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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
   The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a deep set packer with hydrostatic setting actuator. 
   In relatively deep wells, sufficient hydrostatic pressure exists for use in setting a packer. Typical hydrostatic set packers for use in deep wells have actuators which include annular piston areas formed between concentric tubular members. Unfortunately, the large hydrostatic pressures found in deep wells tend to deform these concentric tubular members, so that the actuators are unable to operate satisfactorily. For example, using conventional hydrostatic set packers it has not yet been possible to satisfactorily set the packers at pressures greater than 19,000 psi. 
   Therefore, it may be seen that it would be very beneficial to provide improved hydrostatic set packers for use in deep wells. 
   SUMMARY 
   In carrying out the principles of the present invention, in accordance with an embodiment thereof, a packer and an actuator therefor are provided which are configured for use in high hydrostatic pressure environments. Associated methods are also provided. 
   In one aspect of the invention, a packer for use in a subterranean well is provided. The packer includes an actuator for setting the packer. The actuator includes multiple pistons circumferentially spaced apart from each other. 
   In another aspect of the invention, an actuator for use in a well packer is provided. The actuator includes multiple pistons, each of which is received in a respective one of multiple bores. The actuator further includes a force transmission device. Each of the pistons is releasably coupled to the force transmission device. 
   In yet another aspect of the invention, a method of setting a packer in a subterranean well is provided. The method includes the steps of: increasing pressure on the packer in the well; and displacing multiple pistons relative to respective multiple bores of an actuator of the packer in response to the pressure increasing step, thereby setting the packer in the well. 
   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 a representative embodiment of the invention hereinbelow and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic partially cross-sectional view of a well and a packer therein embodying principles of the present invention; 
       FIG. 2  is an enlarged scale isometric view of an actuator of the packer, depicted in a run-in configuration; 
       FIG. 3  is an isometric view of the actuator, depicted in an actuated configuration; 
       FIG. 4  is an isometric view of the actuator, depicted in the actuated configuration, but with a piston malfunction; 
       FIG. 5  is a quarter-sectional view of the actuator in the actuated configuration; 
       FIG. 6  is a quarter-sectional view of the actuator in the run-in configuration; 
       FIG. 7  is a quarter-sectional view of the packer, illustrating a force transmission arrangement of the packer; and 
       FIG. 8  is a quarter-sectional view of the packer, illustrating a piston relationship to the force transmission arrangement. 
   

   DETAILED DESCRIPTION 
   Representatively illustrated in  FIG. 1  is a well  10  having a packer  12  therein which embodies principles of the present invention. In the following description of the packer  12  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present invention. 
   As depicted in  FIG. 1 , the packer  12  is positioned in a cased wellbore  14  of the well  10 . The packer  12  includes outwardly extendable seal elements  16  for sealingly engaging the wellbore  14 . The packer  12  also includes a slip assembly  18  for grippingly engaging the wellbore  14 . 
   Thus, the packer  12  is capable of both sealing and anchoring a tubular string  20  in the wellbore  14 . Note that, although the wellbore  14  is depicted in  FIG. 1  as being cased, the principles of the invention are also applicable to situations in which a wellbore is uncased. 
   In one beneficial feature of the packer  12 , an actuator  22  of the packer is positioned longitudinally between the seal elements  16  and the slip assembly  18 . The actuator  22  produces both upwardly and downwardly directed forces when it is actuated, and these forces are transmitted directly from the actuator to each of the seal elements  16  and the slip assembly  18 . In this manner, the forces produced by the actuator  22  are more efficiently utilized in the packer  12  than in conventional hydrostatic set packers, resulting in more satisfactory and reliable sealing and anchoring of the tubular string  20 . 
   However, it should be clearly understood that it is not necessary in keeping with the principles of the invention for the actuator  22  to be positioned between the seal elements  16  and the slip assembly  18 . The actuator  22  could instead be positioned below the slip assembly  18  or above the seal elements  16 , for example. The embodiments described herein are used only as examples to illustrate applications of the principles of the invention, and are not to be taken as limiting the invention. 
   Referring additionally now to  FIG. 2 , the actuator  22  is representatively illustrated apart from the remainder of the packer  12 . In this view it may be seen that the actuator  22  includes multiple pistons  24  (a total of ten in this embodiment) received and circumferentially spaced apart in a generally tubular or annular shaped structure  26 . The pistons  24  are each releasably coupled to a force transmission device  28 , which includes a ring  30  through which each of the pistons extends. 
   Furthermore, the actuator  22  includes a setting initiation device  32 . This device  32  is used to prevent the actuator  22  from actuating until a predetermined pressure on the packer  12  is reached, at which point the device permits the actuator to actuate and set the packer. Prior to application of the predetermined pressure, pressure in the well  10  causes the pistons  24  to exert an upwardly directed biasing force on the ring  30 , and also causes the device  32  to exert a downwardly directed biasing force on the ring. 
   The downwardly directed force is greater than the upwardly directed force. However, when the predetermined pressure is applied, a rupture disc  34  of the device  32  is ruptured, thereby exposing an atmospheric chamber  46  (see  FIG. 6 ) of the device to pressure in the well  10 . At this point, the device no longer exerts the downwardly directed force on the ring  30 . These details of the actuator  22  are described more fully below. 
   Note that the chamber  46  may be at atmospheric pressure when the actuator  22  is initially installed, or it could be at another pressure which is less than the pressure expected in the well at the location at which the actuator is to be positioned when it is actuated. It is not necessary in keeping with the principles of the invention for the chamber  46  to be at atmospheric pressure at any particular time, although in a preferred embodiment, the chamber is at atmospheric pressure when the actuator  22  is installed in the well. However, another pressure could be used if desired, such as another pressure less than hydrostatic pressure in the well at the location where the actuator  22  is to be positioned. 
   In  FIG. 3 , the actuator  22  is depicted in a configuration in which the rupture disc  34  has been ruptured. The biasing force exerted by the setting initiation device  32  is now reduced (or completely eliminated), so that the biasing force exerted by the pistons  24  has displaced the ring  30  upward to set the packer  12 . 
   Upward displacement of any of the pistons  24  causes upward displacement of the ring  30 . However, since each of the pistons  24  is releasably coupled to the ring  30 , it is not necessary for all of the pistons to displace in order for the ring to displace. Thus, the ring  30  can displace upward with less than all of the pistons  24 . 
   In  FIG. 4 , the actuator  22  is depicted in its actuated configuration, as in  FIG. 3 , but in this instance one of the pistons (indicated as element  24   a  in  FIG. 4 ) has experienced a malfunction, so that it has not displaced upwardly with the ring  30  and the remainder of the pistons. The malfunction could be due to a leaking seal on the piston, a mechanical bind between the piston and a bore in which it is received, or any other cause. 
   This is a very beneficial feature of the actuator  22 , since it still permits the actuator to set the packer  12 , even though one or more of the pistons  24  experiences a malfunction. For example, if there are ten of the pistons  24  and one of them experiences a malfunction, then about 90% of the maximum setting force can still be output by the actuator  22  to set the packer  12 . In deep wells, where a round trip to replace a malfunctioning packer is extraordinarily time-consuming and expensive, this feature is very desirable. 
   Referring additionally now to  FIGS. 5 &amp; 6 , the actuator  22  is depicted in its actuated configuration ( FIG. 5 ) and run-in configuration ( FIG. 6 ) in quarter-sectional views. It may now be fully appreciated how the pistons  24  are received in bores  36  formed longitudinally in the tubular structure  26 . In addition, it may be clearly seen how each piston  24  is releasably coupled to the ring  30 . 
   Each piston  24  includes an elongated extension  38  which extends through a respective one of multiple openings  40  formed through the ring  30 . The openings  40  are circumferentially spaced apart in the ring  30 , corresponding to the spacing of the pistons  24  in the bores  36  of the structure  26 . A shoulder  42  formed on each of the extensions  38  is larger than the opening  40  through which the extension  38  extends, so that upward displacement of the piston  24  causes the shoulder to engage the ring  30  and displace it upward with the piston. However, note that the ring  30  can be displaced upwardly without the piston  24  displacing upward. 
   Each of the pistons  24  is depicted as being made up of multiple elements, an extension  38  threaded into a seal-carrying member  44 , but it will be appreciated that the pistons could be made up of more or less elements in keeping with the principles of the invention. The bores  36  in which the members  44  are received are separate from each other, and are preferably at atmospheric pressure when the actuator  22  is used with the packer  12  (i.e., an atmospheric chamber exists in each bore  36  above the member  44 ). Thus, each of the bores  36  may be separately pressure-checked prior to running the actuator  22  (e.g., by pulling a vacuum on the individual bores and checking for leakage), and a leak into one of the bores after running the actuator will not affect operation of the pistons  24  in the other bores. 
   Note that the bore  36  above each member  44  may be at atmospheric pressure when the actuator  22  is initially installed, or it could be at another pressure which is less than the pressure expected in the well at the location at which the actuator is to be positioned when it is actuated. It is not necessary in keeping with the principles of the invention for the bore  36  above each member  44  to be at atmospheric pressure at any particular time, although in a preferred embodiment, the bore above each member is at atmospheric pressure when the actuator  22  is installed in the well. However, another pressure could be used if desired, such as another pressure less than hydrostatic pressure in the well at the location where the actuator  22  is to be positioned. 
   Due to the unique construction and configuration of the actuator  22 , the relatively small diameter multiple pistons  24  and bores  36  are not deformed significantly when exposed to high pressures in a well. By circumferentially spacing apart the bores  36  in the structure  26 , the bores are supported by the sidewall of the structure surrounding each bore. In addition, since the pistons  24  are not annular-shaped, they are not deformed significantly by the pressure applied thereto. Thus, the actuator  22  is capable of satisfactory operation at pressures in excess of 19,000 pounds per square inch in a well. 
   The setting initiation device  32  includes the chamber  46  between two sets of seals  48 ,  50 . It will be readily appreciated by one skilled in the art that, when pressure is applied to the actuator  22  in the well  10 , and the setting initiation device  32  is in the configuration shown in  FIG. 6 , a downwardly directed force will be produced by the setting initiation device. Shoulder screws  52  (six in this embodiment) are threaded into an outer housing  54  of the setting initiation device  32  and extend through the ring  30  (similar to the manner in which the pistons  24  extend through the ring), in order to transfer the downwardly directed force to the ring. 
   When the predetermined pressure is reached, the rupture disk  34  ruptures, and the chamber  46  is exposed to the pressure in the well  10 . Thus, the downwardly directed force formerly produced by the setting initiation device  32  is eliminated, and the upwardly directed force produced by the pistons  24  displaces the ring  30  upwardly (upon shearing shear screws  56  in the setting initiation device  32 ). 
   Positioned above each of the shoulder screws  52  is an elongated member  58  of the force transmission device  28 . The force transmission device  28  includes six of the members  58  in this embodiment. The members  58  extend through respective openings  60  (see  FIG. 7 ) formed longitudinally through the structure  26  and circumferentially spaced apart therein. Thus, as the ring  30  displaces upwardly, the members  58  displace upwardly, as well. 
   In  FIG. 6  it may be seen that the ring  30  is in its downward position (prior to the predetermined pressure being applied) and in an upper portion of the illustration one of the members  58  is visible extending somewhat out of its respective opening  60  in the structure  26 . In  FIG. 5  it may be seen that the ring  30  is in its upwardly displaced position (after the predetermined pressure has ruptured the rupture disk  34 ) and in an upper portion of the illustration one of the members  58  is visible extending further out of its respective opening in the structure  26 . This elongation of the actuator  22  from its lower end  62  to upper ends  64  of the members  58  is used to apply biasing forces to the seal element  16  and slip assembly  18  of the packer  12  in order to set the packer. 
   Referring additionally now to  FIGS. 7 &amp; 8 , the packer  12  is depicted with the actuator  22  installed therein. In  FIG. 8 , a quarter-sectional view shows one of the pistons  24  received in its respective bore  36 . In  FIG. 7 , a quarter-sectional view shows one of the members  58  reciprocably received in one of the openings  60  formed through the structure  26 . Note that the upper end  64  of each member  58  is adjacent a lower end of an annular piston  66 . 
   When the members  58  displace upwardly, the piston  66  will be displaced upwardly by the members and will apply a compressive force to the seal elements  16 , causing them to extend outwardly into sealing engagement with the wellbore  14 . The piston  66  provides a backup, in case the other pistons  24  fail to generate enough force (for example, if one or more of the pistons  24  malfunctions) to displace the members  58  upward and compress the seal elements  16  sufficiently. To utilize the piston  66  as a backup, a pressure differential is applied from an interior flow passage  68  (formed longitudinally through an inner tubular mandrel  70  of the packer  12 ) to an exterior of the packer. When a sufficiently large pressure differential is applied, shear screws  72  will shear and the piston  66  will be displaced upwardly by the pressure differential to compress the seal elements  16 . 
   The lower end  62  of the actuator  22  abuts the slip assembly  18 . When the actuator  22  elongates (between the upper ends  64  of the members  58  and the lower end  62  of the actuator), a downwardly directed force is applied from the lower end of the actuator to the slip assembly  18 . This downwardly directed force causes the slip assembly  18  to extend outward into gripping engagement with the wellbore  14 . 
   Note that, because the actuator  22  is positioned between the seal elements  16  and the slip assembly  18 , the actuator is able to apply a compressive force to the seal elements and to the slip assembly  18 , without the need for the force to be transmitted through one of these to get to the other. In addition, the actuator  22  is preferably not secured directly to the mandrel  70 , but is instead reciprocably mounted on the exterior of the mandrel. Thus, when the actuator  22  elongates, the same force applied upwardly by the actuator via the members  58  toward the seal elements  16  is also applied downwardly by the actuator via the lower end  62  toward the slip assembly  18  (i.e., the forces are equal, but oppositely directed). 
   Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.

Summary:
A packer and actuator therefor configured for use in relatively high hydrostatic pressure environments. In a described embodiment, a packer for use in a subterranean well includes an actuator for setting the packer. The actuator includes multiple pistons circumferentially spaced apart from each other.