Well perforating apparatus

A well perforating apparatus comprising:

• (a) an elongated metallic support tube have successive portions which are crushed edge to edge in different predetermined radial directions to form a series of flat-faced support sections on and offset angularly around the support along the longitudinal direction thereof, each two successive flat-faced sections being oriented with perpendicular radial directions so as to provide for orienting explosive charges thereon along four radial directions at 90 degrees,
• (b) means forming longitudinally spaced attachment holes in said suppot sections,
• (c) explosive charges having sealed cases fixed to the support in the attachments holes, each charge case including a metallic body member of sufficient strength for the attachment and being made of extruded steel having a better breaking resistance in the direction of the charge axis than perpendicular to this axis so that the major part of said body opens under the effect of the explosion of the charge while remaining attached by the rear part to said support after the explosion, and a cover member made of a brittle ceramic material for breaking into small size debris after the explosion of the charge,
• (d) means on each of said support sections forming said longitudinally spaced attachment holes therein in pairs with a distance between the centers of each pair smaller than the maximum diameter of a charge perpendicular to its axis, said attachment holes being configured to support the charges with axes substantially perpendicular to said support section flat faces,
• (e) rear parts in the charge cases of reduced diameter for engaging in said attachment holes such that two charges are fixed on each of said support sections with the axes of said two charges oriented in opposite radial directions,
• (f) detonating means including two detonating cords connected respectively to a first series of charges consisting of a charge of each section and to a second series of charges consisting of the other charge of each section, an explosive relay connected to fire the two detonating cords simultaneously, and a detonator operated electrically to set off said explosive relay for firing said two detonating cords to fire the respective series of charges connected thereto, and at least one additional explosive relay spaced longitudinally along the support, each of said additional relays being connected to the two detonating cords to maintain the simultaneous detonation of the two detonating cords,
• (g) means in the rear parts of each charge case forming a detonating cord passage slot for the passage of a detonating cord and positioned so that, after attaching a charge case on a support section, the detonating cord for firing the respective said charge is disposed along the support side directed toward the front of said charge,
• (h) means in each attachment hole forming at least one flat part thereon to prevent the rotation of the charge engaged in this attachment hole, and
• (i) a plurality of removable spacers, some of different predetermined lengths for boreholes having well casings of different diameters, each such spacer being configured for insertion between the charges and said support for better perforating boreholes cased with large diameter well casings, with a reduced clearance between the front parts of the charges and the well casing, and each of said spacers having an annular part of reinforced thickness adapted to surround the rear part of the body of a charge and, inside this annular part, a transverse part adapted to engage in said cord passage slot when the rear part of a charge is placed in the spacer, in order to reduce the volume of fluid inside the spacer while ensuring proper application of the cord against the charge body.

A method for perforating a well with a high charge density, comprising:

• (a) lowering into the well a high charge density perforation apparatus having sealed explosive charge cases with reduced diameter rear parts inserted and fixed, with the axes thereof oriented in opposite radial directions, into respective pairs of longitudinally spaced attachment holes formed in a series of flat-faced support sections on and angularly offset around a support along the longitudinal direction thereof, the support sections having been formed by crushing successive portions of a metallic tube edge to edge in different predetermined radial directions, the charge cases being formed by extruding a steel body member of sufficient strength for the attachment and having a better breaking resistance in the direction of the charge axis than perpendicular to this axis so that the major part of the body opens under the effect of the explosion of the charge while remaining attached to the support by the rear part of the charge case, the distance between the centers of the holes in each such pair of holes being smaller than the maximum diameter of a charge perpendicular to its axis, the holes being configured to support the charges with axes substantially perpendicular to the support section flat faces, the clearance between the front parts of the charges and the well casing being reduced by inserting removable spacers between the charges and the support, for better perforating boreholes cased with large diameter well casings, the charges being connected for firing by two detonating cords connected respectively to a first series of charges consisting of a charge of each section and a second series of charges consisting of the other charge of each section, each detonating cord being connected to each charge through a cord passage slot in the rear parts thereof, and a transverse part on the spacer being engaged into the slot while placing the rear part of the charge in the spacer to reduce the volume of fluid inside the spacer while ensuring proper application of the cord against the charge body, and an electrically operated detonator being connected to the two detonating cords for firing them, and
• (b) firing the charges by means of the electrically operated detonator and the detonating cords.