Drop off apparatus for perforating gun capsule charge carriers

Abstract: A novel dropoff apparatus adapted for use in a perforating gun or other such apparatus adapted to be disposed in a borehole includes an embrittled carrier section connected to a further section of the perforating gun or other such apparatus. The embrittled carrier section includes an embrittled carrier and a explosive charge, such as a capsule charge, mounted on the embrittled carrier. When the charge detonates, since the carrier section is embrittled, the carrier section is severed from further section falls to a bottom of the borehole. The carrier section may undergo geometrical embrittlement by disposing a notch through at least one side of the carrier section; when the charge detonates, the carrier section is severed from the further section of the gun, or other apparatus, along a line connected to the notch, the further section of the gun, or other apparatus, falling to a bottom of the borehole.

Description: DROP OFF APPARATUS FOR PERFORATING GUN CAPSULE CHARGE CARRIERS BACKGROUND OF THE INVENTION The subject matter of the present invention relates to a drop off apparatus for a perforating gun capsule charge carrier. Perforating guns are disposed in oil well boreholes for perforating a formation traversed by the borehole, a well fluid being produced from the perforated formation. The perforating gun includes a carrier and a plurality of capsule charges mounted on the carrier. When the charges detonate, the formation is perforated. The carrier is often deformed as a result of the detonation of the capsule charges. Since the well dimensions are often very small, it is risky if not impossible to retrieve a distorted or deformed carrier strip from the well. In some cases, it is preferable to drop the perforating gun to the bottom of the well after detonating the capsule charges mounted on the carrier. Prior art perforating gun systems include a dropping mechanism which is designed to drop the perforating gun to the bottom of the well. In some prior art systems, the dropping mechanism dropped the head of the perforating gun, or part of it, to the bottom of the well along with the charges. This abandonment of the perforating gun head can be very expensive. In addition, special hardware is often needed to operate the dropping mechanism on the prior art systems. In a further prior art system, disclosed in US-A-4 496 009, the perforating charges are disposed in a sealed tubular carrier, and additional charges just above the perforating charges are detonated simultaneously with the perforating charges to puncture the tubular charge carrier, so letting high pressure well fluids rush into the carrier to force it downwardly, thereby fracturing some shear pins securing the carrier to the head part of the system and allowing the carrier to drop away. SUMMARY OF THE INVENTION It is an object of the present invention to provide a perforating gun system of the same type as the system of US-A-4 496 009, but which is of a particularly simple design. These and other objects of the present invention are accomplished by providing perforating gun systems, and methods of using and manufacturing them, as defined in the appended claims. Further scope of applicability of the present invention will become apparent from the detailed description presented hereinafter. It should be understood, however, that the detailed description and the specific examples, while representing a preferred embodiment of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become obvious to one skilled in the art from a reading of the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS A full understanding of the present invention will be obtained from the detailed description of the preferred embodiment presented hereinbelow, and the accompanying drawings, which are given by way of illustration only and are not intended to be limitative of the present invention, and wherein: figure 1 illustrates a perforating gun having a dropoff apparatus; figure 2 illustrates one embodiment of the dropoff apparatus of figure 1 in greater detail; and figure 3 illustrates another embodiment of the dropoff apparatus of figure 1 in greater detail. DETAILED DESCRIPTION OF THE PRESENT EMBODIMENT Referring to figure 1, a perforating gun having a dropoff apparatus in accordance with the present invention is illustrated. In figure 1, a perforating gun 10 includes a plurality of capsule charges 12 mounted on a carrier strip 14 and a dropoff section 30, in accordance with the present invention, connected to the carrier strip 14 on one end of the plurality of capsule charges 12 and forming an integral part of the carrier strip 14. The dropoff section 30 includes a further section of carrier strip 30a integrally connected to the carrier strip 14 and a further capsule charge 30b mounted to the further section of carrier strip 30a. The further section of carrier strip 30a is actually an "embrittled" or "weakened" version of the carrier strip 14, that is, a portion of the carrier strip 14 corresponding to the dropoff section 30 is made brittle or it is otherwise "weakened" from the standpoint of impact loading and not necessarily from the standpoint of strength. For example, a portion of the carrier strip 14 undergoes either a geometrical or a material embrittlement process to produce the further section of carrier strip 30a, the embrittlement processes being described in more detail below. A detonating cord 16 is connected to each of the plurality of capsule charges 12 and the further capsule charge 30b. The remaining portion of the perforating gun 10 of figure 1 is not important for purposes of the present invention, but nevertheless includes a detonator 18, a ground connection 20, a female connector 22, a fluid to air connector 24, and an adapter head 26. A wireline or other such apparatus 32 is connected to an end of the perforating gun 10, the gun 10 being suspended by the wireline or other apparatus in a borehole adjacent a formation to be perforated. The carrier strip 14 (including the further section of carrier strip 30a before embrittlement) is a steel strip made of carbon steel 1038 with a hardness of about 20-24 Rockwell scale c. The first two digits "10" of the number "1038" indicate that the carrier strip 14 is plain carbon steel, containing no alloys, such as nickel, chromium and/or molybdenum. The last two digits "38" indicate the carbon content of the steel in hundredths of a percent, i.e., 0.38% carbon. In operation, referring to figure 1, the perforating gun 10 is suspended in the borehole by the apparatus 32, such as a wireline. A detonation wave begins to propagate through the detonating cord 16 and first detonates the further capsule charge 30b. The detonation wave then detonates the capsule charges 12. However, all capsule charges 30b and 12 are detonated substantially simultaneously. Detonation of the further capsule charge 30b produces stress and/or strain within the furthersection of carrier strip 30a, enough to cause the further section of carrier strip 30a to break apart. When the further section of carrier strip 30a breaks apart, all capsule charges 12, which have already detonated, are separated from the remaining portion of the perforating gun 10 and fall to the bottom of the borehole. The further section of carrier strip 30a of the dropoff section 30 is modified structurally to produce a brittle condition such that, when the further capsule charge 30b detonates, the further carrier strip 30a breaks apart and separates the plurality of capsule charges 12 from the remainder of the gun 10, the capsule charges 12 and associated carrier strip 14 falling to a bottom of the borehole. The structural modification of the further section of carrier strip 30a to produce a brittle condition may be achieved as follows: 1. Geometrical embrittlement by the introduction of a notch or abrupt change in a section of the further carrier strip 30a so as to constrain the Poisson deformation thereby giving rise to a substantially triaxial local stress state (to be further discussed with reference to figure 2); and 2. Material embrittlement by thermal, chemical, mechanical or thermomechanical treatment which severely limits the ability of the material to plastically deform in response to loading, especially impact loading (to be discussed with reference to figure 3). In ferrous materials, the material embrittlement treatments include, but are not limited to: 2a. localized plastic deformation which exhausts the capacity of the material for substantial further plastic deformation; 2b. cooling from a temperature in the austenite phase field at a rate sufficient to transform the microstructure to martensite, without subsequent tempering, or with subsequent tempering at a temperature which produces "blue brittleness", temper embrittlement, or tempered martensite embrittlement; 2c. localized chilling to below the ductile-brittle transition temperature of the material by, for instance, the application of liquid nitrogen; 2d. localized carburizing, nitriding, or other surface treatment which produces high hardness and limited capacity for plastic deformation; 2e. localized application of an embrittling species such as cadmium, lead, or copper, either on the surface or as a deliberate alloying addition (localized alloying to produce a brittle intermetallic compound or ordering reaction); or 2f. localized neutron irradiation to produce degraded ductility. In non-ferrous metals, the material embrittlement treatments include, but are not limited to: 2g. localized plastic deformation which exhausts the capacity of the material for substantial further plastic deformation; 2h. localized neutron irradiation to degrade ductility; 2i. localized application of an embrittling species, or local alloying to produce a brittle intermetallic compound or ordering reaction; or 2j. precipitation hardening or other heat treatment which increases the strength and limits the capacity for plastic deformation. Any combination of the above processes may be utiliized to embrittle the further section of carrier strip 30a of the dropoff section 30. Referring to figure 2, one embodiment of the drop off section 30 of figure 1 is illustrated. In figure 2, the drop off section 30 includes the further section of carrier strip 30a and the further capsule charge 30b mounted thereon. The further section of carrier strip 30a is shown integrally connected to the carrier strip 14. The further capsule charge 30b is mounted on the further section of carrier strip 30a, and one of the plurality of capsule charges 12 is shown mounted on the carrier strip 14. The detonating cord 16 is connected to each charge. A cord protector 40 protects the detonating cord 16. In accordance with one embodiment of the present invention, the further section of carrier strip 30a has been weakened, that is, the further carrier strip 30a has been geometrically embrittled. The further section of carrier strip 30a has been geometrically embrittled by placing a first notch 30a1 on one side of the further section of carrier strip 30a. A further second notch (not shown in the drawings) could also be placed opposite the first notch on the other side of the further section of carrier strip 30a. The presence of the notch(s) 30a1 on the side(s) of the further section of carrier 30a weakens the further carrier section 30a. When the further capsule charge 30b detonates, the energy produced from the detonation of the further capsule charge 30b applies a very high stress on the further section of carrier 30a adjacent the notch 30a1 (or between the notchs) thereby breaking the further carrier section 30a adjacent to (or between) the notch(s). When this happens, the section of the perforating gun 10 which includes the capsule charges 12 drops off the perforating gun and falls to the bottom of the borehole. It is obvious to one skilled in the art that, in lieu of the notch(s), holes or grooves could be disposed in or through the further section of carrier 30a. The disposition of the holes or grooves through the further carrier section 30a would have the same effect of weakening or geometrically embrittling the further carrier section 30a. Referring to figure 3, another embodiment of the drop off section 30 of figure 1 is illustrated. In figure 3, the drop off section 30 includes the further section of carrier strip 30a and the further capsule charge 30b mounted thereon. The further section of carrier strip 30a is again shown integrally connected to the carrier strip 14. The further capsule charge 30b is mounted on the further section of carrier strip 30a, and one of the plurality of capsule charges 12 is mounted on the carrier strip 14. The detonating cord 16 is connected to each charge. A cord protector 40 protects the detonating cord 16. In accordance with another embodiment of the present invention, the further section of carrier strip 30a has been weakened, that is, the further carrier strip 30a has been materially embrittled. The further section of carrier strip 30a is materially embrittled by processing the further carrier section in accordance with the following treatment process: 1. heat the further carrier section 30a (eg, induction heating) to the austenite region (normally above 1500 to 1600 degrees F); 2. quench the austenite further carrier section 30a in water (or brine solution), thereby transforming its microstructure to martensite (for a 1038 steel, typical hardness is above 45 rockwell scale c). When the further carrier section 30a is materially embrittled in the above manner, it will easily break apart when the further capsule charge 30b detonates. In addition, however, the materially embrittled further carrier section 30a may also be geometrically embrittled on the manner described above (ie, placement of at least one notch adjacent an edge of the further carrier section 30a). The presence of the material embrittlement in the structure of the further section of carrier 30a weakens the further carrier section 30a. When the further capsule charge 30b mounted thereon detonates, the energy produced from the detonation of the further capsule charge 30b applies a very high stress within the materially embrittled further carrier section 30a, thereby breaking (or shattering) the materially embrittled further carrier section 30a. When this happens, the section of the perforating gun 10 which includes the capsule charges 12 drops off the perforating gun and falls to the bottom of the borehole.

Claims: A perforating gun assembly adapted to be disposed in a borehole, the assembly comprising: a carrier (14), said carrier including a first section (30) and a second section (30a)connected to said first section; at least one charge (12) mounted on said first section (30) of said carrier (14); and at least one additional charge (30b) mounted on said second section (30a) of said carrier (14); characterised in that said second section (30a) of said carrier (14) includes a heat treated material having a hardness of above 45 rockwell scale c, such that it shatters when said additional charge (30b) detonates, whereby said first section (30) of said carrier (14) separates from said second section, thereby allowing said first section to drop to the bottom of said borehole. A perforating gun assembly adapted to be disposed in a borehole, the assembly comprising: a carrier (14), said carrier including a first section (30) and a second section (30a) connected to said first section; at least one charge (12) mounted on said first section (30) of said carrier (14); at least one additional charge (30b) mounted on said second section (30a) of said carrier (14); characterised in that said second section (30a) of said carrier (14) includes a geometrically weakened portion (30a1), such that said first section (30) of said carrier (14) separates from said second section (30a) along a line including said geometrically weakened portion (30a1) when said at least one additional charge (30b) on said second section (30a) detonates, thereby allowing said first section to drop to the bottom of said borehole. The perforating gun assembly of claim 2, wherein said geometrically weakened portion (30a1) of said second section (30a) comprises a notch (30a1) disposed in said second section. The perforating gun assembly of claim 2, wherein said geometrically weakened portion of said second section (30a) comprises a hole disposed in said second section. The perforating gun assembly of claim 2, wherein said geometrically weakened portion of said second section (30a) comprises a groove disposed in said second section. a perforating gun assembly adapted to be disposed in a borehole, the assembly comprising: a carrier (14), said carrier including a first section (30) and a second section (30a) connected to said first section; at least one charge (12) mounted on said first section (30) of said carrier (14); and at least one additional charge (30b) mounted on said second section (30a) of said carrier (14); characterised in that said second section (30a) includes a heat treated material having a microstructure comprised of martensite, such that it shatters when said at least one additional charge (30b) detonates, whereby said first section (30) of said carrier (14) separates from said second section, thereby allowing said first section to drop to the bottom of said borehole. The perforating gun assembly of claim 6, wherein the martensite microstructure has a hardness of above 45 rockwell scale c. A method of perforating a well bore, comprising the steps of: lowering a perforating gun assembly into the well bore, said assembly including a carrier (14) having a first section (30) with at least one charge (12) mounted thereon for perforating the well bore and a second section (30a) with at least one additional charge (30b) mounted thereon for causing detachment of the carrier from the rest of said assembly; and detonating the charges (12, 30b) to perforate the well bore and detach the carrier (14) respectively; characterised in that said second section (30a) of the carrier (14) is heat treated so as to render it brittle, such that the detonation of said additional charge (30b) severs the second section (30a) of the carrier (14), thereby allowing said first section (30) to drop to the bottom of the borehole. A method of perforating a well bore, comprising the steps of: lowering a perforating gun assembly into the well bore, said assembly including a carrier (14) having a first section (30) with at least one charge (12) mounted thereon for perforating the well bore and a second section (30a) with at least one additional charge (30b) mounted thereon for causing detachment of the carrier from the rest of said assembly; and detonating the charges (12, 30b) to perforate the well bore and detach the carrier (14) respectively; characterised in that said second section (30a) of the carrier (14) is geometrically weakened by cutting at least one notch, hole or groove in it, such that the detonation of said additional charge (30b) severs the second section (30a) of the carrier (14), thereby allowing said first section (30) to drop to the bottom of the borehole. A method of manufacturing a perforating gun assembly, the method comprising the steps of: forming a single piece of material into a carrier (14), said carrier including a first section (30) and a second section (30a); mounting at least one charge (12) on said first section (30); and mounting at least one additional charge (30b) on said second section (30a); characterised in that, prior to mounting said additional charge (30b) on said second section (30a), said second section is heat treated so as to render it sufficiently brittle to be shattered by detonation of said additional charge (30b). The method of claim 10, wherein the heat treating step comprises the steps of: heating the second section (30a) to an austenite region; and subsequently quenching the second section (30a) in a liquid solution until the microstructure of said second section is martensite. A method of manufacturing a perforating gun assembly, the method comprising the steps of: forming a single piece of material into a carrier (14), said carrier including a first section (30) and a second section (30a); mounting at least one charge (12) on said first section (30); and mounting at least one additionl charge (30b) on said second section (30a); characterised by geometrically weakening said second section (30a) of said carrier (14) so that it will be severed by detonation of said additional charge (30b). The method of claim 12, wherein the geometrically weakening step comprises the step of: placing a notch (30a1) in said second section (30a) of said carrier (14). The method of claim 12, wherein the geometrically weakening step comprises the step of: placing a hole in said second section (30a) of said carrier (14). The method of claim 12, wherein the geometrically weaking step comprises the step of: placing a groove in said second section (30a) of said carrier (14).

Inventors: LOPEZ DE CARDENAS JORGE, LOPEZ DE CARDENAS, JORGE
Applicants: SCHLUMBERGER HOLDINGS, SCHLUMBERGER LTD, SCHLUMBERGER SERVICES PETROL, SCHLUMBERGER TECHNOLOGY BV, SCHLUMBERGER HOLDINGS LIMITED, SCHLUMBERGER LIMITED, SCHLUMBERGER TECHNOLOGY B.V., SERVICES PETROLIERS SCHLUMBERGER, (FORMERLY SOCIETE DE PROSPECTION ELECTRIQUE SCHLUMBERGER)
Application year: 1991
Main classification: E21B43
IPC codes: E21B43