U.S. patent application number 10/691802 was filed with the patent office on 2005-06-02 for apparatus and method for penetrating oilbearing sandy formations, reducing skin damage and reducing hydrocarbon viscosity.
This patent application is currently assigned to Owen Oil Tools LP. Invention is credited to Chawla, Mammohan Singh, Pratt, Dan W..
Application Number | 20050115448 10/691802 |
Document ID | / |
Family ID | 34619767 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050115448 |
Kind Code |
A1 |
Pratt, Dan W. ; et
al. |
June 2, 2005 |
Apparatus and method for penetrating oilbearing sandy formations,
reducing skin damage and reducing hydrocarbon viscosity
Abstract
A shaped charge and a method of using such to provide for large
and effective perforations in oil bearing sandy formations while
causing minimal disturbance to the formation porosity is described.
This shaped charge uses a low-density liner having a filler
material that is enclosed by outer walls made, preferably, of
plastic or polyester. The filler material is preferably a powdered
metal or a granulated substance, which is left largely
unconsolidated. The preferred filler material is aluminum powder,
or aluminum particles, that are coated with an oxidizing substance,
such as TEFLON.RTM., permitting a secondary detonation reaction
inside the formation following jet penetration. The filled liner is
also provided with a metal cap to aid penetration of the gun
scallops, the surrounding borehole casing and the cement sheath.
The metal cap forms the leading portion of the jet, during
detonation. The remaining portion of the jet is formed from the
low-density filler material, thereby resulting in a more
particulated jet. The jet results in less compression around the
perforation tunnel and less skin damage to the proximal end of the
perforation tunnel.
Inventors: |
Pratt, Dan W.; (Fort Worth,
TX) ; Chawla, Mammohan Singh; (College Park,
MD) |
Correspondence
Address: |
PAUL S MADAN
MADAN, MOSSMAN & SRIRAM, PC
2603 AUGUSTA, SUITE 700
HOUSTON
TX
77057-1130
US
|
Assignee: |
Owen Oil Tools LP
|
Family ID: |
34619767 |
Appl. No.: |
10/691802 |
Filed: |
October 22, 2003 |
Current U.S.
Class: |
102/476 |
Current CPC
Class: |
F42B 1/032 20130101;
F42B 1/028 20130101 |
Class at
Publication: |
102/476 |
International
Class: |
F42B 010/00 |
Claims
What is claimed is:
1. A shaped charge comprising: a charge case; an explosive charge;
a liner for retaining the explosive charge within the case, the
liner comprising: a substantially contiguous first liner membrane;
a substantially contiguous second liner membrane; and a
particulated filler material disposed between the first and second
liner membranes, which is substantially unconsolidated.
2. The shaped charge of claim 1 wherein the liner further comprises
a metal cap disposed upon the first liner membrane.
3. The shaped charge of claim 1 wherein the filler comprises
powdered metal.
4. The shaped charge of claim 1 wherein the filler material is a
blend of coarse and fine particles.
5. The shaped charge of claim 1 wherein the first and second liner
membranes are comprised of plastic.
6. The shaped charge of claim 1 wherein the first and second liner
membranes are comprised of polyester.
7. The shaped charge of claim 1 wherein the first and second liner
membranes are comprised of fiberglass.
8. The shaped charge of claim 1 wherein the first and second liner
membranes are comprised of glass.
9. The shaped charge of claim 3 wherein particles of the powdered
metal have a polymer coating.
10. The shaped charge of claim 9 wherein the powdered metal
comprises aluminum and the polymer comprises TEFLON.RTM..
11. The shaped charge of claim 10 wherein the aluminum is
passivated by a polymer coating.
12. The shaped charge of claim 1 wherein the filler material
comprises hollow metal pellets.
13. The shaped charge of claim 1 wherein the filler material
comprises glass balloons.
14. The shaped charge of claim 1 wherein the filler material
comprises nano particles of material from the group consisting
essentially of aluminum, copper, tungsten, copper-coated tungsten,
and TEFLON.RTM.-coated aluminum.
15. The shaped charge of claim 1 wherein the first and second
membranes are contiguously affixed to one another to completely
enclose the filler material.
16. The shaped charge of claim 1 wherein the filler material has a
density that is below formation density.
17. The shaped charge of claim 1 wherein the filler material has a
density that is below 2.7 g/cc.
18. The shaped charge of claim 3 wherein the powdered metal
comprises tungsten.
19. The shaped charge of claim 18 wherein the powdered tungsten is
coated with copper.
20. A shaped charge comprising: a charge case; an explosive charge;
a liner for retaining the explosive charge within the case, the
liner comprising: an outer liner membrane; and a filler material
disposed encapsulated within the liner membrane, the filler
material having a density that approximates formation density
21. The shaped charge of claim 20 wherein the density if the filler
material is equal to or less than, or higher than, 2.7 g/cc.
22. The shaped charge of claim 20 wherein the filler material is
particulated.
23. The shaped charge of claim 20 wherein the filler material
comprises powdered aluminum.
24. he shaped charge of claim 23 wherein the filler material
further comprises TEFLON.RTM..
25. The shaped charge of claim 20 wherein the liner has a shape
from the group consisting essentially of conical, cylindrical,
trumpet, tulip, ball, and hemispherical.
26. A method of perforating a formation comprising: generating a
perforating jet having a metal precursor portion followed by a
substantially particulated portion; penetrating a wellbore casing
with said metal precursor portion; kissing the formation with said
precursor portion; and penetrating said formation with said
particulated jet to form a perforation.
27. The method of claim 26 further comprising the step of
initiating a secondary detonation reaction within the formation to
open pores within the formation surrounding the perforation.
28. The method of claim 27 wherein the step of initiating a
secondary detonation reaction comprises heating air-filled pores in
unconsolidated aluminum and rapidly oxidizing unconsolidated
aluminum via proximity of fluorine atoms in a TEFLON.RTM.
coating.
29. The method of claim 26 wherein the secondary burning reaction
further comprises oxidizing aluminum through a TEFLON.RTM.
coating.
30. The method of claim 26 further comprising the step of disposing
unreacted polymer within the formation to reduce fluid
viscosity.
31. The method of claim 26 further comprising the step of disposing
unreacted TEFLON.RTM. within the formation to reduce fluid
viscosity.
32. An explosively formed penetrator comprising: a charge case; an
explosive charge within said charge case; a liner for retaining the
explosive charge within the case, the liner comprising: a
substantially contiguous first liner membrane; a substantially
contiguous second liner membrane; and a particulated filler
material disposed between the first and second liner membranes, the
filler material being substantially unconsolidated.
33. The explosively formed penetrator of claim 32 wherein the
explosively formed penetrator further comprises a metal cap
disposed upon the first liner membrane.
34. The explosively formed penetrator of claim 32 wherein the liner
forming the precursor jet is conformal to the charge case.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates generally to the design of shaped
charges. In particular aspects, the invention relates to improved
liner design for shaped charges and the use of improved shaped
charges within a wellbore in order to better penetrate oil bearing
sandy formations with minimal skin damage and to reduce hydrocarbon
viscosity. Such a shaped charge features a composite jet that
produces a large diameter hole in the formation, barely disturbing
the formation properties. Such charges will greatly benefit
gravel-packing completions.
[0003] 2. Description of the Related Art
[0004] Shaped charges are used in wellbore perforating guns. A
shaped charge typically consists of an outer housing, an explosive
portion shaped as an inverted cone, and a metal liner that retains
the explosive portion within the housing. When oil-bearing sands
are perforated by conventional shaped charges, the full
oil-producing potential of the formation is often not realized. The
perforated walls tend to get cemented over by the backflow of jet
material from the impacted region. During detonation of the shaped
charge, a high-velocity jet is formed which is preceded by a
mushroom-shaped front end and followed by a slow-moving slug of
material. As the metallic jet penetrates the surrounding oilwell
casing, cement sheath, and formation, portions of the casing and
formation are displaced by the metallic jet and placed into plastic
back flow. This results in an area around the perforation tunnel
where the material that was within the tunnel has been compressed.
