Abstract:
A remotely actuated clamping device for a borehole seismic sensing system. The remotely actuated clamping device includes a clamping mechanism configured to engage a surface of a borehole by actuation of the clamping mechanism. The remotely actuated clamping device also includes a fluid based actuator configured to actuate the clamping mechanism. The fluid based actuator includes a chamber configured to be kept at a pressure that is isolated from an ambient pressure of the borehole. The fluid based actuator also includes a piston within the chamber. The chamber receives a pressurized fluid to move the piston within the chamber to actuate the clamping mechanism. The pressure used to actuate the clamping mechanism is independent of the ambient pressure of the borehole. Also disclosed are methods of operating the device.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/676,565, filed on Jul. 27, 2012, the contents of which are incorporated in this application by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The field of the invention relates to an apparatus and method for clamping a borehole seismic sensor (e.g., an accelerometer, a geophone sensor, etc.) within a borehole (e.g., a well bore) to ensure good coupling to the borehole wall, down hole formations, or both. 
       BACKGROUND OF THE INVENTION 
       [0003]    A sonde is an instrument probe used to automatically obtain information (e.g., vibration, pressure, temperature, etc.) about its surroundings (e.g., underground, under water, in the atmosphere, and the like). Seismic sensors are routinely placed within well bores to obtain information regarding the properties, structure, and activity of the earth in the area surrounding the well bore. Seismic sensor sondes may be individual units or multi-sonde tools linked together via, for example, a cable. In order to obtain accurate seismic data, the sensors or sondes are desirably rigidly coupled to the well bore in order to retrieve the seismic data. Often, the outer surface of a well bore is cemented to the surrounding earth, so that by securing the sensors to the well bore, the sensors are in effect coupled to the earth. 
         [0004]    The sensors are typically lowered into the well bore many hundreds or even thousands of feet before they are clamped into position. Therefore, it is desirable that the clamp have a low drag as it is lowered into position. Typically, the clamping mechanism of a sensor is in the retracted position while lowering the sensor array/string to the desired position. The clamping mechanism or mechanisms is or are actuated (e.g., extended) to lock the sensor or sensors in place after the desired depth is reached. The activation and deactivation of the clamping mechanism is usually performed remotely by an operator at the surface. Actuation can be electronic, hydraulic, pneumatic, or accomplished using any other suitable mechanism. 
         [0005]    Another key parameter of a borehole clamping mechanism is the clamping force versus the total weight of the sensor and housing. It is generally desirable within the industry to have a clamping force-to-weight ratio of 10, whereas clamping forces less than that ratio may not provide an acceptable level of mechanical coupling to the borehole surface. In certain applications, passive bow spring clamps and/or magnetic clamps having a much lower clamping force-to-weight ratio are adequate. These types of clamps are always engaged both during installation and during data collection. As a result of the clamps always being engaged, the total drag force during installation must be overcome by a weight at the bottom of the sensor array or electric tractor; however, there are practical limits to the amount of weight that can be added to the bottom of the sensor array, and tractors require high electrical current, necessitating copper conductors within the entire length of the sensing array and lead cable. 
         [0006]    For borehole clamps that are not passive (i.e., they rely on a remotely actuated mechanism to engage and disengage the clamping force), several variations exist. The most widely used clamp employs an integral electric motor and lead screw arrangement to position a clamping mechanism. Advantages of such an arrangement include a high clamping force and a simple design. Disadvantages of such an arrangement include the need for electrical power in the borehole, and design considerations to avoid sparks or electrical discharges down hole. Most such electrically powered systems have a short lifetime in high temperature borehole environments (e.g., above 150° C.). 
         [0007]    Clamping mechanisms that rely on hydraulic actuation have also been used. Such mechanisms include expandable bladders or actuator arms actuated by hydraulic pressure. Advantages of such hydraulic mechanisms include no electrical power down hole and a high clamping force. Disadvantages of such hydraulic mechanisms include the hydrostatic effects of the wellbore and the height of fluid in the hydraulic line which could be thousands of feet. Alternatively, a high pressure gas can be used to actuate a down-hole clamp, but the gas pressure must be high enough to overcome the down-hole pressure, which may be tens of thousands of pounds per square inch (psi). 
         [0008]    One method that is currently being used to overcome the hydrostatic effects due to the height of the fluid column in a hydraulically actuated system is to use the well bore fluid as the hydraulic fluid. Such systems typically employ a check valve at the bottom of the hydraulic line that allows the well bore fluid to flow into the hydraulic line until the water level in the hydraulic line matches the water level in the well bore. Pneumatic pressure applied from the surface to the hydraulic line closes the check valve and pressurizes the hydraulic line, thus actuating the clamping force. To release the clamping force, a substantially higher and overpressure is applied which releases a blowout plug which relieves the hydraulic pressure. These systems tend to be unreliable, however, and are susceptible to clogging of the valve with wellbore debris. 
         [0009]    With the advent of fiber optic down-hole seismic sensors, electronics and electrical power are often unavailable down hole. Thus, it would be desirable to provide a simple, high-performance borehole clamping system that does not require down-hole electronics or electrical power, and that can operate equally well at both high and low pressures and both high and low temperatures. There remains a need in the industry for such a system. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    To meet this and other needs, and according to an exemplary embodiment of the present invention, a remotely actuated clamping device for a borehole seismic sensing system is provided. The remotely actuated clamping device includes a clamping mechanism configured to engage a surface of a borehole by actuation of the clamping mechanism. The remotely actuated clamping device also includes a fluid based actuator configured to actuate the clamping mechanism. The fluid based actuator includes a chamber configured to be kept at a pressure that is isolated from an ambient pressure of the borehole. The fluid based actuator also includes a piston within the chamber. The chamber receives a pressurized fluid to move the piston within the chamber to actuate the clamping mechanism. The pressure used to actuate the clamping mechanism is independent of the ambient pressure of the borehole. 
         [0011]    According to another exemplary embodiment of the present invention, another remotely actuated clamping device for a borehole seismic sensing system is provided. The remotely actuated clamping device includes a clamping mechanism configured to engage an inside surface of a borehole due to actuation of the clamping mechanism. The remotely actuated clamping device also includes a fluid based actuator configured to actuate the clamping mechanism. The fluid based actuator has a chamber including a piston dividing the chamber into a first region and a second region. The fluid based actuator also has a connecting rod assembly extending through an entire length of the chamber and beyond each of two sides of the chamber. The connecting rod assembly is coupled to the piston such that movement of the piston within the chamber results in movement of the connecting rod assembly. The connecting rod assembly is engaged with the clamping mechanism at a position outside of the chamber such that the clamping mechanism is configured to be actuated by motion of the connecting rod assembly. An area of the fluid based actuator outside of the chamber is configured to be exposed to an ambient pressure of the wellbore. 
         [0012]    According to yet another exemplary embodiment of the present invention, a method of remotely operating a clamping device within a borehole is provided. The method includes the steps of: (a) lowering an array of one or more seismic sensing assemblies into a borehole; and (b) actuating a clamping mechanism of the seismic sensing assembly such that the clamping mechanism is engaged against a surface of the borehole, wherein the clamping mechanism is actuated by applying a fluid pressure to a fluid based actuator of the seismic sensing assembly, wherein the pressure used to actuate the clamping mechanism is independent of the ambient pressure of the borehole. 
         [0013]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0014]    The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures: 
           [0015]      FIG. 1A  is a side view diagram of a seismic sensor in a borehole, with a clamping mechanism of the seismic sensor in a retracted position, in accordance with an exemplary embodiment of the present invention; 
           [0016]      FIG. 1B  is a side view diagram of the seismic sensor of  FIG. 1A  with the clamping mechanism in an extended position; 
           [0017]      FIG. 2A  is a block diagram side view of a portion of a seismic sensor in a borehole, with a clamping mechanism of the seismic sensor in a retracted position, in accordance with an exemplary embodiment of the present invention; 
           [0018]      FIG. 2B  is a side view diagram of the seismic sensor of  FIG. 2A  with the clamping mechanism in an extended position; and 
           [0019]      FIG. 3  is a flow diagram illustrating a method of remotely operating a clamping device within a borehole in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    As will be explained in greater detail below, according to certain exemplary embodiments of the present invention, improved clamping devices for borehole seismic sensors are provided. Exemplary clamping devices for securing down-hole seismic sensors to the inside of a borehole (e.g., a well bore) are provided which improve the mechanical coupling of seismic disturbances from the earth surrounding the borehole to the sensor. Such a clamping device is powered by a fluid based (e.g., pneumatic or hydraulic) actuator that is pressure-compensated to minimize the effects of ambient pressure. The clamping device may be integral to a sonde (e.g., a sensor housing) or it can be fastened to an existing sensor housing. A borehole sensor array includes a string of one or more seismic sensor sondes, each containing one or more seismic sensors. Each of the seismic sensor sondes and/or each of the seismic sensors may include one or more of the inventive clamping devices. The seismic sensors may desirably include a housing to protect the sensors from borehole pressure and fluids. 
         [0021]    As provided above, conventional fluid based actuators may have to overcome the effects of the height of the wellbore fluid column and the height of the fluid in the fluid line which could be tens of thousands of feet. Thus, the pressure required can easily be thousands of psi. According to the present invention, because the fluid based actuator is pressure compensated, a substantially reduced pressure (e.g., on the order of hundreds of psi) may be used to simply overcome a spring in the actuator chamber. This is because the fluid of the borehole (e.g., oil, gas, etc.) acts on both ends of the connecting rod/beam, except within the chamber as described below), and as such, there is no need to overcome the ambient pressure level. 
         [0022]    Referring to  FIGS. 1A and 1B , a seismic sensor  100  (also known as a seismic sensing assembly) is illustrated in a borehole  120 . As will be understood by those skilled in the art, many details of seismic sensor  100  are omitted for simplicity. Further, as will be understood by those skilled in the art, a plurality of seismic sensors  100  may be combined in an array (e.g., along a cable) within borehole  120 . A fluid line  104  (e.g., a pneumatic or hydraulic fluid line) carries a fluid (e.g., gas such as nitrogen or air, or a liquid such as a hydraulic fluid) to a clamping device  102 . 
         [0023]    Clamping device  102  is secured to seismic sensor  100  (e.g., using one or more securing mechanisms). Clamping device  102  has a clamping mechanism  105  (including a clamp arm  106  and a foot member  108 ) and a fluid based actuator  110  (e.g., a pneumatic actuator  110 ) that is configured to operate clamp arm  106  through a connecting rod  112 . More specifically (when the fluid based actuator is pneumatic as described herein), an increase in pneumatic pressure provided by fluid line  104  operates fluid based actuator  110 , which in turn moves connecting rod  112  (e.g., through motion of a piston in fluid based actuator  110 , not shown in  FIG. 1A  or  1 B), which in turn pivotally activates (i.e., extends) clamp arm  106 . When clamp arm  106  is extended, as shown in  FIG. 1B  (with clamp arm  106  in an extended position, as opposed to the retracted position of  FIG. 1A ), foot member  108  coupled (directly or indirectly) to clamp arm  106  presses against an inside surface  120   a  of borehole  120  (e.g., a wall of a well bore). In the exemplary embodiment illustrated in  FIGS. 1A and 1B , clamp arm  106  is a pivoting linkage arm that includes links  106   a,    106   b,  and  106   c  (with pins disposed between the links). An optional cover  122  is illustrated to protect many of the elements of seismic sensor  100 , for example, during lowering of seismic sensor  100  into borehole  120  (or retrieval from borehole  120 ). 
         [0024]    In accordance with various exemplary embodiments of the present invention, the pressure seen by the various elements of seismic sensor  100 , including the ends of connecting rod  112 , but excluding a chamber (including a piston) within fluid based actuator  110 , is an ambient pressure of borehole  120 . This reduces the magnitude of the fluid pressure used to actuate fluid based actuator  110  for actuating the clamping mechanism because the ambient pressure of borehole  120  does not need to be overcome by the applied fluid pressure. 
         [0025]    Fluid based actuator  110  may have a number of different configurations.  FIGS. 2A and 2B  illustrate an exemplary configuration. In  FIGS. 2A and 2B , certain of the reference numerals are the same as for like elements in  FIGS. 1A and 1B , except that the reference numerals begin with the number “2” instead of the number “1.” In  FIGS. 2A and 2B , only a portion of a seismic sensor  200  is illustrated, that is, primarily a fluid based actuator  210  and a clamping mechanism  205  (both being part of a clamping device  202 ) within a borehole  220 . Other elements of the seismic sensor are omitted for simplicity. 
         [0026]    Fluid based actuator  210  shown in  FIGS. 2A and 2B  (referred to hereinafter as a pneumatic actuator) includes a chamber  218  and a piston  214  within chamber  218 . Chamber  218  is defined between walls  218   a,    218   b.  Piston  214  divides chamber  218  into a first region  218   c  and a second region  218   d.  A pneumatic fluid is received by region  218   d  via a pneumatic fluid line  204   a.  Region  218   c  includes a restoring spring  216 . A connecting rod  212  extends through the entire length of chamber  218 . One end of connecting rod  212  extends beyond wall  218   b.  The opposite end of connecting rod  212  extends beyond wall  218   a,  and is coupled (either directly or indirectly, as desired) to clamping mechanism  205 . Clamping mechanism  205  has a clamp arm  206  (including links  206   a,    206   b,  and  206   c  with pins disposed between the links) and a foot member  208 . 
         [0027]    In  FIGS. 2A and 2B , an ambient pressure P 1  within borehole  220  is seen by clamp arm  206 , foot member  208 , and the end portions of connecting rod  212  outside of chamber  210 . Thus, in order to actuate clamp arm  206 , a pneumatic pressure is applied via fluid line  204   a  into region  218   d  of chamber  218 . The pressure in region  218   d  is a pressure P 2 , which is isolated from ambient pressure P 1 . When the pressure within region  218   d  reaches a level needed to move piston  214  within chamber  218 , restoring spring  216  is compressed as shown in  FIG. 2B . Connecting rod  212  is connected (either directly or indirectly) to piston  214 , and as such, when piston  214  moves within chamber  218  connecting rod  212  also moves. In  FIG. 2A , clamp arm  206  is in a retracted position. The movement of connecting rod  212  causes pivoting of pivoting clamp arm  206  into the extended position shown in  FIG. 2B . Extension of clamp arm  206  causes foot member  208  to press against inside surface  220   a  of borehole  220 . When at least a portion of the fluid pressure is removed (e.g., vented) from region  218   d,  restoring spring  216  restores clamp arm  206  to the retracted position shown in  FIG. 2A . 
         [0028]    The devices illustrated in  FIGS. 1A ,  1 B,  2 A, and  2 B, and described above, are exemplary in nature. Alternative arrangements and elements are contemplated. For example, connecting rods  112  and  212  may have varying cross-sectional shapes such as round, square, rectangular, etc. Further, a connecting rod (also referred to as a connecting rod assembly) may be a single piece or multiple pieces coupled together, either directly or indirectly. Likewise, although linkage-based clamp arms are illustrated (elements  106  and  206 ), alternative types of clamping structure may be actuated/driven by the fluid based actuator. 
         [0029]      FIG. 3  is a flow diagram illustrating the steps of a method for remotely operating a clamping device (such as the devices shown in  FIGS. 1A ,  1 B,  2 A, and  2 B) within a borehole in accordance with an exemplary embodiment of the present invention. As will be appreciated by those skilled in the art, certain steps may be rearranged or omitted, or additional steps may be added, within the scope of the present invention. At Step  300 , an array of one or more seismic sensing assemblies (e.g., sondes) is lowered into a borehole. At Step  302 , a clamping mechanism (e.g., mechanisms  105 ,  205  as shown in  FIGS. 1A and 2A ) of each seismic sensing assembly is actuated such that each clamping mechanism is engaged against a borehole surface (e.g., foot members  108 ,  208  engaged against borehole surfaces  120   a,    220   a,  as shown in  FIGS. 1B and 2B ). At Step  304 , physical parameters within the borehole (e.g., vibration, pressure, temperature, etc.) are sensed using one or more sensors within each sonde. The sensors may be, for example, fiber optic sensors. Such fiber optic sensors may include fiber optic transducers, accelerometers, etc. At Step  306 , the sensed physical parameter data are transmitted from the seismic sensing assemblies to surface electronics (e.g., such as interrogator-based electronics) outside of the borehole. For example, such data may be transmitted using fiber optic cables from the borehole to the surface electronics. At Step  308 , the seismic sensing assemblies are released from the borehole surface by releasing fluid pressure from a chamber of each fluid based actuator, thereby restoring the clamping mechanisms to their retracted state (e.g., using a restoring spring such as spring  216  shown in  FIGS. 2A and 2B ). At Step  310 , the array of seismic sensing assemblies is retrieved from the borehole. 
         [0030]    Although illustrated and described above with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention.