U.S. patent application number 10/842318 was filed with the patent office on 2005-11-10 for angled perforating device for well completions.
Invention is credited to Conner, Terry L., Spring, Robert J., Spring, Roger L..
Application Number | 20050247447 10/842318 |
Document ID | / |
Family ID | 35238388 |
Filed Date | 2005-11-10 |
United States Patent
Application |
20050247447 |
Kind Code |
A1 |
Spring, Roger L. ; et
al. |
November 10, 2005 |
Angled perforating device for well completions
Abstract
The present invention is an improvement in the design of a
perforating gun to perforate the casing and rock formations in oil
and gas wells. Perforating guns are cylindrical vessels with
explosive charges at specified intervals designed to shoot
perpendicularly outwardly through the vessel, perforating the
casing and into the rock formation. As most wells are generally
straight and most formations are relatively flat, the perforations
are horizontal in the same direction as the bedding plane of the
rock formations. The present invention is to angle the explosive
charges so as to cause the perforation to shoot at an angle to
horizontal and across the bedding planes of the rock formations.
The angled perforations can result in improved completions in
stratified reservoirs and fractured reservoirs by contacting all
the stratified layers for production and contacting more of the
fractures for production. Similarly, the angled perforations would
contact more of the cleats in coal seams for improved production of
coal be methane. Numerous other examples of reservoir conditions
could make the present invention advantageous in contacting more of
the formation with less perforating charges while at the same time
improving production rates and long term recovery of
hydrocarbons.
Inventors: |
Spring, Roger L.; (Oklahoma
City, OK) ; Spring, Robert J.; (Oklahoma City,
OK) ; Conner, Terry L.; (Oklahoma City, OK) |
Correspondence
Address: |
Brian E. Powley
Brian E. Powley, P.L.L.C.
P.O. Box 720415
Oklahoma City
OK
73172-0415
US
|
Family ID: |
35238388 |
Appl. No.: |
10/842318 |
Filed: |
May 10, 2004 |
Current U.S.
Class: |
166/55.2 |
Current CPC
Class: |
E21B 43/117 20130101;
E21B 43/119 20130101 |
Class at
Publication: |
166/055.2 |
International
Class: |
E21B 043/267 |
Claims
What is claimed is:
1. A well perforating device, within a wellbore, comprising a
plurality of perforating charges positioned by said well
perforating device, each of said perforating charges containing a
hollow cone shaped explosive charge so that upon detonation of the
hollow cone shaped charge a perforating jet is formed that creates
a perforation away from said perforating device into a rock
formation, an improvement comprising; a. positioning said
perforating charges at an angle away from perpendicular to said
well perforating device so as to contact more of said rock
formation adjacent to said wellbore with fewer of said plurality of
perforating charges.
2. The perforating device of claim 1 wherein the need for fewer of
said plurality of perforating charges is a means to reduce stress
to said wellbore and said rock formation.
3. The perforating device of claim 1 wherein said rock formation
has bedding planes.
4. A well perforating device comprising a plurality of perforating
charges positioned by said well perforating device, each of said
perforating charges containing a hollow cone shaped explosive
charge so that upon detonation of the hollow cone shaped charge a
perforating jet is formed that creates a perforation away from said
perforating device into a rock formation, an improvement
comprising; a. positioning said perforating charges at an angle
away from perpendicular to said well perforating device so as to
penetrate a plurality of intervals of higher permeability in said
rock formation.
5. The perforating device of claim 4 wherein said plurality of
intervals of higher permeability are horizontal bedding planes of
said rock formation.
6. The perforating device of claim 4 wherein said plurality of
intervals of higher permeability are fractures in said rock
formation.
7. The perforating device of claim 4 wherein said plurality of
intervals of higher permeability are cleats in a coal
formation.
8. The perforating device of claim 4 wherein the penetration of
said plurality of intervals of higher permeability is a means for
contacting more of said rock formation allowing greater flow of
fluids from said rock formation.
9. The perforating device of claim 4 wherein the penetration of
said plurality of intervals of higher permeability is a means for
decreasing the need for stimulation treatments.
10. The perforating device of claim 4 wherein the penetration of
said plurality of intervals of higher permeability is a means for
contacting more of said rock formation allowing for improved
stimulation treatments.
11. The perforating device of claim 4 wherein angling said
perforating charges away from a horizontal fluid contact in said
rock formation and penetration of said plurality of intervals of
higher permeability is a means for increasing the flow of fluids
from said rock formation while decreasing the change in said
horizontal fluid contact in said rock formation.
12. A perforating charge where an angle away from perpendicular
from the perforating device is incorporated into an angle between a
prima cord holder and the axis of said perforating charge.
13. A charge tube holder with a plurality of supports on which said
perforating charges rest as a means to position said perforating
charges at said angle away from perpendicular to said perforating
device.
14. The charge tube holder of claim 13 wherein a prima cord wraps
around the outside of said charge tube holder.
15. The charge tube holder of claim 13 wherein said perforating
charges and said prima cord are within said charge tube holder.
16. The charge tube holder of claim 13 wherein a plurality of bent
portions of said charge tube holder to further position said
perforating charges at said angle away from perpendicular to said
perforating device.
17. A well perforating device with at least one perforating charge
positioned at an angle away from perpendicular to said well
perforating device as a means to penetrate intervals of higher
permeability in a rock formation.
18. The well perforating device of claim 17 wherein said intervals
of higher permeability are horizontal bedding planes of said rock
formation.
19. The well perforating device of claim 17 wherein said intervals
of higher permeability are fractures of said rock formation.
20. The well perforating device of claim 17 wherein penetration of
said intervals of higher permeability is a means to contact more of
said rock formation allowing greater flow of fluids from said rock
formation.
21. The well perforating device of claim 17 wherein penetration of
said intervals of higher permeability is a means to decrease the
need for stimulation treatments.
22. The well perforating device of claim 17 wherein penetration of
said intervals of higher permeability is a means to contact more of
said rock formation allowing for better stimulation treatments.
23. The well perforating device of claim 17 wherein angling said
perforating charge away from a horizontal fluid contact in said
rock formation and penetrating said intervals of higher
permeability as a means to increase the flow of fluids from said
rock formation while decreasing the change in said horizontal fluid
contact.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not Applicable
BACKGROUND OF THE INVENTION
[0004] The invention relates generally to an improvement in the
design of an oil and gas well perforating device. The improvement
applies to a type of perforating device that is typically lowered
into the well through the casing or tubing in the well to a
position where the explosive charges are detonated at the desired
depth to shoot outwardly perpendicularly from the perforating
device and well casing. The improvement is a method of angling the
explosive charges such that when detonated the charges fire
upwardly or downwardly from horizontal. While angling the explosive
charges will decrease the distance away from the wellbore, there
are many reservoir conditions of the rock formation that can
benefit from perforating at an angle.
[0005] After an oil or gas well is drilled, steel casing is lowered
into the well and cemented to the adjoining rock formations.
Typically perforations are needed to allow the oil or gas from the
desired rock formation to be able to flow into the casing and then
out of the well. The perforations are made by lowering, on a
wireline or tubing, the perforating gun containing explosive
charges to the desired depth and detonating the charges. There are
several different types of perforating guns.
[0006] One type of perforating gun is referred to as a casing gun.
A casing gun is a hollow steel carrier that is lowered into the
casing of the well with the perforations made through screwed in
ports. These screwed in ports are used to allow the ports to be
removed and the hollow steel carrier to be used again.
[0007] A second type of perforating gun is an expendable casing
gun. This is similar to the previously discussed casing gun with
the addition of larger charges that will cause significant
distortion to the hollow steel carrier. The distortion is
sufficient to make the hollow steel carrier useable only one time
and therefore expendable. The larger charges are sometimes needed
when greater penetration is required such as when some of the rock
formation has washed away and there is a greater amount of cement
to penetrate. An expendable casing gun will have scallops cut on
the outer surface of the hollow steel carrier at the location of
the perforating charge or may have no scallops at all which is
referred to as run slick.
[0008] A third type of perforating gun is a tubing conveyed
perforating gun. The tubing is a retrievable string of pipe inside
of the casing that is permanently cemented in place. This is
another type of casing gun except the hollow steel carrier is made
a part of the tubing string rather than being run on a wireline.
Depending on the size of the charge, distortion of the carrier can
be sufficient to make the perforating gun expendable. This type of
gun can have ports, scallops or be run slick.
[0009] All of the previously discussed perforating guns are made to
be lowered into the casing. There are also perforating guns made to
be lowered into the tubing. These through tubing perforating guns
are designed to be utilized while leaving the tubing inside the
well and casing. In order for the perforating guns to be lowered
inside of the tubing requires a smaller diameter perforating gun.
The through tubing perforating guns are lowered through the tubing
to a desired depth, below the bottom of the tubing, at the desired
rock formation and are detonated.
[0010] A fourth type of perforating gun is a through tubing strip
gun run on wireline. This type of perforating gun includes a strip
carrier on which capsule shaped charges may be mounted. The capsule
shaped charges are sealed to protect the charges from the well
environment. At detonation the strip gun is basically blown apart
and the debris drops to the bottom of the well below the
perforations. Any intact portion of the strip gum is then retrieved
through the tubing.
[0011] A fifth type of perforating gun is the retrievable tubing
gun which is like the casing gun in that it uses a sealed carrier
to hold the charges but is a smaller diameter to fit inside the
tubing. The smaller diameter is not as capable of absorbing the
explosive charge and the outer diameter of the hollow carrier is
distorted, making this type of perforating gun expendable. The
carrier will have scallops or be run slick.
[0012] All of the perforating guns discussed utilize a sealed
carrier to protect the perforating charges from the wellbore
fluids, with the exception of the strip gun where each individual
perforating charge has to be sealed from the wellbore fluids. All
of the perforating guns are designed to shoot the explosive charges
perpendicular to the perforating device and the well casing.
Another attribute of perforating guns is the shot density, which
ranges from one to twelve spots per foot with four and six shots
per foot being most common. Another attribute of perforating guns
is the phasing which is the circular pattern that the perforating
charges are spaced around the perforating gun with typical phasing
being 0, 60, 90 120 and 180 degree phasing.
[0013] While the geological dip, the angle of the bedding planes
from horizontal, can widely vary depending on the type of geologic
structure, in many or most areas the dip from horizontal is low and
the rock formations are generally are flat and perpendicular to the
wells that are generally vertical. The result is that the explosive
charges are usually shot horizontally and in the same direction as
the bedding planes of the rock formations. Perforating in the same
general direction as the bedding plane of the rock formation has
its limitations.
[0014] The horizontal layering of the intervals within a rock
formation create horizontal permeability barriers and much greater
horizontal permeability than vertical permeability. Production from
fractured formations is dependent on connecting to the natural
fracture system of the reservoir. With both horizontal and vertical
fractures, perforations at an angle to the bedding plane should
intersect more of the natural fractures of the formation. Angled
perforating also requires fewer perforations to contact the entire
reservoir. Angled perforating should decrease the need for a
stimulation treatment and will increase the effectiveness of
acidizing and fracturing treatments by contacting more of the rock
formation and providing better control of the completion.
[0015] There have been some patented ideas related to perforating
at an angle for very specific reasons different from those of the
present invention. None of these patented ideas related to
perforating at an angle are believed to have been used on a
commercial basis. The GB 701,074 Schlumberger patent relates to
angling the perforations upward to facilitate gravity drainage and
minimizing the tendency of the perforation to become plugged. The
GB 828,306 Schlumberger patent relates to angling the perforations
upward so that the explosive charge from the lowest charge
detonates the next charge above and so on, doing away with the
prima cord between the charges. The GB 833,164 Du Pont patent also
relates to angling the perforation upward so each charge will
detonate the next higher charge on a through tubing strip gun. The
charges go through the tubing axially and expand outward below the
tubing such that the axis of the charges to the casing ranges from
30.degree. for minimum depth of penetration and up to 90.degree.
for maximum depth of penetration.
[0016] The U.S. Pat. No. 3,347,314 Schuster patent uses angled
perforating to closely intersect two perforations to create a
method to circulate out debris and form an enlarged cavity which
can then have fluids injected to stabilize or consolidate the
formation. The U.S. Pat. No. 3,630,282 Lanmon patent also uses
angled perforating to closely intersect two perforations with a low
pressure chamber in the perforating gun such that the debris from
the first and second charges have a place to exist upon firing the
second charge. The U.S. Pat. No. 4,105,073 Brieger patent uses
angled and non-angled perforating to closely intersect or collapse
and communicate two perforations to form a cavity for injection of
fluids to consolidate the formation. Another form provides an
isolated chamber for debris and to enhance the formation of the
enlarged cavity. The U.S. Pat. No. 4,756,371 Brieger patent uses
angled perforating to closely intersect two perforations, which can
then be washed free of debris and compaction by hydraulic
jetting.
[0017] The U.S. Pat. No. 6,283,214 B1 Guinot patent uses angled
perforating to make elliptical perforations having the major axis
of the ellipses aligned with the direction of maximum compressive
stress, and perpendicular to the bedding plane, can minimize sand
production. The U.S. Pat. No. 6,401,818 B1 also uses angled
perforating with elliptical perforations having the major axis of
the ellipses aligned with the direction of maximum compressive
stress, and perpendicular to the bedding plane, to increase
production of hydrocarbons.
[0018] The limited use for angled perforating has been limited to
trying to keep the perforations free from debris, for detonation
from one charge to another without a prima cord, to run a strip gun
through tubing at an angle for greater clearance, creating a cavity
to treat for consolidation, to wash out two closely intersecting
perforations and to create an elliptical perforations perpendicular
to the bedding plane to reduce sand production and increase
hydrocarbon production. The objectives of these patents are
completely different from the objectives of the present invention
that uses angled perforating, or directional perforating, as a
means to make greater contact with high permeability streaks,
fractures and cleats, to assist in controlling flow where there is
a gas/oil, gas/water or a oil/water contact, as a means of opening
all of the formation with less perforations and less cost, creating
less need for stimulation treatments and increasing the success of
stimulation treatments.
[0019] The perforations, made in the rock formation, are a critical
part of the well completion that will affect the production rates
and recovery of the well. There continues to be a need to decrease
costs and improve the performance of flow into the wellbore. Under
many reservoir conditions, the present invention could
significantly increase the flow into the wellbore while also
decreasing costs of the completion.
SUMMARY OF THE INVENTION
[0020] The present invention utilizes existing technology of the
perforating industry in a new way to address a number of reservoir
conditions that can exist in a well. The present invention
perforating device utilizes positioning the perforating charges at
an angle from horizontal to accomplish a variety of different
improvements in completion techniques depending on the specific
reservoir conditions of the rock formation. Angled perforating can
be utilized to intersect bedding planes for permeability streaks,
to intersect rock fractures, to intersect coal cleats, to angle
away from water or gas contacts, to contact more of the rock
formation with less perforations for both less cost and improved
performance during subsequent acid or fracturing treatments. The
present invention can for nominal cost improve the performance of
almost every oil or gas completion. The improvement in the angled
perforation completion can also reduce over all costs by requiring
less perforations and improved stimulation treatments. The present
invention can provide improved completions for greater rates and
recovery while also reducing completion costs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a partial, cross sectional view of a stratified
reservoir with relatively horizontal bedding planes and thin
permeable sands and fractured dolomite separated by an impervious
limestone layers, a tight sand streak, and shale layers with four
thirty-degree angled perforations.
