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CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   The present invention relates generally to methods and apparatus for attaching a sensor to a tubing string for deployment within a wellbore. More specifically, the present invention relates to methods and apparatus for attaching a sensor to a tubing string for deployment within a highly deviated wellbore. 
   During the production of hydrocarbons from an underground reservoir or formation, it is important to determine the development and behavior of the reservoir and to foresee changes which will affect the reservoir. Methods and apparatus for determining and measuring downhole parameters for forecasting the behavior of the reservoir are well known in the art. 
   A standard method and apparatus includes placing one or more sensors downhole adjacent the reservoir and recording seismic signals generated from a source often located at the surface. Hydrophones, geophones, and accelerometers are three types of sensors used for recording such seismic signals. Hydrophones respond to pressure changes in a fluid excited by seismic waves, and consequently must be in contact with the fluid to function. Seismic waves are waves of elastic energy, approximately in the range of 1 to 100 Hz, having both a compressional and a shear component, where the compressional component, or P-wave, oscillates in a direction parallel to propagation of the wave, and the shear component, or S-wave, oscillates in a direction perpendicular to the propagation of the wave. 
   Hydrophones are non-directional and respond only to the compressional component of the seismic wave. They can be used to indirectly measure the shear wave component when the shear component is converted to a compressional wave (e.g. at formation interfaces or at the wellbore-formation interface). Geophones measure both compressional and shear waves directly They include particle velocity detectors and typically provide three-component velocity measurement. Accelerometers also directly measure both compressional and shear waves, but instead of detecting particle velocities, accelerometers detect accelerations, and hence have higher sensitivities at higher frequencies. Accelerometers are also available having three-component acceleration measurements. Both geophones and accelerometers can be used to determine the direction of arrival of the transmitted waves. 
   Other sensors are available that enable various parameters to be measured, especially acoustic noise, natural radioactivity, temperature, pressure, etc. The sensors may be positioned inside the production tubing for carrying out localized measurements of the nearby annulus or for monitoring fluid flowing through the production tubing. While the location within the wellbore of some of these sensors is not critical, in the case of geophones and accelerometers, the sensors must be mechanically coupled to the formation in order to conduct the desired measurement. 
   One method of coupling a sensor to the formation is by providing the wireline sonde with a mechanical arm which can be extended against the wall of the casing. The arm may be extended by mechanical means, fluid pressure, or electrical actuation. When extended, the arm presses the sensor against the opposite wall of the casing with a force sufficient to prevent relative motion of the sensor with respect to the casing. As a rule of thumb, the force applied by the arm should be at least five times the weight of the sensor, and it is not uncommon for sensors to weigh 30 lbs. or more. 
   Another mechanism for coupling a sensor to a formation involves the use of springs to force the sensor against the wall of the casing. The sensor is maintained in a retracted position while the tubing string is run into the wellbore. When the tubing string has reached its deployment location, the springs are released and force the sensor against the casing. As in those designs employing arms, the springs are designed to provide a certain force to push the sensor onto the casing. When operating in highly deviated well sections, including near horizontal and horizontal sections, both spring and arm systems have faced challenges. In contrast to a normal vertical wellbore, where the string is likely to be somewhat centered, in these highly deviated sections the tubing string is likely to rest against the casing with some or all of the weight of the string bearing against the casing wall. 
   Although most spring and arm systems are designed to actuate with a force greater than the weight of the sensor, they may not have enough force to push the string away from the casing, when the sensor is between the casing and the tubing, or sufficient reach to push the sensor against the far wall of the casing, when the tubing is directly against the casing. If the system fails to fully actuate, the sensor may not be maintained in the desired, stable relationship with the wellbore, making data acquisition conditions less than ideal. 
   Thus, there remains a need in the art for methods and apparatus to deploy sensors into highly deviated sections of a wellbore. Therefore, the embodiments of the present invention are directed to methods and apparatus, for attaching a sensor to a tubing string for deployment in a highly deviated wellbore section, that seek to overcome these and other limitations of the prior art. 
   SUMMARY OF THE PREFERRED EMBODIMENTS 
   Accordingly, there is provided herein methods and apparatus for attaching a sensor to a tubing string for installation into a highly deviated wellbore. The preferred embodiments of the present invention are characterized by an apparatus for securely affixing a sensor to a tubing string, wherein the apparatus also provides a sufficient coupling to the casing of the wellbore. The embodiments of the present invention act to provide stable, reliable coupling between a sensor and the casing of a highly deviated wellbore. In this context a stable, reliable coupling is achieved when a sensor is maintained in a position to the wellbore where no relative motion occurs between the sensor and the wellbore during data acquisition. 