Because the material is compressed, it is denser and less permeable
than the undisturbed formation. This decrease in permeability may
be sufficient to preclude hydrocarbons from entering the
perforation tunnel.
[0005] In conventional shaped charges, the liner that retains the
explosive charge within the housing is typically made of a single
monolithic material, principally copper, but also sometimes of
tungsten, brass, molybdenum, lead, nickel, tin, phosphor bronze, or
some combination of these elements. Other prior liner designs have
been made from sintered copper or lightly consolidated copper
powder mixed with graphite and tungsten powders. These liner
designs are better suited for deep penetration of the wellbore
casing and the formation, but cause significant skin damage to the
perforation tunnel and are, therefore, not optimal for use in
oil-bearing formations.
[0006] The inventors of this application have recognized this. With
sandy formations, the depth of the penetration is typically not of
great importance to achieving good production of the well. Sandy
formations have good initial permeability. Of greater significance
is the cleanliness of the perforation. The high compression and
ensuing plastic flow of target material damages the original
permeability of the formation, thus inhibiting the free flow of
hydrocarbons into the wellbore and often necessitating drastic post
perforation treatment. A perforation that results in minimal skin
damage will effectively permit transmission of hydrocarbons into
the wellbore.
[0007] U.S. Patent Application Publication No. 2003/0037692 A1 by
Liu discusses the use of aluminum in shaped charges. Among the
several shaped charge designs discussed are those that employ
aluminum either mixed with the explosive or used as a solid liner
with or without the accompaniment of a copper liner for producing a
deep penetrating jet. He also discusses mixing aluminum with
ferrous oxide to form the liner. In Liu's design, additional energy
is released through a secondary detonation when molten aluminum
reacts with an oxygen carrying substance, such as water. However,
Liu's application teaches mixing of inert powder aluminum with
energetic explosive. This actually reduces the available energy
content per unit volume of explosive, which, in turn, reduces the
likelihood of aluminum undergoing the secondary detonation inside
the hollow carrier gun due to the limited air space in its
interior. Once the solid slug made from the aluminum liner reaches
the formation, it lodges itself into the deep narrow hole made by
the aluminum or copper jet that preceded it. This rapidly cooling
solid slug lodged in the perforation tunnel severely restricts, if
not completely stops, the flow of hydrocarbons into the well.
Reaction of the aluminum slug with the borehole water will be
limited to the exposed surface of the slug, at best.
[0008] The present invention addresses the problems of the prior
art.
SUMMARY OF THE INVENTION
[0009] The present invention provides a shaped charge and a method
of using such to provide for large and effective perforations in
oil bearing sandy formations while causing minimal disturbance to
the formation porosity. Shaped charges are described that use a
low-density liner having a filler material that is enclosed by a
polymer-resin skin, such as plastic or polyester. The filler
material is in the powdered or granulated form and is left largely
unconsolidated. In the preferred embodiments, the filler material
is a metal powder, such as aluminum powder that is coated with a
polymer or other substance, such as TEFLON@, thereby permitting a
secondary reaction inside the formation following detonation. In a
further described embodiment, an explosively formed penetrator
(EFP) is provided with a liner having powdered or granulated filler
material.
[0010] The liner is also provided with a metal cap member for
penetration of the gun scallops, intervening well fluid, and the
surrounding oilwell casing and cement sheath. The metal cap member
forms the leading portion of the jet, during detonation. The
remaining portion of the jet is formed from the low-density,
unconsolidated powder liner, thereby resulting in a more
particulated jet. The jet causes little compression around the
perforation tunnel and the skin damage is minimal.
[0011] In operation, a large diameter perforation hole is created
by a jet of increased diameter rather than by a conventional
focused jet, which is formed of a beam of particles. High target
compression is avoided through the use of a low-density liner. The
jet is slower and much hotter. Hotter jets better open the pores
within the formation and particularly avoid the compressed area
immediately surrounding the perforation tunnel. Once the filler
particles reach the perforation tunnel, the fluorine atom in the
TEFLON.RTM. coating oxidizes the aluminum atom under the prevailing
conditions of high shock pressure and high temperature. This, in
turn, releases a high amount of energy by causing a secondary
detonation in the perforation tunnel. Since the fluorine atoms are
carried by aluminum particles in the stoichometrically correct
proportion, the oxidation reaction is more certain and not
dependent upon the availability of water molecules, as was the case
for the devices described in U.S. Patent Application Publication
No. 2003/0037692 A1 by Liu. Even if the secondary reaction fails,
the elevated temperature of the jet and TEFLON.RTM.reduces
hydrocarbon viscosity. If the coating is a polymer other than
TEFLON.RTM. or another oxidizing agent, the secondary detonation
will not take place and the reduction of hydrocarbon viscosity will
be primarily due to reduction of friction.
[0012] The present invention provides significant advantages over
prior art devices and methods, such as those described in the Liu
patent application. In preferred embodiments of the present
invention, heating of the aluminum is more assured due to the
collapse of air voids present in the unconsolidated aluminum
powder. Air void collapse and high temperatures are developed
locally in the vicinity of aluminum particulates when the
detonation wave resulting from explosive initiation sweeps over the
liner. Also, the present invention is not dependent upon aluminum
particles finding water or other oxygen-carrying molecules to react
with. In preferred embodiments, polytetrafluoroethylene (PTFE) or
TEFLON.RTM., a very powerful oxidizer carrying a large number of
fluorine atoms, is coated onto the aluminum particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For greater understanding of the invention, reference is
made to the following detailed description of the preferred
embodiments, taken in conjunction with the accompanying drawings in
which reference characters designate like or similar elements
throughout the several figures of the drawings.
[0014] FIG. 1 is a side, cross-sectional view of an exemplary
shaped charge constructed in accordance with the present
invention.
[0015] FIG. 2 is a cross-sectional view of an exemplary shaped
charge liner shown apart from other components.
[0016] FIG. 3 is a side, cross-sectional view depicting the
creation of a high velocity jet and following slug resulting from
detonation of the shaped charge depicted in FIG. 1.
[0017] FIG. 4 is a side, cross-sectional illustration of an
exemplary perforation process in accordance with the present
invention.
[0018] FIG. 5 is a side, cross-sectional view of an alternative
exemplary shaped charge having an inset metal cap member.
[0019] FIG. 6 is a side, cross-sectional view of an exemplary
explosively formed penetrator (EFP) constructed in accordance with
the present invention.
[0020] FIG. 7 depicts the EFP shown in FIG. 6 following
detonation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] FIG. 1 illustrates an exemplary shaped charge 10 that is
constructed in accordance with the present invention. The shaped
charge 10 includes an outer charge casing, or case, 12 that is
typically fashioned of metal. The casing 12 defines a charge cavity
14 that is generally hemispherical and presents an open forward end
16. At the rear end of the casing 12, a small aperture 18 is
disposed. A small amount of booster is usually placed in the
aperture 18. A detonator 20 is retained adjacent to the aperture
18. The detonator 20 typically comprises a detonation cord, or
other items known in the art for initiation of a shaped charge. An
explosive charge 22 is disposed within the charge cavity 14 and
within the forward portion of the aperture 18 so as to be in
contact with the booster which is, in turn, in contact with or in
close proximity with the detonator 20. The explosive material may
comprise RDX (Hexogen, Cyclotrimethylenetrinitramine), HMX
(Octogen, Cyclotetramethylenetetranitramine), HNS, PYX or other
suitable high explosives known in the industry for use in downhole
shaped charges. A liner 24 seals the material of the explosive
charge within the charge cavity 14. The liner 24 may assume any
suitable shape, including hemispherical, trumpet, tulip, bell, and
conical (shown).
[0022] The structure of the liner 24 is better appreciated with
reference to FIG. 2. As seen there, the liner 24 includes a pair of
outer membranes 26 and 28 that sandwich a low-density filler
material 30 therebetween so as to provide a double-walled
configuration. The outer membranes 26 and 28 are preferably made of
a substantially contiguous polymer-resin skin, such as plastic or
polyester material that is lightweight. The plastic or polyester
that is used should be of a type that is highly resistant to high
temperatures, such as those present in wellbores. Alternatively,
the outer membranes 26, 28 may be formed of a thin sheet of metal,
such as copper, aluminum, or titanium. It is preferred that the
membranes 26 and 28 be affixed to one another in a contiguous
manner so as to completely enclose the filler material 30. In other
words, the outer membranes 26 and 28 would completely encapsulate
the filler material 30.