[0022] FIG. 2 is a partial, cross sectional view of the same
stratified reservoir as in FIG. 1 with eight conventional prior art
perforations depicting the prior art.
[0023] FIG. 3 is a partial, cross sectional view of a horizontal
well drilled to intersect vertical fractures in a fractured
limestone with four thirty-degree angled perforations that
intersect three vertical fractures.
[0024] FIG. 4 is a partial, cross sectional view of a conventional
vertical wellbore and a relatively horizontal formation, with
horizontal bedding planes, with one prior art perforation and one
angled perforation to show the flow of reservoir fluids depicted by
the arrows.
[0025] FIG. 5 is a partial, cross sectional view of a the same
formation and wellbore as depicted in FIG. 4 during a stimulation
treatment where fluids are pumped into the formation and the arrows
show the flow of the treatment fluids into the formation.
[0026] FIG. 6 is a partial, cross sectional view of a prior art
perforations in proximity of a fluid contact with the dashed arrows
showing the flow of the lighter formation fluid and the other
arrows show the flow of the heavier formation fluid with the fluid
contact depicted by the dashed line through the formation.
[0027] FIG. 7 is a partial, cross sectional view of an angled
perforations in proximity of a fluid contact with the dashed arrows
showing the flow of the lighter formation fluid and the other
arrows show the flow of the heavier formation fluid with the fluid
contact depicted by the dashed line through the formation.
[0028] FIG. 8 is a perspective view of the prior art perforating
charge showing the circular outer case and the prima cord holder
where the prima cord is held in place by a clip that rests in the
small groove around the outer surface of the prima cord holder.
[0029] FIG. 9 is a side view of the prior art perforating charge
shown in FIG. 8 showing the symmetry of the charge and the small
groove on the outside of the prima cord holder.
[0030] FIG. 10 is a cross sectional view of the prior art
perforating charge shown in FIG. 9 through line 10-10 showing the
symmetry of the explosive material packed between the outer case
and the cone shaped charge.
[0031] FIG. 11 is a side view of an angled perforating charge where
the desired angle is achieved by incorporating the angle into the
angle between a prima cord holder and the axis of said perforating
charge.
[0032] FIG. 12 is a cross sectional view of the angled perforating
charge of FIG. 11 through line 12-12 showing the symmetry of the
explosive material packed between the outer case and the cone
shaped charge.
[0033] FIG. 13 is a partial, cross sectional view of the prior art
charge tube holder showing the side of the perforating charges held
in place by the holes cut in the charge tube holder and the prima
cord around the outside used to make convention prior art
perforations perpendicular to the axis of the charge tube
holder.
[0034] FIG. 14 is a partial, cross sectional view of the first
preferred embodiment showing a bottom support from a bent portion
of the charge tube holder with the prima cord around the outside of
the charge tube holder secured by a clip resting in a groove around
the prima cord holder.
[0035] FIG. 15 is a partial, cross sectional view of the second
preferred embodiment where the perforating charges and prima cord
are within the charge tube holder with the perforating charges
supported by a bent portion of the charge tube holder and resting
on the inner surface of the charge tube holder.
[0036] FIG. 16 is a partial, cross sectional view of the third
preferred embodiment where the angle is formed between the prima
cord holder and the shaped charge and the perforating charge is
secured with a clip on prima cord holder outside of the charge tube
holder.
DETAILED DESCRIPTION
[0037] In the following description, details of the present
invention are given to provide an understanding of the present
invention. However, those skilled in the art will know that the
present invention may be practiced without these details and that
numerous variations or modifications from the described embodiments
are possible.
[0038] Rock formations on the surface of the earth are constantly
being eroded by the elements and are redeposited by means of
gravity as sediments. Sediments on the surface of the earth are
generally deposited horizontally whether on land or in water. The
repeated layering of these sediments creates bedding planes. These
sediments are compacted and buried under newer sediments. The
buried sediments eventually form various forms of geological rock
formations. Some of the effects of the bedding planes are
transformed into permanent features of the rock formations. During
the transformation into a rock formation and afterwards, the rock
formations are subjected to extreme temperatures and pressures that
also create permanent features of the rock formations such as
fracturing. Some of the common rock formations are sandstone,
limestone, dolomite, coal and shale. All of these rock formations
have particular characteristics but all of them with the general
exception of shale are capable of having void areas to hold oil and
gas, which is the porosity, and the porosity is interconnected to
allow the flow of the oil and gas to a wellbore, which is the
permeability. The bedding planes result in greater horizontal
permeability than vertical permeability. These rock formations may
be thick clean sections of one particular type of formation or they
are often interspersed. An oil and gas reservoir is often comprised
of a series of sand and shale layers with high permeability
sections separated by impermeable tight layers of the rock or a
layer of shale.
[0039] The surface sediments are deposited horizontally and after
deposition they are subjected to strong geological forces that form
geological structures that can trap hydrocarbons in the porosity of
the rock formation against a shallower impermeable barrier such as
a layer of shale. As a result the angle of the bedding planes of
the rock formation is no longer horizontal and has an angle which
is referred to as the dip of the bedding planes and the rock
formation. The multitude of possible geologic formations could
result in every possible angle from horizontal and even to the
point that a rock formation may be completely overturned. While any
angle from horizontal is possible, many to most times the bedding
planes and rock formations are relatively close to horizontal. Some
of the largest oil and gas fields have relatively low dip to the
beds covering very large areas. This common situation is sometimes
referred to as pancake geology. The dip of the rock formation and
the resulting horizontal and vertical permeability along with any
permeability barriers are important consideration in the completion
of an oil and gas well.
[0040] Another important consideration in many rock formations that
affects the flow of hydrocarbons is horizontal and vertical
fracturing that occurred as the rock formation was formed or
subsequently as a result of geological forces on the rock
formation. Coal has both horizontal and vertical fractures referred
to as cleats. These fractures are areas of very high permeability
and intersecting these fractures can greatly increase rates and
ultimate recoveries as larger areas of the reservoir can be
drained. Intersecting vertical fractures is one of the reasons for
horizontal drilling.
[0041] The vast majority of wells drilled are drilled vertically
with relatively flat geology. This has important ramifications when
considering the typical method in which wells are completed for
production. There have been many different types of completions
utilized. In the past openhole completions were common where the
productive portion of the reservoir was drilled out below the
casing. One advantage of this type of completion was that it opened
up and contacted the entire reservoir in the openhole section.
Problems associated with an openhole completion are the lack of
control for stimulation, managing the depletion of the reservoir,
and dealing with water influx.
[0042] The method of completion that has gained worldwide
acceptance is to drill through the zones of interest, run logging
tools to assess the rock formations of interest, run casing to the
desired total depth, and cement that casing in place. The logging
tools will identify possible accumulations of hydrocarbons and the
type of rock formation as to how it could affect production from
the formation. The high permeability streaks and fractures are hard
to impossible to identify. Then perforating charges are lowered on
wireline or on tubing to the desired depth where the perforating
charges are detonated and penetrate the casing, cement sheath and
rock formation at an angle perpendicular to the casing. Since the
casing is relatively vertical, the perforation is relatively
horizontal. Since the perforation is relatively horizontal and the
layered bedding planes and rock formations are also relatively flat
or horizontal, the perforations typically enter the rock formation
along the lines of the bedding planes. This results in a greater
likelihood that high permeability pay sections and fractures could
be missed. This problem is countered by shooting many shots per
foot with four to six shots per foot being common. This high shot
density is expensive and destructive to the casing and cement
sheath. The number of perforations and shot density sometimes has
to be restricted in order to get a good stimulation treatment.
[0043] FIG. 1 depicts a stratified reservoir with relatively
horizontal bedding planes and seven alternating porous and
permeable formations, sands and dolomite, separated by six
impermeable formations, shale, impermeable limestone and an
impermeable hard streak in a sand. The lithology can be described
from the oldest formation on the bottom as an impermeable shale 2,
overlain by a water sand 4, which in turn is overlain by a thin
shale 6. The oil productive section begins with an oil sand 8,
overlain by a thin shale 10, overlain by another oil sand 12,
overlain by another thin shale 14, overlain by an oil sand 16,
overlain by an impermeable hard streak of sand 18, overlain by
another oil sand 20, overlain by another thin shale 22, overlain by
another oil sand 24, overlain by an impermeable limestone 26,
overlain by an oil filled porous dolomite 28, overlain by more
impermeable limestone 30, which was overlain by a shale 32.
[0044] FIG. 1 shows a perforating gun 34 suspended by a wireline 36
with a prima cord 38 that is attached to four angled perforating
charges 40 that are at an angle of thirty degrees from the
conventional prior art that would be perpendicular to the wellbore.
The lowest perforation 42 penetrated two productive formations
including an oil sand 8, an impermeable shale 10, and another oil
sand 12. The next higher perforation 44 penetrated three productive
formations including an oil sand 12, an impermeable shale 14, an
oil sand 16, an impermeable hard streak in the sand 18, and an oil
sand 20. The next higher perforation 46 penetrated, from the
deepest, an oil sand 20, an impermeable shale 22, another oil sand
24, an impermeable limestone 26, an oil filled porous dolomite 28,
more impermeable limestone 30, and an impermeable shale 32. The
highest perforation 48 penetrated two productive formations
including an oil sand 24, and the porous dolomite 28, along with
the impermeable limestone 26 and 30. The four angled perforations
42, 44, 46 and 48 penetrated or intersected all six of the
permeable formations 8, 12, 16, 20, 24, and 26, contacting all of
the reservoir and opening up all of the reservoir for any
stimulation treatment and for maximum producing rates and
recovery.