   In preferred embodiments, the invention includes at least the following embodiments. One embodiment of an apparatus for collecting data from a wellbore includes a sensor, a tubing string, and a connector that fixes the sensor to the tubing so that there is no relative motion between the sensor and the tubing. One such connector includes a first clamping portion and a second clamping portion adapted to form a clamp assembly around a tubing string. The first clamping portion encloses the sensor and attaches around the tubing string to the second clamping portion. The outside surface of both first and second portions may have a plurality of contact members connected thereto for interfacing with the wellbore. 
   The first clamping portion also provides access to connect a sensor to adjacent sensors in a sensor array. In alternative embodiments, either the first or second portion inside diameter may have one or more gripping dogs to ensure the attachment to the tubing string. The clamp assembly may also have one or more bypass grooves to allow for tubing and/or cabling from adjacent instrumentation packages to bypass the clamping assembly. 
   The present invention may also be embodied as a method for disposing a sensor in a highly deviated or horizontal wellbore. A sensor is placed inside a first clamping portion that is combined with a second clamping portion and compressed against a tubing string using a predetermined force. Once the predetermined force is reached, attachment members are installed attaching the first portion to the second portion. Sensor and clamping assembly is then lowered into the wellbore where, in a highly deviated or horizontal section, the tubing and clamp assembly will come to rest on one side of the casing. 
   When disposed in a highly deviated or horizontal wellbore, the mass of the tubing string will force the clamp assembly to the lowermost portion of the casing. The clamp assembly will come to rest on the inside of the casing, preferably contacting in at least two points, and a coupling will be formed between the sensor and the casing across the clamp assembly and the contact members. 
   Thus, the present invention comprises a combination of features and advantages that enable sensors to be reliably deployed in a highly deviated or horizontal wellbore. These and various other characteristics and advantages of the present invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more detailed understanding of the preferred embodiments, reference is made to the accompanying Figures, wherein: 
       FIG. 1  is a perspective view of a clamp assembly; 
       FIG. 2  is a sectional view of the clamping assembly of  FIG. 1 ; 
       FIGS. 3   a - 3   e  are partial sectional views of a clamp assemblies disposed within a wellbore. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. 
   The preferred embodiments of the present invention relate to methods and apparatus for attaching a sensor to a tubing string for deployment in a highly deviated section of a cased wellbore such that the sensor is maintained in a stable, reliable relationship with the well casing. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. 
   Referring now to  FIG. 1 , sensor clamp assembly  100  can be seen installed on tubing string  110 . Assembly  100  includes a first clamping portion  300  and a second clamping portion  400  disposed around tubing  110 . Assembly  100  also includes a plurality of contact members  120  which are disposed on the outside surface of both first portion  300  and second portion  400 . First clamping portion  300  is connected to second clamping portion  400  by way of a plurality of attachment members (not shown), such as screws or bolts, disposed within a plurality of attachment holes  320 ,  420  in each portion, best shown in FIG.  2 . First portion  300  also preferably has a bypass groove  330  in which may be disposed a cable  140 . Each end of first portion  300  also preferably has an access hole  350  to accommodate interconnection between adjacent sensor assemblies. 
   Referring now to  FIG. 2 , assembly  100 , as installed on tubing  110 , is shown in cross-section. First clamping portion  300  includes sensor cavity  310 , attachment holes  320 , bypass grooves  330 , and inside surface  340 . Second clamping portion  400  includes recesses  410 , attachment holes  420 , and inside surface  440 . Assembly  100  further comprises contact members  120 , sensor  130 , cable  140 , dogs  150 , and dog attachment members  160 . 
   First clamping portion  300  has an inside surface  340  that is curved so as to conform to the outer surface of tubing  110 . Portion  300  also includes sensor cavity  310  which is adapted to receive a sensor  130  and maintain sensor  130  in stable contact with tubing  110 . Either end of cavity  310  has access holes  350  (as shown in  FIG. 1 ) that allow sensor  130  to be connected to adjacent sensors in an array. 
   The outer surface of first portion  300  has one or more lengthwise bypass grooves  330  that are sized to accommodate cable  140  as it extends past assembly  100 . Grooves  330  are preferably adapted to receive a flat-pack, or other low profile, cable but may be adapted to receive any cable or tubing that may bypass assembly  100 . First portion  300  also has a plurality of contact members  120  attached to the outer surface. Contact members are preferably constructed of hardened metallic materials welded, or otherwise attached, in place. First portion  300  also includes a plurality of attachment holes  320  corresponding to attachment holes  420  in second portion  400 . 
   Second clamping portion  400  has an inside surface  440  that is curved so as to conform to the outer surface of tubing  110 . Inside surface  440  may have one or more recesses  410  adapted to receive dogs  150  that attach to lower portion  400  by way of dog attachment members  160 . Alternatively dogs  150  may be welded or brazed to inside surface  440 . Dogs  150  are preferably hardened metal inserts having a raised profile so as to prevent movement of second portion  400  relative to tubing  110 . Dogs  150  may have a rectangular, circular, or other shape as required. Dogs  150  may also be constructed integral to second portion  400 . Second portion  400  also has a plurality of contact members  120  attached to the outer surface. 
   First and second clamp portions  300 ,  400  are preferably constructed from a material similar to that used to construct the casing and tubing used in the well. For instance, in a well using standard carbon steel pipe, portions  300 ,  400  may be constructed from a cast steel material. The use of a similar material simplifies the attachment of contact members  120  and also provides for improved data gathering by minimizing the signal loss as a signal travels across different components. In a well having a composite casing or using composite tubing, upper and lower portions  300 ,  400  may be constructed from a composite or other non-metallic material. 
   During installation, first clamping portion  300 , containing sensor  130 , and second clamping portion  400 , including dogs  150 , are placed around tubing  110 . Portions  300 ,  400  are compressed against tubing  110  and each other and attachment members (not shown) are installed through attachment holes  320  and  420 . The compressive force necessary to securely attach portions  300  and  400  to each other and to tubing  110  may be provided by a hydraulic press, or other type of preloading device, so as to minimize the size of attachment members required. Sensor  130  and dogs  150  bear against tubing  110  to prevent any relative motion between tubing  110  and clamp assembly  100 . Once first portion  300  is securely attached to second portion  400  on tubing  110 , assembly  100  is ready for lowering into a wellbore. 
   Sensor  130  is normally a single sensor component of a sensor array. A sensor array may contain five sensors  130  connected in series on either side of a central processing unit. Individual sensors  130  are normally connected to adjacent sensors and then central unit by small tubing or cable, therefore the relative position of sensors  130  must be maintained. Access holes  350  are provided to allow access to sensor  130  as it is installed in clamp assembly  100 . 
   Referring now to  FIGS. 3   a - 3   e , clamp assembly  100  is shown disposed within casing  500  in a highly deviated or horizontal wellbore. As can be seen in  FIGS. 3   a - 3   e , the mass of tubing  110  forces assembly  100  against the lower portion of casing  500 . Regardless of the orientation of tubing  110 , clamp assembly  100  comes to rest, preferably on contact members  120 , against the inside of casing  500 . Therefore, sensor  130  is set in a stable, reliable relationship with casing  500 . The mass of tubing  110  maintains the position of assembly  100  within casing  500  so that sensor  130  can detect signals from the surrounding formation. 
   Therefore, the embodiments of the present invention provide a sensor assembly that creates a stable, reliable connection between sensor  130 , tubing  110 , and the well casing  500 . By utilizing tubing  110  and attachment assembly  100 , a simple, robust arrangement for disposing a sensor is provided in a highly deviated or horizontal wellbore. One preferred clamping assembly  100  is described but any assembly that is capable of maintaining a secure connection can be used. 
   The embodiments set forth herein are merely illustrative and do not limit the scope of the invention or the details therein. It will be appreciated that many other modifications and improvements to the disclosure herein may be made without departing from the scope of the invention or the inventive concepts herein disclosed. Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, including equivalent structures or materials hereafter thought of, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.

Summary:
A method and apparatus, for deploying a sensor attached to tubing in a highly deviated or horizontal wellbore, that are characterized by a stationary attachment system that securely fixes a sensor to a tubing string such that the sensor is coupled to the casing regardless of the orientation of the tubing within the wellbore. One preferred embodiment includes a clamp assembly that encloses the sensor and clamps around the cubing string. The clamp assembly further includes a plurality of contact members that provide stable contact points between the well casing and the clamp assembly. The embodiments of the present invention act to maintain the sensor in a stable coupling with the casing without any actuation required for installation.