Abstract:
A multi-stage setting tool actuated by hydrostatic pressure downhole is provided with a selectable force-time profile during setting. A first port opens a first piston chamber to hydrostatic pressure which drives a first piston. A force-transmitting member, attached to the piston, is driven in response to the fluid pressure increase in the chamber. The process is repeated with sequential ports and piston chambers. A settable tool is set in response to the driving of the force-transmitting member by the pistons. The combined stroke distances and forces of the pistons are selected to set the tool. Opening of the ports can occur in response to electrical signal and can be conditional on occurrence of a selected event or condition. Speed of setting can be regulated.

Description:
FIELD 
       [0001]    Methods and apparatus are presented for a setting tool operable using wellbore hydrostatic pressure, and more particularly, to a setting tool having a customizable force-time profile. 
       BACKGROUND 
       [0002]    Without limiting the scope of the present inventions, their background is described with reference to setting tools, downhole force generators and downhole power units and improvements thereto. It is typical in hydrocarbon wells to “set” or actuate downhole tools, such as packers, bridge plugs, high-expansion gauge hangers, straddles, wellhead plugs, cement retainers, through-tubing plugs, etc. Additionally, some of these tools are later “unset” for retrieval. Setting tools are run-in, and in some cases retrieved, using various conveyance methods such as a wireline, slickline, or coiled tubing. The generic name for the running tool which provides the large setting forces required is a setting tool. Several types of setting tool and downhole force generators (DFG) are known in the art, including those operated mechanically, electrically, chemically, explosively, hydraulically, electro-mechanically, etc. 
         [0003]    One type of DFG uses electro-mechanical power, where the DFG converts electrical power, typically provided by a battery unit, into mechanical movement, typically rotary or longitudinal movement of a shaft or power rod. One such setting tool is the DPU (trade name) Downhole Power Unit available from Halliburton Energy Services, Inc. Halliburton&#39;s DPU provides an even stroke with a force profile that gradually builds over time. However, the DPU requires a large stack of batteries to drive the motor. The power output needed from the batteries limits the maximum operating temperature for the batteries and for the tool. The use of relatively large quantities of lithium batteries, for higher temperature operations, limits the ability to easily transport the DPU and is a significant cost driver. 
         [0004]    Additionally, some industry pyrotechnic setting tools, such as the Baker 20 Setting Tool, available from Baker Oil Tools, Inc., utilize a pyrotechnic material to generated pressure. A chamber containing a high pressure gas houses a floating hydraulic piston with an oil filled chamber below. The hydraulic oil is pressured by the expanding gas, providing hydraulic power which performs the setting task. Disadvantages to such pyrotechnic setting tools include compliance with extensive and costly regulations, including special shipping and handling by trained personnel, storage on licensed premises, third party notification when shipping, inspections by official personnel, and routine inspections. Further, The Baker 20 setting tool delivers peak force at the beginning of the stroke with diminishing force afterwards, especially as the gas generated by the pyrotechnic reaction cools. 
         [0005]    Hydrostatic setting tools convert ambient hydrostatic pressure in a wellbore into hydraulic force to set the downhole tool. But many prior art hydraulic setting tools suffer from a very quick force-time profile, where the hydrostatic pressure is applied very quickly. The components in the setting tool then move in response at rapid speeds, which can damage sealing elements and break metallic components. 
         [0006]    Further disclosure relating to downhole force generators, their operation and construction, can be found in the following, which are each incorporated herein for all purposes: U.S. Pat. No. 7,051,810 to Clemens, filed Sep. 15, 2003; U.S. Pat. No. 7,367,397 to Clemens, filed Jan. 5, 2006; U.S. Pat. No. 7,467,661 to Gordon, filed Jun. 1, 2006; U.S. Pat. No. 7,000,705 to Baker, filed Sep. 3, 2003; U.S. Pat. No. 7,891,432 to Assal, filed Feb. 26, 2008; U.S. Patent Application Publication No. 2011/0168403 to Patel, filed Jan. 7, 2011; U.S. Patent Application Publication Nos. 2011/0073328 to Clemens, filed Sep. 23, 2010; 2011/0073329 to Clemens, filed Sep. 23, 2010; 2011/0073310 to Clemens, filed Sep. 23, 2010; and International Application No. PCT/US2012/51545, to Halliburton Energy Services, Inc., filed Aug. 20, 2012. 
         [0007]    It is an object of the invention then, to provide a downhole force generator or setting tool with a relatively low cost. It is a further object of the invention to provide a DFG capable of operation in high temperature environments. It is a further object of the invention to provide a DFG which delivers high force over a long stroke. It is a further object of the invention to provide a DFG having a customizable force-time profile. It is a further object of this invention to provide a setting tool which is not subject to the regulations and restrictions of typical pyrotechnic setting tools. Other objects and benefits will be apparent to those of skill in the art. 
       SUMMARY 
       [0008]    In aspects, the present disclosure provides methods and apparatus for setting a tool positioned in a subterranean wellbore. In one embodiment, a method is presented for providing a multi-stage setting force for setting a downhole tool positioned in a subterranean wellbore. In an exemplary method, a first port is opened to a first piston chamber having a first piston mounted therein for sliding movement. A fluid at hydrostatic pressure, flows into the first pressure chamber through the first port, thereby driving the first piston. A force-transmitting member, attached to the first piston, is driven in response to the fluid pressure increase in the first chamber. These steps complete the first stage of the multi-stage setting. A second port is later opened to a second piston chamber, fluidly isolated from the first piston chamber. A fluid at hydrostatic pressure flows into the second piston chamber through the second port, thereby driving the second piston. A force-transmitting member, in operable arrangement with the second piston member, is driven in response to the fluid pressure increase in the second chamber. Thereby, a settable downhole tool is set in response to the driving of the force-transmitting member. The force-transmitting member is driven a first stroke distance in response to a first stroke force created by flowing fluid into the first chamber and a second stroke distance in response to a second stroke force created by flowing fluid into the second chamber. The combined stroke distances and force are selected to set the downhole tool. The second stage of setting, beginning with actuation of the second openable port, is completed when movement stops in response to the fluid flowing into the second chamber. In a preferred embodiment, the second stage begins only after completion of the first stage. Alternately, the second stage can be timed or selected to begin prior to completion of the first stage. The actuation of the stages can occur in response to an electrical signal from the surface, from a battery powered unit downhole, or other methods known in the art, or upon a signal initiated upon the occurrence of a selected event or condition, such as the position of a tool element. The selectively openable ports are preferably electronic rupture discs and can also be valves or other openable or removable fluid barriers. In a preferred embodiment, the method the speed of setting is controlled or regulated, for example, by use of fluid metering devices such as flow nozzles, orifices, inflow control devices, autonomous inflow control devices, or weep holes. The design is modular and can incorporate the addition of third, fourth, etc., stages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
           [0010]      FIG. 1  is a schematic view of a well system including an embodiment of the invention positioned in a subterranean wellbore; 
           [0011]      FIGS. 2A-C  are schematic views of an exemplary embodiment of a multi-stage setting tool according to an aspect of the invention with  FIG. 2A  a schematic view of the multi-stage setting tool in an initial or run-in position,  FIG. 2B  a schematic view of the embodiment of  FIG. 2A  seen in an intermediate or First Stage position, and  FIG. 2C  a schematic view of the embodiment of  FIGS. 2A-B  in a final or Second Stage position; and 
           [0012]      FIG. 3  is a graphical representation of the force-time profile for the setting tool described in  FIGS. 2A-C ; 
           [0013]      FIG. 4  is a schematic detail of a preferred embodiment according to an aspect of the invention, and having an inflow control device for controlling fluid ingress to the tool chambers; 
           [0014]      FIGS. 5A-C  are schematic views of an alternative exemplary embodiment of a multi-stage setting tool according to an aspect of the invention with  FIG. 5A  a schematic view of a multi-stage setting tool in a run-in position,  FIG. 5B  a schematic view of the embodiment of  FIG. 5A  seen in an intermediate position, and  FIG. 5C  a schematic view of the embodiment of  FIGS. 5A-B  seen in a final position; and 
           [0015]      FIGS. 6A-C  are schematic views of an alternative exemplary embodiment of a multi-stage setting tool according to an aspect of the invention with  FIG. 6A  a schematic view of a multi-stage setting tool in a run-in position,  FIG. 6B  a schematic view of the embodiment of  FIG. 6A  seen in an intermediate position, and  FIG. 6C  a schematic view of the embodiment of  FIGS. 6A-B  seen in a final position. 
       
    
    
       [0016]    It should be understood by those skilled in the art that the use of directional terms such as above, below, upper, lower, upward, downward and the like are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure. Where this is not the case and a term is being used to indicate a required orientation, the Specification will state or make such clear. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0017]    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. 
         [0018]    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. 
         [0019]    The inventions disclosed herein are for multi-stage setting tools using downhole hydraulic power to provide downhole force for setting oilfield tools. The preferred embodiments of the invention provide multiple useful features. The tool is preferably electrically activated, with activation by a signal sent via wireline, wireless telemetry or a timer circuit. Wellbore fluid enters the tool via electronic rupture discs, such as Halliburton&#39;s thruster assembly or Halliburton&#39;s thermite-based rupture disc. The preferred embodiments provide for multi-stage activation, with multiple ports used to adjust the force-time profile of the tool stroke. For example, two electronic rupture discs (ERDs) are used to control flow through the two ports. The second ERD is delayed, by the use of a fluid flow device (e.g., fluid diode), check valve, or timer-operated ERD, and subsequently activated at a predetermined time, upon a predetermined contingent (pressure, temperature, rod displacement, etc.) as measured by downhole sensors, or by the user. 
         [0020]      FIG. 1  is a schematic view of a well system including an embodiment of the invention positioned in a subterranean wellbore. A well system  10  is depicted having a wellbore  12  extending through a subterranean formation  14 , shown having casing  16 . The invention can be used in cased or uncased wells, vertical, deviated or horizontal wells, and for on-shore or off-shore drilling. A tubing string  18  is shown having a plurality of tubing sections  20 , a settable downhole tool  30 , a downhole force generator (DFG) assembly  40 , and a force multiplier assembly  50 . A mechanical linkage assembly  60  between the DFG and the downhole tool is provided for transferring the power generated by the DFG into longitudinal or rotary movement, such via a shaft, piston, sleeve, etc. The DFG assembly preferably includes a processor to operate the tool, measure environmental and tool parameters, etc. The settable downhole tools operable by DFG units are not described herein and are well known in the art. For ease of discussion, and by way of example, settable downhole tools such as settable tool  30 , shown as a packer, may be utilized in sealing and anchoring the tubing string at a downhole location. The packer has sealing elements  32  which may be set, along with slips, anchors, etc., as is known in the art. 
         [0021]    The exemplary setting tools described herein are discussed using general schematics. The details and potential designs, details and specifics are known in the art or will be recognized by one of skill in the art. For disclosure relating to setting tools, see the references incorporated herein. 
         [0022]      FIGS. 2A-C  are schematic views of an exemplary embodiment of a multi-stage setting tool according to an aspect of the invention.  FIG. 2A  is a schematic view of a multi-stage setting tool in an initial or run-in position.  FIG. 2B  is a schematic view of the embodiment of  FIG. 2A  seen in an intermediate or First Stage position.  FIG. 2C  is a schematic view of the embodiment of  FIGS. 2A-B  seen in a final or Second Stage position. 
         [0023]    The setting tool  100  is seen in an initial or run-in position and generally describing a setting tool housing  102  defining a first interior chamber  104  and a second interior chamber  106 . Each chamber has an inlet port, a first and second inlet port  108  and  110 , respectively, selectively providing fluid communication between the interior chamber and the annular space defined in the wellbore. Positioned in the first and second ports are a first and second openable or removable fluid barriers,  112  and  114 , respectively. 
         [0024]    A first piston member  116  is mounted for sliding movement in the first chamber  104  and attached to piston rod  118 . A second piston member  120  is mounted for sliding movement in second chamber  106  and attached to the same piston rod  118 . The piston members  116  and  120  are shown schematically and can be cylindrical piston heads, annular pistons, piston sleeves, piston mandrels, etc., as are known in the art. The piston rod  118  extends from second piston member  120  in the second chamber  106  into and through the first chamber  104 , in which the first piston member is located. In a preferred embodiment, the piston rod extends through a hole  124  through a dividing wall  122  between the first and second chambers. The piston rod further extends beyond the setting tool housing  102  and is attachable to a settable tool. In a preferred embodiment, the piston rod extends through a hole  126  in housing end wall  128 . The holes  124  and  126  are sealed about the piston rod and allow reciprocation of the rod. It is understood that the piston rod can be a single length of rod or multiple pieces connected together to form the piston rod, such as by threaded connection, bolted, welded, pin, etc. The free end  130  of the rod is attachable to a settable downhole tool or member thereof, as is known in the art. 
         [0025]    The selectively openable ports  108  and  110  are preferably initially blocked by fluid barriers. In a preferred embodiment, the fluid barriers are rupture discs and more specifically electronic rupture discs (ERDs). ERDs and rupture discs are known in the art by those of skill. The discs can be made of plastic, rubber, metal, ceramic, etc., and can be removed or opened by puncturing, rupturing, melting, burning, etc. Further, the discs can be removed or opened by fluid pressure, mechanical contact, application of chemicals, fluid or heat, etc. In a preferred embodiment, ERDs are employed and are actuated by an electrical charge delivered by wire from the surface, from carried batteries, and/or wireless transmission. 
         [0026]    In alternative embodiments, the selectively openable ports can be valves, such as, for example, solenoid-driven valves, ball valves, gate valves, and the like, or other mechanisms and methods for blocking fluid passage. Where multiple openable ports are used, various types of openable ports can be employed at various points on the tool. Further, the selectively openable ports can be reciprocating, that is, able to be opened and closed, or simply openable, that is, once opened the port cannot be closed until retrieved to the surface. 
         [0027]    The ERD can be an electrically powered mechanical mechanism, such as the thruster or “pin pusher” assembly or, alternately, thermite-based rupture discs, as disclosed in U.S. Patent Application Publication No. 2011/0174504, to Wright, filed Feb. 15, 2010; U.S. Patent Application Publication No. 2011/0174484, to Wright, filed Dec. 11, 2010; U.S. Pat. No. 8,235,103, to Wright, issued Aug. 7, 2012; and U.S. Pat. No. 8,322,426, to Wright, issued Dec. 4, 2012; all of which are incorporated herein by reference for all purposes. One advantage of these ERDs, on which Halliburton Energy Services, Inc., has patents pending, is they take very low electrical power for activation. This allows for low rate batteries, which enables using higher temperature batteries. Halliburton&#39;s ERDs can also operate at extremely high temperature. The thruster assembly can operate to 200C and the thermite-based rupture disc can operate at even hotter temperatures. When coupled with high-temperature electronics, the result is a setting tool that can operate at extreme temperatures. Further, the thruster assembly has been declared “unrated” by the Bureau of Alcohol, Tobacco and Firearms (BATF) and the Department of Transportation (DOT), enabling easier transport and storage. The thermite-based ERD has a relatively low rating compared to some industry standard tools. 
         [0028]    In use, in the preferred embodiment, the multi-stage hydraulic-powered setting tool is fired in stages. As shown in  FIGS. 2A-C , the first and second fluid barriers are opened or removed in sequence. The method will be discussed for a tool utilizing ERDs as fluid barriers. When the first fluid barrier or ERD  112  is actuated, wellbore fluid enters the first chamber  104 . The chamber  104  is initially at a lower pressure than the wellbore pressure, preferably at atmospheric pressure, and sealed closed at the surface. As the environmental temperature heats the tool and gas in the chamber, the pressure will rise. Consequently, the pressure in the chamber at the time of actuation will be somewhat greater than atmospheric pressure. As used herein, the term “near atmospheric” and similar includes these elevated pressures due to environmental effects. Wellbore fluid enters the first chamber through first port  108 . The pressure differential across the lower piston member  116  forces the piston member and attached piston rod  118  downward. Second piston member  120  is also moved downward. The piston members and rod move to a First Stage position, as seen in  FIG. 2B . Note that the fluid pressure in the second chamber  106  below piston member  120  is raised in response to downward movement of the piston rod. The wellbore fluid, at higher pressure than the fluid in chamber  104 , drives the piston members and rod downward until the fluid pressure above the piston member  116 , that is, between the piston member  116  and the divider wall  122 , equalizes with the pressure of the now-compressed fluid in chamber  104  below the piston member  116 , that is, between the piston member  116  and the end wall  128 , in combination with the now-compressed fluid in chamber  106  below piston member  120 , that is, between piston member  120  and divider wall  122 . Stated another way, the force downward on the piston member  116  due to the hydrostatic pressure of the wellbore fluid must be equalized by the combined upward forces from the (now-compressed) chamber fluids below piston members  116  and  120 . When the forces equalize, the piston members will stop downward movement. Note that the piston members and rod are moved a first stroke distance, d 1 , to a First Stage or intermediate position, seen in  FIG. 2B , and not moved the full stroke distance, D. 