[0045] FIG. 2 depicts the same stratified reservoir as in FIG. 1
with conventional prior art perforating charges that are
perpendicular to the wellbore. The conventional prior art
perforating utilizes high shot density to increase the likelihood
of trying to open all of the reservoir but the thin layers can
easily be bypassed when perforating in basically the same direction
of the bedding planes. FIG. 2 shows a perforating gun 50 suspended
by a wireline 52 with a prima cord 54 attached to the conventional
prior art perforating charges 56 that formed the eight prior art
perforations 58 perpendicular to the wellbore. Perforations in the
same direction as the bedding planes generally can only penetrate
one formation and can miss productive formations. In FIG. 2 the
eight prior art perforations 58 in a set density pattern penetrated
only three productive formations 8, 12 and 20 and missed three
other productive formations 16, 24 and 28.
[0046] All of the productive formations illustrated in FIG. 1 and
FIG. 2 were porous and permeable oil filled formations. While not
shown as a separate drawing, some formations produce through
fractures and intersecting those natural fractures is essential to
making a successful completion. Since the identification of these
fractures is almost impossible, the angled perforating, which opens
all the reservoir, would intersect more of the horizontal and
vertical fractures. A common formation that produces through
fractures is a low porosity fractured limestone with both
horizontal and vertical fractures. Such a low porosity fractured
limestone is typical of the type of formation in which it is
advantageous to have a limited number of perforations for
restricted entry during stimulation treatments for better ball
action to ensure treating all of the perforations. Fewer angled
perforations are needed to contact a greater amount or the entire
reservoir while also improving the stimulation treatment.
[0047] FIG. 3 depicts a horizontal well 60 drilled to encounter
vertical fractures 62 in a fractured limestone 64. The drawing
depicts how the angled perforations 66 intersect the vertical
fractures 62. While not shown as a separate drawing, coal seams
have both horizontal and vertical fractures referred to as butt and
face cleats respectively. So the application of angled perforating
for intersecting horizontal and vertical fractures is applicable to
coalbed methane production.
[0048] FIG. 4 depicts the flow into a conventional prior art
perforation 68 and into an angled perforation 72 in a formation
with horizontal bedding planes with the direction of flow
represented by arrows. Since the prior art perforation 68 is in the
same direction as the bedding plane, most of the flow into the
prior art perforation 70 is through the lower vertical permeability
restricting the flow. Since the angled perforation 72 cuts across
the horizontal bedding planes, the flow into the angled perforation
74 is through the higher horizontal permeability. So not only does
angled perforating contact more of the reservoir and open all
permeability channels, but it also allows for less resistance for
all intervals to produce at a greater rate.
[0049] FIG. 5 depicts the flow of an acid treatment in both a
conventional prior art perforation 76 and an angled perforation 80
in a rock formation with relatively horizontal bedding planes with
the flow out of the perforations represented by arrows. Acid, with
many variations, and other fluids are used to clean up the
perforations routinely, usually without even testing the well
naturally. The perforating jet creates a crush zone in the rock
formation surrounding the perforation. Acid in the prior art
perforation 76 exits the crush zone and is pushed preferentially
horizontally down the bedding plane causing the flow out of the
prior art perforation 78 to preferentially treat a horizontal
section of the formation and miss treating portions of the
formation. Acid in the angled perforation 80 exits the crush zone
and moves directly down many bedding planes with the flow out of
the angled perforation 82 treating many bedding planes and much
more of the rock formation. So not only does the present invention
contact more of the reservoir but in doing so provides for better
stimulation of all of the formation which contributes to better
rates and recovery.
[0050] The other stimulation treatment performed on some wells is a
fracturing treatment where fluid and usually a proppant, like sand,
is pumped into the perforations at a high rate and pressure to
crack the rock formation open and fill the crack with the proppant.
Improved contact with more of the rock formation from the angled
perforating may decrease the need for well stimulation and should
improve the performance of any well stimulation treatment. As
previously mentioned, some thick rock formations require limiting
the number of perforations per foot in order to get sufficient
pressures during the fracturing treatment. Angled perforations
provide for improved contact with the rock formation while still
limiting the number of perforations per foot.
[0051] FIG. 6 depicts a well with conventional prior art
perforations 84 in proximity of a fluid contact 86. Gas is lighter
than oil and oil is lighter than saltwater. Fluid contacts in close
proximity to the perforations in a producing well are altered by
the large pressure differential created near the wellbore, which is
referred to as coning. Most commonly producing the oil section
results is lowering the gas/oil contact or raising the oil/water
contact near the wellbore. Conventional prior art perforations
encourage vertical flow and coning. Angled perforating can be used
to angle the perforations away from the fluid contact. Angled
perforating enables higher production rates through the bedding
plane higher horizontal permeability of the rock formation with
less pressure drawdown, which decreases the likelihood of
coning.
[0052] FIG. 6 depicts conventional prior art perforations 84 in the
oil section of a formation and since oil is lighter than water, the
oil floats above the water and a fluid contact 86 is formed in the
formation. The fluid contact 86 is in proximity of the wellbore and
the flow of oil 88 into the prior art perforations 84 is mostly
through the vertical permeability causing a higher pressure drop in
the immediate vicinity of the wellbore causing the fluid contact 86
immediately around the wellbore to rise causing the flow of water
90 to reach the prior art perforations called water breakthrough
and coning which will seriously decrease oil recovery.
[0053] FIG. 7 depicts angled perforations 92 in the oil section of
a formation floating above the water forming a fluid contact 94 in
the formation. The fluid contact 94 is in proximity of the wellbore
and the flow of oil 96 into the angled perforations 92 is mostly
through the higher permeability horizontal permeability allowing
greater production with less pressure drop. With less pressure drop
there is less tendency to for the flow of water 98 to be pulled
towards the angled perforations 92. So the angled perforations 92
benefit by being able to physically aim away from the fluid contact
94, providing greater production rates with less pressure drop at
the wellbore decreasing the likelihood of water breakthrough and
coning which increases the ultimate oil recovery.
[0054] These advantages of angled perforating will not only affect
the success of the initial completion of the well for a higher
producing rate. Angled perforating should also increase ultimate
recovery as intersecting the high permeability sections and
fractures along with better completion treatments should result in
more efficient and greater drainage area and ultimate recovery.
During the producing life of the well, which may be decades, the
angled perforations can also serve to stay cleaner than a
horizontal perforation, regardless of bedding planes, as gravity
helps to constantly remove debris. Another consideration is that
horizontal perforations also have a greater probability of
collapsing in soft unconsolidated rock formations.
[0055] All of the various types of perforating guns used in the
industry could be adjusted to angle the perforations. While some
modification can easily be made, there would inherently be some
increased cost over that of the conventional horizontal
perforating. Any such increase would be more than offset by the
lesser number of perforations to get the same coverage as
horizontal perforating. Angled perforating not only provides for an
improved completion over horizontal perforating, but it can also do
so at a lower cost. The improved contact and coverage of angled
perforating require fewer perforations, which can decrease the cost
to below the cost of conventional horizontal perforating. Added to
the direct lower cost, for an even better completion, is that there
is less stress and less damage done to the casing and to the cement
sheath. Horizontal shot density of four shots per foot and higher
swell the pipe and create a micro annulus between the casing and
cement which could lead to problems with wellbore integrity.
[0056] While all of the various types of perforating guns used in
the industry could be adjusted to angle the perforations, the first
two preferred embodiments presented are modifications of the charge
tube holder that holds the perforating charges in place at the
proper position inside of the hollow steel carrier. The charge tube
holder is usually made out of lightweight metal and are even made
out of cardboard tubes as they merely hold the charge in place
until detonation and are then blown apart. The third preferred
embodiment uses a modification to the charge tube holder along with
a modification to the perforating charges. All of the various
perforating guns previously discussed use such a charge tube holder
inside of the hollow steel carrier with the exception of the strip
gun. The strip gun is basically a holder for pressure sealed
charges and could also easily be modified to perforate at an
angle.
[0057] FIG. 8 is a perspective view of a prior art perforating
charge 100 showing the outer case 102 that is integrally connected
to the prima cord holder 104 and the groove 106 cut around the
outside of the prima cord holder 104 to secure a clip to hold the
prima cord in place. FIG. 9 is a side view of the prior art
perforating charge 100.
[0058] FIG. 10 depicts a cross sectional view through the prior art
perforating charge 100 of FIG. 9 along the line 10-10. FIG. 10
again shows the outer case 102, the prima cord holder 104, and the
groove 106 along with a thin explosive charge called a booster 108
that transfers the detonation of the prima cord to the explosive
material 110 inside the prior art perforating charge 100. The
explosive material 110 is held between the outer case 102 and the
cone shaped charge liner 112. When the explosive material 110 is
packed in a symmetrical shape around the charge liner 112 such that
when the explosive material 110 is detonated, the charge liner
collapses to form a perforating jet that penetrates the casing,
cement sheath and the formation.
[0059] There are numerous ways that a perforating charge or
perforating gun could be modified to be able to angle the
perforations. Three different preferred embodiments are presented.
One of these preferred embodiments incorporated the angle of the
charge into the angle between the prima cord holder 104 and the
outer case 102. The angled charge must maintain the symmetry of the
explosive material 110 around the charge liner 112. FIG. 11 depicts
an angled perforating charge 114 where the angle of the charge is
incorporated into the perforating charge itself. The prima cord
holder 104 is made at an angle to the outer case 102. The
modification simply requires the angle to be incorporated into the
outer case 102. FIG. 11 depicts a thirty-degree angle but a
forty-five degree angle or any other angle could be made by
incorporating the angle into the outer case 102.
[0060] FIG. 12 is a cross sectional view of the angled perforating
charge 114 of FIG. 11. FIG. 12 shows that even with the angle
incorporated into outer case 102 that the symmetry of the explosive
material 110 around the cone shaped charge liner 112 is
maintained.
[0061] FIG. 13 is the prior art charge tube holder 118 that holds
the prior art perforating charges at the conventional horizontal
position. There are two holes cut in the charge tube holder 118
with one being slightly larger that the diameter of the prior art
perforating charge 100 and the other hole is directly opposite the
first and is slightly larger that the diameter of the primer cord
holder 104. The prior art perforating charge 100 is slid through
the larger hole such that the primer cord holder 104 goes through
the smaller hole. The prima cord 120 rests in the primer cord
holder 104 and is held in place with a clip that is secured in the
groove 106. The clip holds the prima cord 120 in place which in
turn holds the prior art perforating charge 100 in the prior art
charge tube holder 118. The prima cord 120 wraps around the prior
art charge tube holder 118 connecting to the next prior art
perforating charge 100.
[0062] It is easier to change the holder of the charge rather than
the charge itself. This is both a matter of being easier, therefore
less costly but also as a matter of functionality. While some
modifications could easily be made to the prima cord holder, the
symmetrical cone shape of the charge must be maintained for the
shaped charge to work properly.
[0063] The first preferred embodiment is depicted in FIG. 14 where
two charges are angled thirty degrees from horizontal with the
upper charge directed up and the lower charge directed down. The
prima cord holders 104 extend through the charge tube holder 122
and are held in place in the same manner as the conventional prior
art horizontal, with the prima cord 120 and clip. Both the upper
charge and the lower charge rest upon bottom supports 126 cut and
bent to the appropriate angle from the material of the charge tube
holder 122. The prima cord 120 in the first preferred embodiment
wraps around the charge tube holder 122.
[0064] The second preferred embodiment is depicted in FIG. 15 where
the charge tube holder 128 is a larger diameter relative to the
conventional prior art perforating charges 130 with the prima cord
132 within the charge tube holder 128. The upper charge is angled
upward, the middle charge is oriented as a conventional prior art
horizontal charge and the lower charge is angled downward. The
perforating charges 130 are such that all of the charges and the
prima cord 132 are within the charge tube holder 128. The
conventional prior art charges 130 rest upon bottom supports cut
and bent to the appropriate angle from the material of the charge
tube holder 128 and are further secured by small bent portions of
the charge tube holder 128. The upper charge, that is angled
upward, has a bottom support 134 and is further secured by
positioning tab 136 that holds the upper charge against the bottom
support 134 and providing space for the prima cord 132 when
directed up. The middle charge, which depicts the prior art method
of perforating horizontally and perpendicular to the charge tube
holder 128, is supported by a bottom support 138 and is further
secured by positioning tab 140 and positioning tab 142. The bottom
charge, that is angled downward, has a bottom support 144 and a
positioning tab 146. The positioning tabs 140, 142 and 146 are in
the path of the detonation of the conventional prior art charges
130 and are blown away during detonation without any appreciable
effect to the perforating jet.
[0065] The third preferred embodiment is depicted in FIG. 16 where
the angled perforating charge 114 of FIG. 11 and FIG. 12 is held in
place by the clip, not shown, that rests in the groove 106 for the
clip to hold the prima cord 132 in the prima cord holder 104. The
prima cord holder 104, prima cord 132 and clip are attached on the
outside of the charge tube holder 148 in the same manner as the
conventional prior art method. The angled perforating charge 114 is
further secured by resting against the charge tube holder 148 where
the outer case 102 of the angled perforating charge 114 extends
beyond the charge tube holder 148.
[0066] Testing has shown no decrease in penetration by the angled
perforating however the tip of the perforation will not be as far
away from the wellbore due to the angle of the perforation. The
thirty-degree perforation would result in the tip of a perforation
farther away from the wellbore than a forty-five degree
perforation. It is the deep penetration of perforating charges used
these days that allows for the present invention to provide its
benefit. No additional burring on the outside of the hollow steel
carrier or the production casing be distinguished.
[0067] As previously discussed, the limited use for angled
perforating has been limited to trying to keep the perforations
free from debris, for detonation from one charge to another without
a prima cord, to run a strip gun through tubing at an angle for
greater clearance, creating a cavity to treat for consolidation, to
wash out two closely intersecting perforations and to create
elliptical perforations perpendicular to the bedding plane to
reduce sand production. None of these objectives are the same as
the objectives of the present invention that uses angled or
directional perforating, as a means to make greater contact with
high permeability streaks, fractures and cleats, to assist in the
controlling flow where there is a fluid contact. Angled perforating
is a means of opening all of the formation, exposing all of the
bedding planes to the perforation, using fewer charges at less
cost, and decreasing the need for stimulation treatment while also
improving the performance of a stimulation treatment. Angled
perforating will cause less stress to the casing, cement sheath and
formation by using fewer perforating charges to completely
perforate the rock formation.
[0068] The design of the present invention and the three preferred
embodiments are much better suited, over the prior art, to
accomplish the objectives stated as well as those inherent therein.
While the three preferred embodiments of the present invention has
been described, numerous changes could be made by those skilled in
the art which are encompassed within the spirit of the invention as
described.
* * * * *