Oilfield perforating self-positioning systems and methods

1. A self-positioning perforating gun comprising:

a gun carrier including a cylindrical sidewall defining an outer surface;

a loading tube received within the gun carrier, the loading tube including a plurality of shaped charges; and

a plurality of protrusions extending outwardly from the gun carrier, the plurality of protrusions including at least three protrusions that are angularly offset from each other about an outer circumference of the gun carrier cylindrical sidewall for providing finite rotational positions of the gun carrier within a wellbore and/or for spacing the outer surface of the cylindrical sidewall from a wellbore casing,

wherein the plurality of shaped charges are angularly offset from the plurality of protrusions.

2. The perforating gun of claim 1 wherein the plurality of protrusions includes N-protrusions at about 360/N-degree intervals about the outer circumference of the gun carrier.

3. The perforating gun of claim 1 wherein the plurality of protrusions includes three protrusions at about 120-degree intervals about the outer circumference of the gun carrier.

4. The perforating gun of claim 1 wherein each the plurality of protrusions define a uniform radial height and wherein the cylindrical sidewall defines an outer diameter, the ratio of the radial height of the plurality of protrusions to the outer diameter of the cylindrical sidewall being between 1:3 and 1:25, inclusive.

5. A self-positioning perforating gun comprising:

a gun carrier including a cylindrical sidewall defining an outer surface;

a loading tube received within the gun carrier, the loading tube including a plurality of shaped charges; and

a plurality of protrusions extending outwardly from the gun carrier, the plurality of protrusions including at least three protrusions that are angularly offset from each other about an outer circumference of the gun carrier cylindrical sidewall for providing finite rotational positions of the gun carrier within a wellbore and/or for spacing the outer surface of the cylindrical sidewall from a wellbore casing,

wherein the loading tube is rotatable within the gun carrier and includes an asymmetric weight for achieving a desired angular orientation of the plurality of shaped charges when the cylindrical casing is inclined at least 45 degrees from vertical.

6. The perforating gun of claim 5 further including first and second electrically conductive rotating pins that are rotatably seated within first and second internal adaptors, the first and second internal adapters being coupled to opposing ends of the loading tube.

7. A self-positioning perforating gun system comprising:

a gun string including first and second perforating guns, each of the first and second perforating guns including:

a gun carrier including a cylindrical sidewall defining an outer surface,

a loading tube received within the gun carrier, the loading tube including a plurality of shaped charges; and

a plurality of protrusions extending outwardly from the gun string, the plurality of protrusions being angularly offset from each other about an outer circumference of the gun string, wherein the plurality of protrusions of the first and second perforating guns are in angular alignment with each other,

wherein the gun string further includes an external adapter that is coupled between the first and second perforating guns, the external adapter including an alignment mechanism to maintain the plurality of protrusions of the first and second perforating guns in angular alignment with each other.

8. The system of claim 7 wherein the alignment mechanism includes a pin-and-slot attachment for coupling opposing ends of the external adapter to the first and second perforating guns.

9. A method comprising:

providing a gun string including first and second perforating guns and an external adaptor, each of the first and second perforating guns including:

a gun carrier including a cylindrical sidewall,

a loading tube received within the gun carrier, the loading tube including a plurality of shaped charges, and

a plurality of protrusions extending outwardly from the gun string and being angularly offset from each other about an outer circumference of the gun string, wherein the plurality of shaped charges are angularly offset from the plurality of protrusions;

positioning the gun string within a wellbore such that the plurality of protrusions of the first and second perforating guns are in angular alignment with each other; and

detonating the plurality of shaped charges.

10. A method comprising:

providing a gun string including first and second perforating guns and an external adaptor, each of the first and second perforating guns including:

a gun carrier including a cylindrical sidewall,

a loading tube received within the gun carrier, the loading tube including a plurality of shaped charges, and

a plurality of protrusions extending outwardly from the gun string and being angularly offset from each other about an outer circumference of the gun string,

positioning the gun string within a wellbore such that the plurality of protrusions of the first and second perforating guns are in angular alignment with each other; and

detonating the plurality of shaped charges,

wherein the loading tube is rotatable within the gun carrier and includes an asymmetric weight for achieving a desired angular orientation of the plurality of shaped charges when the gun string is substantially horizontal.

11. A self-positioning perforating gun system comprising:

a gun string including first and second perforating guns and an external adaptor; and

at least one alignment ring extending around a circumferential portion of the gun string, the alignment ring including a cylindrical collar and a plurality of protrusions extending outwardly from the cylindrical collar, wherein each of the plurality of protrusions are angularly offset from each other about the cylindrical collar,

wherein the at least one alignment ring includes an inwardly-protruding indexing feature and wherein the gun string includes a corresponding recess to maintain the alignment ring in a single angular orientation about the gun string.

12. The system of claim 11 wherein the at least one alignment ring is disposed about the external adaptor.

13. The system of claim 11 wherein the at least one alignment ring includes a first alignment ring disposed about the first perforating gun and a second alignment ring disposed about the second perforating gun.

14. A self-positioning perforating gun comprising:

a gun carrier including a cylindrical sidewall;

a loading tube that is concentrically received within the gun carrier and rotatable with respect to the cylindrical sidewall;

first and second internal adaptors, the first and second internal adaptors being coupled to opposing ends of the loading tube;

a plurality of shaped charges within the loading tube, the loading tube including an asymmetric weight for achieving a desired angular orientation of the plurality of shaped charges when the gun carrier is inclined from vertical by at least 45-degrees; and

first and second electrically conductive rotating pins that are rotatably seated within the first and second internal adaptors, respectively.

15. The perforating gun of claim 14 further including first and second grounding pins that are seated within longitudinal openings in the first and second internal adaptors, respectively, the first and second grounding pins being biased against respective first and second external adaptors that are joined to opposing ends of the gun carrier.

16. The perforating gun of claim 14 further including a plurality of protrusions extending outwardly from the gun carrier for spacing the cylindrical sidewall from a wellbore casing, the plurality of protrusions including at least three protrusions that are angularly offset from each other about an outer circumference of the gun carrier.