Patent Publication Number: US-10316657-B2

Title: Extendable probe and formation testing tool and method

Description:
BACKGROUND 
     In downhole industries such as hydrocarbon exploration and recovery, Carbon Dioxide sequestration, etc., it is often valuable for an operator to measure various formation and or fluid parameters. Such tools are commonly run on wireline but can be conveyed on any string. In one example, fluid mobility in the formation is tested by withdrawing a volume of fluid therefrom through a probe and analyzing drawdown pressures to determine the mobility of that fluid. Equations used by the industry are common and standard and are configured to address variables that are encountered. This unfortunately makes output information good but not optimum since variables inject a measure of uncertainty into the mix. 
     Many different formation testing tools have been used for such endeavors through the years and in general they work well for their intended purposes. Many however are also quite complex and relatively expensive to construct. They are also reliant upon positive hydraulic fluid pressure to extend and to retract thereby necessitating ported hydraulic fluid to different chambers of a piston system. Some of the complexity and engineering requirements of prior tools are driven by these considerations. Further, due to complexity, there are often multiple failure opportunities that require frequent maintenance and may cause downtime for operating tools. 
     Due to the above mentioned drawbacks of existing tools, the art is always receptive to improvements in such tools. 
     SUMMARY 
     An extendable probe for a formation testing tool includes a piston housing having a first diameter portion and a second diameter portion thereof; a piston including a piston base and a piston conduit; a piston base seal disposed between the piston base and the first diameter portion of the piston housing, the piston base seal representing an area; a piston conduit seal disposed between the piston conduit and the second diameter portion, the piston conduit seal representing an area; a pin in operative communication with the piston housing and extending though the piston; a pin seal disposed between the pin and the piston base, the pin seal representing an area; and wherein the piston conduit seal, piston base seal and pin seal each are configured to adhere to the equation: piston conduit seal area=piston base seal area−pin seal area. 
     A method for querying a formation fluid including extending the extendable probe of an extendable probe for a formation testing tool includes a piston housing having a first diameter portion and a second diameter portion thereof; a piston including a piston base and a piston conduit; a piston base seal disposed between the piston base and the first diameter portion of the piston housing, the piston base seal representing an area; a piston conduit seal disposed between the piston conduit and the second diameter portion, the piston conduit seal representing an area; a pin in operative communication with the piston housing and extending thought the piston; a pin seal disposed between the pin and the piston base, the pin seal representing an area; and wherein the piston conduit seal, piston base seal and pin seal each are configured to adhere to the equation: piston conduit seal area=piston base seal area−pin seal area; contacting a formation; withdrawing fluid from the formation; calculating mobility without a volume variable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  is a cross sectional representation of an extendable probe as disclosed herein in a retracted position; 
         FIG. 2  is a cross sectional representation of an extendable probe as disclosed herein in an extended position; 
         FIG. 3  is a cross sectional schematic representation of a formation testing tool in which the extendable probe is disposed; and 
         FIG. 4  is a schematic representation of a wireline string in which a plurality of formation testing tools are disposed depicted in a borehole. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2  simultaneously, an extendable probe  10  is illustrated. The probe  10  as illustrated is configured to maintain constant volume in a sample fluid and to maintain balanced pressure regardless of the degree of extension of the probe  10 . These results will be further explained below after introduction of the components of the probe  10 . 
     The probe  10  comprises a probe housing  12  within which a piston housing  14  is disposed. Attached in sealed relation to the probe housing  12  is pin member  16  that itself comprises a cap  18  and a pin  20 . Cap  18  is sealed to probe housing  12  via seal  22 , which as illustrated is in the form of an o-ring with backups but it will be understood that other seal types could be substituted. It is to be understood that other seals referred to herein are also illustrated as o-ring seals with backups but could be configured as other types of seals. The piston housing  14  is sealed to the probe housing  12  at seals  24  and  26 . Within a bore  28  of piston housing  14  is piston  30  that is sealed to the piston housing at several places as discussed hereunder. Piston  30  is configured to move within the bore  28  to effect the extended and retracted positions of the probe  10 . Piston  30  is sealed to bore  28  by piston base seal  32  and to pin  20  by pin seal  34 . It is to be noticed that the bore  28  though piston housing  14  is configured with two different diameters. A first diameter is denoted L and a second diameter is denoted S in  FIG. 1 , L being a larger diameter than S. First diameter L cooperates with a piston base  36 , sealed as noted by piston base seal  32  and diameter S cooperates with a piston conduit  38  of the piston  30  sealed by piston conduit seal  40 . Axiomatically, the piston base  36  is of a larger diameter than the piston conduit  38 . Seals  32 ,  34  and  40  are instrumental in achieving the benefits of the invention and will be addressed further below. 
     To complete the introduction of components of the probe  10 , piston conduit  38  extends from piston base  36  to a packer support  42 , which itself supports a packer  44 . It is the duty of packer  44  to seal against a formation wall  46  ( FIG. 4 ) when the extendable probe  10  is in use in a manner similar to probes of the prior art. 
     The present inventors have solved the drawbacks of prior art probes mentioned in the background section above by configuring probe  10  in a manner that simplifies the extension and retraction operation while at the same time ensures constant volume and force balance in the tool, thereby enabling better calculations by removing uncontrollable variables. This is achieved by configuring piston  30  such that the piston base  36  and the piston conduit  38  have different diameters. The diameters of piston base  36  and piston conduit  38  are selected to cooperate with diameters L and S of the piston housing  14 . The diameters are selected such that seal areas present in the probe can be balanced against each other to produce a net zero effect for volume and force upon movement of the piston  30  in the piston housing  14 . More specifically, the seals and components are configured such that an area of piston conduit seal  40 =area of piston base seal  32 −area of pin seal  34 . In this way, the volume defined within the piston conduit  38  does not change with the degree of extension of the probe  10 . As such, the previously accepted equation for mobility that included volume as a variable can be simplified with volume as a constant. It will be understood that other volumes associated with fluid samples in the probe and tool are already constant and hence do not require discussion. 
     Probe  10  benefits from actuation that is distinct from more complex configurations of the prior art. Extension and retraction of probe  10  are both affected from a single fluid source acting solely on one area  48  of piston  30 . Applied fluid pressure against area  48  causes the probe to extend until packer  44  contacts a formation wall (not shown). Where fluid pressure is increased above environmental pressure, the probe  10  will extend. Where fluid pressure is reduced below environmental pressure, the probe  10  will retract. In other words, the configuration allows the probe to be pushed out with fluid pressure and sucked back in with a relatively negative pressure. Particularly due to the configuration of probe  10  as set forth herein, the ability to retract the probe  10  simply by creating an underbalanced pressure condition in a volume  50  relative to a pressure condition on the opposite side of seals  32  and  34  leaves opposing surface areas of seals  32 ,  34  and  40  to be used for volume and pressure balancing considerations rather than extension and retraction actuation considerations as in the prior art. 
     Hydraulic fluid ingress and egress to volume  50  is provided through port  54  illustrated in broken lines in  FIG. 2  because it is behind piston housing  14  in this view. It is to be appreciated that the port  54  accesses volume  50  between seals  26  and  22  and fluid migrates between a shoulder portion  60  of cap  18  and a skirt portion  62  of piston housing  14 . 
     Directly connected to the volume constancy of probe  10  is a force balance. Because of the consideration of area of the seals as set forth in the equation above, the force in volume  50  will remain at a set point regardless of pressure on the opposite side of seals  32  and  34 . This removes the requirement for the fluid pressure source to have compensating criteria in its control system which reduces complexity of the overall formation testing tool. Accordingly, the configuration of probe  10  to provide for piston conduit seal  40  area=piston base seal  32  area−pin seal  34  area enables both constant volume and force balance. Force balance is helpful to avoid the overall formation testing tool  70  being forced to extend from a wireline string  80  (see  FIG. 4 ) with which it has been deployed. 
     While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.