GB2420804A

GB2420804A - Well perforating for increased production

Info

Publication number: GB2420804A
Application number: GB0524794A
Authority: GB
Inventors: Roger L Schultz; Michael L Fripp; John D Burleson
Original assignee: Halliburton Energy Services Inc
Current assignee: Halliburton Energy Services Inc
Priority date: 2004-12-06
Filing date: 2005-12-05
Publication date: 2006-06-07
Also published as: GB0524794D0; NO20055763L; NO20055763D0; US20060118303A1

Abstract

Perforation structures which allow increased production of fluids from a well. The perforation structures direct the flow of fluids into the well in a direction having a component parallel to the axis of the well and/or having a component which does not pass through the central axis of the well. Perforations in a productive zone may be slanted downward relative to the central axis of the well. Perforations may be tangentially deviated away from the central axis of the well so that fluid flowing from the perforation has a direction somewhat tangential to the well casing and circular motion is generated in fluids in the well. Fluids flowing through such perforations experience less pressure drop at the perforations, increasing pressure in the well and providing more energy to flow fluids up the well.

Description

WELL PERFORATING FOR INCREASED PRODUCTION

The present invention relates to flow of fluids between an earth formation and a well and more particularly to well structures and equipment that flow fluids between an earth formation and a well in a direction that reduces pressure drop in the fluid as it moves between an earth formation and a well.

Oil and gas wells are drilled from the surface of the earth to and through subsurface formations from which fluids such as oil and gas may be produced. The wells are often lined with steel casing from the surface location of the well down to and through the productive formation or formations. The annulus between the casing and the weilbore is normally filled with cement. The casing and cement form a stable well structure and avoid undesirable flow of fluids, e.g. flow of oil or gas into an aquifer. The casing and cement also seal off the productive formation.

In order to produce fluids from the productive formation, it is common practice to perforate the casing and cement in the productive formation. Perforations have been formed by tools commonly referred to as perforating guns. Early perforating guns included the equivalent of firearm barrels and cartridges and actually fired projectiles through the casing and cement into the formation. Currently, the most common perforating guns use shaped charges to form perforations. Shaped charges typically include a cup shaped housing containing a quantity of explosive. The explosive typically has a conical recess and a conical liner carried in the recess. The liner is typically a metal, such as copper, or a metal alloy. When the explosive is fired, the liner is fluidized into a jet of liquid metal which flows from the open end of the charge at very high velocity and is very effective at forming holes through steel casing and concrete and into the formation rock. The perforations allow oil, gas and other fluids in the formation to flow into the well casing, through which it may flow to the surface location of the well.

Some wells, often horizontal wells, are completed without casing and cement and are often referred to as open hole completions. Such wells often are not perforated, but may be if desired to increase production. Fluids flowing from the productive formations in open hole completions often include produced particulates, typically referred to as sand.

To prevent the flow of the sand to the surface with produced fluids, it is common to use filtering elements, referred to as screens or sand screens, to filter out the sand and allow

I

only fluids to flow into the production stream in the well. Annular space between such screens and the well bore may be filled with particulate material as a filtering material and to support uncased well bores in an operation typically referred to as gravel packing. In some cases the screen is expandable into contact with the well bore and can provide mechanical support without gravel packing.

The present invention provides well structures that flow fluids from a productive earth formation into a production stream in a well in a manner or direction that conserves natural formation pressure and enhances the flow of produced fluids.

In one embodiment, the present invention provides a perforation structure which allows increased production of fluids from a well. The perforation structure flows fluids into the well in a direction having a component parallel to the central axis of the well and/or having a component which does not pass through the central axis of the well.

In one embodiment, at least some of the perforations in a productive zone are slanted downward relative to the central axis of the well, thereby directing flow of fluids into the well in a direction having a component up the well toward the surface location.

In one embodiment, at least some of the perforations are tangentially deviated away from the central axis of the well so that fluid flowing from the perforation has a direction somewhat tangential to the well casing and circular motion is generated in fluids in the well.

In one embodiment, perforations may be both slanted and tangentially deviated to both provide a flow component up the well and to generate circular motion in the well fluids.

The present invention also includes methods and systems for producing perforations that flow produced fluids into a well in a direction having a component parallel to the central axis of the well and/or having a component which does not pass through the central axis of the well.

The present invention includes methods for producing fluids from wells including forming at least some perforations in a producing zone that flow produced fluids in a direction having a component parallel to the axis of the well and/or having a component which does not pass through the central axis of the well, and producing fluids through the perforations.

In yet another embodiment, the invention provides a filtering element in a well that flows fluids into a production stream in the well in a direction having a component parallel to the central axis of the well and/or having a component which does not pass through the central axis of the well.

Reference is made to the accompanying drawings in which: Fig. I is a partially cross sectional view of an embodiment of a perforated portion of a well showing slanted perforation structures and a shaped charge arrangement for forming the structures.

Fig. 2 is a partially cross sectional view of an embodiment of a perforated portion of a well showing a tangentially deviated perforation structure and a shaped charge arrangement for forming the structure.

Fig. 3 is a plot of model test results which illustrate benefits of the invention.

Fig. 4 is a partially cross sectional illustration of an embodiment of an alternative perforation structure and method of forming such structure.

Fig. 5 is an illustration of an embodiment of a perforating gun and casing structure for producing slanted perforations with a horizontal shaped charge.

Fig. 6 illustrates an embodiment of a shaped charge modified to generate a slanted perforating jet while the charge is in a horizontal position.

Fig. 7 illustrates an embodiment of a well casing modification allowing an effectively slanted perforation to be produced by a horizontal perforating jet.

Fig. 8 illustrates an embodiment of a perforating gun in a well casing and various arrangements for reducing reaction forces produced when shaped charges are fired.

Fig. 9 illustrates an embodiment of a well having a filtering element through which produced fluids flow from a producing formation into a production stream in one embodiment of the invention.

Various elements are described herein with reference to their position relative to a well or the central axis of a well. The terms up and down, or up hole and down hole, are used with reference primarily to the surface location of a well. Up or up hole means toward the surface location, while down or down hole means away from the surface location and toward the bottom hole location of the well. For vertical wells, up and down have their common meanings. For slanted or horizontal wells, a first element which is down hole from a second element will not be directly below the second element and may actually be at the same elevation. However, the first element will be farther from the surface location in distance through the well than the second element. A well and its central axis may be shown in the drawings to be in a vertical orientation. However, it is understood that the well, or at least portions of the well, may be deviated or slanted and some portions of a well may be horizontal and therefore the central axis will also be slanted or horizontal.

An annulus, as used in the embodiments, is generally a space between two generally cylindrical elements formed when a first generally cylindrical element is positioned inside a second generally cylindrical element. For example, a casing is a cylindrical element which may be positioned in a weilbore, the wall of which is generally cylindrical forming an annulus between the casing and the wellbore. While drawings of such arrangements typically show the inner element centrally positioned in the second, it should be understood that inner element may be offset and may actually contact a surface of the outer element at some radial location, e.g. on the lower side of a horizontal well. The width of an annulus is therefore typically not the same in all radial directions.

As noted in the background section, it is conventional to perforate wells so that fluids may be produced from productive formations or zones. A common perforating practice is to position a shaped charge, or other perforating device, at about the central axis of a well and directed perpendicular to the central axis of the well. This location and direction has a number of advantages. It has generally been considered desirable to produce the deepest possible perforation, measured in terms of distance into the producing formation, in order to increase the flow of fluids from the formation. Larger charges may produce deeper perforations. As charge size is increased, geometric considerations dictate that the charge be positioned in the center of a perforating gun and therefore on the central axis of the well. For a perforation to extend the greatest distance into the formation, geometric considerations dictate that the charge be aimed directly at, i.e. perpendicular to, the inner surface of the casing and therefore perpendicular to the central axis of the well.

The conventional perforations produced by such charges therefore have a central axis perpendicular to the central axis and the wall of the casing and well.

Formation fluids flowing from conventional perforations generated as described above have a flow direction perpendicular to the central axis of a well and passing through the central axis. The flow direction is therefore aimed directly at the opposite side of the well and the flow impinges upon the opposite side of the well at a ninety degree angle. To travel up the well, the fluids must make a ninety degree turn. The fluids entering the well from one perforation are also flowing perpendicular to the direction of the stream of fluids produced through perforations located farther downhole. These crossing flow paths generate a large amount of turbulence and increase the pressure loss of fluids flowing through the perforations. A part of the energy of the fluids in the formation as a result of natural formation pressure is lost in flowing the fluids through the perforations into the well.

In the present invention, perforations are formed and arranged to reduce the loss of energy of the fluids flowing from the formation into the well as compared to conventional perforations. As a result, the fluid pressure in the well is increased allowing more flow of fluids up the casing or production tubing placed in the casing. The reduction in energy loss through the perforations reduces the pressure drop across the perforations, thereby reducing sand production and/or allowing production rate to be increased without increasing sand production.

Fig. I illustrates one embodiment of the present invention. A well 10 has been drilled through a productive formation 12. A casing 14 has been positioned in the well 10 and cement 16 has been placed in the annulus between casing 14 and well 10. A number of perforations 18 have been formed through casing 14 and cement 16 into the formation 12 to allow fluids to flow from the formation 12 into the casing 14 and therefore into a stream of produced fluids in the casing 14. Each perforation 18 is slanted downward at a slant angle 20 relative to the central axis 22 of the well 10. Fluids flowing from perforations 18 into the casing 14 flow in a direction 24 which has a component parallel to the central axis 22. As indicated by the curved arrow 24, the flow from each perforation 18 will encounter an upward flowing stream of produced fluids from down hole perforations and turn upward to become part of the total uphole stream of produced fluids. The slant angle may desirably be as great as possible. The maximum angle is limited by various practical considerations discussed below, which vary depending upon the system used to form the perforations. It is believed that slant angles from ten to eighty degrees will provide advantages in producing fluids from a well bore.

In this embodiment, the perforations 18 were formed by a number of shaped charges 26. To simplify Fig. 1, only one charge 26 is shown in Fig. 1. The charge 26 may be any conventional shaped charge. Charge 26 may be carried into the well as part of a conventional shaped charge assembly, for example as a capsule charge on an open strip carrier or in a sealed charge carrier. In either case, the charge 26 may be located generally on the axis 22 of the well 10 and may be slanted downward at the slant angIe 20.

The slanted charge 26 therefore produces a downward slanted explosive jet directed along the path 28 to form a slanted perforation 18. As is well known in the perforating art, the charge 26 disintegrates upon detonation and any debris either falls down the well 10 or, if the charge is in a sealed carrier, is returned to the surface of the well with the carrier. As with conventional charge carriers, the charges 26 may be arranged in a spiral pattern as indicated by the pattern of perforations 18 in Fig. 1. A spiral pattern may improve use of space in a perforating gun and may shorten the length of detonating cord between adjacent charges.

Fig. 2 illustrates a second perforation structure according to the invention. In Fig. 2, the well 10, casing 14, cement 16, and formation 12 are viewed down the axis 22 of the well 10. A shaped charge 30, which may be identical to charge 26, is positioned in the well offset from the central axis 22, in this case positioned about half way between the central axis 22 and the casing 14. The charge 30 produces an explosive jet which travels along path 32 deviated at an angle 34 from the conventional radial direction 36 from the central axis 22. A jet following path 32 forms a tangentially deviated perforation 38. It should be understood that a plurality of other perforations may be formed in the casing 14 spaced above and/or below perforation 38 as shown in Fig. 1, for example in a spiral pattern.

Fluids flowing from the formation 12 through perforation 38 into the casing 14 will be directed along the path 32, in the opposite direction of the jet from charge 30, and along the path 40. The path 40 shows that the flow from perforation 38 has a directional component tangential to the wall of casing 14. As noted above, conventional perforations direct the flow of produced fluids directly across the central axis 22 so that they impinge upon the inner surface of the casing 14 at about a ninety degree angle generating turbulence as the flow redirects itself to flow up hole. The flow path 40 not only produces less turbulence, but also may induce a circular flow in the casing 14.

Circular flow of a production stream in a well may have a number of advantages.

Circular flow may be used to at least partially separate produced fluids, i.e. gas, water and oil, down hole. Circular flow may have a hydrocyclone effect to separate water from oil based on gravity, i.e. density, of the fluids. Such partial separation may be part of a first stage separator in a system such as the "Down hole Oil and Water Separator and Method" disclosed in U.S. Patent application serial number 10/924,161 filed on August 23, 2004 and assigned to the assignee of this application, which application is hereby incorporated by reference for all purposes. Circular flow may help produce condensate in gas wells, which condensate may otherwise tend to form on the well casing or tubing. Circular flow may also help prevent scale formation on the casing. In horizontal wells, circular flow may help prevent undesirable separation of phases that can result in collection of water on the lower side of the horizontal well and undesirable nonuniform production with flow of water slugs.

The perforation 38 is tangentially deviated by the angle 34. Fluids produced from formation 12 through the perforation 38 will enter the well 10 with a tangential deviation equal to the angle 34. The terms tangentially deviated and tangential deviation are used herein to indicate that a fluid flow path is at least partially tangential to the casing at the point at which the flow impinges upon the casing as opposed to perpendicular as in conventional perforations.

In Fig. 3, tangential deviation angle 34 is about thirty degrees. This angle positions the charge 30 about half way between the well axis 22 and the well casing 14. It is desirable for angle 34 to be as great as practical. Practical considerations include space to position the charge 30, reduction in depth of penetration as angle is increased, and possible deflection of the perforating jet off the casing 14. These considerations indicate that the deviation angle 34 is desirable from about five degrees to the maximum angle based on the diameter of the well, or a charge carrier, and the diameter of the charge itself.

Preferred angles are between ten and forty degrees and more preferably from about twenty to thirty-five degrees. In a perforating gun, multiple charges 30 preferably are all deviated in the same direction so that circular motion generated by produced fluids is the same for all perforations. It is also desirable to select the deviation angle 38 so that torsional reaction forces from firing charges 30 tend to tighten, rather than loosen, threaded connections in a work string and perforating gun assembly.

While Fig. I illustrates slanted perforations 18, and Fig. 2 illustrates tangentially deviated perforation 38, various combinations of these structures may be used in the present invention. For example, any perforation may be both slanted and tangentially deviated. In a given completion, some perforations may be slanted while others are tangentially deviated. A completion may also include some conventional perforations which are not slanted or tangentially deviated.

Four one-twelfth scale models were built and operated with water to test the embodiments described above. The models simulated a sixty-foot interval with six inch internal diameter casing. In a conventional model, the simulated perforations were not slanted and had no tangential deviation. In a tangent only model, the perforations were not slanted, but were tangentially deviated so that the angle 34 was 30 degrees, which directs the flow at a point half way between the central axis 22 and the wall of the casing 14. In an angled only model, the perforations were slanted so that the angle 20 was about 45 degrees. In a combination model, the perforations were both slanted at about 45 degrees and tangentially deviated at about 30 degrees.

Fig. 3 shows plots of model test results which illustrate benefits of the present invention. The plots are of pressure in pounds per square inch on the vertical axis required to flow the test fluid at the flow rate in gallons per minute on the horizontal axis. The curve 42 for the conventional model shows that conventional perforations require more pressure at all flow rates than any of the above described embodiments. For example, at twenty-five gallons per minute, the conventional perforations model, curve 42, required about twenty- eight pounds pressure, the tangent only model, curve 44, required about twenty-six pounds, the combination model, curve 46, required about seventeen pounds, and the slanted only model, curve 48, required only fifteen pounds. These results indicate that the slanted only embodiment provides the most flow at a given pressure drop and the least pressure loss at a given flow rate. The tangentially deviated embodiment provides better flow than the conventional perforations, but not as good as the slanted only embodiment.

The combination model provides better flow than the tangentially deviated only model, but is not as good as the slanted only model. These results indicate that to achieve the maximum flow rate from a well, perforations should be slanted, but not tangentially deviated. However, if it is desired to obtain a benefit of circular flow in the casing 14, it may be desirable to use the combination embodiment or tangential only embodiment even though the flow rate characteristics may not be as good as the slanted only embodiment.

Using the test model results, calculations were made to determine the flow rate improvements that may be possible by use of the slanted perforation embodiment as compared to conventional perforations. The calculations were based on 3.5 inch production tubing of various length, six inch casing at the perforations, a twenty foot perforated interval and the properties of water. All combinations of flow rate, available pressure drop and tubing length indicated production rate improvement ranging from about five to fifty percent. A set of calculated results are set out below.

Table I - calculated flow rates for conventional perforations and slanted perforations and indicating improved flow rates which may be achieved by the present invention.

Total Pressure Flow Rate (bbllday) Flow Rate (bbl/day) Production Drop (psi) (Standard Perforation) (Angled Perforation) Increase (%) 10,000' of tubing 5.83 1000 1070 7 48.99 3000 3162 5.4 132.06 5000 5257 5.14 5,000' of tubing 3.46 1000 1120 12 29.33 3000 3294 9.8 79.37 5000 5452 9 1,000' of tubing 1.58 1000 1320 32 13.61 3000 3717 23.9 37.22 5000 6109 22.18 100' of tubing 1.162 1000 1509 50.9 10.07 3000 4090 36.3 27.73 5000 6653 33.1 * 3-1/2" Tubing, 6" ID casing at perforations * 20 Foot Perforated Interval * Values computed using the properties of water As noted above, one aspect of the present disclosure addresses conservation of available formation pressure. Pressure drop of fluids flowing through the perforations is reduced so that pressure in the well is increased and is available to drive fluid through the casing, and/or production tubing, at a greater flow rate. The improvement is believed to be due primarily to the direction of flow of produced fluid as it flows into the casing and interacts with the casing and the flow of produced fluids in the casing. Thus, it may not be necessary to slant all of the perforations in a given completion as shown in Figs. I and 2.

Other perforation structures or geometries may provide a desirable fluid flow direction that reduces turbulence and other causes of pressure loss.

Fig. 4 is an illustration of an alternative perforation structure and method of forming such structure. Two shaped perforating charges 50 and 52 are shown positioned in the well 10 at about the same location and directed at about the same location on the casing 14. Charge 50 may be a conventional deep penetrating shaped charge, which is designed to produce a deep perforation 54 extending into the formation 12. Charge 52 may be a charge designed to produce a wide but relatively shallow perforation 56. In this embodiment, both charges 50 and 52 may be located on the central axis 22, positioned at a right angle to the central axis 22. Charge 52 may be positioned above charge 50 by a short distance that causes a lower portion of perforation 56 to overlap the perforation 54.

The two charges may be fired simultaneously or sequentially. The combined perforation is a deep perforation 54 with an opening at the casing 14 which is slanted and directs the flow of fluids upwards as indicated by the arrow 58, like the slanted perforations 18 of Fig. 1. It will be appreciated that the charges 50 and 52 may be closely spaced as indicated or may be spaced apart and fired at different times or from different perforating guns which have been positioned to provide the overlapping double perforation as illustrated. If desired, the shallow charge 52 may be slanted to provide more space between the charges 50, 52 while providing the desired overlap of the perforations 54, 56. This embodiment allows use of horizontal perforating charges and their deeper penetration potential instead of slanted charges as in the Fig. I embodiment.

Fig. 5 illustrates another embodiment in which a conventional horizontal shaped charge 58 may be used to produce a slanted perforation. The charge 58 is shown positioned in a sealed charge carrier housing 60 that is positioned inside a well casing 62.

Charge carrier housings typically have thinned areas adjacent the jet firing end of shaped charges, commonly referred to as scallops. The thinned areas reduce the energy required for the jet to exit the housing, thereby providing more energy for perforating the casing 62, etc. In this embodiment, a scallop 64 may be provided with a nonuniform thickness that causes the jet from charge 58 to turn in a downhole direction as indicated by the arrow 66, thereby producing a slanted perforation. The casing 62 is also illustrated with a similar nonuniform thickness scallop on its outer surface that may also cause deflection of the jet from charge 58. Either or both of the nonuniform scallops 64 or 68 may be used as desired. The scallops 64 and 68 may also be formed in the inner surfaces of housing 60 and casing 62 if desired, although it may be easier to machine the outer surfaces.

Fig. 6 illustrates a modification to a conventional shaped charge that may allow the shaped charge 70 to have a central axis 71 positioned perpendicular to a central axis of a well, but to fire a penetrating jet at an angle other than perpendicular to the well axis. The charge 70 includes a conventional cup shaped metal housing 72. A quantity of explosive 74 is carried in the housing 72. A generally conical shaped recess 76 is provided in the output or jet firing end of the charge 70. In conventional shaped charges, the recess 76 is centrally located in the housing 72. In this embodiment, the innermost end or bottom 78 of the recess 76 is not centered in the housing 72. The offset in the recess 76 may cause a jet fired by charge 70 to be angled or deviated from the normal horizontal direction 71 as indicated by the arrow 80. The charge 70 also includes a generally conical liner 81, e.g. copper, lining the recess 76. The liner material fluidizes to form the jet produced by firing charge 74. Conventional liners have symmetrical thickness around central axis 71 of the charge 70, but may vary in thickness from the innermost end 78 to the open end of the charge. In this embodiment, one side 82 of liner 81 is made thicker than an opposite side 84. The nonsymmetrical liner 81 may also cause the jet to exit the charge along the path deviated from the central axis 71 of the charge housing 72. Such a charge may be carried into a well and fired from an otherwise conventional charge carrier and may produce desirable slanted perforations.

Fig. 7 illustrates another embodiment that allows use of conventional shaped charges fired perpendicularly to a well central axis to produce a perforation 86 that may flow fluids into a well in a direction having a component aligned with the well central axis.

A well casing 88 has been modified by expanding a portion 90 to provide a curved inner surface 92. A conventional shaped charge has been fired in a conventional direction perpendicular to a well axis 94 producing the perforation 86 into a productive formation.

However, the charge was positioned near the lower edge of the inner curved area 92 so that the perforation opening in the casing 88 is slanted upward to some extent. Produced fluids from perforation 86 may flow into the casing 88 in a direction 96 having a desirable upward component. The curved section 90 may extend around the casing 88 as indicated to facilitate alignment with a perforating gun or may be formed as a circular area on only one side of casing 88. Alternatively, equivalent casing shapes may be formed by cutting a hole in the casing 88 and welding on the outside a spherical or conical member providing an upward slanted surface through which a perforation may be formed as shown in Fig. 8. In Fig. 1, all the perforations 18 slant down at about the same angle 20.

The model for slanted perforations used an angle 20 of about 45 degrees. For maximum flow improvement, it may be desirable to select the angle 20 to be as large as practical. As noted above, angles 20 from ten to eighty degrees should enhance production. The angle of the test model was selected according to this criteria. Positioning of slanted shaped charges in a perforating gun becomes more difficult as the slant angle is increased, it is possible that the perforating jet may deflect off the inner surface of the casing if the slant angle is too large. As the slant angle 20 is increased, the radial depth of the perforation is reduced. The slanted perforating charges also produce a reaction force that will tend to drive a perforating gun up hole, possibly damaging the work string on which the gun is conveyed into the borehole. For these various practical considerations, when using shaped charges a practical range of slant angles 20 may be from about fifteen to fifty degrees, preferably from about fifteen degrees to thirty degrees and it may be desirable to select the slant angle 20 to be about 25 degrees. It may also be desirable to provide additional elements in the perforating system to accommodate or reduce reaction forces generated by firing a perforating gun carrying slanted shaped charges. Fig. 8 illustrates various elements and arrangements of elements which may accommodate or reduce the reaction forces.

In Fig. 8, a perforating gun 100 is shown positioned in a well casing 102 in preparation for perforating the casing. The gun 100 has been conveyed into this position by a work string 104, which may be a wireline, coiled tubing, drill string, or other work string known in the art. Between the work string 104 and the gun 100 is a shock absorbing or reducing section 106.

A plurality of arrows 108, 110, 112, and 114 indicate the directions of perforating jets which may be produced by shaped charges carried within the perforating gun 100. In this embodiment, the jets 108 at the upper end of the gun 100 have a larger slant angle 20 than intermediate jets 110. The jets 108 would generate a larger uphole reaction force than the jets 110. Modeling has indicated that the slant angle 20 of upper perforations is more effective in reducing perforation pressure loss and therefore more effective at increasing production, possibly because flow from upper jets encounters more total flow of produced fluids in the casing 102. As a result, it may be desirable to provide upper perforations with the greatest practical slant angle and lower perforations with smaller slant angles 20. The total reaction force may be reduced by the smaller angles in the lower perforations.

Perforations 112 near the bottom of a producing zone may actually be at a zero slant angle as illustrated. In addition it may be desirable to provide one or more shaped charges 114 at the bottom of the gun 100 with a large uphole slant to provide a downhole reaction force to counter some of the reaction forces from the upper charges. As the upward slant of charges 114 is increased, the downward reaction force is increased and if the angle is large enough, the jets 114 may not actually penetrate the casing 102. If the jets 114 actually produce downward slanted perforations, they will be at the bottom of the productive zone and should not interfere with the fluids produced from up hole perforations.

The shock absorbing or reducing section 106 may include one or more mechanisms for preventing reaction forces from the gun 100 from damaging the work string 104. The work string may be attached to the section 106 by a sliding piston 116. This arrangement may allow the section 106 to slide up the work string 104 without transferring energy to the work string 104. Fluid in the borehole and gravity may absorb sufficient energy to stop the gun 100. The sliding piston arrangement may also allow rotation of the perforating gun relative to the work string 104, to accommodate rotation of the gun 100 if it contains tangentially deviated charges as illustrated in Fig. 2.

The shock absorbing or reducing section 106 may include one or more slips 118 which may be deployed to engage the casing 102 and resist upward movement of the gun 100. The slips 118 may be deployed before firing the gun 100 by a signal from the surface location of the well and an energy source in the section 106. Alternatively, the slips may be actuated by weights and levers within section 106, similar to braking systems which prevent elevators from falling. In one embodiment, section 106 may be used to anchor the gun 100 in position in the casing 102 and the work string 104 may be disconnected and moved up hole a safe distance. After firing of the gun 100, the work string may be reconnected and used to remove the gun 100 from the well.

Alternatively, the section 106 may simply be a collapsible cylinder which may be crushed by gun 100 if it is driven up hole with sufficient force.

In the above description of the Fig. 8 embodiment, the angles of various perforating charges 108, 110, 112 were selected to provide improved flow rate with minimum reaction force. In general this resulted in the upper charges having greater slant angles 20 than the lower charges. The slant angles may be varied along the length of a perforation gun and possibly from one side to the other to accommodate other parameters. For example, in horizontal boreholes, it may be desirable for the perforations on the top of the well bore to be more or less slanted than the perforations on the bottom. Due to pressure drop along the length of a horizontal well section, the production from the toe, i.e. the portion farthest from the vertical portion of the well, is often less than desired. To increase production from the toe, it may be desirable to provide greater slant angle for perforations in the toe portion of a slanted cased well, than in the heel portion, i.e. the portion adjacent the vertical portion of the well. The slant angles may be selected and varied to accommodate other formation characteristics.

It is believed to be desirable to fire charges in a perforating gun from the top down to minimize the total reaction force. This firing sequence is consistent with available perforating guns that normally have a firing head at the top connected to a work string for receiving a firing signal. The firing head normally is connected to an upper end of a length of detonating cord which extends down through the perforating gun and is coupled to each charge carried in the gun. While the charges all fire within a very short time, the top charges are fired first in this arrangement. As discussed above, the gun 100 may move up hole as a result of reaction forces from firing the guns 108, etc. It is possible that the lower guns 110, 112 may move before they actually fire. When firing is performed with conventional detonation cord, the detonation speed is faster than the speed of sound in the perforating gun and essentially no movement should occur between firing of the charges.

Low speed detonation cords are known and, if used, it may be desirable to adjust the spacings between successive charges to account for movement of the gun 100 during firing.

The above described embodiments preferably include the use of shaped charges to form the perforation structures in boreholes. Shape charges may be preferred because they are the current standard devices used to form well perforations. The charges and systems for handling and firing the charges are readily available. However, as noted above, certain characteristics of shaped charges may limit the practical maximum slant angle 20 and may require additional system elements to control reaction forces. As a result, it may be desirable to use alternative perforating systems. Various alternatives may have certain advantages for forming slanted perforations. Alternatives include lasers, mechanical boring, e.g. mills and drills, and hydraulic jetting. None of these alternatives produces large reaction forces. Lasers and mechanical boring are more suited to producing highly slanted perforations than conventional horizontal perforations, due to the shapes of the tools themselves. That is, they tend to work best with a long central working axis and may be able to form perforations extended a great distance into the productive formation. When using these alternative perforating systems, the upper end of the desirable range of angles 20 from ten to eighty degrees is possible and preferred. Thus the preferred range may be from forty-five to eighty degrees and more preferably from fifty to seventy degrees. Hydraulic jetting may have an advantage in producing perforations with a desirable slant angle of about 45 degrees. Hydraulic jetting has been found to abrade and form holes in steel most effectively which the hydraulic jet is applied to the steel surface at from about 35 degrees to about 55 degrees and preferably at about 45 degrees.

The above description of embodiments is with respect to production of fluids from wells. In many cases, waste or treating fluids are injected into earth formations through perforated well casings. For example, produced water is often separated from produced oil and the water is often injected into a disposal zone. Producing zones are often fractured after perforating and before the well is put on production. During the fracturing process it is common to pump fluids down a well and out the perforations at very high pressure and high flow rate. It is desirable to achieve sufficient pressure in the producing formation to cause fracturing without exceeding safe working pressure in the pumping equipment, tubing, casing, etc. used to convey the fracturing fluids to the formation. Treating fluids other than fracturing fluids may also be pumped down an well and through perforations into an earth formation. It is believed that just as the above described perforation structures reduce pressure drop of fluid flowing from the formation into the well bore, they will also reduce the pressure loss across the perforations when fluids are pumped from the well into the formation. As a result, the pressure in the well bore may be reduced while achieving a desirable fracturing pressure in the formation or a desirable injection pressure in a disposal zone. For injected fluids that are pumped down the well and into the formation, the downward slanted perforations of Fig. I may provide a benefit. If waste fluids are separated down hole at or near a producing formation, they may be flowed up hole for injection in a disposal formation located above the producing formation. In that case, it may be desirable for perforations in the disposal formation to be slanted upward relative to the central axis of the well to improve flow of fluids flowing up hole and into the disposal zone.

Fig. 9 illustrates an alternative embodiment that may be useful in open hole wells or in wells that are cased, but produce sand and require sand screens and possibly gravel packing. A well 120 is shown as including a casing 122 and cement 124 between the casing 122 and a productive formation 126. A number of conventional perforations are shown extending through the casing 122 and cement 124 into the formation 126. If desired, the casing 122 and cement 124 may be omitted and the well 120 may be completed as an open hole. If completed as an open hole, the perforations 128 may also be omitted if desired.

In this embodiment, a filtering element 130 is positioned inside the well 120, and, if casing 122 is used, within the casing 122. The filtering element 130 is a somewhat conventional wire wrapped screen that has been modified according to the invention. The screen 130 includes a base pipe 132 having slots or perforations 134 that allow free flow of fluids into the interior 136 of the screen 130. The interior 136 is coupled to a production string that carries a produced fluid stream up hole to the surface location of the well. The base pipe 132 is surrounded, or wrapped, by several layers of elongated metal elements, commonly referred to as wires or ribs. A number of longitudinally extending ribs 138 may be attached to the outer surface of the base pipe 132. A spiral wrap of wires, or one continuous wire, 140 may be attached around the ribs 138. The wire 140 has a rectilinear cross section designed to provide a sand filtering function. The outer edge 142, relative to the axis 144 of the screen 130, of the wire 140 has a longer dimension than the inner edge 146 that is connected to the ribs 138. An upper edge 148 of the wire 140 may be about perpendicular to the outer and inner edges 142, 146. A lower edge 150 of the wire 140 is slanted so that the spacing 152 between adjacent wraps of wire 140 is smaller on the outer edge than the spacing 154 on the inner edge. The spacing 152 is selected to be small enough to restrict the flow of sand produced from the formation 126, or to restrict the flow of aggregate used to form a gravel pack around the screen 130. By slanting the lower edge 150 of wire 140 but not the upper edge 148, an up hole slanted flow path 156 is generated between adjacent wraps of the wire 140. This up hole slanted flow path 156 directs fluids produced from the formation 126 into the produced fluid stream in screen 130 in a direction having a component in alignment with the central axis 144 and conserves available formation pressure to enhance production.

As noted above, the space between the screen 130 and the well 120 may be gravel packed with particulates to filter out produced sand and support the formation 126. A gravel pack is more likely to be used if casing 122 and cement 124 are omitted, but may also be used in cased and perforated wells. If a gravel pack is used, especially in an open hole completion, flow through the gravel pack may be primarily in a radial direction. As a result, use of slanted perforations as shown in Fig. 1 may provide little advantage in a gravel packed completion, but may be used if desired. But when the radial flow of produced fluids passes through the screen 130, it will be directed along the flow path 156 having an upward component. The openings 134 through base pipe 130 are normally much wider than the thickness of the base pipe 130, and should not substantially redirect fluid flowing in the direction produced by flow path 156. In contrast, the flow path 156 has a length at least as large as its width, and preferably at least twice as large as its width, so that it may impart a desired direction to fluids flowing through the path 156 Conventional gravel packs have little directional affect on produced fluids and the fluids normally flow in a radial direction from the higher pressure in the formation to the lower pressure in the well. However, systems, referred to as pumpable screens, have been developed in which a settable mixture may be pumped into an annulus between a production tubing and a borehole and allowed to set into a rigid, but porous, mass that functions as a sand filter. Porosity may be generated by including elements that dissolve, leaving open spaces in the mixture after it has set. By selecting the sizes, shapes and orientations of these dissolvable elements possibly in combination with some other aligning force, such as a magnetic field, the rigid mass may direct fluids in a desired direction in accordance with the present invention.

While the present invention has be illustrated and described with reference to various perforation structures and methods of forming such structures, it is apparent that various changes to the structures may be made and other systems and methods for forming such structures may be used within the scope of the present invention as described in the appended claims.

It will be appreciated that the above invention can be modified.

Claims

1. A method for completing a cased well having a central axis, comprising forming perforations through the casing, the perforations shaped to flow fluids into the well in a direction that reduces pressure drop across the perforations relative to conventional perforations.

2. A method according to claim 1, wherein the perforations flow fluids in a direction having a component parallel to the direction of flow of fluids in the well.

3. A method according to claim I or 2, wherein the perforations flow fluids in a direction that does not pass through the central axis of the well.

4. A method according to claim 1, 2 or 3, wherein the perforations flow fluids in a direction having a component parallel to the axis of the well and not passing through the central axis of the well.

5. A method according to any of claims 1 to 4, wherein the perforations extend through the casing into a producing formation at a downward angle of from ten to eighty degrees relative to the central axis of the well.

6. A method according to any of claims I to 4, wherein the perforations extend through the casing into a producing formation at a downward angle of from 15 degrees to 50 degrees relative to the central axis of the well.

7. A method according to any of claims 1 to 4, wherein the perforations extend through the casing into a producing formation at a downward angle of from 15 degrees to 30 degrees relative to the central axis of the well.

8. A method according to any of claims I to 4, wherein the perforations extend through the casing into a producing formation at a tangentially deviated angle of at least five degrees relative to the central axis of the well.

9. A method according to any of claims I to 4, wherein the perforations extend through the casing into a producing formation at a tangentially deviated angle of from 10 degrees to degrees relative to the central axis of the well.

10. A method according to any of claims 1 to 4, wherein the perforations extend through the casing into a producing formation at a tangentially deviated angle of from 20 degrees to degrees relative to the central axis of the well.

11. A method according to any preceding claim, further comprising using shaped charges to form the perforations.

12. A method according to claim 11, further comprising positioning shaped charges in the well and slanted relative to the central axis of the well to fire a perforating jet at a downward angle relative the central axis.

13. A method according to claim 11, further comprising positioning shaped charges in the well between the central axis and the casing.

14. A method according to any of claims I to 10, further comprising forming a perforation by positioning a first shaped charge in a cased well and directed at the casing, the first shaped charge adapted to produce a first perforation, positioning a second shaped charge in the cased well directed at an area on the casing at least partially overlapping the first perforation, and firing said first shaped charge and said second shaped charge in either order.

15. A method according to any of claims I to 10, further comprising forming a perforation by positioning a first shaped charge in a cased well and directed at the casing, the first shaped charge adapted to produce a first perforation having a center, a lower edge, a first diameter and a first depth, positioning a second shaped charge in the cased well directed at a point on the casing between the center and lower edge of the first perforation, the second shaped charge adapted to produce a perforation having a second diameter smaller than said first diameter and a second depth greater than said first depth, and firing said first shaped charge and said second shaped charge in either order.

16. A method according to any of claims I to 10, further comprising forming a perforation by deforming a portion of said casing to provide a slanted area on an inner surface of the casing that is not parallel to the central axis, positioning a shaped charge in the casing directed at the slanted area, and firing the shaped charge.

17. A method according to any of claims I to 10, further comprising forming a perforation by deforming a portion of said casing to provide an upward facing area on an inner surface of the casing, positioning a shaped charge in the casing directed at the upward facing area, and firing the shaped charge.

18. A method according to any of claims I to 10, further comprising using one of laser and mechanical boring to form the perforations.

19. A method according to claim 18, wherein the perforations extend through the casing into a producing formation at a downward angle of from about 50 degrees to about 80 degrees relative to the central axis of the well.

20. A method according to any of claims I to 10, further comprising using hydraulic jetting to form the perforations.

21. A method according to claim 20, wherein the perforations extend through the casing into a producing formation at a downward angle of about 35 degrees to about 55 degrees relative to the central axis of the well.

22. A completion in a cased well, comprising a plurality of perforations through the casing shaped to flow produced fluids into the casing in a direction that reduces pressure drop across the perforations relative to conventional perforations.

23. A completion according to claim 22, wherein the perforations are shaped to flow fluids in a direction having a component parallel to the direction of flow of fluids in the well.

24. A completion according to claim 22 or 23, wherein the perforations are shaped to flow fluids in a direction having a component parallel to the axis of the well and in the direction of flow of fluids in the well.

25. A completion according to claim 22, 23 or 24, wherein the well has a central axis and the perforations are shaped to flow fluids in a direction that does not pass through the central axis of the well.

26. A completion according to any of claims 22 to 25, wherein the well has a central axis and the perforations are shaped to flow fluids in a direction having a component parallel to the axis of the well and not passing through the central axis of the well.

27. A completion according to any of claims 22 to 26, wherein the perforations extend through the casing into a producing formation at a downward angle of from about 10 degrees to about 80 degrees relative to the central axis of the well.

28. A completion according to claim 27, wherein the plurality of perforations are vertically spaced along a length of the casing and the downward angle of the perforations varies along the length of the casing.

29. A completion according to claim 28, wherein upper perforations are slanted at greater angles than lower perforations.

30. A completion according to claim 28, further comprising at least one perforation extending through the casing into a producing formation at an angle of about ninety degrees relative to the central axis of the well.

31. A completion according to any of claims 22 to 25, wherein the perforations extend through the casing into a producing formation at a downward angle of from 15 degrees to degrees relative to the central axis of the well.

32. A completion according to any of claims 22 to 25, wherein the perforations extend through the casing into a producing formation at a tangentially deviated angle of from 15 degrees to 30 degrees relative to the central axis of the well.

