1. Field of the Invention
This invention relates to apparatus and methods for perforating wells, and more particularly, to a stackable gun system and method of use utilizing a plurality of perforating guns which may be individually positioned in a wellbore and individually removed therefrom.
2. Description of the Related Art
In the past, perforating systems for use in completing or reworking wells have been run into wells on a pipe string or wire line and positioned and supported on a hanger. Another method for positioning the perforating assemblies entails running them into the well on a slick line and lowering them to the desired position in the well, where they are anchored to the well casing. The slick line is typically detached and removed from the perforating assembly before the perforating operation.
It is preferable to seat one or more perforating guns on a hanger or anchor that has been lowered and set in the casing at the desired depth. After the perforating guns are in position, the lowering equipment can be removed from the vicinity of the perforation, or from the well entirely. Thus the amount of unnecessary equipment in the vicinity of the perforation is minimized.
Conventional hangers, however, must be run into the well before any tubing string is installed because the hangers are typically too large to pass through a tubing string. If a tubing string is already in place in a well, as in the case of a well being reworked, it is difficult to position a hanger in the casing below the end of the tubing string without first removing the tubing string. Removal of the tubing string is undesirable, particularly in cases where the tubing string comprises expensive pipe and/or connections and it is preferred to keep the handling of the string to a minimum. In such cases, a wireline which can be either a slick line or a braided electric line can be used to lower individual perforating guns through the tubing to the desired depth. The disadvantage to using a wireline is that each gun is fired separately, resulting in pressure and flow from the formation begin as soon as the first gun is fired. This can greatly prolong the perforating operation.
Hence, there is a need for stackable perforating gun system that can be run through the production tubing, anchored in the larger casing below the end of the tubing string, fired as a unit and retrieved from the well after firing.
The system should be able to support several perforating guns, so that a desired length of pipe can be perforated simultaneously. The system, including the hanger and the individual gun sections, should also be self-centering in the casing, with the centralizers also being passable through the tubing string. If the gun system components do not centralize in the casing, it will be difficult or impossible to mate the individual sections for proper operation.
After perforation, the perforating guns can either be retrieved or dropped to the bottom of the well, depending on several factors. Hence, a support should be adaptable either to maintain its position in the casing or to release itself from the casing and drop to the bottom upon perforation. Other objects and advantages of the invention will appear from the following description.
The present invention provides a stackable perforating gun system in which a plurality of gun sections or sections may be individually run through production tubing, positioned in a wellbore, fired as a unit, and individually retrieved, as necessary. This tool can be run on coiled tubing, slick line or braided electrical wireline.
The stackable perforating gun system of the present invention may be described as a well perforating apparatus comprising a through tubing retrievable bridge plug engagable with a portion of a cased wellbore for providing a gun support within the wellbore, and a plurality of perforating gun sections, one of the gun sections being supported by the retrievable bridge plug. The remainder of the gun sections are supported by an adjacent gun section. Each gun section is centralized at each end with a coil spring actuated folding arm type centralizer which is passable in either direction, through the production tubing.
In one embodiment, the bridge plug is an automatically releasing bridge plug.
The invention may also be said to include a method of perforating a casing of a well, wherein the method comprises the steps of lowering a through tubing retrievable bridge plug through a production tubing and into the enlarged casing section below the bottom of the production tubing. Energizing the bridge plug such that the bridge plug fixedly engages the casing. Lowering a first perforating gun section into the casing, supporting the first perforating gun section in the casing on the retrievable bridge plug adjacent to a first portion of a subsurface formation to be perforated, lowering an additional perforating gun section into the casing, supporting the additional perforating gun section on the first perforating gun section adjacent to another portion of the subsurface formation, and firing the perforating gun sections and thereby perforating the casing. The step of lowering an additional perforating gun section into the casing may be repeated as many times as necessary or desired. That is, the additional perforating gun section may be one of the plurality of additional perforating gun sections, each of the additional gun sections being supported on an adjacent perforating gun section.
The method may further comprise a step of retrieving at least one of the perforating gun sections from the casing and may further comprise a step of retrieving the retrievable bridge plug.
The method may further comprise releasing the bridge plug from engagement with the casing after firing the perforating gun sections, thereby allowing the gun system to drop to the bottom of the hole.
Examples of the more important features of the invention thus 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 invention that will be described hereinafter and which will form the subject of the claims appended hereto.