Abstract:
A seismic sensor comprising a coil assembly suspended in a magnet field produced by a magnet assembly, and a locking mechanism for preventing the coil assembly from moving freely until a seismic event is initiated at the surface or within an earth formation to collect seismic data.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to seismic sensors, and more particularly to seismic sensors, such as geophones and accelerometers, which are designed to withstand seismic survey operations where rough handling can reasonably be anticipated, for example, logging while drilling operations as well as on land seismic applications. 
       BACKGROUND 
       [0002]    In the oil and gas industry seismic tools are deployed downhole and on the surface to provide operationally significant information about borehole and formation attributes adjacent the tools. Borehole seismic data can be utilized to determine subsurface stratigraphy and refine surface seismic data. However, the conditions in which such seismic tools are deployed can be extremely harsh. 
         [0003]    More specifically, drilling operations are performed by rotating a drill bit under high normal pressure of 20,000 pounds or so to crush through rock formations. The variable lithology of earth formations and the high pressure and operational temperatures of 150 to 175° C. make the environment adjacent a drill bit and drill collar very rugged and subject to high pressure shocks as the drill bit crushes through formations forming a rugose borehole. Notwithstanding this harsh operating environment it is desirable to make downhole logging while drilling measurements including measurements with relatively delicate seismic equipment such as geophones and accelerometers. Similarly, it is common to use seismic sensors in other rough and harsh operating conditions. The harsh environments however make use of delicate sensors such as geophones and accelerometers problematic. 
         [0004]    In seismic data monitoring or collection conventional geophones or accelerometers may be used which include a coil assembly sensitively suspended in a magnetic field produced by a magnet assembly. Vibrations of the earth induced by seismic sources, for example, at the surface of the earth, produce relative motion between the suspended coil assembly and the magnetic field. This motion induces an electrical signal which is proportional to the relative velocity between the coil assembly and the casing of the geophone. When shocks occur due to the normal operation of the seismic tool the centering springs of the geophones can be damaged to an extent that the seismic tool must be retrieved from the borehole to change the geophone. 
         [0005]    In the past, a significant amount of borehole and formation data has been acquired by embedding sensors within a drill collar so that logging operations can be performed concurrently with drilling. Although it would be desirable to supplement the large amount of data already acquired by direct measurement of seismic waves with a geophone in the past such delicate instruments have been unable to survive the harsh environment for a practical length of time. 
         [0006]    The limitations of conventional seismic sensor designs for operation in environments noted in the preceding are not intended to be exhaustive but rather are among many which may tend to reduce the effectiveness of previously known sensor mechanisms in field operation. The above should be sufficient, however, to demonstrate that sensor structures existing in the past will admit to worthwhile improvement for harsh shock applications. 
       SUMMARY 
       [0007]    Embodiments disclosed herein provide a geophone or an accelerometer including a locking mechanism for selectively preventing a coil assembly from inadvertent movement and damage. In certain embodiments herein, the locking mechanism may be actuated by one or more of fluidic or electromagnetic or piezoelectric action. 
         [0008]    One embodiment herein comprises a geophone with a first fluid bladder (which fluid can be a gas or liquid) and a second fluid bladder formed on an inner surface of a top end cap and a bottom end cap of the geophone, respectively. The first and second fluid bladders are connected to a source assembly. When inflated, the first bladder and the second bladder abut against the springs supported coil assembly of the geophone to prevent a coil assembly of the geophone from moving freely. 
         [0009]    Another embodiment comprises a three-component geophone, each of which is a geophone similar in structure to the geophone described above. The fluid bladders in each of the three geophones are connected to a common fluid source assembly. When inflated, the bladders in each of the three geophones abut against springs of the geophones to prevent coil assemblies of the geophones from moving freely. 
         [0010]    Another embodiment herein comprises a geophone with a tubular magnet mounted on an inner surface of a side wall of the geophone, a bobbin positioned inside the tubular magnet which is resiliently mounted to the side wall by means of springs, at least one coil mounted around the bobbin, and a first damper mechanism and a second damper mechanism mounted on the center region of the inner surfaces of the top end cap and the bottom end cap of the geophone, respectively. When the damper mechanisms are turned on, damper plates of the damper mechanisms abut against a top end and a bottom end of the bobbin, respectively. 
         [0011]    Another embodiment of the subject invention comprises a geophone including a central pole piece connected to a top end cap and a bottom end cap of the geophone, wherein a locking mechanism is located inside the central pole piece. 
         [0012]    In aspects disclosed herein, a seismic sensor comprises a housing; at least one magnet mounted within the housing; a coil assembly mounted within the housing; at least one spring assembly connected to the housing and the coil assembly for supporting the coil assembly for transduction within the magnet; and a locking mechanism for preventing the coil assembly from moving when the sensor is in an OFF status. The locking mechanism may be configured for activation by fluidic action. The fluid activated locking mechanism may comprise at least one fluid bladder and a fluid source assembly. The housing may be configured for positioning within a borehole or may be configured for positioning at the surface. In aspects herein, the locking mechanism may comprise a rotatable locking disc. 
         [0013]    In other aspects of the present disclosure, a geophone for detecting seismic events in a downhole logging while drilling environment comprises a housing operable to be positioned within a borehole; at least one permanent magnet for creating a magnetic field mounted within the housing; a coil assembly mounted within the housing; at least one spring assembly connected to the housing and the coil assembly for supporting the coil assembly for transduction within the magnetic field; and a fluid activated locking mechanism for preventing the coil assembly from moving when the geophone is in an OFF status. The fluid locking mechanism may comprise at least one damper plate operable to abut the coil assembly. 
         [0014]    In yet other aspects herein, a geophone for detecting seismic events in a downhole logging while drilling environment may comprise a housing having a first end cap and a second end cap operable to be positioned within a borehole; a pole piece connected to the first end cap and the second end cap; at least one permanent magnet for creating a magnetic field mounted within the housing; a coil assembly mounted within the housing; at least one spring assembly connected to the housing and the coil assembly for supporting the coil assembly for transduction within the magnetic field; and a locking mechanism for preventing the coil assembly from moving when the geophone is in an OFF status, wherein the locking mechanism is configured for activation by one or more of fluidic, electro-magnetic and piezoelectric action. In aspects disclosed herein, the locking mechanism may be located inside the pole piece and the locking mechanism may comprise a solenoid. 
         [0015]    A three-component geophone for detecting seismic events in a downhole logging while drilling environment comprises a first geophone, a second geophone, and a third geophone oriented along three mutually orthogonal axes; a housing containing the first geophone, second geophone, and third geophone; wherein each of the first geophone, second geophone and third geophone comprises a housing; at least one permanent magnet for creating a magnetic field mounted within the housing; a coil assembly mounted within the housing; at least one spring assembly connected to the housing and the coil assembly for supporting the coil assembly for transduction within the magnetic field; and a locking mechanism for preventing the coil assembly from moving when the sensor is in an OFF status, wherein the locking mechanism may be configured for activation by fluidic action, the fluid activated locking mechanism comprising a fluid source assembly connected to the housing containing the first geophone, second geophone and third geophone; and at least one fluid bladder. In aspects herein, the fluid activated locking mechanism may comprise at least one locking disc actuated by the fluid bladder. In other aspects herein, the fluid activated locking mechanism may comprise at least one diaphragm with a corrugated surface. In yet other aspects, the fluid activated locking mechanism may comprise at least one bellows. The fluid activated locking mechanism may comprise a liquid and/or a gas. 
     
    
     
       THE DRAWINGS 
         [0016]    Other aspects of the present disclosure will become apparent from the following detailed description of embodiments thereof taken in conjunction with the accompanying drawings wherein: 
           [0017]      FIG. 1  is a schematic view of a typical derrick and a logging-while-drilling (LWD) system where a drill string is positioned within a borehole and a well logging segment near a drill bit is shown within a borehole; 
           [0018]      FIG. 2  is a more detailed view of the distal end of a drill string including a drill collar with a geophone, seismic package embedded within a portion of the thick walled drill collar; 
           [0019]      FIGS. 3A and 3B  show a schematic view of a geophone according to one embodiment disclosed herein; 
           [0020]      FIG. 4  shows a geophone according to another embodiment disclosed herein; 
           [0021]      FIG. 5  shows a schematic view of a three-component geophone to detect seismic events as they impact a three dimensional coordinate system; 
           [0022]      FIG. 6  shows a schematic view of a geophone according to another embodiment disclosed herein; 
           [0023]      FIG. 7  shows a schematic view of a three-component geophone utilizing individual geophones as depicted in  FIG. 6 ; 
           [0024]      FIGS. 8A and 8B  show a schematic view of a geophone according to yet another embodiment disclosed herein; 
           [0025]      FIGS. 9A and 9B  show a schematic view of a geophone according to yet another embodiment disclosed herein; 
           [0026]      FIGS. 10A and 10B  disclose another embodiment of the present disclosure including an internal channel for a fluid actuation mechanism; 
           [0027]      FIG. 11  discloses a locking mechanism and securement assembly to prevent both translation and rotation of a suspended assembly; 
           [0028]      FIGS. 12A and 12B  disclose one embodiment of a diaphragm used to form a bladder locking mechanism of a geophone according to one embodiment of the present disclosure; 
           [0029]      FIGS. 13A ,  13 B and  13 C disclose additional embodiments of diaphragms according to the disclosure herein; 
           [0030]      FIG. 14  is a partial cross-sectional view of a geophone disclosing engagement of a rotation and translation locking system in accordance with one embodiment of the present disclosure; 
           [0031]      FIGS. 15A and 15B  disclose views of a mechanical securement assembly in accordance with the subject disclosure; 
           [0032]      FIGS. 16A and 16B  disclose yet another embodiment of a locking mechanism in accordance with the present disclosure; and 
           [0033]      FIGS. 17A ,  17 B and  17 C disclose yet further views of a mechanical locking mechanism in accordance with the embodiments disclosed herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    Turning now to the drawings, wherein like numerals indicate like parts, the disclosure herein is directed to the concept of shock resistant seismic sensors such as surface and downhole seismic sensors designed for high shock environments. For example, the seismic sensors disclosed herein may be logging-while-drilling geophones and accelerometers, which include internal selective locking mechanisms operable for a harsh downhole drilling collar environment. In other aspects according to the present disclosure, the seismic sensors may be utilized for moving checkshots as described in co-pending, commonly owned, U.S. patent application Ser. No. 11/681,788, titled “Methods and Apparatus for Performing Moving Checkshots.” In yet other aspects, the seismic sensors may be surface implanted sensors for purposes of seismic surveying. 
         [0035]      FIG. 1  discloses a drilling derrick  100  positioned over a well or borehole  102  being drilled into an earth formation  104 . The drilling derrick has the usual accompaniment of drilling equipment including a processor  106  and recorder  108  of the type used for measurements-while-drilling (MWD) or logging-while-drilling (LWD) operations. A more detailed disclosure of conventional drilling equipment of the type envisioned here is described in Schlumberger&#39;s Wu et al. published U.S. Patent Application No. 2006/0120217, the disclosure of which is incorporated herein by reference as though set forth at length. 
         [0036]    The borehole  102  is formed by a drill string  110  carrying a drill bit  112  at its distal end  114 . The drill bit crushes its way through earth formations as the drill string is rotated by drilling equipment within the drilling derrick or a hydraulic motor positioned at the distal end of the drill string or bottom hole assembly. The depth of a well to a desired production zone will vary but may be as much at 25,000 feet or more beneath the surface of the earth. Operational pressures of 20,000 pounds and temperatures of 150 to 175° C. are often encountered. Moreover, the varying lithology of rock formations makes shocks to a drill collar during a drilling operation not unusual. Unintended shocks can, however, severely damage or even break the delicate suspension springs of the geophones or accelerometers. 
         [0037]      FIG. 2  discloses a more detailed view of the distal end of a drill string  200 . In this the drill string terminates with a drill bit  202  which is screwed into a drill collar  204 . The drill collar has a relatively thick side wall of two to four inches and is extremely heavy to provide weight for the drill bit as it is rotated to crush a borehole  206  through surrounding formation rock  208  into the earth. 
         [0038]      FIG. 2  also discloses a receiving structure  210  that is cut into the sidewall of the drill collar  204  and serves to receive a seismic sensing assembly of the types discussed below. 
         [0039]      FIGS. 3A and 3B  illustrate a geophone according to one embodiment herein. The geophone comprises moving coils  311  and  312  mounted on a bobbin  314 , a magnet  315 , a pole piece  322 , springs  318   a  and  318   b , and a housing  320 . The magnet may be a permanent magnet, an electromagnet, or other types of magnets know in the art. The springs  318   a  and  318   b  may be disc springs, spider springs, or other spring configurations where appropriate. Two fluid bladders  330   a  and  330   b  are mounted on the inner surfaces of two end caps  321   a  and  321   b  around pole piece  322  of the geophone such that when inflated, the two fluid bladders  330   a  and  330   b  will abut against the springs  318   a  and  318   b , respectively. A pipe  331  has an end penetrating through the top end cap  321   a  to connect to the fluid bladder  330   a , and the other end penetrating through the bottom end cap  321   b  to connect to the bladder  330   b . The pipe  331  is further connected to a fluid source assembly  332 . The fluid source assembly  332  includes a sleeve  336 , which accommodates a spring  333 , a piston  334 , and a rod  335  formed with the piston  334 . The rod  335  may be connected to a suitable actuator to drive the piston  334 . In this, any suitable fluidic, mechanical, electromagnetic, or piezoelectric actuator may be employed for purposes of the locking mechanism as described hereinafter. For example, a solenoid (not shown) may be used to provide active force to the rod  335  and the piston  334  to compress the spring  333 . 
         [0040]    As shown in  FIG. 3A , when the geophone is in a passive mode, namely, not in use, the spring  333  of the fluid source assembly is in an extended condition. Fluid within the pipe  331  is thus compressed. The fluid bladders  330   a  and  330   b  are then inflated and abut against the springs  318   a  and  318   b , respectively, and prevent the coil assembly, which includes the springs  318   a  and  318   b , and the bobbin  314 , from moving freely. 
         [0041]      FIG. 3B  shows a geophone in an active mode, namely, in operation, according to an embodiment of the present disclosure. When a solenoid, for example, is turned on, the solenoid drives the piston  334  through the rod  335  to compress the spring  333 . Fluid within the pipe  331  flows into the space in the fluid source assembly  332 , which leads to a decrease in the fluid pressure in the pipe  331 . The fluid bladders  330   a  and  330   b  are then deflated and release the coil assembly. The fluid within the pipe  331  may be filled with air, nitrogen, oil, water, alcohol, hydraulic fluid, or other fluids depending upon the specific application. 
         [0042]      FIG. 4  illustrates a geophone  400  according to another embodiment of the present disclosure. Similar to the geophone  300  shown in  FIGS. 3A and 3B , the geophone  400  includes two annular torus shaped, fluid bladders  430   a  and  430   b  mounted on the respective inner surfaces of two end caps  421   a  and  421   b  and around pole piece  422  of the geophone. When the two fluid bladders are inflated, the two fluid bladders  430   a  and  430   b  will abut against the springs  418   a  and  418   b , respectively. A port  423  is formed on the housing of the geophone  400  for providing a fluid channel between the inside and the outside of the geophone. A fluid passage  410  is formed inside the pole piece  422 . The fluid passage  410  has a first branch  411 , which is formed inside first end cap  421   a  and connected to the first fluid bladder  430   a . The fluid passage has a second branch  412 , which is formed inside the second end cap  421   b  and is connected to the second fluid bladder  430   b.    
         [0043]    The fluid passage  410  is connected to a fluid source assembly (not shown) which supplies fluid pressure to the two toric fluid bladders or releases fluid from the two fluid bladders through the fluid passage  410 . When the geophone is in an OFF status, fluid pressure will be supplied to the two fluid bladders  430   a  and  430   b  through the fluid passage  410 . The two fluid bladders are thus inflated to abut against the springs  418   a  and  418   b , respectively. When the geophone is in operation, the fluid in the two fluid bladders  430   a  and  430   b  will be released by the fluid source assembly and the two fluid bladders will deflated to release the springs  418   a  and  418   b.    
         [0044]      FIG. 5  illustrates a three-component geophone  500  according to another embodiment of the present disclosure. The three-component geophone  500  includes a housing  510  containing a first geophone  520 , a second geophone  521 , and a third geophone  522 . The three geophones  520 ,  521  and  522  are oriented along the orthogonal axes of a three-dimensional rectangular coordinate system. Each geophone has the same structure as the geophone  400  as shown in  FIG. 4 . Each geophone has a fluid passage  541 ,  542 , and  543 , respectively. A fluid source assembly  530  supplies fluid to or releases fluid from the fluid bladders of the three geophones through a pipe  540 , which has three branches  540   a ,  540   b  and  540   c  connected to fluid passages  541 ,  542 , and  543  of the geophones, respectively. When the three-component geophone is in an OFF status, fluid pressure will be supplied to the fluid bladders of each geophone  520 ,  521 ,  522  through the pipe  540 . The fluid bladders of each geophone are thus inflated to abut against the springs of each geophone. When the three-component geophone is in operation, fluid within the fluid bladders of each geophone will be released by the fluid source assembly and the fluid bladders are deflated to thereby release the springs of each geophone. 
         [0045]      FIG. 6  illustrates a geophone  600  according to another embodiment. The geophone  600  comprises a tubular magnet  610  fixed to the inside of housing  620 . The tubular magnet  610  may be formed from a number of discrete pieces or a single piece magnet may be used. A tubular bobbin  640  is positioned inside the tubular magnet  610  and is secured to the housing of the geophone by means of springs  630   a  and  630   b . The springs  630   a  and  630   b  allow the bobbin  640  to translate in an axial direction but hold it relatively securely in the radial direction. The springs  630   a  and  630   b  may be circular springs, or other types of springs where appropriate. A pole piece  655  is provided inside the tubular bobbin  640 . 
         [0046]    A coil  650  is wound around the outer surface of the bobbin  640  and so is likewise moveable relative to the magnet  610 . Two fluid bladders  660   a  and  660   b  are formed around the pole piece  655  on the center region of the inside surfaces of two end caps  670   a  and  670   b  of the geophone. A hole  680  may be formed on the housing  620  of the geophone to allow fluid to flow between the inside and outside of the geophone. A pipe  691  has a branch  691   a  penetrating through the top end cap  670   a  and connects into the fluid bladder  660   a , and has another branch  691   b  that penetrates through the bottom end cap  670   b  and connects into the fluid bladder  660   b . The pipe  691  may have a third branch  691   c  to connect to other geophones. 
         [0047]    The pipe  691  has one end connected to a fluid source assembly  690 , which comprises a spring  692 , a piston  693 , and a piston drive unit  694 . The fluid source assembly  690  supplies fluid to or releases fluid from the fluid bladders  660   a  and  660   b  through the pipe  691 . When the geophone is in OFF status, the spring  692  is in a released status and the fluid pressure inside the pipe is higher than the fluid pressure inside the geophone. Due to the fluid pressure difference, the fluid bladders  660   a  and  660   b  are inflated and abut against the top end  641   a  and the bottom end  641   b  of the bobbin  640 , respectively, and thus prevent the coil assembly, which includes springs  630   a  and  630   b , and tubular bobbin  640 , from moving axially. When the geophone is in operation, the fluid source assembly  690  is turned on and the piston drive unit  694  retracts the piston  693 . The fluid within the pipe  691  flows into the space in the fluid source assembly  690 , which leads to a decrease in the fluid pressure in the pipe  691 . The fluid bladders  660   a  and  660   b  are thus deflated and release the springs  630   a  and  630   b.    
         [0048]      FIG. 7  illustrates a three-component geophone system according to another embodiment of the present disclosure. The three-component geophone system includes a housing  710  containing a first geophone  720 , a second geophone  730 , and a third geophone  740 . The three geophones  720 ,  730  and  740  are oriented along the three orthogonal axes x, y, and z of a three-dimensional rectangular coordinate system. Each geophone has a structure and operation similar to that of the geophone  600  as shown in  FIG. 6 . Unlike geophone  600 , however, geophones  720 ,  730  and  740  have only one common fluid source assembly  750 . 
         [0049]    Each geophone has two fluid bladders connected to the fluid source assembly  750  through a common pipe  760 . When the three-component geophone is in an OFF status, fluid pressure will be supplied to the fluid bladders of each geophone  720 ,  730  and  740  through the pipe  760 . The fluid bladders of each geophone are thus inflated to abut against the centering springs of each geophone. When the three-component geophone is in operation, the fluid in the fluid bladders of each geophone will be released by the fluid source assembly  750  and the fluid bladders are thus deflated to thereby release the springs of each geophone. 
         [0050]      FIGS. 8A and 8B  illustrate a geophone according to yet another embodiment. The geophone  800  comprises a tubular magnet  810  fixed to the inside of a housing  820 . The tubular magnet  810  may be formed from a number of discrete pieces or a single piece magnet may be used. A tubular bobbin  840  is positioned inside the tubular magnet  810  and secured to the housing of the geophone by means of centering springs  830   a  and  830   b . The springs  830   a  and  830   b  allow the bobbin  840  to move freely in the axial direction but hold it relatively securely in the radial direction. The springs  830   a  and  830   b  may be circular springs, or other springs where appropriate. A coil  850  is wound around the outer surface of the bobbin  840  and so is likewise moveable relative to the magnet  810 . A pole piece  855  is provided inside the tubular bobbin  840 . Two damper mechanisms  860   a  and  860   b  are mounted on the top end cap  821   a  and bottom end cap  821   b , respectively. The two damper mechanisms  860   a  and  860   b  have similar structures and only damper mechanism  860   a  is described further here. 
         [0051]    The damper mechanism  860   a  includes a solenoid portion  861   a , a shaft portion  862   a , and a damper plate  863   a . The damper plate  863   a  is located on the inside surface of the end cap  821   a . The damper mechanism  860   a  has the same longitudinal axis as that of the bobbin  840 . The damper plate  863   a  may be of a round and flat shape with a diameter slightly larger than the outside diameter of the bobbin  840 . When the geophone is in an OFF status, the solenoid is turned off and the shaft  862   a  pushes the damper plate  863   a  against the top end of the bobbin  840 . The damper mechanism  860   b  functions in a similar way. Thus, the coil assembly is locked and prevented from moving longitudinally, as shown in  FIG. 8A . When the geophone is in operation, the solenoid is turned on and the damper plates are retracted away from the ends of the bobbin and thus release the coil assembly as shown in  FIG. 8B . 
         [0052]      FIGS. 9A and 9B  illustrate a geophone  900  according to another embodiment of the present disclosure. The geophone  900  comprises a housing  910 , a cylindrical center pole piece  920  mounted between the top end cap  911   a  and the bottom end cap  911   b  of the geophone  900 . A tubular magnet  930  is fixed to the inside of the housing  910 . A tubular bobbin  950  is positioned around the pole piece  920  and secured to the housing  910  of the geophone by means of springs  940   a  and  940   b . The springs allow the bobbin  950  to translate in the axial direction relative to the magnet. A coil  960  is wound around the outer surface of the bobbin  950  and so is likewise moveable relative to the magnet  930 . 
         [0053]    A locking mechanism  990  may be located inside the pole piece  920 . As shown in  FIG. 9B , the locking mechanism  990  comprises a solenoid  921  including a spring  922  and a tapered portion  923  extending from the plunger of the solenoid  921  (not shown). The locking mechanism  990  further comprises two or more locking pins  991 , each of which has a head end  991   a  and a tail end  991   b . The locking pins  991  may be arranged in such a way that the tail ends  991   b  of the locking pins have a constant contact with the tapered portion  923 . When the solenoid  921  is deactivated, the spring  922  turns from a compressed state to an uncompressed state, and the upward movement of the plunger of the solenoid  921  causes the tapered portion  923  to apply force to the locking pins  991  to push the locking pins outwardly. Thus, the locking pin heads  991   a  will be pushed outside the pole piece  920  and the pin heads will contact one or both the springs to hold down the springs  940   a  and  940   b , and thus hold down the whole coil assembly. 
         [0054]      FIGS. 10A and 10B  illustrate a three-component geophone  1000  according to one embodiment of the present disclosure. The three geophones  1020 ,  1040  and  1060  are mounted in a housing  1010 . The three geophones  1020 ,  1040  and  1060  have similar structures and only geophone  1020  will be described here as an example. The geophone  1020  includes two annular torus shaped bladders  1022   a  and  1022   b  formed on the inner surface of two end caps  1024   a  and  1024   b  around the pole piece of the geophone such that when inflated, the two bladders  1022   a  and  1022   b  will abut against the springs  1028   a  and  1028   b , respectively. The bladders may be formed by rubber, plastic or metal. Two fluid passages  1026   a  and  1026   b  are formed inside the two end caps  1024   a  and  1024   b  to connect to the two bladders  1022   a  and  1022   b , respectively. 
         [0055]    The three-component geophone  1000  further comprises a fluid supply assembly  1006 , which may include a piston  1008  and a spring. A groove  1012   a  is formed in the housing  1010 . The fluid supply assembly  1006  may be formed outside the three-component geophone  1000  and connect to the groove  1012   a  through a hole  1014 . When the fluid supply assembly  1006  is ON, the piston  1008  is pushed downward and the fluid enters the housing  1010  of the three-component geophone. Because the fluid inside the geophones has pressure, the fluid inflates the bladders through each fluid passage of the geophones.  FIG. 10B  is a sectional-view of the three-component geophone taken along section lines  10 B- 10 B in  FIG. 10A . 
         [0056]    It will be seen in  FIGS. 10A and 10B  that grooves  1012   a  and  1012   b  extend longitudinally and radially via channels  1012   c  and  1012   d  within housing  1010  such that each bladder on each end of the three geophones is simultaneously connected to the fluid system by channels within the interior of the closed housing  1010  and thus the housing itself functions as a fluid line. 
         [0057]      FIG. 11  shows a cross-sectional view of a geophone  1100  according to another embodiment herein. Only one portion of the geophone is shown in this figure. The geophone  1100  includes an annular-shaped moving coil holder  1120 , which has a protrusion edge  1122  formed along its peripheral edge. The protrusion edge  1122  is formed in a tapered way which is thicker at the bottom and thinner at the top. The moving coil  1130  may be configured to include an edge  1132  corresponding to the protrusion edge  1122  of the moving coil holder such that when the bladder  1110  is inflated, the protrusion edge  1122  will abut against the edge  1132  of the moving coil  1130 . Thus, the moving coil  1130  can be locked securely in position and is prevented from moving axially and radially. 
         [0058]      FIGS. 12A and 12B  illustrate a diaphragm  1200 , which may be used to form a bladder, according to another embodiment of the present disclosure.  FIG. 12A  shows a top view of the diaphragm.  FIG. 12B  shows a cross-sectional view of the diaphragm. The diaphragm  1200  may be annular-shaped and have corrugation  1210  formed on its edge. The diaphragm may be made of rubber, metal or plastic. 
         [0059]      FIGS. 13A ,  13 B and  13 C show a diaphragm  1300 , which has a similar structure as the diaphragm depicted in  FIGS. 12A and 12B , except that a plurality of protrusions  1310  may be formed on the surface of the diaphragm  1300 . The protrusions may be of a triangular-shape as shown in  FIG. 13B , or a sphere-shape, as shown in  FIG. 13C . 
         [0060]      FIG. 14  shows a cross-sectional view of a geophone according to yet another embodiment. The geophone may include bladders made of diaphragm  1410 , which has a similar structure as the diaphragm depicted in  FIG. 13 . The geophone also includes a frame  1420  for holding a moving coil  1430  with a bobbin  1440 . A plurality of cavities  1422  formed on the frame  1420  have a shape corresponding to the protrusions  1412  such that when the diaphragm  1410  is inflated, the protrusions  1412  will be inserted into the cavities  1422 . Thus, the moving coil  1430  will be prevented from moving axially, radially, and rotationally. 
         [0061]      FIGS. 15A and 15B  illustrate a geophone  1500  according to another embodiment of the present disclosure.  FIG. 15A  shows a cross-sectional view of the geophone  1500  having a moving coil  1560  and a bobbin  1580  with a spring  1540  attached thereto. Only one portion of the geophone is shown. The end cap  1510  has four holes  1512  formed thereon. An annular disk  1520  is mounted on the inner surface of the end cap  1510  by a spring  1522 . The spring  1522  has one end connected to the end cap  1510  and the other end connected to the disk  1520  as shown in  FIG. 15A . Four pistons  1524  are connected to the annular disk  1520  through the four holes  1512 . While drilling, low pressure is kept inside the geophone. When external pressure increases to a certain degree, the disk  1520  will be pushed by the spring  1522  to abut against the moving coil spring  1540  of the geophone due to the pressure difference. By reducing the external pressure, the disk is retracted due to the pressure difference and releases the moving coil  1560  of the geophone  1500 . Alternatively, fluid lines or exterior housing channels may be connected to the base of each piston  1524 . In another embodiment, the pistons  1524  may be connected to an electrical motor, which may be used to drive the pistons  1524  to push against the disk  1520 . 
         [0062]      FIG. 16  illustrates a geophone  1600  according to another embodiment herein.  FIG. 16A  shows a cross-sectional view of the geophone  1600 . The geophone  1600  has a similar structure as the geophone depicted in  FIGS. 15A and 15B , except that a bellows  1610  is used in geophone  1600 .  FIG. 16B  shows a cross-sectional view of the bellows  1610 . 
         [0063]      FIGS. 17A ,  17 B and  17 C illustrate a geophone  1700  according to another embodiment.  FIG. 17A  shows a cross-sectional view of the geophone  1700 . The geophone  1700  includes an arm  1710  formed on an annular disk  1720  and extends outside the geophone housing  1730  through a hole  1732  formed on the housing  1730 . By screwing the annular disk  1720 , the disk may lock the moving coil  1740  of the geophone  1700 . For example, the arm  1710  may be connected to a suitable spring to move the arm  1710  (as depicted in  FIG. 17C ) and turn the disk  1720  to lock against the moving coil  1740  of the geophone  1700 . A suitable actuator may be employed to pull the arm  1710  against the spring force to release the moving coil  1740  of the geophone  1700  during seismic measurements. In this, any suitable fluidic, mechanical, electromagnetic, or piezoelectric actuator may be employed for purposes of the locking mechanism depicted in  FIGS. 17A to 17C . For example, a solenoid (not shown) may be used to provide active force to the arm  1710  and the annular disk  1720  against the force of the spring (note  FIG. 17C ). 
         [0064]    Although certain activation mechanisms have been described above, other mechanisms may also be used. In this, the locking devices described herein may be activated by electro-magnetic and/or piezoelectric actuators. Such additional activation mechanisms may be designed and configured according to the principles described above. For example, the rotatable locking disc of  FIGS. 17A-17C  may be activated by one or more of fluidic, electro-magnetic, and piezoelectric action. As used herein, the expression fluid is intended to have its broad meaning and includes gases such as air, nitrogen or other gas compositions as well as liquids such as oil, water, alcohol, hydraulic fluid and other liquids. Where expressions have multiple meanings it is intended that the expression used is intended to be inclusive and have the broadest meaning unless there is a specific limitation noted. 
         [0065]    The various aspects of the invention were chosen and described in order to best explain the principles of the invention and its practical application. The preceding description is intended to enable those of skill in the art to best utilize the invention in various embodiments and aspects and with modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims.