Abstract:
A downhole tool and capillary biasing system includes a housing; an intrusion fluid contained within a portion of the housing; a capillary biasing member in fluid contact with the intrusion fluid; and a pressure application configuration capable of pressurizing the intrusion fluid within the housing and method.

Description:
BACKGROUND 
       [0001]    In the hydrocarbon recovery industry, methods for recovering desired hydrocarbons consistently improve, resulting in wells having longer productive lives. With extended well life comes longevity/durability issues for individual well components. Components that are required to operate for a very long time and potentially for a large number of cycles are biasing members. These can be springs such as coil springs or can be gas charged piston cylinders, for example. Over time and cycling such biasing devices tend to break down, losing, for example, their resiliency or sealing function for gas, respectively. In either case, the biasing power of the device is reduced. Sometimes such biasing power is regulated and in others although not regulated, reduced biasing power is simply costly from the standpoint of production. In both cases, remedial action is necessary to restore biasing power. Generally, remediation entails replacement of the component at issue. As one of skill in the art is well aware, many replacement operations require an interruption in production. As interruptions or even reductions in production is never well received due to the massive sums of money lost, the art is generally receptive to new devices that enhance overall longevity and cycle life. 
       SUMMARY 
       [0002]    A downhole tool and capillary biasing system includes a housing; an intrusion fluid contained within a portion of the housing; a capillary biasing member in fluid contact with the intrusion fluid; and a pressure application configuration capable of pressurizing the intrusion fluid within the housing. 
         [0003]    A method for biasing a downhole tool includes pressurizing a non-wetting fluid to intrude into a non-wettable matrix within a housing of the downhole tool; maintaining the pressure on the fluid until a spring force from the matrix is required. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
           [0005]      FIG. 1  is a schematic cross sectional view of one embodiment of a device in combination with a capillary spring biasing member in a valve closed position; and 
           [0006]      FIG. 2  is a schematic cross sectional view of one embodiment of a device in combination with a capillary spring biasing member in a valve open position. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    The downhole tools  10  of the present invention are to be biased by a capillary biasing member  12  utilizing a porous matrix  14  having pore sizes selected to enhance the capillary response sought in connection with the present disclosure. In one embodiment, the pore size is about 5 nanometers in diametric dimensions or dimensions associated with irregular shapes of the pores. The matrix  14  is a non-wettable material at least with respect to fluids that are intended to be used therewith. Selection of both the matrix  14  material and a fluid  16  is important to operation of the capillary biasing member  12  as the biasing force is achieved directly from the non-wettable nature of the material and fluid combination. Materials for matrix  14  include but are not limited to silica based materials as these are available with a range of surface areas, pore volumes, and pore radiuses and a thermal stability to about 1500° F. It is also relatively easy to hydrophobize silica materials utilizing such materials as Organosilanes. Well temperature in the target area is to be considered when determining which material combination to use since for example, partial structural degradation of hydrophobized silicas occurs at various temperatures such as for example, about 300° F.-350° F. for alkyl-silicas, about 400° F.-450° F. for fluorinated alkyl-silicas, and about 500° F. for dimethylsiloxane-silicas. Depending upon what downhole tools is implicated and where in the hole it might be located, different choices can be made as to desired material. 
         [0008]    Desired pore sizes for the matrix  14  are in one embodiment, as noted is about 5 nanometers in a direction transverse to an axial direction of the pore. What is important about the pores is that they exhibit a desired level of capillary action (due to both the dimensions thereof and the hydrophobicity). The desired level is to be determined per application such that sufficient force can be realized from the capillary spring for the particular application. Such a range enables the matrix to resist an intrusion fluid  18  until ambient pressure levels become relatively high. This dictates the power available in the biasing member  12  since whatever pressure is required to force the intrusion fluid  18  into the matrix  12 , is the pressure that will become available when the intrusion fluid  18  is allowed to disassociate from the matrix  12  due to a reduction in the pressure holding the fluid in the matrix  12 . The matrix  12  thus stores the same high pressure for use at a desired time. This can be hundreds of atmospheres. Thermodynamically, as the fluid  18  intrudes into the pore spaces of the matrix  18  under pressure, the mechanical work consumed to force the fluid  18  into the pores is converted into interfacial energy of newly created surfaces. Since the process is reversible, the consumed energy is reconstitutable back to useable energy. For materials with nanometer size pores, the intrusion-extrusion pressure can reach hundreds of atmospheres presenting an enormous potential to convert and store energy in a small package. 
         [0009]    The fluid  18  utilized in conjunction with the matrix is a non-wetting fluid that may in some applications be a liquid. As intrusion fluids, three types of liquids are exemplary: (I) water, (II) organic liquids with high surface tension, and (III) liquid metals and alloys. 
         [0010]    I. Water (y=72 mJ/m 2 , T bp =212° F.) is safe and inexpensive. For hydrophobic silicas with 5 nm pores, the intrusion pressure about 1,000-about 2,000 psi depending on the hydrophobicity of the pores. Although, boiling point of water is below average well temperature, evaporation will not occur since the capillary biasing system is closed. And water should not evaporate at less than about 500° F.-600° F. at the pressures contemplated for the system. 
         [0011]    II. High surface tension organic liquids are also contemplated. Two exemplary 
         [0012]    organic liquids are ethyleneglycol (y=48 mJ/m 2 , T mp =9° F., T bp =388° F.) and formamide (y=58 mJ/m 2 , T mp =36° F., T bp =410° F.). For 5 nm pores, the intrusion pressure for these fluids  18  is about 700- about 1,500 psi. 
