Abstract:
A retrievable frac packer is provided which allows frac operations to be conducted with a single, retrievable tool, with the capability of providing positive zone production indications during production testing.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to frac packers which can be used in downhole environments, retrieved, and reconditioned for further use rather than requiring the time and expense to drill out, and thus destroy, the tool after use.  
       BACKGROUND OF THE INVENTION  
       [0002]     To “frac” a well involves the introduction of media, typically containing a proppant, into a zone surrounding the wellbore to create flow conduits in the surrounding earth. In the interest of cost reduction, it is desirable to carry out such an operation as quickly as possible, and with as few trips up and down the wellbore as possible. For frac operations, it is necessary to introduce a seal in the wellbore to prevent the frac fluid from travelling further downhole than the desired frac zone.  
         [0003]     However, wells often have multiple production zones as well as multiple zones where performing the frac operation is desirable. Therefore, the seal which is introduced into the wellbore must be, or is certainly preferably, removable to allow free communication with the wellbore below. Various combinations of devices have been used to accomplish these goals. For example, drillable frac packers are used which allow a single tool to perform the needed tasks. However, these tools require expensive surface support equipment in order to be drilled out after the frac operation is completed. Drilling out such tools is time consuming, and therefore expensive, and can result in undesirable damage to the inside of the wellbore. Further, tool cost using this approach is driven up because the tools themselves must be considered as expendable.  
         [0004]     Another approach is to use a packer in combination with a separate, retrievable bridge plug, with the two tools straddling the frac zone. However, such an approach requires two separate tools to perform a single task, adding cost and complexity to the process. Accordingly, it is desirable to provide a single, retrievable frac packer tool, which can be reconditioned and reused rather than being used once and being destroyed.  
         [0005]     Further, because these tools are often used in wells with multiple frac zones, it is desirable to provide a frac tool which provides bi-directional flow control, thereby providing the capability of not only sealing off the well down-hole of the packer from pressure from above during the frac operation, but also allowing flow from below to be selectively closed off. It is further desirable to provide such tools with flagging media, such as dyes, so that tools used in different frac zones may contain differentiating markings within the flagging media, and thus provide the surface operators with confirmation of the existence of production flow at different levels in the wellbore.  
         [0006]     The interests of keeping costs down additionally makes it desirable to provide a retrievable frac packer which is sufficiently compact and lightweight to allow it to be run-in on wireline, coiled tubing, or other deployment methods and which has the flexibility to be settable either by wireline, hydraulic pressure, or other setting methods, including combinations of hydraulic and mechanical methods.  
         [0007]     Accordingly, it is an object of the invention to provide a retrievable frac packer which provides a single-tool capable of allowing the frac operation to proceed, but which may be retrieved and reconditioned for repeated use.  
         [0008]     It is a further object of the invention to provide such a tool that can also be retrieved in groups of two or more tools at a time, reducing the number of downhole trips required to retrieve the tools when there are multiple frac zones in a well.  
         [0009]     It is another object of the invention to provide a retrievable frac packer that provides bidirectional flow control.  
         [0010]     It is yet another object of the invention to provide a retrievable frac packer that can provide confirmation to surface operators of the downhole level or levels which are producing product flow.  
         [0011]     It is still a further object of the invention to provide a retrievable frac packer which can be run-in on wireline, coiled tubing, or another type of tool string, and which can be set by either wireline, hydraulic methods, or other setting methods.  
       SUMMARY OF THE INVENTION  
       [0012]     The invention is a frac packer that comprises an annular body comprising a circumferential seal that can be set by compression. When the tool is run downhole, the seal is in the “un-set” position, allowing clearance between the tool and the surrounding casing. A check valve is provided within the annular body to preclude downhole flow of fluid through the tool once the tool is set in the desired position.  
         [0013]     At the desired depth, the tool is set by wireline control, hydraulic pressure, mechanical means, or a combination of these techniques to compress and engage the circumferential seal with the inner wall of the surrounding casing. Compression pressure is applied to the seals by an upper compression member in slidable engagement with the annular body of the tool, and by a lower compression member in slidable engagement with the annular body of the tool. Downward travel of the lower compression member may be resisted by mechanical stops. However, in the preferred embodiment, the lower compression member is biased upward by mechanical means, such as a spring, to provide improved sealing force and to assist in the release of the tool after the frac operation. If the tool is to be utilized in wells in which multiple tools will be retrieved simultaneously, such a mechanical biasing is necessary to insure that the tools will release properly and move further down the wellbore to retrieve a deeper set frac packer, and retrieve properly.  
         [0014]     A slip is preferably present in slideable engagement with the annular body of the tool on the downhole side of the seal, so that the compression setting of the tool also activates the slip into locking engagement with the casing in the wellbore, thus securing the tool against slippage within the casing before, during, or after the frac operation.  
         [0015]     Once compressed into sealing engagement with the well casing, the position of the upper compression member relative to the annular body of the tool is locked by a selectively releasable latch, such as a ratcheting mechanism, so that the seal is held in sealing engagement with the well casing during the frac operation. Release of the latch is preferably accomplished by mechanical means, such as a shear means, like studs or screws, so that the tool may be released from its sealing engagement with the well casing by a jarring effect or other mechanical force controllable from the surface.  
         [0016]     Inside the annulus of the annular body of the tool, a first check valve is positioned to allow fluid flow from the downhole end of the tool upward, but not from the uphole end of the tool downward. Thus, flow can be allowed through the tool from below if necessary, while simultaneously sealing the environment downhole of the tool from pressure above the tool during the frac operation.  
         [0017]     The tool may also be configured with a second check valve positioned in opposed configuration to and uphole of the first check valve, creating a region within the annulus of the tool through which no flow may occur. This second check valve preferably comprises a degradable ball seal, which will degrade at a calculated time to allow upwardly-directed flow through the tool, or a mechanically releasable seal which will open when frac pressure reaches the tool.  
         [0018]     In conjunction with such a second check valve, the tool may be configured with a flagging media, such as a dye package, so that when flow begins through the tool the flagging media will be released to flow to the surface. In this configuration, multiple tools with differently-marked flagging media may be used in multiple commingled production zones to provide confirmation at the surface of which of the commingled zones are flowing.  
         [0019]     In the preferred embodiment, the downhole end of the annular body of the tool is provided with a grip capable of latching onto the uphole end of another of such tools. Thus, when frac operations are completed in a wellbore with multiple zones, each tool may be released in turn, then moved downhole to latch onto and release the next lower tool. In this way, multiple tools may be retrieved simultaneously, reducing the number of trips required to clear the tools from the wellbore. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1A  is a sectional view of one embodiment of the retrievable frac packer of the present invention in the run-in position.  
         [0021]      FIG. 1B  is a sectional view of the embodiment depicted in  FIG. 1A , with an optional flagging media package added.  
         [0022]      FIG. 1C  is a sectional view of the embodiment depicted in  FIG. 1A , with a second check valve incorporated.  
         [0023]      FIG. 2A  is sectional view of an alternative embodiment of the retrievable frac packer depicted in  FIG. 1A , with the first check valve replaced with an alternative sliding sleeve and sealing ball valve.  
         [0024]      FIG. 2B  is an expanded sectional view of the alternative check valve of  FIG. 2A , with the sliding sleeve of the valve in its initial position.  
         [0025]      FIG. 2C  is an expanded sectional view of the alternative check valve of  FIG. 2A , with the sliding sleeve of the valve in its final position.  
         [0026]      FIG. 3A  is a sectional view of the retrievable frac packer of  FIG. 1C , shown in the set position.  
         [0027]      FIG. 3B  is a sectional view of the retrievable frac packer of  FIG. 3A , shown with the degradable ball having dissolved and with flow occurring through the tool.  
     
    
     DETAILED DESCRIPTION  
       [0028]     Referring to  FIGS. 1A and 1B , one embodiment of the retrievable frac packer of the present invention is shown. The retrievable frac packer  10  comprises an annular body  12 , which can be run-in to an appropriate position in a well casing  14 . Compressible seal  16  is positioned to be placed into sealing engagement with the inner wall  18  of the well casing  14 . Upper compression member  20  is moveable by wireline control, hydraulic setting means, or a combination of hydraulic and mechanical means (not shown) to force upper linkage  22  downward against the compressible seal  16 .  
         [0029]     Such movement will also force lower compression member  24  downward, compressing mechanical biasing spring  26 , and applying upward force against compressible seal  16 . The downward movement of lower compression member  24  also will force slip  28  outward into mechanical engagement with the inner wall  18  of the well casing  14 .  
         [0030]     Downward movement of upper compression member  20  also engages latch  30  into a locking position by moving ratchet arm  32  into locking engagement with ratchet base  34 . Spring  36  applies biasing force to aid in holding ratchet arm  32  into a locked position once set. Sliding push sleeve  37  allows the downward force to be transmitted to seal base sleeve  39  through a path other than through shear means  38 , protecting shear means  38  from excessive force during the setting operation.  
         [0031]     When release of the retrievable frac packer  10  from its set position is desired, an upward jar may be applied, shearing shear means  38 . This in turn will allow the upward movement of upper linkage  22 , which interlocks with ratchet arm  32 , thus releasing latch  30  and allowing upper compression member  20  to move upward. Bias force from compression spring  26  further assists in this upward movement, relieving pressure against compressible seal  16  and allowing slip  28  to release its mechanical engagement with the inner wall  18  of well casing  14 .  
         [0032]     First check valve  42  allows the retrievable frac packer  10  to protect the region below from hydraulic pressures above so that frac operations may proceed. However, first check valve  42  also allows flow testing of the well to occur without removing the retrievable frac packer  10  from the well. For such purposes, a flagging media such as dye pack  44  may be carried downhole within the annulur body of the retrievable frac packer  10 . In a multiple production zone well, multiple retrievable frac packers  10  may be inserted into different production zones with uniquely-marked flagging media, providing confirmation on the surface of which zones are flowing.  
         [0033]     Referring to  FIG. 1C , an alternative embodiment of the retrievable frac packer  10  is shown incorporating a second check valve  46 . In this embodiment, second check valve  46  incorporates a degradable ball  48 , allowing the retrievable frac packer  10  to be run in to the well as a bridge plug. After a calculated time in the well environment, the degradable ball  48  will dissolve, allowing the retrievable frac packer  10  to operate as described above.  
         [0034]     Referring to  FIG. 2 , an alternative embodiment of the retrievable frac packer  10  of  FIGS. 1A-1C  is shown. First check valve  42  of  FIG. 1  is replaced by a sliding sleeve valve  242 . For run-in, sliding sleeve valve  242  seals in both directions, and allows retrievable frac packer  210  to be run-in as a bridge plug. Once in position, hydraulic pressure may be applied, for example, at the same time frac operations are conducted above the retrievable frac packer  210 , sliding sleeve  250  into an open position  252  and allowing sliding sleeve valve  242  to function in the same manner as first check valve  42  of  FIG. 1 .  
         [0035]     Referring now to  FIGS. 3A and 3B , retrievable frac packer  310  is shown in the set position. Upper compression member  320  has been moved downward relative to the annular body  312  of retrievable frac packer  310 . Compressible seal  316  is in sealing contact with the inner wall  318  of the well casing  314 . Latch  330  is set by the interlocking of ratchet arm  332  with ratchet base  334 , preventing loss of compression force against compressible seal  316 . Slip  328  is also forced outward into mechanical engagement with the inner wall  318  of well casing  314 , resulting from the downward movement of lower compression member  324  relative to the annular body  312  of retrievable frac packer  310 .  
         [0036]     As shown in  FIG. 3A , the initial setting of retrievable frac packer  310  allows frac operations to proceed. First check valve  342  and compressible seal  316  prevent fluid flow downhole of the retrievable frac packer  310  during frac operations. After the degradable ball  348  has dissolved, second check valve  346  “opens,” and flow may be tested prior to removal of the retrievable frac packer  310 , as shown in  FIG. 3B . Upward flow pressure opens first check valve  342 , allowing test production flow to proceed up the wellbore.  
         [0037]     The above examples are included for demonstration purposes only and not as limitations on the scope of the invention. Other variations in the construction of the invention may be made without departing from the spirit of the invention, and those of skill in the art will recognize that these descriptions are provide by way of example only.