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BACKGROUND  
       [0001]     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 pressure communication assembly external to casing with various forms of connectivity to a pressure source.  
         [0002]     It is known to use a chamber positioned in a wellbore and connected to a tube or control line extending to the surface for monitoring pressure in the wellbore. Pressure applied to the tube at the surface provides an indication of pressure in the wellbore at the chamber. Such systems are described in U.S. Pat. Nos. 4,976,142 and 5,163,321, and in U.S. Patent Application Publication No. 2004-0031319. The entire disclosures of these documents are incorporated herein by this reference.  
         [0003]     However, these prior systems involve installing completion or production equipment in the wellbore and (if casing or liner and cement is installed) perforating the casing or liner and cement, or otherwise forming a fluid path between the wellbore and a formation or zone of interest. These operations are relatively expensive and time-consuming. In addition, the equipment installed in the wellbore at least partially obstructs the wellbore.  
         [0004]     Therefore, it may be seen that improvements are needed in the art of monitoring pressure in wells. It is among the objects of the present invention to provide such improvements.  
       SUMMARY  
       [0005]     In carrying out the principles of the present invention, well systems and associated methods are provided which solve at least one problem in the art. One example is described below in which a pressure communication assembly includes a chamber positioned external to a casing string. Another example is described below in which a passage is formed for fluid communication between the chamber and a pressure source after the casing string is cemented in the well.  
         [0006]     In one aspect of the invention, a well system is provided which includes a casing string positioned in the well. A bore extends longitudinally through the casing string. A chamber is attached to the casing string and positioned external to the casing string bore. A device provides fluid communication between an interior of the chamber and a pressure source external to the casing.  
         [0007]     In another aspect of the invention, a method of monitoring pressure in a well includes the steps of: installing a casing string in the well with a chamber positioned external to a through bore of the casing string, and the chamber being isolated from the well external to the casing string; and then actuating a device to thereby provide fluid communication between the chamber and the well external to the casing string.  
         [0008]     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, in which similar elements are indicated in the various figures using the same reference numbers.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a partially cross-sectional schematic view of a well system embodying principles of the present invention;  
         [0010]      FIG. 2  is an enlarged scale cross-sectional schematic view of a pressure communication assembly which may be used in the well system of  FIG. 1 ;  
         [0011]      FIG. 3  is an enlarged scale cross-sectional schematic view of a first alternate construction of the pressure communication assembly;  
         [0012]      FIG. 4  is a cross-sectional schematic view of the first alternate construction, with a passage having been formed between a chamber of the assembly and an earth formation;  
         [0013]      FIG. 5  is a cross-sectional schematic view of a second alternate construction of the pressure communication assembly;  
         [0014]      FIG. 6  is a cross-sectional schematic view of the second alternate construction, with a passage having been formed between a chamber of the assembly and an earth formation;  
         [0015]      FIG. 7  is a cross-sectional schematic view of a third alternate construction of the pressure communication assembly;  
         [0016]      FIG. 8  is a cross-sectional schematic view of a fourth alternate construction of the pressure communication assembly;  
         [0017]      FIG. 9  is a cross-sectional schematic view of the fourth alternate construction, with a passage having been formed between a chamber of the assembly and an earth formation;  
         [0018]      FIG. 10  is a cross-sectional schematic view of a fifth alternate construction of the pressure communication assembly; and  
         [0019]      FIG. 11  is a cross-sectional schematic view of a sixth alternate construction of the pressure communication assembly. 
     
    
     DETAILED DESCRIPTION  
       [0020]     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. The embodiments are described merely as examples of useful applications of the principles of the invention, which is not limited to any specific details of these embodiments.  
         [0021]     In the following description of the representative embodiments of the invention, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. In general, “above”, “upper”, “upward” and similar terms refer to a direction toward the earth&#39;s surface along a wellbore, and “below”, “lower”, “downward” and similar terms refer to a direction away from the earth&#39;s surface along the wellbore.  
         [0022]     Representatively illustrated in  FIG. 1  is a well system  10  which embodies principles of the present invention. A casing string  12  has been installed in a wellbore  14  of the well, and cement  16  has been flowed into an annular space between the casing string and the wellbore. A bore  18  extends longitudinally through the casing string  12 .  
         [0023]     Note that the well system  10  is only one example of a wide variety of possible uses of the invention, and is described herein so that a person skilled in the art will appreciate how the invention is made and used. Accordingly, the casing string  12 , cement  16  and other elements of the well system  10  should be understood to represent a variety of similar elements used in well operations.  
         [0024]     For example, “casing,” “casing string” and similar terms should be understood to include equipment known as “liner” and other forms of protective linings installed in wellbores, whether made of metal, composite materials, expandable materials or other materials, and whether segmented or continuous. As another example, “cement, “cementing” and similar terms should be understood to include any hardenable material used to secure and seal a wellbore lining in a well, such as epoxy or other polymer materials, non-cementitious materials, etc.  
         [0025]     The well system  10  also includes multiple pressure communication assemblies  20 ,  22 ,  24 ,  26  spaced apart along the casing string  12 . As depicted in  FIG. 1 , the pressure communication assemblies  20 ,  22 ,  24 ,  26  are used to monitor pressure in respective spaced apart zones or earth formations  28 ,  30 ,  32 ,  34 . Note that the formations  28 ,  30 ,  32 ,  34  may be individual formations, or merely separate zones within a common formation, and one or more of the formations may be part of a common fluid reservoir.  
         [0026]     Each of the assemblies  20 ,  22 ,  24 ,  26  includes a chamber  36  and a control line or capillary tube  38  connected to the chamber and extending to a remote location, such as the earth&#39;s surface. At the remote location, the tubes  38  are connected to a pressure gauge including, for example, a transducer and instrumentation (not shown) for monitoring pressure applied to the tubes at the remote location. For establishing fluid communication with the formations  28 ,  30 ,  32 ,  34 , each of the assemblies  20 ,  22 ,  24 ,  26  also includes a connectivity device  40 .  
         [0027]     At this point several beneficial features of the well system  10  can be appreciated. The assemblies  20 ,  22 ,  24 ,  26  do not obstruct the bore  18  of the casing string  12 . Completion or production equipment does not have to be installed in the casing string  12  prior to utilizing the assemblies  20 ,  22 ,  24 ,  26 . The casing string  12  does not have to be perforated in order to monitor pressure in the formations  28 ,  30 ,  32 ,  34 .  
         [0028]     Furthermore, although the assemblies  20 ,  22 ,  24 ,  26  are cemented in place along with the casing string  12 , the devices  40  are provided to form passages between the chambers  36  and the formations  28 ,  30 ,  32 ,  34 . Thus, the devices  40  isolate the chambers  36  from the cement  16  during the cementing operation, and subsequently provide fluid communication between the chambers and the formations  28 ,  30 ,  32 ,  34 .  
         [0029]     The use of the multiple assemblies  20 ,  22 ,  24 ,  26  allows the integrity of the cement  16  to be tested after the cementing operation (e.g., to determine whether fluid isolation is achieved by the cement in the annular space between the casing string  12  and the wellbore  14 ). In addition, the multiple assemblies  20 ,  22 ,  24 ,  26  permit vertical interference tests to be conducted between the formations  28 ,  30 ,  32 ,  34 .  
         [0030]     Note that it is not necessary in keeping with the principles of the invention for multiple pressure communication assemblies to be installed, since a single pressure communication assembly could still be used to monitor pressure in a pressure source downhole. Also, it should be understood that an earth formation or zone is only one type of pressure source which may be monitored using the principles of the invention. For example, another pressure source could be the interior bore  18  of the casing string  12 .  
         [0031]     Referring additionally now to  FIG. 2 , a schematic cross-sectional view of a pressure communication assembly  42  which may be used for any of the assemblies  20 ,  22 ,  24 ,  26  in the well system  10  is representatively illustrated. The assembly  42  could be used in other well systems also, without departing from the principles of the invention.  
         [0032]     In this embodiment, the assembly  42  includes a chamber housing  44  which is eccentrically arranged about the casing string  12 . The housing  44  is welded, or otherwise sealed and secured, to the exterior of the casing string  12 , so that the housing becomes an integral part of the casing string. It will be readily appreciated by those skilled in the art that the housing  44  could instead be integrally formed with a section of the casing string  12 .  
         [0033]     A bow spring  46  ensures that the device  40  is biased against an inner wall of the wellbore  14 , so that a large volume of cement  16  is not disposed between the device and the wellbore. This facilitates the later forming of a passage  48  for providing fluid communication between the chamber  36  and a zone or earth formation  50 .  
         [0034]     Referring additionally now to  FIG. 3 , a cross-sectional view of a first alternate construction of the assembly  42  is representatively illustrated. In this view, the cement  16  has been placed about the housing  44  and casing string  12 , but the passage  48  between the chamber  36  and the formation  50  has not yet been formed.  
         [0035]     The device  40  in this construction of the assembly  42  includes a frangible member  52 . The frangible member  52  could be, for example, a rupture disk of the type known to those skilled in the art, and which breaks or otherwise opens in response to a predetermined pressure differential applied across the rupture disk.  
         [0036]     The pressure differential could be applied by applying pressure to the tube  38  connected to the chamber  36  from the surface. However, other methods of applying the pressure differential could be used in keeping with the principles of the invention. For example, a propellant could be ignited to create increased pressure in the chamber  36 , pressure in the chamber and/or external to the chamber could be increased or decreased to apply the pressure differential, etc.  
         [0037]     Referring additionally now to  FIG. 4 , the assembly  42  is depicted after the pressure differential has been applied and the member  52  has broken. As a result, the passage  48  has now been formed between the chamber  36  and the formation  50 .  
         [0038]     In addition, sufficient pressure has been applied to the formation  50  to cause small fractures  54  to be formed in the formation rock. These fractures  54  can increase the mobility of fluid in the formation  50  toward the wellbore  14 , for example, by overcoming the skin damage caused during drilling and other previous operations. Furthermore, those skilled in the formation fracturing and testing arts will appreciate that a variety of characteristics of the formation  50  may be determined using the capabilities of the assembly  42  to directly monitor pressure in the formation, whether or not the fractures  54  are formed.  
         [0039]     For example, the pressure communication assembly  42  may be used to repeatedly test the formation  50  over time by injecting and/or withdrawing fluid into or out of the formation. A transient pressure response of the formation  50  to this fluid transfer may be monitored by the pressure gauge at the remote location. This will enable a determination of properties of the formation  50  (such as relative permeability) over time.  
         [0040]     Repeated micro-transient testing allows the determination of zonal relative permeabilities. This process is made possible by the pressure connectivity to the surface which is provided by the system  10  with the isolated pressure communication assemblies  20 ,  22 ,  24 ,  26  in observation positions relative to the zones or formations  28 ,  30 ,  32 ,  34 . Repeated mini or micro drawdown and build-up pressure testing or injection and fall-off testing can be performed using this system  10  with the assemblies  20 ,  22 ,  24 ,  26  isolated behind the casing string  12  for monitoring pressure of single zones that are not producing in this well. Pressure transient analysis of this data can determine changes in reservoir permeability due to fluid saturation changes within the zones over time.  
         [0041]     Note that it is not necessary in keeping with the principles of the invention for the fractures  54  to be formed. The passage  48  could be formed without also forming the fractures  54 .  
         [0042]     Referring additionally now to  FIG. 5 , a schematic cross-sectional view of another alternate construction of the assembly  42  is representatively illustrated. In this embodiment, the device  40  includes a member  56  which is displaced in response to application of a predetermined pressure differential.  
         [0043]     The member  56  could be, for example, a plug of the type known as a pump-out plug or disc. Instead of breaking like the frangible member  52  described above, the member  56  displaces when the pressure differential is applied.  
