipment, well
plugging, decreased production of oil or gas, or production of
the fines along with the oil or gas.
[0016] Sand control is often used in soft
formations. Examples of sand control techniques include, but
are not limited to, depositing a filtercake in a portion of the
soft formation, using slotted liners and/or screens, and gravel
packing .
[0017] In filtercake deposition, a fluid (such as a
slurry) , that commonly includes calcium carbonate and polymers,
is introduced into the wellbore. The fluid flows into a desired
portion of the subterranean formation. The ingredients in the
fluid can form a permeable network, known as the filtercake,
which binds fines, such as sand, together. After the filtercake
has formed, oil or gas can be produced through the
interconnected pores in the filtercake, but most of the fines
will remain bound to the filtercake and not be produced along
with the oil or gas.
[0018] It is often desirable to remove at least a
portion of a filtercake at some stage in the production process.
One common technique for removing a filtercake is to perform an
acid wash. In an acid wash, a wash pipe is inserted into the
wellbore. A n acid is then flowed through the wash pipe and into
the desired portion o f the formation. The acid can come in
contact with the filtercake. The acid can chemically react with
some of the ingredients in the filtercake, causing those
ingredients to solubilize, and thus causing the filtercake to be
removed from the subterranean formation.
[0019] Another sand control technique is using
slotted liners and/or screens. A slotted liner can be a
perforated pipe, such as a blank pipe. A screen usually
contains holes that are smaller than the perforations in a
slotted liner. The liner and/or screen can cause bridging o f
the fines against the liner or screen as oil or gas is being
produced. Gravel packing is often performed in conjunction with
the use of slotted liners and screens. Gravel is proppant
having a particle-size class above sand, which is defined as
having a largest dimension ranging from greater than 2
millimeters (mm) up to 64 mm. Gravel is commonly placed in a
portion o f an annulus between the wall of the wellbore and the
outside of the screen. The gravel helps to trap fines from
entering the production equipment or plugging the porous
portions o f the liner or screen.
[0020] Some of the problems associated with using a
screen include, premature plugging of the holes in the screen
and corrosion of the screen via contact with corrosive fluids in
the well. In order to help protect a screen, the screen can be
coated with a variety of materials. A thermoplastic material
can be used to coat a porous substrate, such as a perforated
pipe or a screen. A s used herein, the term "thermoplastic"
means a material that becomes liquid when heated, freezes to a
solid, glassy substance when cooled sufficiently, and is capable
of being remelted and remoulded. A thermoplastic material
includes both crystalline regions and amorphous regions. The
crystalline regions contribute to the material's strength and
rigidity properties, while the amorphous regions contribute
elastic properties . A thermoplastic material is elastic and
flexible above the glass transition temperature that is specific
for each type of material. The glass transition temperature is
normally the midpoint in a temperature range for that material,
which is in contrast to the melting point of a pure crystalline
substance, such as water.
[0021] Because it is common for a section of a
perforated pipe and a screen to be at least 30 feet long, it is
difficult to coat the entire section of pipe or screen using a
thermoplastic material. It is impossible, or difficult at best,
to use prior coating methods to coat an entire section of pipe
or screen in one application when the coating is a thermoplastic
material. A novel method of coating a porous substrate with a
thermoplastic material comprises application of the material
from the outside of the porous substrate (i.e., from the outer
diameter or outer perimeter of the porous substrate) .
[0022] A method of coating a first porous substrate
with a thermoplastic material comprises the steps of: rotating
the substrate about an axis of the substrate; and applying the
material in a liquefied state onto the substrate, wherein the
step of applying is performed from the outside of the substrate.
In another embodiment, a method of coating a porous substrate
with a thermoplastic material comprises the steps of: connecting
a first porous substrate to a rotator; rotating the substrate
about an axis of the substrate; pumping the material in a
liquefied state from a receptacle to an application head; and
applying the material in a liquefied state onto the substrate,
wherein the step of applying is performed from the outside of
the substrate. Some of the advantages of the coated substrate
include: the material coated on the substrate can help prevent
premature plugging of the substrate due to fines migration; the
material coated on the substrate can provide a chemical means by
which to help dissolve at least a portion of a filtercake; and
the coated substrate can provide a non-porous media. As used
herein, the term "substrate" means an object having at least one
surface to which a substance (e.g., a thermoplastic material)
adheres. As used herein, the term "porous" means openings, such
as holes or perforations, in a substrate that allow fluid to
flow through.
[0023] Turning to the Figures, Fig. 1 is a
schematic of the apparatus 10 according to an embodiment for
coating a porous substrate. Fig. 2 is a schematic of the
apparatus 10 according to certain embodiments for coating the
porous substrate. The method includes coating at least a first
porous substrate with a thermoplastic material. The material is
capable of being heated to a liquid state. The material is
capable of being cooled to a solid state. The material is
capable of being reheated from a solid state into a liquid
state. According to an embodiment, the material is capable of
removing at least a portion of a filtercake. For example, the
material can remove the filtercake by dissolving some of the
ingredients of the filtercake. Accordingly, the material can
remove at least a portion of a filtercake by chemically reacting
with at least some of the ingredients in the filtercake, thus
causing those ingredients to solubilize. Preferably, the
material is an acid. By way of example, if the material is an
acid and is contacted with water, then some of the compounds in
the material can dissociate and free up hydrogen ions. These
hydrogen ions can then chemically react with a t least some o f
the ingredients {e.g., calcium carbonate) in the filtercake,
thus causing those ingredients t o solubilize. According t o a n
embodiment, the material i s selected from the group consisting
o f polylactic acid, polyglycolic acid, and combinations thereof.
[0024] The method includes coating a t least a first
porous substrate. The method can further include coating a
second porous substrate. The porous substrate can b e any type
o f substrate that i s capable o f being coated with a
thermoplastic material. It is t o b e understood that any
reference to "the substrate" i s meant to include a first
substrate (singular) , a second substrate (singular) , o r a first
and second o r more substrates (plural) without the need to
continually refer to the substrate in both, the singular and
plural forms.
[0025] The substrate 401/402 i s preferably hollow.
In one embodiment, the substrate i s tubular in shape. If the
substrate is tubular in shape, then the substrate will have an
outer diameter (O.D.) and an inner diameter (I.D.) . According
to another embodiment, the substrate i s non-tubular in shape.
Examples o f non-tubular shapes include, but are not limited to,
a square, a rectangle, and a triangle. I f the substrate i s nontubular
in shape, then the substrate will have an outer
perimeter and an inner perimeter. A n example o f a first
substrate 401 includes, but is not limited to, a screen. A s
depicted in Fig. 3 , the first porous substrate 401 i s a wirewrap
screen. A n example o f a second substrate 402 includes, but
is not limited to, a pipe. The pipe can b e perforated (causing
the pipe to b e porous) and the screen can contain holes (causing
the screen to b e porous) . According t o another embodiment, and
a s depicted in Figs. 3 and 4 , the second substrate 402 i s
positioned inside the first substrate 401. For example, the
pipe can b e positioned inside the screen. According to another
embodiment, the second porous substrate can b e attached to the
first porous substrate. For example, and a s depicted in Fig. 3 ,
the second porous substrate 402 {e.g., a pipe) can b e attached
at its O.D. t o the I.D. o f the first porous substrate 401 (e.g.,
a screen) . There can also b e a space between the second porous
substrate 402 and the first porous substrate 401, a s depicted in
Fig. 4 .
[0026] The method can further include the step o f
connecting the substrate 401/402 to a rotator 501. The rotator
501 can b e connected to a first holding device 500. The
apparatus 10 can further include a second holding device 500.
Preferably, the substrate 401/402 is connected at one end to the
rotator 501, which is connected to the first holding device 500
and connected at the other end to the second holding device 500.
According to another embodiment, the second holding device 500
further includes a rotator 501. In an embodiment, the
rotator (s) 501 i s capable o f rotating the substrate.
Preferably, the substrate 401/402 is capable o f free rotation
about its axis. For example, the substrate 401/402 can b e
connected to the rotator (s) 501 and/or the second holding device
500 such that neither the rotator nor the holding device impedes
rotation o f the substrate.
[0027] The method includes the step o f rotating the
substrate 401/402 about an axis o f the substrate 401/402. The
substrate can b e rotated at a desired frequency. For example,
the rotator 501 can b e set to rotate a t the desired frequency,
such a s a desired revolutions per minute (rpm's). The desired
frequency can b e selected based on a desired weight o f the
material to b e coated on a given length o f the substrate. For
example, the desired frequency can b e selected based on how many
pounds o f the material i s to b e coated on each foot o f the
substrate 401/402 (lb/ft) . The desired weight per length can
vary .
[0028] The material can be held or stored in a
receptacle 100. At room temperatures, the material is
preferably in a solid state 101. The receptacle 100 can further
comprise a receptacle heating element 103. The method can
further include the step of heating at least a portion of the
material in the receptacle 100 to a liquefied state 102. The
receptacle heating element 103 is depicted in Fig. 1 as being
positioned towards the top of the receptacle 100 and on top of
the material; however, the element 103 can also be positioned at
a location other than towards the top of the receptacle. For
example, the element 103 can also be positioned at the bottom or
towards the bottom of the receptacle 100. According to an
embodiment, at least a portion of the material contained in the
receptacle 100 is heated via the receptacle heating element 103.
Preferably, the at least a portion of the material is heated to
at least a temperature such that the material becomes a liquid
102.
[0029] The method can also include the step of
pumping the thermoplastic material in a liquefied state 102 from
the receptacle 100 to an application head 302. The step of
pumping can occur after the step of heating at least a portion
of the material in the receptacle 100 to a liquefied state 102.
The apparatus 10 can comprise a pump 104. The pump 104 can be
located adjacent to the receptacle heating element 103.
Preferably, the pump 104 comprises a pump heating element {not
shown) . If the receptacle heating element 103 is located at a
position other than at the top of the material (such as at the
bottom of the receptacle 100) , then the apparatus 100 can
further include a pump tubing (not shown) . The pump tubing can
be positioned inside the receptacle. Accordingly, one end of
the pump tubing can contact the liquefied material 102 contained
in the receptacle 100 and the other end of the pump tubing can
be connected to the pump 104 . The method can further include
the step of activating the pump 104 to pump the material in a
liquefied state 102 from the receptacle 100 to the application
head 302 . According to an embodiment, when the pump is
activated, the liquefied material 102 will travel through the
pump tubing towards the pump.
[0030] The apparatus 10 can further include a feed
tube 200 . The feed tube 200 can be connected at one end to the
pump 104 and connected at the other end to the application head
302 . In this manner, the pump 104 can cause the liquefied
material to move from the receptacle 100, through the feed tube
200, and into the application head 302 . According to an
embodiment, the pump has a variable flow rate. For example, the
pump 104 can be used to control the flow rate of the material in
a liquefied state 102 from the receptacle 100 to the application
head 302 . Preferably, the feed tube 200 is heated. By heating
the feed tube 200, the material can be maintained in a liquefied
state. The feed tube 200 is preferably heated to at least a
minimum temperature such that the material is maintained in a
liquefied state 102 .
[0031] According to certain embodiments, the
material is pumped into the application head 302 . Preferably,
the application head 302 further comprises an application head
heating element {not shown) . In this manner, the material can
be maintained in a liquefied state. The temperature of the
application head heating element is preferably variable. The
temperature of the application head heating element can be set
to a desired temperature. In a preferred embodiment, the
desired temperature is at least a minimum temperature such that
the material is maintained in a liquefied state.
[0032] According to an embodiment, the application
head 302 is positioned relative to the outside of at least a
portion of the substrate 401/402. In a preferred embodiment,
the application head 302 completely surrounds the outside of at
least a portion of the substrate 401/402 (shown in Figs. 1 and
3 ) . The application head 302 can further comprise a seal 305
{shown in Figs. 3 and 4 ) . The seal 305 can contact the O.D. of
the first substrate 401. In this manner, the seal 305 can help
apply the material onto the substrate 401/402.
[0033] The method includes the step of applying the
material in a liquefied state onto the substrate, wherein the
step of applying is performed from the outside of the substrate.
Examples of applying include, but are not limited to, spraying
the material onto the substrate, flowing the material onto the
substrate, and injecting the material into the substrate. It
should be understood that the step of applying can be performed
in a variety of ways such that the material is maintained in a
liquefied state 102 and can be applied from the outside of the
substrate onto and/or into the substrate, and the preceding
examples are not to be construed as the only ways of achieving
such a result. When there is only a first porous substrate 401,
the step of applying can comprise applying the liquefied
material onto the O.D. of the first substrate through the porous
portion of the first substrate and into the I.D. of the first
substrate. When there is a first and second porous substrate
401 and 402, the step of applying can comprise applying the
liquefied material onto the O.D. of the first substrate 401,
through the porous portion of the first substrate, through the
I.D. of the first substrate, and then onto the O.D. of the
second substrate 402, through the porous portion of the second
substrate, and into the I.D. of the second substrate. The step
of applying can comprise injecting the material onto the O.D.
and into the porous portions and the I.D. The step o f applying
can comprise forcing the material onto the O.D. and into the
porous portions and the I.D. Preferably, the material is
capable o f adhering to a surface o f the substrate 401/402.
According to an embodiment, the material coats the O.D. and the
I.D. o f the substrate 401/402. According to this embodiment, it
is preferred that the material fills the porous portions o f the
substrate. The material in a liquefied state, can coat the
outside o f the substrate, fill the porous portions o f the
substrate, and coat the inside o f the substrate.
[0034] The method can further include the step o f
causing the application head 302 to travel axially along the
length o f the substrate 401/402. The apparatus 10 can also
include a drive motor 301. The drive motor 301 can b e connected
in any manner that allows for movement o f the application head
302. B y way o f example, the drive motor 301 can b e connected
directly to the application head 302. B y way o f another
example, and a s depicted in Fig. 2 , the drive motor 301 can b e
connected to an application head platform 303. In this
embodiment, the application head 302 can also b e connected to
the platform 303. The apparatus 10 can also include a first
pair o f guide rails 502 and optionally, a second pair o f guide
rails 503. The rails can help guide and support the application
head 302 o r the application head and the drive motor 302 and
301. Preferably, the platform 303 travels axially along the
length o f the substrate unimpeded. The platform 303 can further
include a mobilizer, a pair, or more than one pair o f mobilizers
304. The mobilizer 304 can b e any device that allows o r assists
the platform 303, and the application head 302, o r the
application head and drive motor 302 and 301, to travel along
the guide rails 502/503. A n example o f a mobilizer includes,
but is not limited to, a wheel 304. According to certain
embodiments, the drive motor 301 and the application head 302
travel axially along the length of the substrate. According to
other embodiments, the drive motor 301, the application head
302, and the platform 303 travel axially along the length of the
substrate .
[0035] The distance that the application head 302
{and any other components) travels axially along the substrate
401/402 can be controlled. According to an embodiment, the
application head 302 (and any other components) travels axially
along the length of the substrate 401/402 for a desired
distance. Preferably, the length of the feed tube 200 is such
that it allows the application head 302 {and any other
components) to travel axially along the length of the substrate
401/402 for the desired distance. In one embodiment, the
desired distance is at least 90% of the total length of the
substrate 401/402 . According to another embodiment, the desired
distance is the entire length of the substrate 401/402 .
[0036] The step of applying can further include
coating the substrate 401/402 with a desired quantity of the
material per a given length of the substrate. For example, the
substrate can be coated with a desired pounds of material per
foot of substrate {lbs/ft) . One of the advantages of the
material is that it can be used to help remove a portion of
filtercake. When the material is to be used for removing a
portion of a filtercake, then the desired quantity of coated
material can be determined based on the concentration of certain
ingredients in the filtercake {e.g., the concentration of
calcium carbonate) . By way of example, the desired quantity can
be determined based on the amount of available acid from the
material capable of dissolving at least a portion of a
filtercake containing a given concentration of calcium
carbonate. In order to achieve the desired quantity of coating,
it may be necessary to apply excess material in a liquefied
state 102 onto the substrate 401/402 because some of the
material being applied onto the substrate may not adhere to the
substrate. The desired quantity can be achieved by at least
regulating the flow rate of the fluid out of the application
head or regulating the speed at which the application head
travels along the length of the substrate. The substrate
401/402 can be coated a second time to achieve the desired
quantity. There may be other ways of achieving the desired
quantity, and the preceding examples are not meant to be
construed as the only ways of achieving such a result.
[0037] The method includes the step of rotating the
substrate 401/402 about an axis of the substrate 401/402. The
substrate 401/402 can be rotated for a desired period of time.
According to an embodiment, the desired period of time is at
least how long it takes for the application head 302 to travel
the desired distance along the length of the substrate 401/402.
According to another embodiment, the desired period of time is
at least 10 minutes after the application head 302 has traveled
the desired distance along the length of the substrate 401/402.
According to yet another embodiment, the desired period of time
is the time it takes for the material to become a solid on the
substrate after the step of applying. According to certain
embodiments, because the substrate 401/402 is being rotated at
least for the time that the material is being applied onto the
substrate 401/402, the material in a liquefied state is
inhibited from collecting or pooling on at least a portion of
the I.D. of the substrate 401/402. Referring to Fig. 3 , without
the rotation of the substrate 401/402, the material in a
liquefied state 102, can collect or pool at the bottom of the
substrate 401/402. Moreover, by rotating the substrate 401/402
during the step of applying, the material can flow from the I.D.
of the substrate back through the porous portions of the
substrate and onto the O.D. of the substrate, providing a better
coating on the substrate. The method can further comprise the
step of cooling the material or allowing the material to cool to
a solid state after the step of applying.
[0038] The apparatus 10 can further include a
collector 600 . The collector 600 can collect any excess
material that does not adhere to the substrate 401/402 .
[0039] The coated substrate can be used for a
variety of applications. One example of such an application is
the oil and gas industry. In an embodiment, the method can
further include the step of placing the coated substrate 401/402
in at least a portion of a subterranean formation after the step
of applying. If the method includes the step of cooling or
allowing to cool, then the step of placing can occur after the
step of cooling or allowing to cool. According to this
embodiment, the method can also include the step of contacting
the substrate 401/402 with a liquid, such as water, to cause at
least a portion of the material to remove at least a portion of
a filtercake.
[0040] In some applications, it would be desirable
to remove the material or allow the material to be removed from
the substrate 401/402 after a certain length of time. For
example, in the case where the coated substrates include a
perforated pipe and a screen, and the substrates are used in a
wellbore, it may be desirable to remove the material or allow
the material to be removed from the substrates after a desired
period of time (such as for production of oil or gas from the
subterranean formation) . Preferably, the material is capable of
being removed from the substrate at a predetermined length of
time. Examples of removing or allowing the material to be
removed include, but are not limited to: allowing the coated
material to come in contact with at least a minimum temperature
high enough to heat the material to a liquefied state;
contacting the material with a heat source (e.g., a heated
liquid or a heated gas) such that the material becomes a liquid;
allowing the material to come in contact with a compound that at
least partially solubilizes the material; and contacting the
material with a compound that at least partially solubilizes the
material .
[0041] Therefore, the present invention is well
adapted to attain the ends and advantages mentioned as well as
those that are inherent therein. The particular embodiments
disclosed above are illustrative only, as the present invention
may be modified and practiced in different but equivalent
manners apparent to those skilled in the art having the benefit
of the teachings herein. Furthermore, no limitations are
intended to the details of construction or design herein shown,
other than as described in the claims below. It is, therefore,
evident that the particular illustrative embodiments disclosed
above may be altered or modified and all such variations are
considered within the scope and spirit of the present invention.
While compositions and methods are described in terms of
"comprising," "containing," or "including" various components or
steps, the compositions and methods also can "consist
essentially of" or "consist of" the various components and
steps. Whenever a numerical range with a lower limit and an
upper limit is disclosed, any number and any included range
falling within the range is specifically disclosed. In
particular, every range of values (of the form, "from about a to
about b," or, equivalently , "from approximately a to b")
disclosed herein is to be understood to set forth every number
and range encompassed within the broader range of values. Also,
the terms in the claims have their plain, ordinary meaning
unless otherwise explicitly and clearly defined by the patentee.
Moreover, the indefinite articles "a" or "an", as used in the
claims, are defined herein to mean one or more than one of the
element that it introduces. If there is any conflict in the
usages of a word or term in this specification and one or more
patent s ) or other documents that may be incorporated herein by
reference, the definitions that are consistent with this
specification should be adopted.

WHAT I S CLAIMED I S :
. A method of coating a first porous substrate with a
thermoplastic material comprising the steps of:
rotating the substrate about an axis of the substrate;
applying the material in a liquefied state onto the
substrate, wherein the step of applying is performed f
the outside of the substrate.
2 . The method according to Claim 1 , wherein the material is
selected from the group consisting of polylactic acid,
polyglycolic acid, and combinations thereof.
3 . The method according to Claim 1 , further comprising coating
a second porous substrate.
4 . The method according to Claim 3 , wherein the first
substrate and the second substrate are hollow.
5 . The method according to Claim 1 , further comprising the
step of connecting the substrate to a rotator.
6 . The method according to Claim 1 , wherein the substrate is
rotated at a desired frequency.
7 . The method according to Claim 1 , further comprising an
application head.
8 . The method according to Claim 7 , wherein the application
head further comprises an application head heating element.
9 . The method according to Claim 7 , wherein the application
head is positioned relative to the outside of at least a portion
of the substrate.
10. The method according to Claim 9 , wherein the application
head completely surrounds the outside of at least a portion of
the substrate.
11. The method according to Claim 7 , further comprising the
step of pumping the material in a liquefied state from a
receptacle to the application head.
12. The method according to Claim 11, wherein the receptacle
further comprises a receptacle heating element.
13. The method according to Claim 7 , further comprising the
step of causing the application head to travel axially along the
length of the substrate during the step of applying.
14. The method according to Claim 13, wherein the application
head travels axially along the length of the substrate for a
desired distance.
15. The method according to Claim 1 , wherein the step of
applying comprises applying the liquefied material from the
outer diameter of the substrate through the porous portion of
the substrate and into the inner diameter of the substrate.
16. The method according to Claim 1 , wherein the material coats
the outside of the substrate, fills the porous portion of the
substrate, and coats the inside of the substrate during or after
the step of applying.
17. The method according to Claim 16, wherein the step of
applying further comprises coating the substrate with a desir
quantity of the material per a given length of the substrate.
18. The method according to Claim 1 , wherein the substrate i
rotated for a desired period of time.
19. The method according to Claim 18, wherein the desired
period of time is the time it takes for the material to become a
solid on the substrate.
20. A method of coating a porous substrate with a thermoplastic
material comprising the steps of:
connecting a first porous substrate to a rotator;
rotating the substrate about an axis of the substrate;
pumping the material in a liquefied state from a receptacle
to an application head; and
applying the material in a liquefied state onto the
substrate, wherein the step of applying is performed from
the outside of the substrate.