[0023] The filler material 30 is granulated or powdered and
preferably largely unconsolidated. In preferred embodiments, the
filler material 30 comprises a micro-sized or nano-sized metal
powder, most preferably aluminum powder. Aluminum is a preferred
filler material since it is highly reactive during detonation and
releases explosive power in the presence of an oxidizer. Aluminum
burns hot and releases significant amounts of thermal energy during
the course of the detonation and perforation of a wellbore.
Alternatively, the filler material 30 may comprise aluminum powder
intermixed with a polymer powder, such as TEFLON.RTM.. In a
particularly preferred embodiment, the filler material 30 comprises
a polymer-coated metal powder, such as aluminum powder coated with
TEFLON.RTM. polymer. This combination of substances is particularly
desirable since it provides for secondary "special effects" during
perforation and after detonation. Specifically, the TEFLON.RTM.
passivates the highly reactive aluminum powder during manufacturing
and storage and permits controlled oxidation of the aluminum
particles when initiated. Additionally, the fluorine in TEFLON.RTM.
feeds the oxidation reaction in an oxygen-poor downhole environment
and typically contributes to a secondary detonation inside the
formation following jet penetration. In case the secondary reaction
fails, the hot-burning aluminum opens the pores within the
formation surrounding the perforation, thereby providing for better
flow of hydrocarbons into the perforation tunnel and the wellbore.
This increases the perforation temperature and reduces interstitial
fluid viscosity. Unreacted TEFLON.RTM. advantageously reduces
in-situ hydrocarbon viscosity as well.
[0024] In an alternative embodiment, the filler material 30 might
also comprise a metal powder coated with another metal, for
example, tungsten powder coated with copper. Alternatively, the
filler material 30 might be made up of hollow metal pellets or
micro-balloons of metal or glass.
[0025] As noted, the filler material 30 is largely unconsolidated
and is not compressed or sintered together. In the preferred
embodiments, the density of the filler material 30 within the liner
24 is close to the formation density. As a practical matter, the
density of the filler material is preferably below 2.7 g/cc, or the
approximate density of solid aluminum. Uniformity in filling of the
liner 24 with the filler material 30 is preferably achieved by
vibration of the liner 24 during filling, depending upon the mass
and particle size of the filler material 30.
[0026] A metal cap member 32 is affixed to the first membrane 26 of
the liner 24 in the apex region of the casing 12. If the filled
liner 24 is hemispherical in shape, then the metal cap 32 will also
be a cap of sphere and reside in the polar region of the filled
liner 24. The metal cap 32, in general, is conformed to the shape
of the liner 24, whatever shape the liner 24 may be. The metal cap
32 is fashioned from a suitable metal material, including copper,
brass, bronze, tungsten, or tantalum. FIG. 5 illustrates an
alternative design for a shaped charge 10' wherein the metal cap
member 32' is inset within the liner 24. In practice, this design
may have advantages for security of the cap by ensuring that the
cap member 32' is largely located inside of the liner 24 and is
less likely in some situations to be prematurely unsested from the
liner 24 prior to detonation.
[0027] FIG. 3 illustrates the shaped charge 10 following
detonation. The radially inner portion of the liner 24 primarily
forms a forward-penetrating jet 34 while the radially outer
portions of the liner 24 primarily form the slow-moving slug 36
that follows. It is noted that the leading portion 38 of the main
jet 34 has a greater radial diameter than that created by most
conventional shaped charges. The metal cap 32 makes a jet, which
has sufficient density and mass to penetrate the casing of the
wellbore and any gun scallops or protective cover that surrounds
the perforating gun, provides the forward portion 38 of the jet 34.
The uncollapsed portion of the liner 39 separates the main jet from
the slug. The use of low-density, unconsolidated filler material 30
in the liner 24 causes the remaining portions of the jet 34 and the
slug 36 to be more particulated than the corresponding conventional
jets and slugs formed of tungsten, copper and similar solids or
heavier materials.