         [0029]    At a later time, the second ERD  114  is activated and wellbore fluid enters the second chamber  106  above the second piston member  120 . The second chamber (like the first) is initially filled with a compressible fluid, such as air, nitrogen, a noble gas, or steam, and is at a lower pressure, such as near atmospheric pressure, than the wellbore fluid. Wellbore fluid enters the first chamber through second port  110 . The pressure differential across the second piston member  120  drives the piston member  120 , thereby moving the piston rod (and first piston member  116 ) further downward, by a second stroke distance, d 2 , to a Second Stage or final position, as seen in  FIG. 2C . Note that there is now more than twice the force driving the piston rod downward. The force more than doubles since the area on the first piston member is partially occluded by the piston rod. The wellbore fluid, at higher pressure than the fluid in chamber  104 , drives the piston members and rod downward until the combined fluid pressure above the first and second piston members  116  and  120  equalizes with the combined pressure of the now-compressed fluids in chambers  104  and  106  below the piston members  116  and  120 . That is, the total downward forces on the piston members  116  and  120  must be equalized by the total upward forces above the piston members. The piston rod and heads are moved to a Second Stage or final position, seen in  FIG. 2C , and moved the total stroke length, D, of the assembly. It is also possible that the piston members and rod cease movement when mechanically stopped, such as by the piston member  116  contacting a chamber delimiter. 
         [0030]    In the preferred embodiment, the first and second ERD  112  and  114  are connected to the wellbore fluid and the wellbore fluid enters the chambers  104  and  106 . In an alternative embodiment, the first and second ERD  112  and  114  are connected to a third fluid-filled chamber that is exposed to hydrostatic pressure. Preferably, the third chamber is filled with a clean fluid. The use of a clean fluid ensures that the openings created by the ERD  112  and  114  or the openings in a fluid restrictor (see restrictor  132  in  FIG. 4 ) are not blocked by particles present in the wellbore fluid. The clean fluids in the third chamber are pressurized with hydrostatic pressure by using either a moving piston, a moving baffle, a flexure, or other pressure equalizing device. In alternative embodiments, screens and filters prevent or limit incursion of debris. 
         [0031]      FIG. 3  is a graphical representation of the force-time profile for the setting tool described in  FIGS. 2A-C . The force in view is the drive-force generated by piston rod or drive rod or shaft  118  for actuating a downhole tool. The result of having separate actuation of the first and second fluid barriers  112  and  114  is to create a unique force-time profile for the setting tool. The firing of the second barrier  114  can be delayed by a predetermined time, a time period adapted to the downhole situation, a time contingent upon another event (such as, for example, measured displacement of the drive rod, estimated velocity of the drive rod, or a temperature corresponding to the temperature of the compressed fluid in chamber  104 ), or by manual control. The force-time profile can be selected by design parameters of the piston assembly, pressure chambers, and use of flow restrictors, as explained below. As can be seen in  FIG. 3 , the solid line indicates the force-time profile without use of flow restrictors and the dashed line indicated the profile when restrictors are used. The multi-stage aspect of the tool is designated by Stage identifiers, where the First Stage begins with the opening of the first fluid barrier and the Second Stage begins with opening of the second fluid barrier. The use of a multi-stage setting tool allows for a comparatively larger setting force over the setting force generated by a single-stage tool. This relative increase in available force allows for hydrostatically setting higher-force tools even at shallower depths or lower wellbore pressures. The use of a multi-stage setting tool tends to flatten or smooth the force-time profile when compared to single stage tools. The addition of restrictors tends to further smooth the force-time profile and results in a force that gradually builds over a longer period of time when compared to a similar system without restrictors. 
         [0032]      FIG. 4  is a schematic detail of a preferred embodiment according to an aspect of the invention, and having an inflow control device for controlling fluid ingress to the tool chambers. Preferably, there is a flow restrictor  132  positioned along the flow path from the wellbore to the first chamber  104 . An exemplary embodiment, seen in  FIG. 4 , has a flow restrictor  132  mounted across a fluid passageway  134  (shown positioned in port  108 ) between the fluid barrier  112  and the first chamber  104 . The fluid passageway extends from a wellbore port  136  and inlet port  104 . The flow restrictor regulates fluid flow rate from the wellbore to the chamber. Consequently, the flow restrictor slows down how quickly the wellbore fluid pushes on the piston. The flow restrictor can be a flow nozzle, orifice, an inflow control device (ICD), autonomous inflow control device (AICD), a fluidic diode, weep holes, etc., as are known in the art. In a preferred embodiment, a device similar to a fluidic diode can be used. This device slows the fluid entering the device and lengthens the time it takes for the force to build. Preferably a flow restrictor is also positioned to control fluid flow into the second chamber  106 . 
         [0033]      FIGS. 5A-C  are schematic views of an alternative exemplary embodiment of a multi-stage setting tool according to an aspect of the invention.  FIG. 5A  is a schematic view of a multi-stage setting tool in an initial or run-in position.  FIG. 5B  is a schematic view of the embodiment of  FIG. 5A  seen in an intermediate or First Stage position.  FIG. 5C  is a schematic view of the embodiment of  FIGS. 5A-B  seen in a final or Second Stage position. To the extent that the alternative embodiment is similar to the embodiments explained elsewhere herein, certain details will be understood by practitioners of skill in the art and not described again with reference to  FIGS. 5A-C . 
         [0034]    The setting tool  200  is seen in an initial or run-in position and generally describing a setting tool housing  202  defining a first interior chamber  204  in selective fluid communication with the wellbore fluid through a first inlet port  208 , and a second interior chamber  206  in selective fluid communication with the wellbore fluid through a second inlet port  210 . Positioned in the first and second ports are a first and second openable or removable fluid barriers,  212  and  214 , respectively. 
         [0035]    In the alternative embodiment, the piston rod is constructed in multiple segments. A first piston member  216  is mounted for sliding movement in the first chamber  204  and attached to a first piston rod  218 . The first piston rod  218  extends from first piston member  218  through the first chamber  204 , in which the first piston member is located, and extends through a hole in end wall  228 . The piston rod further extends beyond the setting tool housing  102  and the free end  230  is attachable to a downhole settable tool. 
         [0036]    A second piston member  220  is mounted for sliding movement in second chamber  206  and attached to a second piston rod  221 . Second piston rod  221  is attached to second piston member  220  and extends from the piston member downward through the second chamber  206 , in which the piston member  220  is slidably mounted, and through a hole  224  in dividing wall  222 . 
         [0037]    The selectively openable ports  208  and  210  are initially blocked by fluid barriers  212  and  214 . In a preferred embodiment, the fluid barriers are ERDs, as explained above. More specifically, the preferred ERD is a thruster or pin pusher assembly. 
         [0038]    In use, the multi-stage hydraulic-powered setting tool is fired in stages. As shown in  FIGS. 5A-C , the first and second fluid barriers are opened or removed in sequence. When the first ERD  212  is actuated, high pressure wellbore fluid enters the first chamber  204 , which is at a lower pressure, preferably near atmospheric pressure. The pressure differential across the lower piston member  216  forces the piston member and attached piston rod  218  downward. Second piston member  220  and attached second piston rod  221  remain stationary. The first piston member and rod move to a First Stage position, as seen in  FIG. 5B . Note that the first piston member  216  and rod  218  are moved a first stroke distance, d 1 , to a First Stage or intermediate position, seen in  FIG. 5B . Note that hydrostatic pressure will also act with an upward force on the second piston rod  221  at its free end  223 . 
         [0039]    At a later time, the second ERD  214  is activated and high pressure wellbore fluid enters the second chamber  206  above the second piston member  220 . Wellbore fluid enters the second chamber through second port  210 . The pressure differential across the second piston member  220  drives the second piston member  221  and second piston rod  221  downward, the rod sliding through a hole in the divider wall  222 . The free end  223  of the second piston rod  221  (or a contact element affixed thereto) is moved downward and into contact with the first piston member or rod. The second piston assembly adds its driving force to the first piston assembly, thereby moving the first piston member and rod further downward by a second stroke distance, d 2 , to a Second Stage or final position, as seen in  FIG. 5C . The total stroke distance, D, is the combined first and second stroke distances, d 1  and d 2 . Although the pistons are shown as being the same diameter, different diameter pistons could be used to create different forces for each stage. 
         [0040]      FIGS. 6A-C  are schematic views of an alternative exemplary embodiment of a multi-stage setting tool according to an aspect of the invention.  FIG. 6A  is a schematic view of a multi-stage setting tool in an initial or run-in position.  FIG. 6B  is a schematic view of the embodiment of  FIG. 6A  seen in an intermediate or First Stage position.  FIG. 6C  is a schematic view of the embodiment of  FIGS. 6A-B  seen in a final or Second Stage position. To the extent that the alternative embodiment is similar to the embodiments explained elsewhere herein, certain details will be understood by practitioners of skill in the art and not described again with reference to  FIGS. 6A-C . 
         [0041]    The setting tool  300  is seen in an initial or run-in position and generally describing a setting tool housing  302  defining a first interior chamber  304  in selective fluid communication with the wellbore fluid through a first inlet port  308 , and a second interior chamber  306  in fluid communication with the wellbore fluid through a second inlet port  310 . Positioned in the first port is a first openable or removable fluid barrier  312 . 
         [0042]    In this embodiment, the system is designed such that a single selectively actuable fluid barrier  312 , preferably an ERD, is needed for activation of the assembly. Sliding elements or sleeves  313  prevent the open port  310  from transmitting wellbore pressure to the upper piston during run-in and until the fluid barrier  312  is opened or removed. The sleeves  313  are attached to the second piston member  320  such that movement of the head results in movement of the sleeve. The sleeve  313  is initially positioned blocking the second port  310 , preventing inflow of wellbore fluid to the second chamber  306 . 
         [0043]    After the fluid barrier  312  is actuated (opened or removed), wellbore fluid enters first chamber  304  above first piston member  316 , driving the piston rod  318  downward. When the piston assembly strokes far enough that sleeve  313  uncovers the second port  310 , wellbore fluid enters the second chamber  306  and provides additional force, provided by hydrostatic pressure acting on second piston member  320 , for stroking the piston rod  318 . The piston rod is constructed as a single segment extending through both chambers and having a free end  330  below the tool assembly and attachable to a downhole settable tool. The piston assemblies can take various arrangements, including those described elsewhere herein. 
         [0044]    The selectively openable port  308  is initially blocked by a fluid barrier  312 . In a preferred embodiment, the fluid barrier is an ERD, as explained above. More specifically, the preferred ERD is a thruster or pin pusher assembly. 
         [0045]    In use, the multi-stage hydraulic-powered setting tool is fired in stages. As shown in  FIGS. 6A-C , the first fluid barrier is opened or removed. High pressure wellbore fluid enters the first chamber  304 , which is initially at a lower pressure, preferably near atmospheric pressure. The pressure differential across the lower piston member  316  forces the piston member and attached piston rod  318  downward a first distance, d 1 . Force is kept relatively low during this portion of piston stroke. Second piston member  320  and attached sleeve  313  are also moved downward as they are attached to piston rod  318 . The piston members, rod, and sleeve, are moved to a First Stage position, as seen in  FIG. 6B . As the sleeve  313  is moved downward, it eventually uncovers port  310  and high pressure wellbore fluid enters the second chamber  306  above the second piston member  320 . The pressure differential across the second piston member  320  drives the second piston member  321  and attached piston rod  318  downward a second stroke distance, d 2 . The piston rod  318  and its free end  330  moves a total stroke distance, D. The second piston assembly adds its driving force to the first piston assembly, thereby moving the piston rod further downward to a Second Stage or final position, as seen in  FIG. 6C . In a preferred embodiment, the second chamber  306  has a greater volume than first chamber  304  to accommodate the sliding elements or sleeves  313 . The additional volume slows the filling of the second chamber  304 , lengthening the time of the force stroke. 
         [0046]    It is understood that the schematic views of the various piston assemblies are not limiting. Alternative piston assemblies will be apparent to those of skill in the art. For example, annular pistons and rods can be employed where it is desired to leave a central passageway through the tool assembly. Further, it is understood that three or more piston assemblies in like number of chambers can be utilized to provide additional setting force and additional setting Stages. That is, the multiple stage assemblies disclosed herein are modular and can be stacked or used in series or parallel to provide additional setting force and/or to elongate setting time. 
         [0047]    Further, it is understood that design of the elements of the tool assembly can be selected to provide a customized force-time profile. The dimensions of the piston members, rods, and chambers can be selected. The volume, initial pressures and entrapped fluid of the chambers can be selected. The first, second, and total stroke distances can be selected. Further, the timing of the Second Stage (or further later Stages) can be timed with regard to the beginning, completion, or intermediate point of the First Stage (or other prior Stage). For example, the Second Stage can be actuated upon: cessation of movement due to the First Stage, during movement of the First Stage, upon movement of a selected stroke distance of the First Stage, upon completion of the complete stroke distance achievable by the First Stage, etc. Stated another way, later stages can be timed in relation to prior stages to supply a smoother force-time profile. 
         [0048]    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 the 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.