         [0044]     Referring additionally now to  FIG. 6 , the assembly  42  is depicted after the member  56  has displaced and the passage  48  between the chamber  36  and the formation  50  has been formed. The fractures  54  may be formed if desired, as described above.  
         [0045]     Referring additionally now to  FIG. 7 , a schematic cross-sectional view of another alternate construction of the assembly  42  is representatively illustrated. This alternate construction is similar in most respects to the  FIG. 2  embodiment. However, as depicted in  FIG. 7  the assembly  42  includes multiple connectivity devices  40 , the housing  44  is concentrically arranged about the casing string  12 , and no bow spring  46  is used to bias the housing to one side of the wellbore  14 .  
         [0046]     Since the devices  40  are not biased against the walls of the wellbore  14  by the bow spring  46 , the devices  40  in the  FIG. 7  embodiment may include features which permit them to be extended outward upon installation of the assembly  42  in the well. In this manner, the presence of the cement  16  between the devices  40  and the formation  50  may be eliminated, or at least substantially reduced.  
         [0047]     Referring additionally now to  FIG. 8 , a schematic cross-sectional view of another alternate construction of the assembly  42  is representatively illustrated. Similar to the  FIG. 7  embodiment, this construction of the assembly  42  includes two of the connectivity devices  40 .  
         [0048]     As depicted in  FIG. 8 , the assembly  42  and casing string  12  have been installed in the wellbore  14 , but they have not yet been cemented therein. Instead, mud  58  fills the annular space between the housing  44  and the wellbore  14  at this point.  
         [0049]     The devices  40  each include an extension member  62  in the form of a sleeve having a piston externally thereon. The piston is received in a seal bore in an outer sleeve  64 . A frangible member  52 , similar to that used in the  FIG. 3  embodiment and described above, closes off the interior of the extension member  62 .  
         [0050]     When a predetermined pressure differential is applied to the devices  40 , the extension members  62  will displace radially outward to approach or preferably contact the inner wall of the formation  50  on each side of the housing  44 . In this manner, the presence of cement  16  between the frangible members  52  and the wellbore  14  may be reduced or eliminated. The extension members may be displaced radially outward prior to and/or during the cementing operation.  
         [0051]     Referring additionally now to  FIG. 9 , the assembly  42  is representatively illustrated after the extension members  62  have been extended outward, the cement  16  has been placed about the housing  44 , and the frangible members  52  have been broken. The frangible members  52  are broken in a manner similar to that described above for the  FIG. 3  embodiment, by applying an increased pressure differential to the devices  40  after the extension members  62  are extended outward.  
         [0052]     When the frangible members  52  are broken, the passages  48  are formed, thereby providing fluid communication between the chamber  36  and the formation  50 . In addition, fractures  54  may be formed if desired, as described above.  
         [0053]     Referring additionally now to  FIG. 10 , a schematic cross-sectional view of another alternate construction of the assembly  42  is representatively illustrated. This embodiment is similar to the embodiment of  FIGS. 7-9 , in that it includes multiple connectivity devices  40 . However, the assembly  42  depicted in  FIG. 10  includes explosive charges  60  in the connectivity devices  40 .  
         [0054]     The explosive charges  60  are preferably of the type used in well perforating guns and known as shaped charges. Other types of explosive charges may be used if desired, any number of explosive charges may be used, and the explosive charges may be detonated in any manner (for example, mechanically, electrically, hydraulically, via telemetry, using a time delay, etc.) in keeping with the principles of the invention.  
         [0055]     As depicted in  FIG. 10 , the assembly  42  and casing string  12  have been cemented in the wellbore  14 . The explosive charges  60  may now be detonated to thereby form the passages  48  and provide fluid communication between the formation  50  and the chamber  36 .  
         [0056]     Referring additionally now to  FIG. 11 , another alternate embodiment of the assembly  42  is representatively illustrated. In  FIG. 11 , the assembly  42  and casing string  12  are shown apart from the remainder of the well system  10  for clarity and convenience of illustration and description, but it should be understood that in actual practice the assembly and casing string would be installed in the wellbore  14  as described above and depicted in  FIG. 1 . Of course, the assembly  42  of  FIG. 11  may be used in other well systems in keeping with the principles of the invention.  
         [0057]     The assembly  42  of  FIG. 11  is similar to the assembly of  FIG. 10 , in that it includes the explosive charges  60  for providing fluid communication between the chamber  36  and the formation  50 . However, the assembly  42  as depicted in  FIG. 11  is secured to the exterior of the casing string  12 , for example, using clamps  66  and the explosive charges  60  are vertically aligned, rather than being radially opposite each other as in the  FIG. 10  embodiment.  
         [0058]     In addition, a pressure operated firing head  68  is included in the device  40  for controlling detonation of the explosive charges  60 . The firing head  68  may be similar to conventional pressure operated firing heads used for well perforating guns. The firing head  68  may be used to detonate the charges  60  in the  FIG. 10  embodiment, if desired. The explosive charges  60  are preferably detonated after the assembly  42  and casing string  12  have been cemented in the wellbore  14 .  
         [0059]     A predetermined pressure differential applied to the firing head  68  causes the firing head to detonate the explosive charges  60 , thereby forming the passages  48  and providing fluid communication between the chamber  36  and the formation  50 . The pressure differential may be between, for example, the chamber  36  and an internal chamber of the firing head  68 . The pressure differential may be applied to the firing head  68  by applying pressure to the chamber  36  via the tube  38  from a remote location, such as the surface.  
         [0060]     It may now be fully appreciated that the well system  10  and associated methods described above provide many benefits in well operations and monitoring of downhole pressure. Furthermore, a variety of new techniques have been described for providing fluid communication between the formation  50  and the chamber  36  of the assembly  42 . It should be clearly understood that the invention is not limited to only these techniques, since other techniques could be used in keeping with the principles of the invention.  
         [0061]     In addition, although the formation  50  and the formations  28 ,  30 ,  32  and  34  of  FIG. 1  are described above as being pressure sources to which the chamber  36  may be connected downhole, other pressure sources could be connected to the chamber in keeping with the principles of the invention. For example, the chamber  36  could be placed in fluid communication with the interior of the casing string  12  by positioning the frangible member  52 , plug member  56  or explosive charges so that the passage  48  is formed between the chamber and the bore  18  of the casing string. Thus, the interior of the casing string  12  could be a pressure source which is connected to the chamber  36  downhole.  
         [0062]     Once the chamber  36  is placed in fluid communication with the pressure source downhole, pressure in the pressure source may be monitored by displacing a known fluid (such as helium, nitrogen or another gas or liquid) through the tube  38  and into the chamber. Pressure applied to the tube  38  at the surface or another remote location to balance the pressure applied to the chamber downhole by the pressure source provides an indication of the pressure in the pressure source. Various techniques for accurately determining this pressure (including use of optical fiber distributed temperature sensing systems, etc.) are well known to those skilled in the art, and some of these techniques are described in the U.S. patents and patent application discussed above.  
         [0063]     Even though the pressure communication assembly  42  and its alternate embodiments have been illustrated and described as each including only one type of the device  40  (for example, including the frangible member  52 , displaceable member  56  or explosive charge  60 ), it will be appreciated that any combination of the types of devices could be provided in a pressure communication assembly (for example, to provide redundancy). Furthermore, any number of the devices  40  may be provided in the pressure communication assembly  42  and its alternate embodiments.  
         [0064]     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 within the scope of 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 pressure communication assembly external to casing with various forms of connectivity to a pressure source. A well system includes a casing string positioned in the well, with a bore extending longitudinally through the casing string; a chamber attached to the casing string and positioned external to the casing string bore; and a device which provides fluid communication between an interior of the chamber and a pressure source external to the casing. A method of monitoring pressure in a well includes the steps of: installing a casing string in the well with a chamber positioned external to a through bore of the casing string, and the chamber being isolated from the well external to the casing string; and then actuating a device to thereby provide fluid communication between the chamber and the well external to the casing string.