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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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REFERENCE TO A MICROFICHE APPENDIX

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BACKGROUND OF THE INVENTION

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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° for minimum depth of penetration and up to 90° for maximum depth of penetration.

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.

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.

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.

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

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Claims

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.