SELECTIVE CONTROL OF FLOW THROUGH A WELL SCREEN
TECHNICAL FIELD
This disclosure relates generally to equipment utilized
and services performed in conjunction with a subterranean
well and, in an example described below, more particularly
provides for selective control of flow through a well
screen.
BACKGROUND
It can be advantageous to be able to selectively
control flow through a well screen. In the past, aluminum
plugs have been installed in a well screen base pipe, in
order to block flow through the well screen until the
aluminum plugs are dissolved. Unfortunately, a large volume
of acid had to be circulated from the earth's surface down
to the well screen, in order to initiate dissolving of the
plugs. This method was inefficient, costly and timeconsuming.
Therefore, it will be appreciated that improvements are
needed in the art of selectively controlling flow through
well screens.
SUMMARY
In the disclosure below, a well system and associated
method are provided which bring improvements to the art of
controlling flow through well screens. One example is
described below in which acid is selectively released from
an acid containing structure in a well screen assembly.
Another example is described below in which water or another
aqueous fluid is flowed into contact with a well screen
assembly, in order to permit flow through a sidewall of a
well screen.
In one aspect, the present disclosure provides to the
art a method of selectively controlling flow through a well
screen. The method can include installing the well screen
in a wellbore, and then exposing the well screen to an
aqueous fluid, thereby permitting flow through the well
screen.
In another aspect, a well screen assembly for use in a
subterranean well is provided by this disclosure. The well
screen assembly can include a well screen and an acid
containing structure which at least partially dissolves in
response to contact with an aqueous fluid, whereby flow
through the well screen is selectively permitted.
These and other features, advantages and benefits will
become apparent to one of ordinary skill in the art upon
careful consideration of the detailed description of
representative examples below and the accompanying drawings,
in which similar elements are indicated in the various
figures using the same reference numbers.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic partially cross-sectional view of
a well system and associated method which can embody
principles of the present disclosure.
FIG. 2 is an enlarged scale schematic cross-sectional
view of a well screen assembly which may be used in the well
system and method of FIG. 1 .
FIG. 3 is a schematic cross-sectional view of another
configuration of the well screen assembly.
FIG. 4 is a schematic cross-sectional view of yet
another configuration of the well screen assembly.
DETAILED DESCRIPTION
Representatively illustrated in FIG. 1 is a well system
10 and associated method which can embody principles of this
disclosure. In the example depicted in FIG. 1 , a well
screen assembly 12 has been interconnected in a tubular
string 14 (such as a production tubing string), and has been
installed in a wellbore 16. The wellbore 16 is illustrated
as being lined with casing 18 and cement 20, but in other
examples the wellbore could be uncased or open hole in a
zone surrounding the well screen assembly 12.
It is many times advantageous to circulate fluid
through the tubular string 14 during installation. It can
also be advantageous to be able to internally pressurize the
tubular string 14 upon installation (for example, to set a
packer 22 ).
For these reasons and others, it can be beneficial to
be able to prevent fluid flow through a sidewall of the well
screen assembly 12 during installation, and later
selectively permit flow through the sidewall. When flow is
permitted through the sidewall of the well screen assembly
12, a fluid portion of a gravel packing slurry can enter the
assembly, fluid 24 can be produced from an earth formation
26 surrounding the wellbore 16, etc.
At this point, it should be pointed out that the well
system 10 illustrated in FIG. 1 and described herein is
provided as merely one example of a wide variety of well
systems which can embody the principles of this disclosure.
Therefore, it should be clearly understood that the
principles of this disclosure are not limited at all to any
of the details of the well system 10.
Referring additionally now to FIG. 2 , an enlarged scale
cross-sectional view of the well screen assembly 12 is
representatively illustrated. The assembly 12 is depicted
in FIG. 2 as including a well screen 28 and an acid
containing structure 30.
The well screen 28 includes a filter portion 32 of the
wire-wrapped type. However, any type of filter portion
(such as, wire mesh, sintered, pre-packed, etc.) may be
used, as appropriate for a particular application.
The well screen 28 also includes a drainage layer 34
comprising multiple longitudinally extending rods. However,
any type of drainage layer may be used, as desired.
