Patent Grant
8127654
The present application relates generally to perforating and more specifically to perforating guns having a volume reduction device that conforms to the profile of shaped charges to reduce internal gun volume and to help support the shaped charges.
To complete a well, one or more formation zones adjacent a wellbore are perforated to allow fluid from the formation zones to flow into the well for production to the surface or to allow injection fluids to be applied into the formation zones. A perforating gun string may be lowered into the well and the guns fired to create openings in casing and to extend perforations into the surrounding formation.
When the shaped charge is detonated a portion of the liner forms a jet portion of the liner. The jet is propelled away from the jacket in a direction toward a target. Another portion of the liner is propelled away from the jacket and forms what is known as a slug or carrot portion of the liner. The slug or carrot portion is not propelled to the same extent as the “jet”. When the shaped charge is used in a perforating gun, the target is normally a cased downhole formation. Upon detonation, the jet portion of the liner is propelled through the casing and penetrates the downhole formation to enhance recovery of downhole hydrocarbons. The slug portion, on the other hand, is designed to break up upon contact with the casing.
The explosive nature of the formation of perforation tunnels shatters sand grains of the formation. A layer of “shock damaged region” having a permeability lower than that of the virgin formation matrix may be formed around each perforation tunnel. The process may also generate a tunnel full of rock debris mixed in with the perforator charge debris. The extent of the damage, and the amount of loose debris in the tunnel, may be dictated by a variety of factors including formation properties, explosive charge properties, pressure conditions, fluid properties, and so forth. The shock damaged region and loose debris in the perforation tunnels may impair the productivity of production wells or the injectivity of injector wells.
In connection with those and other issues, there is continued need to improve the overall performance of perforating and perforating guns in many aspects. The present application addresses a number of present needs in that area.
An embodiment according to the present application includes a perforating device. The perforating device has an elongated tubular housing and a loading device supporting a plurality of shaped charges. The loading device and the shaped charges are located inside the housing. A volume reduction device is adapted to fit with the loading device and to conform to the profile of the shaped charges thereby filling open volume in the housing.
The following is a brief description of drawings relating to various embodiments of the present application.
In the present description, numerous details are set forth to provide an understanding of the various embodiments. However, it will be understood by those skilled in the art that those embodiments presented may be practiced without many details and that numerous variations or modifications from the described embodiments may be possible.
In the specification and appended claims, the terms “connect”, “connection”, “connected”, “in connection with”, and “connecting” are used to mean “in direct connection with” or “in connection with via another element”; and the term “set” is used to mean “one element” or “more than one element”. As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and “downwardly”, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly described some embodiments.
A typical shaped charge has a metal jacket or a charge case. High explosive material is disposed inside the metal jacket. A liner retains the explosive material in the jacket during the period prior to detonation. A primer column provides a detonating link between a detonating cord and the explosive.
Overbalance and underbalance are significant factors in successful perforating jobs. One popular method of obtaining clean perforations is underbalanced perforating. A perforation carried out with a lower wellbore pressure than the formation pressure is underbalanced. The pressure equalization is achieved by fluid flow from the formation and into the wellbore. This fluid flow carries some of the damaging rock particles. However, underbalance perforating may not always be effective and may be expensive and unsafe to implement in certain downhole conditions.
Fracturing of the formation to bypass the damaged and plugged perforation may be another option. However, fracturing is a relatively expensive operation. Moreover, clean, undamaged perforations are required for low fracture initiation pressure (one of the pre-conditions for a good fracturing job).
Acidizing, another widely used method for removing perforation damage, is not most effective for treating sand and loose debris left inside the perforation tunnel.
During the detonation of perforating guns in a wellbore, fluid pressure transients are produced due to local and global differences in pressure between the gun, wellbore and fluid in the reservoir. These pressure transients can give rise to both underbalance and overbalance conditions in the wellbore. U.S. Pat. No. 6,732,798, incorporated herein by reference in its entirety, describes methods for controlling an underbalance in a wellbore.
Perforating guns generally include a housing that is tubular in shape and forms an outer barrier of the perforating gun. Shaped charges are located inside the housing. The shaped charges are generally loaded into and/or supported by a loading device, often referred to as a “loading tube”. The loading device can take many forms. The loading device can be a central longitudinal structure where the shaped charges are connected thereto. The loading device can be a flat plate where the shaped charges are supported against the plate. The flat plate can be instead formed with a helical twist having the shaped charges connected thereto. Also, the loading device can be in the shape of a tube having openings for placement and support of the shaped charges. An additional internal structure can be part of the tube shaped loading device to support the apex portion of the shaped charges.
The present application relates to modification of a perforating gun system to help control (e.g., reduce) underbalance conditions that would normally be produced by a perforating gun with a housing, a loading device and shaped charges supported by the loading device. According to the present application, a modification that reduces underbalance conditions is the additional inclusion into a perforating gun of a volume reduction device. The volume reduction device can be adapted to conform to the external profile of the shaped charges thereby taking up free internal gun volume while supporting the shaped charges. The volume reduction device can be adapted to conform to the internal shape of a tubular shaped loading device. If the loading device is central in style or a plate, then the volume reduction device can be adapted to conform to the shape of the housing. Further, the volume reduction device can conform to the profile of the shaped charges.
In an embodiment, gun pressure is controlled by the balance of total explosive mass inside the gun to free internal volume in the gun. To make a PURE (underbalanced) design, reduction of gun pressure is used, i.e., the ratio of total explosive mass to free internal volume is decreased. However, in some perforating job designs (PURE and non-PURE) it is needed to increase the gun pressure, i.e., increase the ratio of total explosive mass inside the gun to free internal volume in the gun.
A benefit according to present embodiments is reduction of underpressure. According to the present application, free volume in the perforating gun is reduced beyond the volumes normally displaced by the loading device, and shaped charges by adding the volume reduction device. The internal gun volume can be reduced to an even greater degree by adding more components inside the gun, e.g., by adding loading tube volume reduction sleeve(s), thread relief volume reduction insert(s), and/or adapter volume reduction insert(s).
Another benefit of present embodiments relates to low debris perforating. The volume reduction device contributes to low shaped charge case debris by supporting and conforming to the shape of each of a plurality of shaped charges inside the loading tube insert assembly. When detonation occurs, the shaped charge case(s) are inclined to remain intact due to containment provided by the volume reduction device fitting around the shaped charges. Hence, the loading tube insert assembly reduces the amount of shaped charge case debris that could potentially exit from the perforating gun and into the well.
A volume reduction device 5 is located inside the loading tube 7 and is configured to fit around and conform to the shaped charges 8.
The shaped charges 8 can be configured in a number of patterns.
The assembly shown in
In an embodiment the volume reduction device 5 is a tubular part with a hollow central passage 10 that extends the entire longitudinal distance of the volume reduction device 5. Openings 9 extend from the surface of the volume reduction part 5 near the inner part of the loading tube 7 to the hollow center passage 10. A detonation cord 11 extends though the hollow center passage 10.
In an embodiment, the volume reduction device 5 can be a single unified part that extends from the top part of the loading tube 7 to the bottom part of the loading tube 7. In that case, the single volume reduction device 7 conforms to and surrounds plural shaped charges 8.
In an embodiment, the volume reduction device 5 can be made from plural parts that are each tubular in shape and have plural indentations that are adapted to conform to the shape of shaped charges 8. Each of those parts that make up the volume reduction device 5 has a cavity 10 extending through the center of the volume reduction device 5 to accommodate a detonation cord 11.
An embodiment includes a volume reduction part 5 that has two halves separated longitudinally. This configuration helps simplify construction of the volume reduction part 5 as internal milling or molding is not required.
An embodiment includes a volume reduction device 5 that is made from a plurality of parts that together make up a volume reduction device 5 that conforms to and surrounds plural shaped charges 8 that are located inside a perforating gun 1.
A bottom plug 13 can be connected with the lower part of the housing 3. Inserts 14 can be made in connection with the bottom plug 13 that takes up additional volume thereby increasing the underbalance reduction. Volume reduction thread inserts 15 can also be used to take up additional space.
The volume reduction device 5 is preferably made from metal. However, the volume reduction device 5 could be made from other materials such as ceramics and or composite materials, so long as they can adequately survive the perforating operation.
Accordingly, although only a few embodiments have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this application. The description of various preferred embodiments and related features herein is not meant in any way to unduly limit the scope of any claims related to the present application.
The present application claims priority to U.S. Provisional Application No. 61/187,858 that was filed on Jun. 17, 2009, the entirety of which is incorporated herein by reference.
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