Abstract:
A logging tool for use in a wellbore having a sensor portion for making measurements. The tool has a sleeve enclosing the sensor portion and made of a material that is transparent to the measurements being made. One or more structural elements having physical characteristics different from the material comprising the sleeve are carried on the sleeve to enhance the mechanical properties of the sleeve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of, and is a continuation of, U.S. patent application Ser. No. 11/740,981, filed Apr. 27, 2007, which claims priority to and the benefit of US Provisional Application No. 60/796,460, filed May 1, 2006, both applications of which are hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    The present invention pertains to logging tools for use in a wellbore, particularly logging tools having housings made of soft base material relative to the hardness of the wellbore wall or casing disposed in the wellbore. 
         [0004]    2. Related Art 
         [0005]    Logging tools are commonly used, in oil and gas exploration, for example, to ascertain or infer properties of the subsurface formations encountered by a wellbore. Logging tools may be used while drilling the wellbore, or may be run into the wellbore after drilling, for example, on a wireline. Various types of logging tools may be run, depending on the measurement type. Such measurement types may include, but are not limited to, resistivity, nuclear magnetic resonance (NMR), gamma ray, spontaneous potential, and dielectric constant. 
         [0006]    Generally, the bulk of a logging tool is made of very strong material, such as steel. However, often a portion of the tool contains sensors that must communicate in some way with the surrounding environment. For example, resistivity sensors require electromagnetic signals to pass into and from the formation so that information characterizing the formation properties can be obtained. For the signals to pass into or be received from the formation, the sensors are preferably mounted on an electromagnetically transparent medium. Such transparent media may comprise composite, non-metallic materials. A disadvantage to the composite, non-metallic material is its relative softness compared to the formation or casing. In many cases, that relative softness allows wear and tear of the sleeve to occur at an unacceptable high rate. For example, a NMR tool has powerful magnets that are strongly attracted to the steel casing through which the tool must pass before reaching the uncased portion of the wellbore. The magnetic force causes the tool to be dragged against the casing, causing scraping and wear. 
       SUMMARY  
       [0007]    A logging tool for use in a wellbore having a sensor portion for making measurements. The tool has a sleeve enclosing the sensor portion and made of a material that is transparent to the measurements being made. One or more structural elements having physical characteristics different from the material comprising the sleeve are carried on the sleeve to enhance the mechanical properties of the sleeve. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a sleeve  10  in a tool assembly according to one embodiment of the present invention. 
           [0009]      FIG. 2  is a side view of the sleeve  10  of  FIG. 1 . 
           [0010]      FIG. 3   a  shows schematically a top view of the reinforcement material in the sleeve  10  of  FIG. 1 . 
           [0011]      FIG. 3   b  shows an enlarged view of one of the recessed areas in the reinforcement material of  FIG. 3   a.    
           [0012]      FIG. 4  shows a perspective view of a portion of the sleeve  10  of  FIG. 1  in which the recessed area has an overlapping material covering the recessed area. 
           [0013]      FIG. 5  shows a cross sectional view of a sleeve  10  according to one embodiment of the present invention in which the reinforcement material is an insert disposed in receiving grooves in the sleeve  10 . 
           [0014]      FIG. 6  is a cross sectional view of a housing according to one embodiment of the present invention in which the wall of the housing is thickened on one side. 
           [0015]      FIG. 7   a  shows a perspective view according to one embodiment of the present invention in which inserts are disposed asymmetrically around the circumference of the sleeve  10 . 
           [0016]      FIG. 7   b  shows a cross sectional view of a portion of the sleeve  10  of  FIG. 7  containing the inserts. 
           [0017]      FIG. 7   c  shows a cross sectional view of an alternative embodiment having a thickened wall on one side. 
           [0018]      FIG. 8  is a schematic drawing showing an articulated pad in accordance with one embodiment of the present invention. 
           [0019]      FIG. 9  is a schematic drawing of a side view showing one of the pads of  FIG. 8 . 
           [0020]      FIG. 10  is a schematic drawing of a cross sectional view of the pad of  FIG. 9 . 
           [0021]      FIG. 11  is a plan view showing one embodiment according to the present invention in which a portion of the sleeve  10  allows signal to pass and another portion blocks the passage of the signal. 
           [0022]      FIG. 12  is a perspective, partially cut away view showing one embodiment according to the present invention in which the sleeve  10  has electrodes disposed therein along with electrical connections to the electrodes. 
           [0023]      FIG. 13   a  is a perspective view showing a removable standoff ring constructed in accordance with an alternative embodiment of the present invention 
           [0024]      FIG. 13   b  shows a cross sectional view of the removable standoff ring of  FIG. 13   a.    
           [0025]      FIG. 14  shows an alternate embodiment in which the reinforcement material comprises rings inserted into a sleeve in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    The invention pertains to a housing, sleeve, or enclosure  10  for a downhole tool  12  having a sonde or sensor section. The invention protects the tool&#39;s interior from the wellbore environment while maintaining a high degree of transparency to measurements being made. To maximize the protection, the enclosure has substantial mechanical integrity such that it is able to maintain its geometry as well as its protective qualities (i.e., resistance to wear and/or physical deterioration) for a substantial period (e.g., many trips in/out of the well). Numerous logging tools contain a sonde or sensor section that needs a housing, sleeve  10 , or enclosure that does not impede the propagation or reception of the signal or energy being used for a measurement. Such tools include, but are not limited to; Magnetic Resonance tools, Resistivity tools, Pipe Inspection/Corrosion tools, Radial/Axial/Tangential Cameras, and Magnetometer-based tools. The principle of measurement may include signals or energy from one or more of the following types: electrical, magnetic, electromagnetic, nuclear, acoustic, photo, etc. The present invention allows having such a housing, sleeve  10 , cover, etc. (transparent to elements of measurements), but possessing better mechanical integrity. 
         [0027]    Referring to  FIG. 1 , a non-conductive sleeve  10  made of a composite material, for example, is used to enclose the sonde section of a tool  12  that transmits and receives an electromagnetic signal as a basis for its measurement (e.g., magnetic resonance). A strong permanent magnet may be disposed in such a tool  12 . In such cases, as the tool  12  passes through a cased section of the well, it is pulled against the casing wall by the attractive magnetic force between the casing and the magnet. The axial sliding of the sleeve  10  against the steel casing while experiencing the substantial attractive transverse force produces significant wear on the sleeve  10 . This wear can shorten the life of the sleeve  10 , alter its geometry, reduce its mechanical integrity, and reduce its protective qualities against the wellbore environment. The invention, in one embodiment, uses bearing elements  14  (e.g., metallic skids, pads, buttons, etc.) having much tougher mechanical properties than the sleeve  10  base material. The bearing elements are strategically located and embedded in the sleeve  10  base material so as to strengthen the sleeve  10  and protect it against wear. The elements or inserts  14  perform their mechanical function without affecting the physics of the measurement or the placement of the tool  12  in the required section of the wellbore (i.e., non-intrusive geometry). The sleeve  10  can be run on a wireline, in TLC modes (Tough Logging Conditions—pipe conveyed logging) in which mechanical loading is severe, and in D&amp;M assemblies (Drilling and Measurement—Logging While Drilling). 
         [0028]      FIG. 2  shows a sleeve  10  made out of a thermoplastic composite or any electrically non-conductive material that includes several hard and strong inserts  14 . The inserts  14  provide wear resistance and strength to the sleeve  10 . The inserts  14  cover part or all of the axial length of the sleeve  10  and are positioned around the circumference, covering the sleeve  10  partly or fully. The inserts  14  may include overlaps  16  of the sleeve&#39;s material in several locations to secure the inserts  14  onto the sleeve  10 . The inserts  14  may have recessed areas  18  to allow for the composite overlap  16 , as shown in  FIGS. 3   b  and  4 . The thickness of the sleeve  10  may also be increased where the inserts  14  are located such that those areas can provide standoff from the casing or wellbore wall. Alternatively, the insert  14  may be trapped in the sleeve  10  periphery by geometrical constraints  20 , as shown in  FIG. 5 . For example, the insert  14  can have a large chamfer on each side to ensure the inserts  14  are trapped in concave grooves  20  in the sleeve  10 . 
         [0029]    Other embodiments of the invention may include, singularly, in plurality, or in combination, embedded members  22  that are electrically isolated electrodes used to measure wellbore properties (see  FIG. 12 ). The measurement capability of an electrode  22  may be its primary function or secondary to being a strengthening member. As a strengthening member, improvement in tensile and compressive load bearing capacity may be had since those loads on the sleeve  10  are shared by the stronger elements. Besides having a generally more robust design for normal use, this can be important when running tools on drill pipe or during fishing operations. The inserts  14  can also improve bending strength to withstand loads experienced during transverse loading at the surface or in the well; for example passing through a severe dog-leg. An alternative embodiment to the reinforcement elements  14  is having a section with a thickened wall  24 , as shown in  FIG. 6 . Either embodiment leads to improved collapse resistance by increasing the over-all yield strength to hoop stress. This may be critical if the enclosure is protecting sensitive internal components and the spacing between the enclosure and components is small. 
         [0030]    The increased mechanical strength helps preserve the sleeve&#39;s outer geometry when subjected to flexure or wear. This is important, for example, in cases in which maintaining the geometric shape of the enclosure is critical to maintaining measurement accuracy or to maintain a mechanical function such as seal integrity or interaction with other parts. In addition, use of reinforcing inserts  14  or thickened wall  24  improves resistance to changes in or degradation of mechanical properties due to temperature. Generally, for most materials, certain mechanical properties are diminished as temperature is elevated. This is especially true for non-metallic materials such as composites, elastomers, etc. Placing reinforcing inserts  14  having higher resistance to thermal effects in strategic areas can increase the enclosure&#39;s over-all resistance to thermal effects. This is also true for chemical resistance improvement. Improved shock or impact resistance can also be achieved by the present invention. That is, failures due to high strain rate can be reduced by strategic placement of the reinforcement inserts  14 . This may be particularly important at low temperatures (e.g., below OF) where the elasticity (or modulus of elasticity) of non-metallic materials such as composites, elastomers, etc. decreases dramatically. 
         [0031]    A further embodiment forces the tool  12  to self-orient in a certain azimuth or relative heading in the wellbore. By making one sector of the tool  12  heavier, the tool  12  can be forced to orient itself with the heavy side on the low side of the well. This can be achieved by either increasing the wall thickness on one side of the housing  10  ( FIG. 6 ) or by embedding inserts  14  of higher density on the desired heavy side, or both. 
         [0032]    The reinforcement inserts  14  can be made to extend beyond the outside diameter of the housing  10 , as shown in  FIGS. 7   a  and  7   b , to create a desired stand-off (gap) between the tool housing  10  and the wellbore wall. This is particularly important for logging tools whose measurements require a particular stand-off. The embodiment in  FIG. 7   c  achieves the desired stand-off using a thickened wall  24 . 
         [0033]    In another embodiment ( FIG. 14 ), the reinforcing inserts  14  can be rings  26  that are placed at certain points along the length of the sleeve  10 . These rings  26  are positioned along the length of the sleeve  10  in relation to the sensors (not shown) that are located inside the sleeve  10 . The number and location of the rings  26  depends on the available space and mechanical requirements. Ultimately, the rings  26  should be placed such that they have minimum interference with the sensor measurement. In particular, it may be desirable to place the reinforcing rings  26  above and below the sensor section. 
         [0034]    The sleeve  10  can also be protected by standoff sleeves  28  that generate enough space between the sleeve  10  and the borehole wall to prevent or to reduce sleeve wear. An embodiment of such a standoff sleeve  28  is shown in  FIGS. 13   a  and  13   b.  The standoff sleeve  28  shown in  FIGS. 13   a  and  13   b  can be designed to generate standoff between the front of the sensor, the back of the sensor, or any other side of the sensor. The standoff sleeve outer surface may be hardened to reduce wear. The stand-off sleeves can carry measurement sensors that are connected to electronics in the tool  12  similar to that shown in  FIG. 12 . 
         [0035]    The standoff sleeve  28  of  FIGS. 13   a  and  13   b  has grooves  30  between ridges  32 . These grooves  30  are designed to facilitate flow of wellbore fluid and cuttings in the annulus of the wellbore. At least one standoff sleeve  28  is needed to generate the gap between the sleeve  10  and the borehole wall. The standoff sleeve  28  may be attached to the logging tool  12  above or below the sensor section. Alternatively, the standoff sleeve  28  may be attached to the sleeve  10  in locations where it would have minimum interference with sensor operations. In another embodiment, multiple standoff sleeves  28  may be used and placed above and below the sleeve  10 , in addition to being deployed on the sleeve  10 . 
         [0036]    Improved vibration resistance can be achieved using reinforcement inserts  14 . The inserts  14  can modify the natural or resonant frequency of an enclosure  10 . As such, the resistance to vibrate at a particularly harmful frequency (e.g., during land transport) may be increased by the present invention. 
         [0037]    Just as it is important to have measurement transparency in some sections of the housing, sleeve, cover, etc., it may also be important to shield or shunt other sections to block the passage of signal. The invention, as shown in  FIG. 11  and disclosed herein, may be implemented using one or more inserts  14 , for the purpose of shielding or shunting the signal (emission or reception) from the transmitters and/or sensors. This applies to all previously mentioned principles of measurement. 
         [0038]    As mentioned above, in one embodiment the electrically conductive but isolated inserts  14  may be used solely as electrodes  22 , or their function may be combined for mechanical purposes. The application for such electrodes  22  or sensor terminals may include, but is not limited to, measuring SP (Spontaneous Potential), making fast-responding well fluid temperature measurements (for example, to detect leaks or inflow), and measurement of well fluid electrical properties such as resistivity (or its inverse, conductivity). There may also be cases in which an electric potential, for example an electrical ground, needs to connect across the non-conductive housing. Conductive inserts  14  may be strategically placed in the non-conductive housing  10  and electrically connected at the required points to make an electrical connection.  FIG. 12  shows an embodiment in which a connector is embedded in the sleeve  10  to electrically connect the electrode to, for example, a circuit board. 
         [0039]    Situations arise in which the friction between a tool  12  and the wellbore wall needs to be reduced to successfully deploy (lower) the tool  12 , particularly when the tool  12  is conveyed by wireline or slickline. Those cases may include high angle wells (say, greater than 45-degrees inclination) and/or wells having high pressure relative to the effective hanging weight of the tool  12 . Tools with sondes having non-metallic housings typically have higher coefficients of friction than metallic housings, and hence have a more difficult time descending into the well. In the past, rollers were used to assist deployment. The problem with that option is the risk of failure is increased because the rollers add length to the assembly and increase the number of connections that may fail. That option also adds cost. The present invention can solve the problem because the inserts  14  in the non-metallic housings will reduce the coefficient of friction. 
         [0040]    In another embodiment, the present invention may be implemented in logging tools that contain a deployable sensor section  34  (e.g., a pad connected to an articulating mechanism).  FIGS. 8-10  show one such embodiment. The inserts  14  may be strategically placed in the pad  34  to improve the mechanical properties of the pad structure, to improve wear resistance, and to serve as sensor electrodes. 
         [0041]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be envisioned that do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention shall be limited only by the attached claims.