[0028] FIG. 4 illustrates an exemplary perforation process
utilizing a shaped charge constructed in accordance with the
present invention. Wellbore 40 is shown disposed through a sandy
oil-bearing formation 42. The wellbore 40 has casing 44 that is
retained by cement 46. A perforating gun 48 is shown disposed
within the wellbore 40 by the tubing string 50. The perforating gun
48 may be of any of a number of types used in the industry, but
includes at least one shaped charge 10, of the type described
earlier. The shaped charge 10 is shown to have created a
perforation 52 through the casing 44, cement 46 and formation 42.
For comparison, a standard perforation 54 is also shown in FIG. 4.
A perforation resulting from the inventive formation 42 surrounding
the perforation 52. A compression zone 58 is illustrated about the
standard perforation 54 wherein the formation material has been
compressed into a state that is less porous and denser. The
perforation 52 is also of greater diameter than the perforation 54
and is not as deep. As noted, when the filler material 30 is
composed of TEFLON.RTM.-coated aluminum powder, the jet 34 and slug
36 will tend to provide a secondary explosion within the formation
which will release a lot of heat, which in turn, will increase
porosity and reduce viscosity of fluids within the formation.
[0029] A shaped charge constructed in the manner described above
also provides an advantage when used in sandy formations with
respect to shock, or acoustic impedance matching of the formation.
The shock impedance provided by the more highly particulated jet 34
and slug 36 more closely matches the shock impedance of a sandy
formation. As a result, there is a decreased amount of shear damage
and skin damage to the surrounding formation.
[0030] Referring now to FIGS. 6-7 there is shown an explosively
formed penetrator (EFP) charge 60 that is constructed in accordance
with the present invention. The EFP 60 is a type of shaped charge.
As can be seen, the EFP is roughly hemispherical in shape and
includes an outer charge case 62 that defines an interior charge
cavity 64. Explosive material 66, such as RDX, is molded into the
cavity 64 and conforms to the interior walls of the cavity 64. A
liner 67 encloses the explosive material 66 within the cavity 64
and is conformal with the walls of the cavity 64. The liner 67 is
formed of particulated filler materials, as described earlier,
encased within an outer membrane (not shown) of plastic or metal,
as described previously. A metal cap member 68 is affixed to the
central area of the liner 67 in a polar location, as shown. In a
preferred embodiment, the metal cap member 68 is formed of
copper.
[0031] FIG. 7 illustrates the EFP 60 following detonation and
illustrates the formation of a particulated penetrator 70. As the
detonation progresses, the formation will be penetrated, or
"kissed," by the penetrator 70 to form a perforation. The term
"kissed," as used herein, means to impact upon the surface of the
formation while substantially not penetrating it and substantially
not destroying the formation's porosity or permeability. Following
this, a secondary detonation reaction will occur within the
formation as the filler material, preferably aluminum, reacts with
fluorine atoms in the formation water and, if present, TEFLON.RTM.
in the filler material.
[0032] Generally speaking, the present invention improves upon
several aspects of the prior art, including the Liu patent
application by providing the following results or advantages:
[0033] 1) aluminum reaches a high temperature during and following
detonation. This is accomplished by making the liner from
unconsolidated powder that carries many air pockets.
[0034] 2) aluminum reacts with oxidizer to create a secondary
detonation. This is accomplished by coating the aluminum particles
with fluorine-carrying TEFLON.RTM.. Fluorine reactivity with
aluminum is always higher than that of oxygen.
[0035] 3) Aluminum delivers substantially all of its secondary
detonation energy inside the perforation tunnel and not outside in
the borehole or the hollow carrier gun.
[0036] 4) The resulting aluminum slug cannot block the hydrocarbon
flow. This is facilitated by use of unconsolidated aluminum
particles in the liner that, upon explosive action, produces a
particulated slug.
[0037] Those of skill in the art of shaped charges will recognize
that numerous modifications and changes can be made to the
illustrative designs and embodiments described herein and that the
invention is limited only by the claims that follow and any
equivalents thereof.
* * * * *