Abstract:
A method of separating fluids that actuate a downhole tool from well fluids is disclosed. The assembly permits equalization or circulation through the running string for delivery of the downhole tool to the desired location. The circulation passage is closed and the clean fluid is displaced into the downhole tool by pressure applied to a movable barrier, At the end of the clean fluid displacement, a lateral port is opened to allow retrieval without pulling a wet string.

Description:
PRIORITY INFORMATION 
   This application claims the benefit of U.S. Provisional Application No. 60/333,792 on Nov. 28, 2001. 

   FIELD OF THE INVENTION 
   The field of this invention relates to systems to separate incompatible fluids downhole and more particularly in the context of isolation of fluid to inflate an inflatable from the other fluids in the well bore. 
   BACKGROUND OF THE INVENTION 
   Inflatables are used downhole for a variety of applications. Typically a valve that opens responsive to applied pressure regulates the inflatable. In some applications there can be a series of valves. In either case, the valve assembly is sensitive to solids that may be present in well fluids. One example is in high-pressure wells where very dense mud formulations are required for pressure control. In these instances the mud contains a significant amount of grit that can undermine the operation of the valves on the inflatable. Another problem is settlement of solids. If solids in appreciable quantities get into the inflatable and settle out, then the inflatable will not go back down sufficiently when deflated and will present problems when it is time to retrieve it. Mixing of fill fluids and well fluids could cause a reaction that creates a very viscous emulsion or worse, a resulting compound that hardens inside the inflatable, making subsequent extraction of the inflatable difficult, if not impossible. 
   In the past, attempts were made to overcome this problem. One technique involved putting clean fluid, such as water above the inflatable and topping it off with a large plug of grease. The idea was that the grease plug would remain cohesive and displace the clean fluid into the inflatable, without allowing the grit laden well fluids an opportunity to reach the delicate valve system on the inflatable. This system was unreliable as the downhole temperatures may reduce the grease viscosity and allowed well fluids to get by the plug and into the inflatable. Another attempt involved a downhole pump powered with a wireline. The pump was disposed in a clean fluid and the wireline extended through a movable barrier with the well fluids on top. As the pump delivered the clean fluid to the inflatable, the well fluid acted on the barrier to push it downhole along the electric line. The problem was that the electric line had an irregular outer surface and it was difficult in some applications to obtain a good seal between the stationary electric line and the bushings in the movable barrier. Apart from that the arrangement required special equipment to run the electric line to power the pump. There were cost and physical space concerns involved in the deployment of this arrangement. Efforts to provide a regular outer surface on the electric line through the use of a smooth coating were successful in some applications but were abandoned as being too costly and unreliable in the elevated temperatures in some existing deep well applications. 
   Accordingly, what was needed was a simple system to separate fluids to ensure reliable inflatable operation. At the same time, the system had to accommodate running in while circulating or allowing equalization of well fluids into the string during run-in. The system would also need to allow fluid communication from inside to outside the string during retrieval to prevent pulling out a wet string, laden with the weight of well fluids internally. Ideally, the system would be simple to construct and to operate, using familiar components as much as possible and requiring no specialty equipment at the surface or complicated procedures that would necessitate specialty service company personnel or unique training for the rig hands. These benefits in a variety of combinations are some of the beneficial aspects of the present invention. These and other features of the apparatus and the methods of the present invention will be more readily appreciated by a review of the description of the preferred embodiment, which appears below. 
   SUMMARY OF THE INVENTION 
   A method of separating fluids that actuate a downhole tool from well fluids is disclosed. The assembly permits equalization or circulation through the running string for delivery of the downhole tool to the desired location. The circulation passage is closed and the clean fluid is displaced into the downhole tool by pressure applied to a movable barrier. At the end of the clean fluid displacement, a lateral port is opened to allow retrieval without pulling a wet string. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic representation of the invention using a separate circulation valve; and 
       FIG. 2  is a schematic representation of the invention using an integrated circulation valve; 
       FIG. 3  is an alternative embodiment to FIG.  2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , a conveyance pipe  10 , which can be rigid tubing, drill pipe snubbing pipe, coiled tubing or the like is used to convey a downhole tool  12  to a desired location. The downhole tool  12  can be any one of a variety of known downhole tools, but in the preferred embodiment it is an inflatable tool. Mounted above the inflatable tool  12  is a landing/seal collar  14 . It has a lower outlet  16  and connects to the inflatable with a thread  18  or a mechanism that auto-releases upon application of a predetermined pressure over and above the inflation upper pressure limit where the inflate valve closes. Using threads  18  release can occur by rotation of the string  10 . Other connection and release devices may be employed without departing from the scope of the invention. Landing/seal collar  14  has a chamber  20  filled with a clean fluid at the surface. The volume used is preferable about 125% or more of the anticipated necessary volume to fully activate the inflatable  12 . A wiper plug or dart of known construction  22  is inserted above the fluid in chamber  20 . Other movable barriers, which seal peripherally, are also contemplated. Wiper plugs or darts are used commonly in casing cementing operations to isolate cement from other well fluids as those well fluids push on the wiper or the dart to displace cement to the annular space around the casing until the wiper or dart is “bumped” when it reaches a receptacle. 
   Mounted above the landing/seal collar  14  is a circulating valve  24  of a known construction such as models H300-55 or H330-51 made by Baker Oil Tools. Above that is a fill up sub  26  of known construction such as models H330-78 or H300-98 made by Baker Oil Tools. The incompatible well fluid is disposed above the wiper  22 . 
   This embodiment of the system operates in the following manner. As the inflatable  12  is lowered to the desired depth, an aperture  28  on the fill up sub  26  is open. This allows well fluid to enter the tubing  10  as it is lowered in the well and also allows circulation, if necessary. When the desired depth is reached, a ball (not shown) is dropped into the fill up sub to essentially close off aperture  28  while at the same time allowing flow around the ball to permit the application of applied fluid pressure onto the wiper  22 . Well fluids pushing on wiper  22  reduce the volume of chamber  20 , as clean fluid is displaced into the inflatable  12  through lower outlet  16 . After the inflatable  12  is set and released such as by undoing thread  18 , for example, the wiper is landed in the bottom of the landing/seal collar  14 . Thereafter, pressure is built up above the wiper  22  and in circulating valve  24 . There is a piston (not shown) inside the circulating valve  24 , which is responsive to applied pressure to shift positions and expose a port  30 . With port  30  open, the tubing  10  can be pulled and it will drain so that a wet string is not created which could overtax the surface equipment used to pull it up or to allow for further displacement of fluids such as cement. It should be noted that aperture  28 , once closed by the dropping of a ball, remains closed for the duration of the procedure. The circulation valve  24  is needed because the isolating mechanism, which comprises the wiper  22 , prevents draining the tubing  10  during removal. Surface personnel will see a pressure spike as the wiper  22  bottoms, followed by a quick drop in pressure as the port  30  is opened. 
   The alternative method is shown in FIG.  2 . It differs from the  FIG. 1  method in that a separate circulating valve  24  has been moved from the position below the fill up sub  26  to a lower position inside chamber  20 . The steps to set and release the inflatable  12  in  FIG. 2  are identical with the  FIG. 1  operation. The difference lies in the pressurization above the wiper  22  after release from the inflatable  12 . As the wiper  22  moves downwardly, it physically engages the relocated circulation valve  24  and shifts a sleeve (not shown) that is internal to the circulation valve until a port  32  aligns with a port  34  on the housing of the landing/seal collar  14 . The string can now drain as it is being pulled out of the hole.  FIG. 3  shows a similar concept except a sleeve  33  is held by shear pin  35  to initially cover aperture  37 . The wiper  22  eventually displaces sleeve  33  to allow the string to drain during removal. 
   Those skilled in the art can appreciate that the apparatus and method of the invention is simple and inexpensive and offers a reliable technique to isolate clean fluid for use in an inflatable or other downhole tool, while at the same time allowing the tubing to fill automatically during run in and drain during retrieval from the wellbore. Many different movable barriers are contemplated to sealing separate the clean fluid from the surrounding well fluid. Use of known components, reduces costs, and insures more reliable operation due to familiarity with the equipment by rig personnel. 
   The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: