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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       REFERENCE TO APPENDIX  
       [0003]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0004]     1. Field Of The Invention  
         [0005]     This disclosure relates generally to an isolation system for oil and gas wells and, more particularly, to a formation isolation system comprising a first integral and actuatable isolation device and a second isolation device.  
         [0006]     2. Description Of The Related Art  
         [0007]     A typical hydrocarbon well may utilize one or more gravel packs and screen assemblies to enhance production from, for example, unconsolidated formations. It is desirable in such wells to isolate each producing formation using a variety of flow control devices, such as packers and valves. It is also desirable to provide bi-directional isolation and interventionless actuation, such as interventionless opening, of one or more of the isolation devices. It is not unheard of, however, for the interventionless or mechanical actuation system to become fouled and unusable. In such circumstances, the isolation device, such as, for example, a ball valve, may need to be be drilled or milled out of the completion string. Such fouling and recovery efforts are obviously undesirable.  
         [0008]     This application for patent discloses an improved isolation system and method of use comprising a first isolation device that is integral with the system, such as a pressure actuated valve or mechanically actuated valve, and a second isolation device, such as a plug, so that when both devices are closed, the formation is isolation and when the first device is open and the second device is closed, the formation is not isolated.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     One aspect of the invention comprises an isolation system for an oil or gas well having an isolation section and a first isolation device integral with the isolation section. A second isolation device comprising a plug may be sealingly coupled to the isolation section such that a hydrocarbon-bearing formation adjacent the isolation system is isolated from production when the first and second isolation devices are closed and such that the formation is not isolated from production when the first isolation device is opened and the second device remains closed.  
         [0010]     Another aspect of the invention comprises a method of isolating a reservoir in a well by providing an isolation system comprising an integral first isolation device and a sealing portion for a second isolation device; inserting a plug as the second isolation device into the isolation system to isolate the formation; and removing the formation isolation by interventionlessly actuating the first isolation device while the second device remains closed. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0011]      FIG. 1  illustrates an isolation system according to the present invention prior to completion.  
         [0012]      FIG. 2  illustrates an isolation system according to the present invention after a service tool has been run out of the well and prior to completion.  
         [0013]      FIG. 3  illustrates the isolation system of  FIG. 2  prior to setting the second isolation device.  
         [0014]      FIG. 4  illustrates the isolation system of  FIG. 3  after the second isolation device has been locked in place.  
         [0015]      FIG. 5  illustrates the isolation system of  FIG. 4  after the second isolation device has been released from a service tool.  
         [0016]      FIG. 6  illustrates the isolation system with the reservoir below the isolation system sealed off from production.  
         [0017]      FIG. 7  illustrates the isolation system of  FIG. 6  after the first isolation device has been opened to allow production from the reservoir. 
     
    
       [0018]     While the inventions disclosed herein are susceptible to various modifications and alternative forms, only a few specific embodiments are shown by way of example in the drawings and are described in detail below. The figures and detailed descriptions of these specific embodiments are not intended to limit the breadth or scope of the inventive concepts or the appended claims in any manner. Rather, the figures and detailed written descriptions are provided to illustrate the inventive concepts to a person of ordinary skill in the art as required by 35 U.S.C. § 112.  
       DETAILED DESCRIPTION  
       [0019]     One or more illustrative embodiments incorporating the invention disclosed herein are presented below. Not all features of an actual implementation are necessarily described or shown for the sake of clarity. For example, the various seals, vents and others design details common to oil well equipment are not specifically illustrated or described. It is understood that in the development of an actual embodiment incorporating the present invention, numerous implementation-specific decisions must be made to achieve the developer&#39;s goals, such as compliance with system-related, business-related and other constraints, which vary by implementation and from time to time. While a developer&#39;s efforts might be complex and time-consuming, such efforts would be, nevertheless, a routine undertaking for those of ordinary skill the art having benefit of this disclosure. Also, the use in this application of relative terms, such as, but not limited to, left, right, up, down, inside and outside, is not meant to preclude interchanging one for the other in other embodiments. Such relative terms are merely used for clarity of discussion of the particular embodiments disclosed herein.  
         [0020]     In general terms, a formation isolation system has been created comprising a first isolation device integral with the isolation system in the well bore and a second isolation device that is not integral with the isolation system, which devices in combination isolate the formation of interest. The first isolation device may comprise a valve, such as a mechanical on/off valve, a variable choke valve, a shifting sleeve valve, a hydraulic or applied pressure actuated on/off or variable choke valve, or any combination thereof.  
         [0021]     The second isolation device may comprise a plug. Once the first and second isolation devices achieve zonal isolation, the first isolation device may be selectively opened, such as by pressure actuation or mechanical actuation, to permit productive flow from the previously isolated formation and thereafter closed to again isolate the particular formation. The second isolation device may be retrieved from the well or simply removed from its seat for post-completion services, as desired.  
         [0022]     Turning now to  FIG. 1  for a more detailed description of a presently preferred embodiment of the present invention, a completion system  10  is illustrated comprising a screen assembly  20  positioned adjacent a producing and usually unconsolidated formation (not shown). The screen assembly  20  is shown positioned up hole from a packer  30 , which effectively seals the completion system  10  above and below the packer  30 . The completion system  10  further comprises an isolation system  12 , which in the embodiment illustrated in  FIG. 1  comprises a first isolation device  16  comprising a mechanical valve  50  and a pressure actuated valve  60 , and a second isolation device profile lock  40 . Also shown in  FIG. 1  is an upper packer  70  and service tool  80 .  
         [0023]     As illustrated in  FIG. 1 , the mechanical valve  50  of the first isolation device  16  is shown in the open condition, which permits fluid communication between the annular region  14  adjacent the isolation system  12  and the inside of the completion system  10 .  
         [0024]     The pressure-actuated valve  60  of the first isolation device  16  is shown in the closed position. In this particular embodiment, the pressure-actuated valve  60  is biased to the closed position.  
         [0025]     Prior to isolating the particular formation adjacent screen assembly  20 , the service tool  80  may be withdrawn from the completion system  10 . As the service tool is withdrawn, a shifting profile  82  may engage a corresponding profile  52  on the mechanical valve  50  to close the valve, thereby precluding fluid communication across the valve.  FIG. 2  illustrates the completion system  10  with the first isolation device  16 , i.e., the pressure actuated valve  60  and the mechanical valve  50 , in the closed position.  
         [0026]      FIG. 3  illustrates a second isolation device  18  in the form of a plug  90  being run into the well and the completion system  10  by service tool  80 . In this sense, the second isolation device  18  is not integral to the isolation systems  12  as compared to first isolation device  16 . The tool profile  82  engages the corresponding profile on mechanical valve  50  and opens the valve. The isolation plug  90  and locking profile  40  are constructed such that the plug  90  can pass through the profile  40  when a locking element  42  is in an initial position (position  44  shown in  FIGS. 1 and 2 ). The service tool profile  82  engages the locking profile element  42  and causes the element  42  to move to a secondary position  46 . Continued travel of the tool  80  releases the profile  82  from the element  42 .  
         [0027]     As illustrated in  FIG. 4 , subsequent up hole travel of the tool  80  causes the isolation plug  90  to engage the locking element  42 . Because the mechanical valve  50  is in the open state, the well pressure above and below the isolation plug  90  is substantially equal and fluid communication exists above and below the plug  90 . When the plug  90  is locked into place with locking profile  40 , the plug  90  and profile  40  create a fluid tight seal to well fluid pressures above and below the plug  90 . The sealing system utilized by the second isolation device  18  may comprise elastomers, such as o-rings or other materials suitable for the intended environment.  
         [0028]     Continued up hole travel of the service tool  80  causes the isolation plug  90  to release from the tool  80 . In the presently described embodiment, the isolation plug  90  is releasably locked to the tool  80  by one or more shearable pins  92  having combined shear strength of between about 10,000 and 20,000 pounds of force. It will be appreciated that selection of the type of the releasable lock (such as shear pins, retractable dogs and other equivalent structures) and the loads or pressures at which the lock releases, are well within the design choice of those of ordinary skill in this art having benefit of this disclosure.  
         [0029]      FIG. 5  illustrates the isolation plug  90  locked into position in the isolation system  12  after the preferred shear pins  92  have been released.  FIG. 5  also illustrates that the service tool profile  82  engages the mechanical valve profile  52  once again and closes the valve  50 .  
         [0030]      FIG. 6  illustrates the well, or at least the particular formation adjacent screen assembly  20 , in a closed-in condition. This closed-in or isolated condition is formed by the closed mechanical valve  50  and the closed pressure actuated valve  60 , which comprise the integral first isolation device  16 , and the sealed plug  90 , which comprises the second isolation device  18 . In this condition, production fluids from the formation adjacent the screen assembly  20  may not enter the interior of the completion system  10  up hole of the isolation system  12 .  
         [0031]     When it is desired to produce fluids from the formation of interest, the presently described embodiment allows such production to begin without intervening into the well.  
         [0032]     For example, the pressure-actuated valve  60  of the first isolation device  16  may be any of a number of conventional pressure actuated valves, such as the Pressure Actuated Circulating Valve offered by BJ Services. As is typical for these types of valves, actuation is initiated by applying differential pressure from the valve ID to the OD.  
         [0033]     Initial actuation pressure unlocks the valve while maintaining pressure integrity.  
         [0034]     Reducing the actuation pressure to equal the annular pressure allows the valve to cycle to the full open position. Other types and designs of interventionless-open valves may be used as well.  
         [0035]     Once opened, as illustrated in  FIG. 7 , well fluids may flow from the formation through the screen assembly  20  into the completion system  10  below the isolation system  12 , in to the annular region  14 , through the now-opened pressure actuated valve  60  and into the interior of the completion system  10  above the isolation system  12 .  
         [0036]     In the event that the pressure-actuated valve  60  fails to open, the valve  60  may be fitted with a mechanical opening and or closing system. For example, the BJ Services Pressure Actuated Circulating Valve includes a backup mechanical shifting profile that allows the valve to be opened and closed with a service tool  80  such as BJ Services Multi-Action Shifting Tool. It will be appreciated that the mechanical valve  50  described above may also be opened with a similar service tool.  
         [0037]     The flow areas in the presently preferred embodiment are designed to be substantially similar so that no one component acts as a substantial flow restrictor. For example, an embodiment incorporating the present invention may be constructed such that the primary flow path through the first isolation device  16 , e.g., pressure actuated valve  60 , has a inside diameter (ID) of about 4.5 inches, yielding an ID flow area of about 15.9 square inches. The valved flow area through valve  60  may be about 17.0 square inches comprising 8 flow slots 3.0 inches long by 0.75 inch wide. The flow area through the annular region  14  may be about 16.8 square inches and the flow are through the screen assembly may be about 17.9 square inches. Thus, in the presently preferred embodiment, the relevant flow areas are substantially the same. This type of design can limit additional pressure drop across the isolation system  12  during production to about 1 psi at 10,000 barrels of oil per day; about 2.3 psi at 20,000 BOPD and about 5.3 psi at 30,000 BOPD. For injection services, the additional pressure drop may be limited to about 1 psi at 30,000, 40,000 and 50,000 BOPD.  
         [0038]     The second isolation device  18 , which in this presently preferred and described embodiment is isolation plug  90 , may be retrieved by conventional means, such as a service tool  80 , or it may be knocked loose from its sealed position to allow post-completion servicing of the well. For example, isolation plug  90  may be constructed with a release system  94  that permits a service tool to both engage the plug for retrieval and release it from its locked and sealed position. Alternately, the release  94  may be actuated with out engaging the plug  90 , thereby allowing the plug to fall or float, as the case may be. If the plug  90  becomes stuck in the locking profile  40  and cannot be retrieved or knocked loose, the plug can be milled or drilled out of the isolation system  12 . For embodiments that use a plug as the second isolation device  18 , the plug may be of conventional construction, including, but not limited to, alloy steel, aluminum or composite materials. It will often times be desirable to construct the plug or other second isolation device  18  to be more easily drilled or milled than a conventional alloy steel ball valve isolation device.  
         [0039]     The embodiment described above is only one of many different embodiments that may be constructed to capitalize on the present invention. For example, although the first isolation device  16  of the preferred embodiment comprises a mechanical valve  50 , such as the Multi-Service Valve offered by BJ Services, and a pressure actuated valve  60 , such as the Pressure Actuated Circulating Valve offered by BJ Services, embodiments of the present invention may be constructed in which the first isolation device comprises a mechanical valve only or a pressure actuated valve only or any combination of other valves. Further, the second isolation device  18  may be constructed with a built-in fluid bypass to equalize well fluid pressure above and below the device while it is being locked in position. In the embodiments illustrated above, for example  FIG. 5 , removing the service tool  80  from the second isolation device  18  may cause the fluid bypass to close.  
         [0040]     It will be appreciated by those of ordinary skill in this art having the benefit of this disclosure that features illustrated with respect to the embodiments described herein may have application or utility with another embodiment described herein or with another embodiment of the invention inspired by this disclosure. For example, the embodiments illustrated herein have been described in terms axially acting sleeve valves. It is well within the scope of the invention to utilize other types of mechanically and pressure actuated valves. The invention has been described in the context of preferred and other embodiments and not every possible embodiment of the invention has been described. Obvious modifications and alterations to the described embodiments are available to those of ordinary skill in the art. The disclosed and undisclosed embodiments are not intended to limit or restrict the scope or applicability of the invention, but rather, in conformity with the patent laws, this patent is intended to protect all such modifications and improvements to the full extent that such falls within the scope or range of equivalent of the following claims.

Summary:
An isolation system for an oil and gas well is described wherein the system comprises an isolation section and a first isolation device integral with the section and a second isolation device sealingly engaged to the section. The first isolation device may be a pressure-actuated valve and the second isolation device may be a plug.