33. A method for increasing production of fluids from a cased well, comprising flowing fluids into the well through perforations shaped to flow fluids into the well in a direction that reduces pressure drop across the perforations relative to conventional perforations.

34. A method according to claim 33, further comprising flowing fluids in a direction having a component parallel to the axis of the well and in the direction of flow of fluids in the well.

35. A method accordign to claim 33 or 34, further comprising flowing fluids in a direction that does not pass through the central axis of the well.

36. A perforating gun assembly, comprising a charge carrier having a central axis, an upper end and a lower end, a plurality of downward directed shaped charges carried on the carrier and positioned to fire perforating jets at a downward angle relative to the central axis, and a reaction force absorber coupled to the carrier.

37. A perforating gun assembly according to claim 36, wherein the reaction force absorber comprises a cylinder coupled to the charge carrier and a piston carried within the cylinder and adapted for coupling to a work string.

38. A perforating gun assembly according to claim 36, wherein the reaction force absorber comprises one or more slips adapted for engagement with a well casing.

39. A perforating gun assembly according to claim 36, wherein the reaction force absorber comprises a crushable member having a first end coupled to the charge carrier and a second end adapted for coupling to a work string.

40. A perforating gun assembly according to any of claims 36 to 39, further comprising at least one upward directed shaped charge carried on the carrier and positioned to fire a perforating jet at an upward angle relative to the central axis.

41. A perforating gun assembly according to claim 40, wherein the downward directed shaped charges comprise more than half of the shaped charges carried on the carrier and the at least one upward directed shaped charge is carried proximate the lower end of the carrier.

42. A hydrocarbon production well, comprising a borehole in a hydrocarbon producing formation, a conduit in the borehole flowing produced fluids up the well, a flow path from the producing formation to the conduit, the flow path shaped to direct fluids entering the conduit in a direction having a component in the direction of flow of produced fluids in the well.

43. A well according to claim 42, wherein the flow path comprises a perforation extending into the producing formation at a downward angle of less than ninety degrees relative to a central axis of the well.

44. A well according to claim 42 or 43, further comprising a filter element in the well and coupled to the conduit, the filter element having a flow path slanted at a downward angle of less than ninety degrees relative to a central axis of the well.

45. A well according to claim 42, 43 or 44, wherein the flow path has a length at least as large as its width.

46. A filtering device for use in a producing hydrocarbon well, comprising a base pipe having an interior space defining a conduit for produced fluids, and having perforations allowing produced fluids to flow from the exterior of the base pipe into the conduit, a filter layer carried on the outer surface of the base pipe and having flow paths sized to allow flow of produced fluids and to restrict flow of particulate material, the flow paths shaped to direct fluids flowing through the filter layer into the conduit in a direction having a component parallel to the direction of flow of produced fluids in the conduit.

47. A filtering device according to claim 46, wherein the filter layer comprises a wire wrapped screen.

48. A filtering device according to claim 46, wherein the filter layer comprises a settable mixture.

49. A method for separating multiple fluids in a stream of fluids in a well, the fluias produced from an earth formation, comprising forming a flow path between the formation and the well directing fluids from the formation into the well in a direction that does not pass through a central axis of the well, whereby circular motion is induced in the stream of fluids in the well and the multiple fluids at least partially separate due to density differences.

50. The method of claim 49, further comprising forming tangentially deviated perforations into the formation.

51. A method for completing a cased well in an earth formation, comprising forming perforations through the casing, the perforations shaped to flow fluids between the earth formation and the well in a direction that reduces pressure drop across the perforations relative to conventional perforations.

52. A method according to claim 51, wherein the perforations flow fluids in a direction having a component parallel to the direction of flow of fluids in the well.

53. A method according to claim 51 or 52, wherein the well has a central axis and the perforations flow fluids in a direction that does not pass through the central axis of the well.

54. A method according to claim 51, 52 or 53, wherein the well has a central axis and the perforations have a downward angle of from ten to eighty degrees relative the central axis.

55. A method according to claim 54, further comprising flowing fluids from the earth formation into the well.

56. A method according to any of claims 51 to 55, further comprising flowing fluids from the well into the formation.

57. A method according to any of claims 51 to 56, further comprising using one of shaped charges, laser boring, mechanical boring to form the perforations.

58. A method according to claim 56, wherein the well has a central axis and the perforations have a downward angle of from ten to eighty degrees relative the central axis, further comprising flowing the fluid down the well and into the formation.

59. A method according to claim 58, further comprising flowing waste fluids down the well and into the formation.

60. A method according to claim 58, further comprising treating fluids down the well and into the formation.

61. A method according to claim 58, further comprising flowing fracturing fluids down the well and into the formation.

62. A method according to claim 56, wherein the well has a central axis and the perforations have an upward angle of from ten to eighty degrees relative the central axis, further comprising flowing the fluid up the well and into the formation.

63. A perforating gun assembly, comprising a charge carrier having a central axis, an upper end and a lower end, a plurality of downward directed shaped charges carried on the carrier and positioned to fire perforating jets at a downward angle relative to the central axis, and at least one upward directed shaped charge carried on the carrier and positioned to fire a perforating jet at an upward angle relative to the central axis.

64. A perforating gun assembly according to claim 63, wherein the downward directed shaped charges comprise more than half of the shaped charges carried on the carrier and the at least one upward directed shaped charge is carried proximate the lower end of the carrier.

65. A method substantially as described with reference to and as shown in the accompanying drawings.

66. A completion substantially as described with reference to and as shown in the accompanying drawings.

67. A perforating gun assembly substantially as described with reference to and as shown in the accompanying drawings.

68. A hydrocarbon production well substantially as described with reference to and as shown in the accompanying drawings.

69. A filtering device substantially as described with reference to and as shown in the accompanying drawings.