BACKGROUND OF THE DISCLOSURE

1. Field of Disclosure

[0001] The present disclosure relates to an apparatus and method for completing a well.

2. Description of the Related Art

[0002] Hydrocarbon producing wells typically include a casing string positioned within a wellbore that intersects a subterranean oil or gas deposit. The casing string increases the integrity of the wellbore and provides a path for producing fluids to the surface. Conventionally, completing a well involves cementing the casing to the wellbore face and subsequently perforating the formation by detonating shaped explosive charges. When detonated, the shaped charges generate a jet that penetrates through the casing and cement and forms a tunnel of a short distance into the adjacent formation. A perforating tunnel may be a principal source of tortuosity in the unconventional, hydraulically fractured reservoir. Perforating may also create micro fracturing in the near well bore, which can create thief zones that take away from the desired areas for fracking, where natural fractures occur. Tortuosity and thief zones can significantly impair flow of production fluids out of the formation.

[0003] Referring to FIG. 1, there is shown a section of a wellbore 10 that has been completed in a conventional manner. Tunnels 11 formed by a perforating tool penetrate through a wellbore tubular 14, such as casing, and a surrounding cement sheath 16, and extended a certain distance, up to eight inches or more, into a formation 18. For simplicity, the wellbore tubular 14 and the cement sheath 16 may be referred to as a "production structure. " The production structure may also include other production equipment installed in the well. The formation 18 may be an unconventional formation, such as shale. With this prior art technique, the location and orientation of the cracks / fractures caused during the hydraulic fracturing activity may be induced to occur proximate to the tunnels 11. Fractures 20 illustrate how such fractures may be located and oriented. However, the location and orientation of such fractures may not be best suited for efficient fluid flow due to tortuosity and the creation of thief zones.

[0004] The present disclosure departs from conventional perforating techniques by minimizing or eliminating the creation of tunnels in a formation.

SUMMARY OF THE DISCLOSURE

[0005] In aspects, the present disclosure provides a method for completing an unconventional subterranean formation. The method may include the steps of positioning a completion tool in a deviated section of the wellbore that intersects the unconventional formation, forming at least one opening in a production structure without substantially penetrating into a surrounding formation by activating the completion tool; and fracturing the formation by pumping a fracturing fluid through the at least one opening.

[0006] In aspects, the present disclosure further provides a perforating tool for performing the disclosed completion operations. The perforating tool may include shaped charges that have a charge case, a liner disposed in the charge case, and an explosive material filling an interior of the charge case. In one arrangement, the liner has an inner concave surface and an outer concave surface. An angle defining the inner concave surface may be less than an angle defining the outer concave surface.

[0007] The above-recited examples of features of the disclosure have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the disclosure that will be described hereinafter and which will form the subject of the claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For detailed understanding of the present disclosure, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein:

FIG. 1 is a schematic sectional view of a portion of a horizontal well that is perforated and fractured in a conventional manner;

FIG. 2A is a schematic sectional view of a portion of a horizontal well that is perforated according to one embodiment of the present disclosure;

FIG. 2B is a schematic sectional view of the FIG. 2A well portion that is being fractured;

FIG. 3 is a sectional view of a shaped charge made in accordance with one embodiment of the present disclosure; and

FIGS. 4A-C are sectional views of shaped charge liners made in accordance with embodiments of the present disclosure; and

FIG. 5 is a schematic sectional view of one embodiment of an apparatus of the present disclosure as positioned within a well penetrating a subterranean formation.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0009] Aspects of the present disclosure provide methods and related perforating tools for completing unconventional formations, such as hydrocarbon-bearing shale formations. For the present disclosure, an "unconventional" formation is generally a formation that has a permeability that is less than ten millidarcy (raD). Many "unconventional" formations have a permeability between one nano-darcy (nD) and one millidarcy (raD). Contrary to traditional perforating techniques, perforating tools according to the present disclosure are designed to only open holes in the well tubulars and surrounding cement sheathing. The rock and earth surrounding the wellbore is only minimally, at most, impacted by the perforating jets generated by the perforating tool. Thus, there may be a significant reduction, if not elimination, of tortuosity and instances of micro fractures. Thus, by leaving the formation face largely intact, the effectiveness of subsequent hydraulic fracturing operations may be improved.

[00010] The perforating and fracturing methodologies of the present disclosure are illustrated with reference to Figs. 2A and 2B. In FIG. 2A, there is shown a section of a wellbore 10 that has been perforated according to embodiments of the present disclosure. A perforating gun 140, the details of which are described below, has formed openings 22 that penetrate through the production structure (i.e. , wellbore tubular 14 and the cement sheath 16) but do not extend into the formation 18. Practically speaking, in some instances, a tunnel 11 (Fig. 1) may extend from one or more openings 22 an insubstantial distance into the formation 18. For the purposes of the present disclosure, a penetration distance in the formation 18 that no greater that three inches is defined a "non-substantial" penetration length. In some applications, a "non-substantial" penetration length is no greater than two inches.

[00011] Fig. 2B illustrates a subsequent fracturing activity wherein a pressurized fracturing fluid 30 is directed into the openings 22. It should be noted that the fracturing fluid 30 acts on a face 32 of the formation 18 that is immediately next to the cement sheath 16. The face 32 of the formation 18 is the circumferential surface that defines the wellbore 10. The pressure associated with hydraulic fracturing may now cause the formation to separate at naturally weaker locations in the vicinity of the openings 22. This may lead to fractures that better align with the opening 22. That is, the fractures have fluid connections with the opening 22 that promotes fluid flow with reduced resistance to flow. Fractures 34 illustrate how such fractures may be located and oriented.

[00012] The perforating openings 22 of Figs. 2A and B may be formed by using perforating tool having shaped charges specially configured for limited perforation. In embodiments, at least three aspects of a shaped charged may be configured to limit the distance a perforating jet travels: the materials making up a shaped charge liner, the shape of the shaped charge liner, and the explosive mix of the shaped charge.

[00013] Referring to FIG. 3, there is shown a cross section of an explosive shaped charge 40. The shaped charge 40 has a charge case 42. The charge case 42 has an interior surface or wall 44 that defines a hollow interior of the charge case 42. The charge case 42 is open at the outer end and tapers inward. Disposed within the interior of the case 42 is a liner 48. The liner 48 tapers inward from a base 50, located at the outer end, to a nose portion 52. The liner 48 is open at the base 50 and has a hollow interior. Disposed between the liner 48 and interior wall 44 of the casing 42 is an explosive material 54. The explosive material 54 extends from the interior of the case 42 through channel formed in the innermost end of the case 42. The case 42 receives a detonating cord (not shown) for detonating the explosive material 54.

[00014] One factor affecting depth of penetration is the material making up the liner 48. Conventionally, materials that tend to form a dense and compacted perforating jet are favored because of the traditional emphasis on depth of penetration. Embodiments of the present disclosure use materials that form a perforating jet that is less dense and relatively diffuse. Such a perforating jet exhausts energy while perforating the production structure and has insufficient mass to displace the formation. The liner 48 may be formed of materials such as aluminum, zinc, molybdenum, copper, magnesium, or other low density materials. In embodiments, the liner may also include low density materials such as thermoplastic polymers (PTFE, UHMW, etc).

[00015] Another factor effecting depth of penetration is liner shape or geometry. Liner shape can influence how and when the energy released by the explosive material interacts with the liner 48. For example, the liner 48 formed as a shallow bowl may form a perforating jet that is wider and flatter than a liner having an acute conical shape. Also, the liner may use shapes such as a truncated, parabolic, plugged apex, near EFP angled liner.

[00016] Referring now to Figs. 4A-C, there are shown non- limiting embodiments of liners 48 that may limit penetration to only the production structure. In Fig. 4A, the liner 48 has an inner concave surface 51 and an outer concave surface 53. The inner concave surface 51 is defined by an angle 56 that is less than an angle 55 defining the outer concave surface 53. For example, the angle 55 may be one to ten degrees greater than angle 56. Illustrative non-limiting angle pairs may be: 80 degrees for angle 56 and 82 degrees for angle 55, 82 degrees for angle 56 and 83 degrees for angle 55, 85 degrees for angle 56 and 88 degrees for angle 55, 90 degrees for angle 56 and 91 degrees for angle 55, etc. In certain embodiments, the angle 56 defining the inner concave surface may be between one and two degrees less than an angle 55 defining the outer concave surface. Additionally, an apex 60 of the liner 48 may have a thickness that is greater than any other thickness of the liner 48.

[00017] A variant of the Fig. 4 A embodiment is that the angle 56 is greater than the angle 55. For example, the angle 55 may be one to ten degrees less than angle 56. Illustrative non-limiting angle pairs may be: 80 degrees for angle 55 and 82 degrees for angle 56, 82 degrees for angle 55 and 83 degrees for angle 56, 85 degrees for angle 55 and 88 degrees for angle 56, 90 degrees for angle 55 and 91 degrees for angle 56, etc. In certain embodiments, the angle 55 defining the inner concave surface may be between one and two degrees less than an angle 56 defining the outer concave surface.

[00018] Thus, generally, the angle 55 defining the inner concave surface may be between one and two degrees different from the angle 56 defining the outer concave surface.

[00019] In Fig. 4B, the liner 48 has an inner surface 70 and an outer surface 72, both of which are defined by composite geometries. The inner surface 70 has an outer convex section 74 and an inner concave section 76. Likewise, the outer surface 72 has an outer convex section 78 and an inner concave section 80. Inflexion point 82, 84 for the inner and outer surfaces 70, 72 can be positioned at a midpoint or closer to the apex 60. [00020] In Fig. 4C, the liner 48 has an inner concave surface 90 and an outer concave surface 92. The inner concave surface 90 is defined by an angle 94 that is greater than an angle 96 defining the outer concave surface 92. For example, the angle 94 may be one to ten degrees greater than angle 96. Illustrative non-limiting angle pairs may be: 81 degrees for angle 96 and 84 degrees for angle 94, 83 degrees for angle 96 and 85 degrees for angle 94, 88 degrees for angle 96 and 91 degrees for angle 94, 90 degrees for angle 96 and 93 degrees for angle 94, etc. In embodiments, the angle defining the inner concave surface is between one and two degrees less than an angle defining the outer concave surface. Additionally, an apex 60 of the liner 48 may have a thickness that is greater than any other thickness of the liner 48, the thickness being the distance separating the surfaces 90, 92. The thickness may be a multiple of the thickness of the immediately adjacent liner sections. The multiple may be between two to fifteen times.

[00021] In addition to liner configuration and materials, the explosive material 54 may be formulated to generate a perforating jet that has limited perforation capabilities. Traditional explosive compositions seek to shape and propel the perforating jet to have maximum penetration ability. In accordance with the present disclosure, the explosive material 54 may include compositions that release an amount of energy, in the form of shock waves and heat that lower the detonation velocity, which then lowers jet speed. For example, the explosive material 54 can include inert or energetic additives that lower the overall energy density or include energy reducing additives at selected locations in the charge case 42. Illustrative explosive materials include RDX (Hexogen, Cyclotrimethylenetrinltramine), HMX (Octagon, Cyclotetramethylenetetranitramine), CLCP, HNS, and PYX.

[00022] Further, the charge case 42 may have a shape or geometry selected to limit effective "backup," which can ten reduce the amount of energy imparted on the liner 48. The reduction in energy can lead to slower jet velocities and less penetration. The charge case 42 may be formed of steel, aluminum, zinc, metal alloys, non-metal composites, glass, etc. The material may be solid or powdered metal. The charge case 42 may also include features designed to limit penetration by interrupting the formation of a portion of the jet. [00023] The above perforating tools may be used to complete a hydrocarbon producing well. Referring to FIG. 5, there is shown a well construction and/or hydrocarbon recovery facility 100 positioned over a subterranean formation of interest 102. The formation 102 is an unconventional formation. The facility 100 can include known equipment and structures such as a rig 106 and a production structure 108. The production structure 108 can include casing, liners, cement, and other wellbore equipment. A work string 110 is suspended within a wellbore 10 from the rig 106. The work string 110 can include drill pipe, coiled tubing, wire line, slick line, or any other known conveyance means. The work string 110 can include telemetry lines or other signal/power transmission mediums that establish one-way or two-way telemetric communication. A telemetry system may have a surface controller (e.g., a power source) 112 adapted to transmit electrical signals via a suitable cable or signal transmission line.

[00024] A perforating gun 140 is shown in a deviated section 142 of the wellbore 10. By deviated, it is meant a section of the wellbore 10 is not vertical. The deviation from a vertical datum can be between one to ninety degrees (horizontal) or greater in some instances. In embodiments, the deviation may be greater than thirty degree, greater than forty five degree, or greater than sixty degrees. By way of reference, a deviation less than ninety degrees would have the section 142 pointed downward and a deviation greater than ninety degrees would have the section 142 pointed upward. By "pointed," it is meant the direction along which the wellbore 10 was drilled.

[00025] When fired, the perforating gun 140 creates one or more openings 22 as shown in Fig. 2A. The nature of the unconventional formation 102 is that the rock and earth, which is usually a type of shale, is highly non-permeable. Therefore, fluids residing in the formation 102 will not flow to the openings 22 at any meaningful flow rate. To promote fluid flow, a fracturing operation is performed in a conventional manner; i.e. , by pumping a fracturing fluid at a specified pressure via the work string 110 to the openings 22. Because the openings 22 do not extend into the formation, the permeability of the formation has not be adversely affected during the perforating activity. Thus, the pressure applied by the fracturing fluid has a greater likelihood of causing fractures at naturally weaker locations along the face of the formation 102. [00026] By way of a non-limiting example, an illustrative working example of a shaped charge configured to form the opening 22 of Figs. 2A and 2B is described below. As noted above, at least three aspects of a shaped charge may be varied to obtain the openings 22: (i) the materials making up a shaped charge liner, (ii) the shape of the shaped charge liner, and (iii) the explosive mix of the shaped charge.

[00027] The exemplary shaped charge was configured to open an hole of a production structure formed of a steel tubular and having a thickness of 0.361 inches. The cement has a thickness of 1.5 inches. A liner generally as shown in FIG. 4A included the following materials; aluminum, zinc, molybdenum, copper, and magnesium. The angle of the liner inner surface 56 was 90° and the liner outer surface 55 was 91°. The explosive mix included RDX.

[00028] The size of the opening 22 was 0.38 inches in diameter, with 1.13 inches penetration into the stressed shale formation. In embodiments, this technology is designed so that the depth of penetration into the formation is no more than three times the hole size diameter. Conventional perforating charges in the same working example above have penetration values 7 inches or greater into the formation.

[00029] In different aspects, the methods of completing an unconventional formation intersected by a deviated wellbore may use completion equipment other than a perforating gun. Any completion tool configured to form an opening 22 while forming a tunnel 11 having an insubstantial length may be used. For example, a milling tool or a sidewall drilling assembly may be used to form the openings 22 in the production structure. An illustrative completion assembly may utilize an electric or hydraulic motor to provide rotary power to a drill bit. Another hole opening completion tool may utilize an abrasive fluid stream. For example, a high pressure fluid source may supply the abrasive fluid to a nozzle. The nozzle can form a fluid jet that erodes the material making up the wellbore tubular to form the opening 22.

[00030] The foregoing description is directed to particular embodiments of the present disclosure for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope of the disclosure. Thus, it is intended that the following claims be interpreted to embrace all such modifications and changes.