         [0013]    III. Metals and metal alloys as intrusion fluids include: Solder (Sn—Pb alloy, surface tension y=470 mJ/m 2 , melting temperature T mp =360° F.); Wood&#39;s metal (Bi—Pb—Sn—Cd alloy, y˜400 mJ/m 2 , T mp ˜about 160° F.); Pb (T mp =621° F.), Sn (y=550 mJ/m 2 , T mp =450° F.). This group of liquids is characterized by high surface tensions resulting in very high amounts of energy that can be stored in a given amount of a porous solid. Liquid metals do not wet glass and silica surfaces, so untreated silica can be used as a porous solid. For silicas with 5 nm pores, the intrusion pressure will be about 15,000 psi. 
         [0014]    The amount of energy stored in a porous media is about y S, where y is the surface tension of a liquid and S is the surface area of the pores in the matrix. For example, for one kilogram of silica with S equal to about 500 m 2 /g (typical value for mesoporous silicas), about 25 kJ of energy can be stored (using organic liquids with y equaling about 50 mJ/m 2 ), about 35 kJ (using water with y equaling about 70 mJ/m 2 ), and about 200 kJ (using liquid metal with y equaling about 400 mJ/m 2 ). 
         [0015]    The extrusion pressure is determined by the surface tension of liquid (y), pore radius (R), and a receding contact angle (θ) between the liquid and the pore surface. The basic relationship is given by the Laplace equation: P=−2y.θ/R. Using porous solids with R equal to about 5 nm, the extrusion pressure is about 600 psi (organic liquids-fluorinated surface, θ equal to about 100 degrees); about 1,100 psi (water fluorinated surface, θ equal to about 100 degrees); and about 14,700 psi (Wood&#39;s alloy-silica, θ about 130 degrees). It should be noted that the extrusion pressure may decrease (sometimes significantly) due to wetting hysteresis in the pores of the matrix  14 . In one example, using 500 psi, a 600 lbs force can be obtained if this pressure is applied to an about 1.2 square inch surface. For a 1 kg mass of porous silica (pore volume˜0.5 cm 3 /g), for example, a maximal extrusion volume is 500 cm 3 , which translates into about 40 inches of linear displacement in a column with a diameter of about 1 inch. Thus it is clear that a highly efficient and useful biasing member can be constructed utilizing the capillary biasing member disclosed herein. 
         [0016]    In combination with downhole tools, such as the safety valve illustrated in the figures, the capillary biasing member  12  can be configured to take the place of a conventional spring whether that be a resilient deformable material or a fluid actuated cylinder and piston arrangement. Important to the concept is providing a sufficient spring force that is achievable at a reasonable actuation force done through calculation as explained above, and to ensure a reliable sealing regime. 
         [0017]    Referring to  FIGS. 1 and 2  simultaneously, one embodiment of the downhole tool  10  with capillary biasing member  12  is illustrated in cross section. In these figures, a safety valve is illustrated but it is to be understood that this is by way of example only and that other downhole tools that employ biasing arrangements are also contemplated. 
         [0018]    One of skill in the art will recognize the overall appearance of the valve  10  with a housing  20 , a flapper  22 , a hydraulic control line connector  24 , a control fluid chamber  26 , a piston  28 , and a flow tube  30 . One of skill in the art would also expect to see a coil spring known as a power spring bearing against the piston  28  but it is this structure that is being dispensed with in favor of the capillary biasing member  12 . 
         [0019]    The hydraulic control line connector is a pressure application configuration for this embodiment but it is to be appreciated that application of pressure is not limited to externally applied pressure as in from a hydraulic line but that the pressure application configuration could also be a configuration of components that allow of a volumetric reduction in the containing space where the intrusion fluid is maintained. Such a volumetric reduction will increase pressure in the intrusion fluid identically to achieving the same through the application of hydraulic pressure. In either case, the pressure of the intrusion fluid may be increased to above the intrusion pressure of the matrix  14  to operate the capillary biasing system. 
         [0020]    As there must be an intrusion fluid, it is necessary to provide for a leak tight environment for the fluid  18 . To this end, a fluid piston  32  is positioned between the fluid  18  and the piston  28  creating a mechanical interface so that it is directly acted upon by the piston  28  to move toward the member  12  when hydraulic pressure is applied at the chamber  26 . In so doing, the flow tube  30  is moved in a direction associated with the opening of the flapper  22 . Because the fluid piston  32  is fluidically sealed using such as O-rings  34  and  36  to its adjacent structures, the intrusion fluid  18  cannot react but to experience an overall pressure increase until the pressure thereof exceeds the intrusion pressure of the matrix  14  and intrusion to the matrix  14  results as discussed above. While this is occurring, the flow tube  30  is moving to open the flapper  22  and when the motion is completed, the tool is in a position as is illustrated in  FIG. 2 . The tool  10  will remain in this position until pressure at connector  24  is reduced below the intrusion pressure and the fluid is extruded from the matrix  14 . The extrusion of fluid is at a pressure equal to the intrusion pressure and thus acts as a strong biasing member to move the flow tube  30  uphole thereby allowing the flapper  22  to close. Maximal displacement is determined by the volume of the liquid extrusion, which is limited by the total pore volume of the matrix  14 . 
         [0021]    While the operation of the tool  10  has been described with respect to a safety valve, it is to be understood that any downhole tool requiring a biasing member could be reconfigured with the capillary biasing system providing for a lightweight, cycle fatigue limited, highly efficient and simple operation. Moreover, the capillary spring provides a high power (force and stroke) biasing member packagable in a small volume (radial dimension limitations or limited axial dimensions or both, for example) which is extremely beneficial to an industry such as the hydrocarbon recovery industry due to the limited space available for any particular component of any downhole tool. For exemplary purposes only and without limitation, some other uses of the capillary spring include injection control valve, setting mechanisms, shock absorbers, damping tools, as a media for an inflation packer, for a reactive core packer, etc. 
         [0022]    While preferred embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.