The filter portion 32 and drainage layer 34 are
positioned on a generally tubular base pipe 36 having
openings 38 in a sidewall thereof. The openings 38 are
blocked by plugs 40 which, in this example, are preferably
made of an aluminum material, although other materials may
be used, if desired.
The plugs 40 block flow through a sidewall of the well
screen 28. However, the plugs 40 can be selectively
dissolved, when desired, by releasing an acid from the acid
containing structure 3 0 .
In the example of FIG. 2 , the acid containing structure
3 0 is in the form of a generally tubular sleeve positioned
in a flow passage 4 2 extending longitudinally through the
base pipe 3 6 . When interconnected in the tubular string 14
in the well system 1 0 , the flow passage 4 2 extends through
the tubular string for production of the fluid 2 4 to the
surface .
The acid containing structure 3 0 depicted in FIG. 2 is
made of a polylactic acid material which releases acid when
the material dissolves in response to contact with water or
another aqueous fluid 4 4 . The released acid, in turn,
dissolves the plugs 4 0 , thereby permitting flow of the fluid
2 4 through the sidewall of the well screen 2 8 .
Thus, flow through the sidewall of the well screen 2 8
can be selectively permitted by merely contacting the
structure 3 0 with an aqueous fluid 4 4 . The fluid 4 4 can be
conveniently flowed through the tubular string 14 to the
well screen assembly 12 , or otherwise brought into contact
with the structure 3 0 (for example, the fluid 2 4 produced
from the formation 2 6 could comprise an aqueous fluid) from
an interior and/or an exterior of the well screen 2 8 .
Note that there is no need to circulate a volume of
acid from the surface and through the tubular string 14 to
the well screen 2 8 . Instead, the acid is already present at
the well screen 2 8 when it is installed in the wellbore 1 6 .
Thus, safety, convenience and efficiency are all enhanced by
use of the well screen assembly 12 .
Referring additionally now to FIG. 3 , another
configuration of the well screen assembly 12 is
representatively illustrated. The configuration of FIG. 3
is similar in many respects to the configuration of FIG. 2 ,
but differs in at least one significant respect, in that the
acid containing structure 30 of FIG. 3 comprises a container
46 which contains an acid 48 therein.
The container 46 could be made of a polylactic acid
material, or another material which is dissolvable in
response to contact with the aqueous fluid 44. The acid 48
could be hydrochloric acid, sulfuric acid or any other acid
which is capable of dissolving the plugs 40.
Other suitable degradable materials for the container
46 include hydrolytically degradable materials, such as
hydrolytically degradable monomers, oligomers and polymers,
and/or mixtures of these. Other suitable hydrolytically
degradable materials include insoluble esters that are not
polymerizable . Such esters include formates, acetates,
benzoate esters, phthalate esters, and the like. Blends of
any of these also may be suitable.
For instance, polymer /polymer blends or monomer /polymer
blends may be suitable. Such blends may be useful to affect
the intrinsic degradation rate of the hydrolytically
degradable material. These suitable hydrolytically
degradable materials also may be blended with suitable
fillers (e.g., particulate or fibrous fillers to increase
modulus), if desired.
The choice of hydrolytically degradable material also
can depend, at least in part, on the conditions of the well,
e.g., well bore temperature. For instance, lactides may be
suitable for use in lower temperature wells, including those
within the range of 15 to 65 degrees Celsius, and
polylactides may be suitable for use in well bore
temperatures above this range.
The degradability of a polymer depends at least in part
on its backbone structure. The rates at which such polymers
degrade are dependent on the type of repetitive unit,
composition, sequence, length, molecular geometry, molecular
weight, morphology (e.g., crystallinity , size of spherulites
and orientation), hydrophilicity , hydrophobicity , surface
area and additives. Also, the environment to which the
polymer is subjected may affect how it degrades, e.g.,
temperature, amount of water, oxygen, microorganisms,
enzymes, pH and the like.
Some suitable hydrolytically degradable monomers
include lactide, lactones, glycolides, anhydrides and
lactams .
Some suitable examples of hydrolytically degradable
polymers that may be used include, but are not limited to,
those described in the publication of Advances in Polymer
Science, Vol. 157 entitled "Degradable Aliphatic Polyesters"
edited by A . C . Albertsson. Specific examples include
homopolymers , random, block, graft, and star- and hyperbranched
aliphatic polyesters.
Such suitable polymers may be prepared by
polycondensation reactions, ring-opening polymerizations,
free radical polymerizations, anionic polymerizations,
carbocationic polymerizations, and coordinative ring-opening
polymerization for, e.g., lactones, and any other suitable
process. Specific examples of suitable polymers include
polysaccharides such as dextran or cellulose; chitin;
chitosan; proteins; aliphatic polyesters; poly (lactides );
poly (glycolides ); poly (e-caprolactones );
poly (hydroxybutyrates ); aliphatic polycarbonates;
poly (orthoesters ); poly (amides ); poly (urethanes );
poly (hydroxy ester ethers); poly (anhydrides ); aliphatic
polycarbonates; poly (orthoesters ); poly (amino acids);
poly (ethylene oxide); and polyphosphazenes .
Of these suitable polymers, aliphatic polyesters and
polyanhydrides may be preferred. Of the suitable aliphatic
polyesters, poly (lactide) and poly (glycolide) , or copolymers
of lactide and glycolide, may be preferred.
The lactide monomer exists generally in three different
forms: two stereoisomers L- and D-lactide and racemic D,Llactide
(meso-lactide ). The chirality of lactide units
provides a means to adjust, among other things, degradation
rates, as well as physical and mechanical properties.
Poly (L-lactide) , for instance, is a semi-crystalline
polymer with a relatively slow hydrolysis rate. This could
be desirable in applications where a slower degradation of
the hydrolytically degradable material is desired.
Poly (D, L-lactide) may be a more amorphous polymer with
a resultant faster hydrolysis rate. This may be suitable
for other applications where a more rapid degradation may be
appropriate .
The stereoisomers of lactic acid may be used
individually or combined. Additionally, they may be
copolymerized with, for example, glycolide or other monomers
like e-caprolactone , 1,5-dioxepan-2-one, trimethylene
carbonate, or other suitable monomers to obtain polymers
with different properties or degradation times.
Additionally, the lactic acid stereoisomers can be modified
by blending high and low molecular weight poly (lactide ) or
by blending poly (lactide ) with other polyesters.
Plasticizers may be present in the hydrolytically
degradable materials, if desired. Suitable plasticizers
include, but are not limited to, derivatives of oligomeric
lactic acid, polyethylene glycol; polyethylene oxide;
oligomeric lactic acid; citrate esters (such as tributyl
citrate oligomers, triethyl citrate, acetyltributyl citrate,
acetyltriethyl citrate); glucose monoesters; partially fatty
acid esters; PEG monolaurate; triacetin; poly(ecaprolactone
); poly (hydroxybutyrate) ; glycerin-l-benzoate-
2,3-dilaurate ; glycerin-2-benzoate-l ,3-dilaurate ; starch;
bis (butyl diethylene glycol )adipate ; ethylphthalylethyl
glycolate; glycerine diacetate monocaprylate; diacetyl
monoacyl glycerol; polypropylene glycol (and epoxy,
derivatives thereof); poly (propylene glycol )dibenzoate,
dipropylene glycol dibenzoate; glycerol; ethyl phthalyl
ethyl glycolate; poly (ethylene adipate )distearate ; di-isobutyl
adipate; and combinations thereof.
The physical properties of hydrolytically degradable
polymers depend on several factors such as the composition
of the repeat units, flexibility of the chain, presence of
polar groups, molecular mass, degree of branching,
crystallinity, orientation, etc. For example, short chain
branches reduce the degree of crystallinity of polymers
while long chain branches lower the melt viscosity and
impart, among other things, elongational viscosity with
tension-stiffening behavior.
The properties of the material utilized can be further
tailored by blending, and copolymerizing it with another
polymer, or by a change in the macromolecular architecture
(e.g., hyper-branched polymers, star-shaped, or dendrimers,
etc.). The properties of any such suitable degradable
polymers (e.g., hydrophobicity , hydrophilicity , rate of
degradation, etc.) can be tailored by introducing select
functional groups along the polymer chains.
For example, poly (phenyllactide) will degrade at about
l/5th of the rate of racemic poly (lactide) at a pH of 7.4 at
55 degrees C . One of ordinary skill in the art with the
benefit of this disclosure will be able to determine the
appropriate functional groups to introduce to the polymer
chains to achieve the desired physical properties of the
degradable polymers.
Polyanhydrides are another type of particularly
suitable degradable polymer. Examples of suitable
polyanhydrides include poly(adipic anhydride), poly(suberic
anhydride), poly(sebacic anhydride), and poly (dodecanedioic
anhydride). Other suitable examples include, but are not
limited to, poly(maleic anhydride) and poly(benzoic
anhydride ).
Referring additionally now to FIG. 4 , another
configuration of the well screen assembly 12 is
representatively illustrated. In this configuration, the
acid containing structure 30 is external to the base pipe
36, but is still in close proximity to the plugs 40.
As depicted in FIG. 4 , the structure 30 is positioned
in the drainage layer 34 of the well screen 28. However, in
other examples, the structure 30 could be positioned in the
filter portion 32, in an outer shroud (not shown), or in any
other portion of the well screen 28.
Note that the aqueous fluid 44 contacts the structure
30 from an exterior of the well screen 28 in the example of
FIG. 4 . The structure 30 in this configuration could be
similar to that described above for the FIG. 2 configuration
(in which the structure is made of an acidic material, such
as polylactic acid, etc.), or similar to that described
above for the FIG. 3 configuration (in which the structure
comprises a dissolvable container having an acid therein) .
It may now be fully appreciated that this disclosure
provides significant advancements to the art of selectively
controlling flow through a well screen in a well. In each
of the examples described above, there is no need to
circulate acid to the well screen 28 in order to dissolve
plugs 40 therein. Instead, an acid containing structure 30
is present in the well screen assembly 12 when it is
installed in the wellbore 16.
The above disclosure provides to the art a method of
selectively controlling flow through a well screen 28. The
method can include installing the well screen 28 in a
wellbore 16, and then exposing the well screen 28 to an
aqueous fluid 44, thereby permitting flow through the well
screen 28.
Exposing the well screen 28 to the aqueous fluid 44 can
include: a ) contacting an acid containing structure 30 with
the aqueous fluid 44, b ) dissolving at least a portion of an
acid containing structure 30, c ) releasing an acid 48 from a
structure 30 containing the acid 48, d ) contacting a
polylactic acid structure 30 with the aqueous fluid 44, e )
dissolving a polylactic acid structure 30, and/or f )
dissolving at least one plug 40 which blocks flow through
the well screen 28.
Installing the well screen 28 in the wellbore 16 may
include installing an acid containing structure 30 in the
wellbore 16 with the well screen 28. The acid containing
structure 30 may be at least partially dissolvable in
response to contact with the aqueous fluid 44.
Installing the acid containing structure 30 in the
wellbore 16 can include positioning the acid containing
structure 30 within an interior longitudinal flow passage 42
of the well screen 28, positioning the acid containing
structure 30 external to a base pipe 36 of the well screen
28, and/or positioning the acid containing structure 30
proximate at least one plug 40 which blocks flow through the
well screen 28.
Also provided by the above disclosure is a well screen
assembly 12 for use in a subterranean well. The well screen
assembly 12 can include a well screen 28 and an acid
containing structure 30 which dissolves in response to
contact with an aqueous fluid 44, whereby flow through the
well screen 28 is selectively permitted.
The acid containing structure 30 may comprise
poly lactic acid. The poly lactic acid may form a container
46 which contains another acid 48.
At least one plug 40 may prevent flow through the well
screen 28. The plug 40 preferably dissolves in response to
contact with acid released from the acid containing
structure 30.
The acid containing structure 30 may be positioned
within an interior longitudinal flow passage 42 of the well
screen 28, external to a base pipe 36 of the well screen 28,
and/or proximate at least one plug 40 which blocks flow
through the well screen 28. The acid containing structure
30 may be attached to a base pipe 36 of the well screen 28.
It is to be understood that the various examples
described above may be utilized in various orientations,
such as inclined, inverted, horizontal, vertical, etc., and
in various configurations, without departing from the
principles of the present disclosure. The embodiments
illustrated in the drawings are depicted and described
merely as examples of useful applications of the principles
of the disclosure, which are not limited to any specific
details of these embodiments.
In the above description of the representative examples
of the disclosure, directional terms, such as "above,"
"below," "upper," "lower," etc., are used for convenience in
referring to the accompanying drawings. In general,
"above," "upper," "upward" and similar terms refer to a
direction toward the earth's surface along a wellbore, and
"below," "lower," "downward" and similar terms refer to a
direction away from the earth's surface along the wellbore.
Of course, a person skilled in the art would, upon a
careful consideration of the above description of
representative embodiments, readily appreciate that many
modifications, additions, substitutions, deletions, and
other changes may be made to these specific embodiments, and
such changes are within the scope of the principles of the
present disclosure. Accordingly, the foregoing detailed
description is to be clearly understood as being given by
way of illustration and example only, the spirit and scope
of the present invention being limited solely by the
appended claims and their equivalents.

WHAT IS CLAIMED IS:
1 . A method of selectively controlling flow through a
well screen, the method comprising:
installing the well screen in a wellbore; and
then exposing the well screen to an aqueous fluid,
thereby permitting flow through the well screen.
2 . The method of claim 1 , wherein exposing the well
screen to the aqueous fluid further comprises contacting an
acid containing structure with the aqueous fluid.
3 . The method of claim 1 , wherein exposing the well
screen to the aqueous fluid further comprises dissolving at
least a portion of an acid containing structure.
4 . The method of claim 1 , wherein exposing the well
screen to the aqueous fluid further comprises releasing an
acid from a structure containing the acid.
5 . The method of claim 1 , wherein exposing the well
screen to the aqueous fluid further comprises contacting a
polylactic acid structure with the aqueous fluid.
6 . The method of claim 1 , wherein exposing the well
screen to the aqueous fluid further comprises dissolving a
polylactic acid structure.
7 . The method of claim 1 , wherein exposing the well
screen to the aqueous fluid further comprises dissolving at
least one plug which blocks flow through the well screen.
8 . The method of claim 1 , wherein installing the well
screen in the wellbore further comprises installing an acid
containing structure in the wellbore with the well screen.
9 . The method of claim 8 , wherein the acid containing
structure is at least partially dissolvable in response to
contact with the aqueous fluid.
10. The method of claim 8 , wherein installing the acid
containing structure in the wellbore further comprises
positioning the acid containing structure within an interior
longitudinal flow passage of the well screen.
11. The method of claim 8 , wherein installing the acid
containing structure in the wellbore further comprises
positioning the acid containing structure external to a base
pipe of the well screen.
12. The method of claim 8 , wherein installing the acid
containing structure in the wellbore further comprises
positioning the acid containing structure proximate at least
one plug which blocks flow through the well screen.
13. A well screen assembly for use in a subterranean
well, the well screen assembly comprising:
a well screen; and
an acid containing structure which dissolves in
response to contact with an aqueous fluid, whereby flow
through the well screen is selectively permitted.
14. The well screen assembly of claim 13, wherein the
acid containing structure comprises polylactic acid.
15. The well screen assembly of claim 14, wherein the
polylactic acid forms a container which contains another
acid.
16. The well screen assembly of claim 13, wherein at
least one plug prevents flow through the well screen, and
wherein the plug dissolves in response to contact with acid
released from the acid containing structure.
17. The well screen assembly of claim 13, wherein the
acid containing structure is positioned within an interior
longitudinal flow passage of the well screen.
18. The well screen assembly of claim 13, wherein the
acid containing structure is positioned external to a base
pipe of the well screen.
19. The well screen assembly of claim 13, wherein the
acid containing structure is positioned proximate at least
one plug which blocks flow through the well screen.
20. The well screen assembly of claim 13, wherein the
acid containing structure is attached to a base pipe of the
well screen.