Abstract:
In one example, a land based seismic sensing device includes: a seismic sensing unit having a seismic sensor in a housing configured to be buried in the ground; a control unit including a battery in a weather resistant housing configured to be exposed above ground; and a flexible cable mechanically and electrically connecting the seismic sensing unit and the control unit. The cable includes a weather resistant jacket and an electrically conductive element inside the jacket detachably connected between electronic circuitry in the sensing unit and electronic circuitry in the control unit. In one example, the control unit housing includes a first compartment configured to stow the seismic sensing unit and a second compartment configured to stow the cable.

Description:
BACKGROUND 
       [0001]    Seismic surveys are conducted to map subsurface features, for example to help locate oil and gas reservoirs. Land based seismic surveys may include hundreds or thousands of individual seismic sensors placed in the ground in a grid pattern over an area covering many square kilometers. An explosive charge, seismic vibrator or other suitable source of acoustic energy generates sound waves that propagate through subsurface features. The vibrations of sound waves reflected back toward the surface are sensed by the seismic sensors in the grid. Signals from the sensors are collected and used to map the subsurface features in the survey area. The operating conditions surrounding the seismic sensors can adversely affect the accuracy of the sensors. Wind, windborne debris, rain and other background disturbances can expose the sensors to significant unwanted vibration. 
       DRAWINGS 
       [0002]      FIG. 1  is a block diagram illustrating one example of a seismic sensing device in which a sensing unit is housed separate from the control unit. 
         [0003]      FIG. 2  is an elevation view illustrating one example of a seismic sensing device, such as that shown in  FIG. 1 , in which the sensing unit is tethered to the control unit through a detachable cable. The sensing device is shown in a deployed configuration in  FIG. 2  with the sensing unit completely buried in the ground and the control unit above ground. 
         [0004]      FIGS. 3 and 4  are perspective views of the seismic sensing device of  FIG. 2  in an un-deployed configuration in which the sensing unit is stowed on the control unit. 
         [0005]      FIG. 5  is a partial cut-away view of the sensing device of  FIGS. 2-4  showing in more detail the sensing unit stowed on the control unit. 
         [0006]      FIGS. 6 and 7  are perspective views illustrating the cable assembly of the sensing device shown in  FIGS. 2-4  detached from the sensing unit and the control unit. 
         [0007]      FIG. 8  is a detail view illustrating the cable end from  FIGS. 6-7  that connects to the sensing unit. 
         [0008]      FIGS. 9 and 10  are details views illustrating the cable end from  FIGS. 6-7  that connects to the control unit. 
         [0009]      FIG. 11  is a detail view showing another example for the cable end that connects to the control unit. 
     
    
       [0010]    The same part numbers are used to designate the same or similar parts throughout the figures. 
       DESCRIPTION 
       [0011]    A new seismic sensing device has been developed to help improve sensor performance. In one example of the new sensing device, the sensing unit is tethered to the control unit through a flexible cable and configured to be buried completely underground. Isolating the sensing unit from the control unit and completely burying it minimizes the adverse effects of wind, windborne debris, rain and other background disturbances. Also, completely burying the sensing unit helps better couple the seismic sensor to ground vibration. In one example, the control unit for the new sensing device includes exterior compartments for stowing the seismic sensing unit and the cable when the sensing unit is not deployed, to help protect the sensing unit during transportation and storage. 
         [0012]    The scope of protection for the new sensing device is not limited by these examples or by the specific details described below. Rather, the scope of protection is defined by the Claims that follow this Description. 
         [0013]      FIG. 1  is a block diagram illustrating one example of a seismic sensing device  10  in which a sensing unit  12  is housed separate from the control unit  14 .  FIG. 2  is an elevation view illustrating one example implementation of seismic sensing device  10  in which the sensing unit  12  is tethered to the control unit  14  through a detachable cable assembly  15 . The sensing device  10  is shown in a deployed configuration in  FIG. 2  with the sensing unit  12  completely buried in the ground and the control unit  14  exposed above ground. A seismic sensing device  10  is also sometimes commonly referred to as a “node.” A seismic survey may include hundreds or thousands of sensing nodes  10  laid out in a grid pattern over the survey area. The main tasks for each node  10  are to measure ground vibration and store the data representing the measurements until completion of the survey. These tasks must be performed in varied, often extreme environmental conditions. 
         [0014]    Referring first to  FIG. 1 , in the example shown, sensing unit  12  includes an accelerometer MEMS (micro electromechanical system) or other suitable seismic sensor  16 , an ASIC (application specific integrated circuit) or other suitable operating circuitry  18 , a memory  20 , a clock  22 , and a power supply  24 . Seismic readings taken by sensor  16  may be stored in memory  20  while sensor node  10  is deployed during a survey and subsequently uploaded for mapping along with data from other nodes. ASIC  18  may include, for example, time-sync circuitry so that the timing of seismic readings from sensor  16  may be aligned with the seismic source and readings from other sensor nodes. MEMS sensor  16  and ASIC  18  may be housed together as a single electronic module  25 . 
         [0015]    In the example shown, control unit  14  includes a rechargeable battery  26 , a power supply  28 , a GPS (global positioning system)  30 , a wireless transceiver  32 , and a microcontroller  34  and associated memory  36 . Battery  26  powers sensing unit power supply  24  (through cable assembly  15 ) and control unit power supply  28 . A wireless transceiver  32  may include, for example, a radio  38  and antenna  40 . Transceiver  32  puts each sensor node  10  in communication with a local operating base, typically a mobile communications center, from which survey activities are controlled. 
         [0016]    As described in more detail below with reference to  FIG. 5 , control unit  14  may also include an on/off switch  42  that detects the presence and/or absence of seismic sensing unit  12  in the control unit stowage compartment. When sensing unit  12  is removed from the stowage compartment, switch  42  automatically turns on device  10  (through control unit  14 ). When sensing unit  12  is placed into the stowage compartment on control unit  14 , switch  42  automatically turns off device  10  (through control unit  14 ). The use of an automatic on/off switch  42  helps reduce the power consumed by sensing device  10 . 
         [0017]      FIGS. 2-5  illustrate one example of a seismic sensing device  10  in which the sensing unit  12  is tethered to the control unit  14  through a detachable cable assembly  15 . Sensing device  10  is shown in a deployed configuration in  FIG. 2 , with sensing unit  12  buried in the ground and control unit  14  exposed above ground, and in an un-deployed configuration in  FIGS. 3-5 , with sensing unit  12  stowed on control unit  14 . Referring to  FIGS. 2-5 , sensing unit  12  includes a housing  44  configured to be completely buried in the ground, as shown in  FIG. 2 . Sensing unit housing  44  houses the operative components of sensing unit  12 , for example an accelerometer MEMS  16 , ASIC  18 , memory  20 , clock  22 , and power supply  24  shown in  FIG. 1 . In the example shown, sensing unit housing  44  forms a spike to make it easier to bury unit  12  underground. 
         [0018]    Control unit  14  includes a weather resistant housing  46  configured to be exposed above ground when device  10  is deployed, as shown in  FIG. 2 . Control unit housing  46  houses the operative components of control unit  12 , for example a rechargeable battery  26 , a power supply  28 , a GPS  30 , a wireless transceiver  32 , and a microcontroller  34  and associated memory  36  shown in  FIG. 1 . (Transceiver antenna  40  is shown in  FIGS. 2 and 3 .) Control unit housing  46  includes an exterior first compartment  48  configured to stow seismic sensing unit  12 . Housing  46  also includes an exterior second compartment  50  configured to stow cable assembly  15 . In the example shown, control unit housing  46  includes a curved handle  52  and a groove  54  in handle  52  forms the cable stowage compartment  50 . Also, in the example shown, sensing unit stowage compartment  48  is positioned at the bottom of housing  46  away from handle  52  and opposite the cable attachment to maximize the length of cable that can be stowed on control unit  14 . 
         [0019]    Referring to  FIG. 5 , control unit  14  may also include an on/off switch  42  that detects the presence and/or absence of seismic sensing unit  12  in stowage compartment  48  Switch  42  automatically turns control unit  14  on and off depending on the presence of absence of sensing unit  12  in stowage compartment  48 . Thus, when seismic sensing unit  12  is removed from stowage compartment  48 , switch  42  automatically turns on control unit  14 . When sensing unit  12  is placed into stowage compartment  48 , switch  42  automatically turns off control unit  14 . Although any suitable detector/switch may be used,  FIG. 5  depicts generally a Reed switch  42  activated by the presence of a magnet  56  in sensing unit  12 . 
         [0020]    Cable assembly  15  mechanically and electrically connects sensing unit  12  and control unit  14 .  FIGS. 6 and 7  are perspective views illustrating cable assembly  15  detached from units  12  and  14 .  FIG. 8  is a detail view illustrating the cable end  58  that connects to sensing unit  12 .  FIGS. 9 and 10  are detail views illustrating the cable end  60  that connects to control unit  14 . Referring to  FIGS. 6-10 , cable assembly  15  includes a cable  62 , a first connector assembly  64  at end  58  for detachably connecting to sensing unit  12 , and a second connector assembly  66  at end  60  for detachably connecting to control unit  14 . Cable  62  includes a weather resistant jacket  68  and a set of electrical conductors  70  inside jacket  68 . (The exposed ends of conductors  70  are visible in  FIGS. 8-10 .) 
         [0021]    Referring to  FIGS. 6 and 8 , first connector assembly  64  includes a pin connector  72  mounted to a printed circuit board  74  that is connected to cable conductors  70 . Printed circuit board  74  is supported on a rigid frame  76  attached to one end of cable  62 . The parts are covered by an elastomeric molding or other suitable weather resistant protective cover  78 . Pin connector  72  is exposed through cover  78  for connecting to a corresponding connector in sensing unit  12 . An elastomeric cover  78  helps seal the connection when cover  78  is secured to sensing unit housing  44  with screws or other suitable fasteners, as shown in  FIGS. 2 ,  3  and  5 . 
         [0022]    Referring to  FIGS. 6 ,  7 ,  9  and  10 , second connector assembly  66  includes a pin connector  80  mounted to one side of a printed circuit board  82  and a pair of conductive contact pads  84  mounted to the other side of printed circuit board  82 . Printed circuit board  82  is connected to cable conductors  70  and supported on a rigid frame  86  attached to the other end of cable  62 . The parts are covered by an elastomeric molding or other suitable weather resistant protective cover  88 . Pin connector  80  is exposed through one side of cover  88  for connecting to a corresponding connector in control unit  14 . Contact pads  84  are exposed through the other side of cover  88  for connecting to a circuit external to control unit  14 . An elastomeric cover  88  helps seal the connection when cover  88  is secured to control unit housing  46  with screws or other suitable fasteners, as shown in  FIGS. 2 and 3 . 
         [0023]    In another example for second connector assembly  66 , shown in  FIG. 11 , the pin connector and printed circuit board are omitted. Referring to  FIG. 11 , the end  60  of cable  62  extends through protective cover  88 . Cable conductors  70  are connected directly to a connector  80  for making a detachable connection to a mating connector (not shown) in control unit  14 . In this example, contact pads  84  ( FIG. 6 ) are supported by a rigid frame  86  that also serves as a spacer within protective cover  88 . The wiring  90  for contact pads  84  is connected separately to a second connector  92  for connection to a mating connector (not shown) in control unit  14 . 
         [0024]    Contact pads  84 , for example, may be connected to a charging circuit for a rechargeable battery  26  in control unit  14  (through PCB  82  and connector  80 ). The exposed charging pads  84  connect with mating contacts in a charging module configured to hold control unit  14  when seismic sending device  10  is not deployed. Although two contact pads  84  are shown, any suitable number of pads may be used. Integrating battery charging contacts  84  into a detachable/replaceable cable assembly  15  has several benefits. First, each replacement cable  15  gives fresh charge contacts  84  to the control unit  14 , helping to increase the reliability of control unit  14 . Second, the need for an additional penetration into control unit housing  46  is avoided, also helping to increase the reliability of control unit  14 . Third, the need for an additional printed circuit board or other circuitry to support the charge pads is avoided, helping to reduce the cost of control unit  14 . And, of course, the use of a detachable and therefore replaceable cable assembly  15  in general helps extend the useful life of sensing unit  12  and control unit  14 . 
         [0025]    As noted at the beginning of this Description, the examples shown in the Figures and described above do not limit the scope of the invention. Other examples are possible. Accordingly, these and other examples, implementations, configurations and details may be made without departing from the spirit and scope of the invention, which is defined in the following Claims.