Abstract:
A measurement device, method, and integrated module for a cable array for determining a downhole parameter are provided. The measurement device, method and integrated module may include a first strain gauge mounted perpendicularly along a central axis of a tension member and a second strain gauge mounted a distance away from but parallel to the central axis of the tension member. The first strain gauge and the second strain gauge may be configured to measure strain induced by at least one of tension or downhole pressure. In addition, the measurements from the first and the second strain gauge may be used to determine the tension at that point in the cable array.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of a related U.S. Provisional Application Ser. No. 62/264,864, filed Dec. 09, 2015, entitled “System and Method for Measuring Cable Tension or Pressure,” to Makito KATAYAMA, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section. 
         [0003]    In downhole operations such as seismic measurement, a current business trend is to have an increasing number of sensor modules for a cable array. In part, because large quantities of sensor module recordings contributes to a combination of reduced operation time and results in providing a higher quality of data. For example, some companies produce downhole seismic array tools which have more than 100 receiver modules within a single array structure. 
         [0004]    In order to use more receivers, one element for further development of downhole array tools is the efficient use of a stress member of the cable. The large number of mechanical joints of the tension member between the cable and the many modules result in increasing tool weight due in part to the complexity of the mechanical connections. 
         [0005]    In such long array tools, cable tension measurements are required to detect points or locations where cable stacking is occurring. Cables with integrated modules may be used to help avoid numerous complex and heavy mechanical connections. However, with a cable comprising integrated modules, cable tension cannot be readily measured because tension force is not applied directly to the integrated sensor module. 
       SUMMARY 
       [0006]    This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
         [0007]    Embodiments of the claimed disclosure may comprise a measurement device for determining tension in a cable array. The measurement device may include a first strain gauge mounted perpendicularly along a central axis of a tension member and a second strain gauge mounted a distance away from but parallel to the central axis of the tension member. The first strain gauge and the second strain gauge may be configured to measure strain induced by at least one of tension or downhole pressure. In addition, the measurements from the first and the second strain gauge may be used to determine the tension at that point in the cable array. 
         [0008]    Additional embodiments of the claimed disclosure may comprise a method for determining a parameter along an integrated sensor module in a cable array. The method may include mounting a first strain gauge along and orthogonal to a central axis of a tension member and mounting a second strain gauge apart from but parallel to the central axis of the tension member. The method may further include reading the strain measurements from the first strain gauge and the second strain gauge and computing the parameter from the readings. 
         [0009]    Other embodiments of the claimed disclosure may comprise an integrated sensor module containing configured to measure a downhole parameter. The integrated sensor module may include a module housing having an interior surface. The integrated sensor module may further include a first strain gauge mounted to one end of the interior surface and a second strain gauge mounted to a side of the interior surface, where the one end is orthogonal to the side. The tension and pressure induced compression of an exterior of the housing may be measured by the first and second strain gauge. The downhole parameter may be determined from the first and second strain gauge measurements. 
         [0010]    Other or alternative features will become apparent from the following description, from the drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Certain embodiments will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying drawings illustrate only the various implementations described herein and are not meant to limit the scope of various technologies described herein. The drawings are as follows: 
           [0012]      FIG. 1  is a schematic illustration of a downhole array cable and module, according to an embodiment of the disclosure; 
           [0013]      FIG. 2  is a schematic illustration of a downhole module, according to an embodiment of the disclosure; 
           [0014]      FIG. 3  is a schematic illustration of cable tension and responding stress being applied to a module, according to an embodiment of the disclosure; and 
           [0015]      FIG. 4  is a schematic illustration of pressure and responding stress being applied to a module, according to an embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Reference throughout the specification to “one embodiment,” “an embodiment,” “some embodiments,” “one aspect,” “an aspect,” or “some aspects” means that a particular feature, structure, method, or characteristic described in connection with the embodiment or aspect is included in at least one embodiment of the present disclosure. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, methods, or characteristics may be combined in any suitable manner in one or more embodiments. The words “including” and “having” shall have the same meaning as the word “comprising.” 
         [0017]    As used throughout the specification and claims, the term “downhole” refers to a subterranean environment, particularly in a wellbore. “Downhole tool” is used broadly to mean any tool used in a subterranean environment including, but not limited to, a logging tool, an imaging tool, an acoustic tool, a permanent monitoring tool, and a combination tool. 
         [0018]    Embodiments of this disclosure concern a method to allow the measuring of cable tension from a module integrally located in a cable assembly for downhole array tools. In a downhole operation such as seismic measurement, it is a generally increasing trend to have as many sensor modules provided on an array cable as possible. This may be due in part because a large numbers of sensor recording modules can result in minimal operation time while providing high quality data. 
         [0019]    To gain more receivers, efficient use of a cable stress member is one component to consider for the further development of a downhole array tool. The use of many mechanical joints for tension members located between the cable and the modules results in an increased tool weight. In some cases, the increased tool weight is because the multiple mechanical connections are relatively heavy and complex. To resolve this issue, some cable assemblies have addressed how to avoid extraneous mechanical connections between cable and modules. These ideas include locating the modules inside of the armored cable (e.g., module integrated cable or cable with integrated modules). 
         [0020]    In long array tools, cable tension measurements can be used to detect cable stacking points or locations along the tool. These cable tension measurements have previously been incorporated at the mechanical connections between the cable and the modules. However, module integrated cables are more efficient in their use of components and generally avoid correspondingly large numbers of mechanical connections for large numbers of integrated modules. As a result, when using a module integrated cable, cable tension cannot be as readily measured because the tension force is not applied directly to the connection between the sensor module and the cable. 
         [0021]    Embodiments of this disclosure include methods to measure the cable tension for a module integrated cable. Generally, some exemplary embodiments of the cable tension measurement system use an understanding that the cable tension is correlated to the compression stress applied to the module housing. In some embodiments, the measurement system comprises two (2) strain gauges and an associated acquisition system. 
         [0022]    Referring generally to  FIG. 1 , this figure illustrates a downhole cable array system  100  comprising a plurality of integrated modules  120  connected by a module integrated cable  110 , according to an embodiment of this disclosure. The downhole operation shown in the figure may be for a wireline deployed seismic measurement, but other embodiments may not be limited to this exemplary application. The figure has multiple integrated modules  120  in the module integrated cable  110  and is shown in a deviated wellbore  12  extending at an angle from vertical. 
         [0023]    In this exemplary embodiment, as seen in exemplary  FIG. 2 , an integrated module  120  and module integrated cable  110  is surrounded by a tension member  250  that extends beyond the integrated module  120  and corresponding module integrated cables  110  to the next integrated module, cables, components, or to the surface of the well bore. The tension member  250  in this embodiment is shown in a relatively continuous manner as encompassing, surrounding, or containing the integrated module  120  and module integrated cables  110  and down. 
         [0024]    A cable tension measurement system for such a downhole cable array system  100  may use the relationship between cable tension and compression stress on the integrated module  120  housing. The compression stress applied to the integrated module  120  housing can be converted to cable tension at that point in the cable array system  100 . 
         [0025]    Referring generally now to exemplary  FIG. 3 , tension  340  (see arrows) is applied along the cable array system  100  resulting in compressive stress to the integrated cable  120  housing. In some embodiments of the tension measurement system, two strain gauges are used and located on inner surfaces of the housing of the integrated module  120 . Other embodiments may include more strain gauges some less, while still other embodiments may position the strain gauges in alternative or multiple positions. In this example, one strain gauge  310  is provided on an edge of the integrated sensor module&#39;s  120  housing (i.e., top, or left hand side of the figure) and another strain gauge  320  is provided on the cylindrical surface of the housing (i.e., side). 
         [0026]    When deployed, there are two significant types of stresses that need to be taken into consideration: compression  330  due to the tension  340  in the tension member  250  and compression  330  due to surrounding downhole pressure ( FIG. 3  compression arrows represent a combination of tension induced compression and compression due to downhole pressure). When tension  340  is applied to the cable array system  100 , the outer cylindrical surface of integrated modular  120  housing is compressed due to the reaction of the tension member. However, the top and bottom edges (i.e., left and right sides as shown, where strain gauge  310  is also shown as located for example) of the integrated sensor module&#39;s housing each edges of sensor housing aren&#39;t compressed. 
         [0027]    Strain gauge  310  measures the strain induced by tension  340  and the strain induced by pressure  430  (see  FIG. 4 ). Strain gauge  320  also measures the strain induced by tension  340  and the strain induced by downhole pressure  430  acting on the top and bottom edges of the integrated module  120 . However, each of the strain gauges  310  and  320  have different degrees of sensitivity to either pressure induced strain and tension induced strain. By comparing the results of the two strain gauges,  310  and  320 , the pressure effects can be removed from the measurements, resulting in the strain primarily produced by tension  340 . The tension  340  can be determined using an experimentally or mathematically determined relationship between the measured strain in the integrated module housing  120  and corresponding tension  340 , such as in a constant pressure environment for example. 
         [0028]    Turning generally now to  FIG. 4 , when downhole pressure  430  is applied to the integrated module  120  housing, compression is applied to every surface of integrated sensor module housing. The two types of compression (i.e., due to applying tension to the tension member and due to the surrounding conditions in the wellbore) are linearly independent to the two strains on the housing. Accordingly, pressure and the tension can be separately determined at the same time by using the two strain gauges  310  and  320 . 
         [0029]    By measuring the tension through the use of strain gauges, stacking locations along the cable array can be determined. Stacking refers to instances where a cable may become snagged or movement inhibited because of friction or some obstruction located downhole. Stacking is much more prevalent in deviated wells, requiring the use of a tractor or other mechanism to pull the cable array along the wellbore. Stacking would be indicated by comparing the tension measurements from one integrated sensor module to the other integrated sensor modules. As measurements are taken further down the cable array system  100 , there should be a corresponding decrease in tension as the weight induced by the below suspended components of the cable array system  100  are reduced. 
         [0030]    For a fully deployed, substantially vertical wellbore with no interior obstructions, the tension measurement for each integrated sensor module should be a function of the length or mass of cable array extending below the specific module. When the tension values do not correspond or correlate to their relative position in the cable array, this could provide an indication of stacking, i.e., a location where the cable array is caught on an obstruction or where friction forces counteract the mass effects of the cable array. 
         [0031]    Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this disclosure. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. 
         [0032]    In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.