The present invention relates generally to equipment and operations utilized in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a single trip perforating and fracturing/gravel packing method. 
In well completion operations, it is very beneficial to minimize the number of trips into the well, since each trip into the well is typically time consuming, is expensed to the well operator, and increases the chances that damage will inadvertently be caused to the well, a fishing job will be needed, etc.  Thus, service companies performing these completion operations generally strive to accomplish as many objectives as possible for each trip into the well. 
One way of accomplishing multiple objectives in a single trip into the well is to combine various portions of the overall well completion.  For example, in a cased well completion, it is generally necessary to perforate a casing or liner lining the wellbore, and it may be desired to also stimulate and/or gravel pack one or more perforated zones of the well.  If the perforating and stimulation/gravel packing operations can be combined in a single trip into the well, the economics, speed and convenience of the well completion are enhanced. 
It is well known to combine perforating and fracturing/gravel packing operations in a single trip into the well.  In a typical combined operation, one or more perforating guns are suspended below a fracturing/gravel packing assembly and interconnected in a tubular string installed in the well.  The perforating guns are positioned in the wellbore opposite a particular zone intersected by the well, the guns are fired to perforate the zone, and then the fracturing/gravel packing assembly is positioned opposite the perforated zone.  The zone is fractured, or otherwise stimulated, and/or gravel packed as desired.  The perforating guns remain attached to the fracturing/gravel packing assembly, or are dropped off in the well. 
Unfortunately, it may be undesirable to leave the guns attached to the fracturing/gravel packing assembly, or to drop off the guns in the well.  For example, the presence of the guns in the well may impede access to a portion of the well or the guns may restrict fluid flow in the well.  Furthermore, it may be desired to perform other operations, such as additional perforating and/or fracturing/gravel packing operations, in close proximity to the prior completion operation, such as when multiple closely spaced zones are to be individually completed in the well.  Additionally, in relatively horizontal portions of wells, the guns cannot generally be dropped off. 
Note that perforating guns could be conveyed by wireline, electric line, coiled tubing, etc.,  in such operations, but this would require the additional wireline, electric line, etc.  trip into the well, would require mobilization of the wireline, electric line, etc.  rig, would not attain the performance advantages of tubing conveyed perforating guns, and would not resolve the problem of use in horizontal wells. 
Thus, it may be seen that it would be quite advantageous to provide a well completion system and method which permit perforating guns to be retrieved from a well after a well completion operation.  It would also be advantageous to provide such system and method wherein the benefits of tubing conveyed perforating are retained.  Additionally, it would be desirable to provide such system and method with features which permit multiple closely spaced completions in the well.  Furthermore, it would be advantageous to provide a well completion system which includes a perforating assembly which has an outer dimension that is reduceable in the well, so that at least a portion of the perforating assembly may be displaced through a restriction in the well after perforating. 
Where multiple well completion operations are combined into a single trip into the well, it is frequently difficult to resolve the problem of how to control actuation of the various items of equipment installed downhole.  For example, various packers may need to be set, one or more firing heads may need to be operated, etc.  Thus, it may be seen that it would be beneficial to provide a well completion system and method which enhances the convenience and safety of such operations. 
In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method of completing a well is provided in which a perforating assembly and a well treatment assembly are interconnected in a tubular string and conveyed into the well.  The method does not require that any perforating gun be dropped off in the well or otherwise remain in the well, but permits the perforating gun(s) to be retrieved from the well.  Well completion systems are also provided, as well as methods which permit enhanced convenience and safety in operating various equipment associated with the systems. 
In one aspect of the present invention, a method is provided which includes the steps of installing a perforating gun and a well treatment assembly in a well, and displacing the perforating gun through at least a portion of the well treatment assembly.  The well treatment assembly may include a well screen, and the perforating gun may be displaced through an inner passage of the well screen.  The perforating gun and well treatment assembly may be installed in the well, and the perforating gun retrieved from the well after firing, in a single trip into the well. 
In another aspect of the present invention, a method is provided in which perforating guns are initially laterally spaced apart when installed in a well, and then are laterally compressed in the well.  This method permits the guns to be retrieved side by side from the well through a portion of a well treatment assembly, while enabling the guns to be positioned in close proximity to a wall of the well when the guns are fired, for enhanced perforating performance. 
In still another aspect of the present invention, a method is provided in which perforating guns are initially laterally spaced apart when installed in a well, and then are longitudinally spaced apart after the guns are fired.  This method also permits the guns to be in close proximity to a wall of the well when fired, yet pass through a portion of a well treatment assembly portion after being fired.  Other methods for decreasing a size of at least a portion of a perforating assembly downhole are provided as well. 
In yet another aspect of the present invention, methods are provided for actuating various items of equipment of a well completion assembly.  In one of these methods, a packer of a well treatment assembly is set by applying fluid pressure to a line, which line is also utilized to apply fluid pressure to a firing head for firing a perforating gun.  In another of these methods, a series of fluid pressure applications are utilized to arm a packer.  In still another of these methods, a signal comprising fluid pressure pulses is utilized to arm and/or set a packer. 
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings.