Abstract:
An apparatus and method for orienting and for coupling geophones relative to soil. A hammer device oriented to the vertical drives a head into the soil to generate a case opening. Vertical orientation of the case opening and depth automatically orients a geophone case to vertical and further controls the coupling of the geophone to the soil. Such combination facilitates orientation of the geophone to the selected compass heading and significantly reduces corrective data processing. Control over case opening placement in different soil conditions is automatically provided, and data regarding local position and orientation is recorded for future data processing. Operator errors are reduced and overall production efficiency is enhanced.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of geophones coupled with soil to detect seismic source energy. More particularly, the invention relates to an improved apparatus and method for coupling a geophone to soil. 
     Seismic operations deploy geophones along survey lines. The geophones are coupled to the soil at selected locations and detect source seismic energy reflected from subsurface geologic formations and interfaces and refracted to the surface. Movement of the surface exists along any degree of the three axes, and can be measured with three sensor geophones located in a single housing. 
     The effectiveness of geophone coupling to soil is essential to the accurate collection of seismic data. Three sensor geophones detect the magnitude and direction of transmitted seismic energy along different axes. Geophone orientation variations from vertical introduce significant error in measurements regarding the source direction of reflected seismic energy. Slight inclinations from vertical or from a selected compass heading can be adjusted during data processing, however additional processing time, cost and effort is required. Geophones typically integrate level indicator bubbles in the geophone case, however orientation of geophones to such bubbles requires movement of the geophone case after the case is initially planted in the soil. Such movement loosens the attachment between the geophone and soil This loose attachment creates a boundary interface between the soil and geophone which reduces coupling effectiveness and accuracy of the geophone sensed data. 
     Geophone sensor placement is complicated in regions having varying soil conditions. In different seismic survey regions, the soil can range from marsh to consolidated or unconsolidated soil to bedrock. The hardness of each soil condition can vary greatly within a lateral distance of several meters, thereby complicating efforts to effectively couple geophones to the soil. If the geophone is not adequately planted into the soil, flow noise from wind and moving water can adversely affect the seismic data recorded. When the geophone stakes are planted into the soil, wind and moving water exert forces against the geophone which are increased by the moment arm height of the geophone. Such environmental forces cause case flexure and resonance which generate acoustic “noise” and which reduce seismic data quality and require additional data processing procedures. 
     Conventional three component geophones use surface mounted assemblies having spikes on the lower end of the geophone housing, and such geophone cases couple the case bottom to the soil with the sensors located above the coupling point. Lateral movement of the soil and coupled case bottom is not accurately sensed at the case upper end because of case flexure and resonance. Field personnel plant each geophone by aligning the geophone case to the proper compass heading, and by monitoring a bubble level indicator to assure the vertical orientation of the geophone case. Because conventional geophone cases are planted on the surface, field personnel must bend downward as the geophone is planted. This process is time consuming, tiring, and leads to geophone installation errors. 
     Various systems have been developed to plant geophones in soil. U.S. Pat. No. 4,300,220 to Goffet al. (1981) disclosed a geophone holder having a frame for supporting three geophones along principal axes of sensitivity. U.S. Pat. No. 4,838,379 to Maxwell (1989) disclosed a receptacle for receiving a geophone and for permitting the release of the geophone from the receptacle. A magnetic compass and bubble level were located one meter from:.the geophone receptacle and facilitated manual installation of the geophone. U.S. Pat. No. 5,007,031 to Erich (1991) disclosed a geophone planting tool for engaging the outer geophone case as the geophone was planted into soil. U.S. Pat. No. 5,010,531 to McNeel (1991) disclosed a geophone housing having soil anchoring spikes and a level mechanism for adjusting the spikes relative to the geophone housing. U.S. Pat. No. 5,124,956 to Rice et al. (1992) disclosed a geophone housing anchored to the soil with a bow spring or drill bit larger than the housing. U.S. Pat. No. 5,231,252 to Sansone (1993) disclosed an open seismic sensor platform having a spike for anchoring each geophone to the soil. 
     Other devices have been developed to anchor geophones to the seafloor or to stabilize geophones against dislocation. U.S. Pat. No. 5,142,499 to Fletcher (1992) disclosed a setting tool for releasably anchoring geophone spikes to a seafloor. U.S. Pat. No. 5,189,642 to Donoho et al. (1993) disclosed a marine seismic recorder having a ballast ring cooperating with a geophone package, and United States Patent No. 5,253,223 to Svenning et al. (1993) disclosed a marine geophone package having an electronic angle gauge together with geophones arranged in the x, y and z axes. U.S. Pat. No. 5,434,828 to Ldgan (1995) disclosed a geophone stabilizer for reducing movement of the geophone due to water currents and other environmental forces. 
     Other devices have been developed to expedite geophone placement in land based seismic operations. For example, U.S. Pat. No. 5,315,074 to Berquist (1994) disclosed a tractor mounted device having a push tube for planting a geophone. A vibration device was connected with a push tube to facilitate soil penetration by the geophone. Although such device is useful in unconsolidated soils, the device is limited in survey regions when the hardness and composition of the soil varies. 
     The accuracy of seismic data significantly depends on the proper orientation of geophone housings and on the effective coupling of such housings to local soil conditions. The efficiency of seismic operations depends on the ability to quickly and accurately deploy geophones in the desired locations. Accordingly, a need exists for improved geophone planting devices and methods for coupling geophones to soil. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus and method for coupling a seismic geophone to soil. The apparatus comprises a portable chassis, a frame engaged with the chassis, an orientation device engaged with the frame for selectively orienting the frame to vertical, and a hammer moveable relative to the frame to contact the soil in a vertical direction for generating a case opening suitable for insertion of the geophone, wherein the hammer is retractable from the case opening generated by the hammer. 
     In different embodiments of the invention, a template prevents dislocation of the soil as the hammer is retracted from the case opening. A controller can control movement of the hammer in a vertical direction, and a positioning device can identify the case opening location. 
     The method of the invention comprises the steps of moving a portable chassis to a selected position, operating an orientation! device engaged with a frame mounted to the chassis to selectively orient the frame to vertical, moving a hammer relative to the frame to contact the soil in a vertical direction to form a case opening suitable for insertion of the geophone, ceasing downward movement of the hammer at a selected position sufficient to form a case opening having a selected shape, and retracting the hammer from said case opening without disturbing the soil compaction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a portable chassis supporting a frame for guiding a hammer vertically downwardly into contact with soil. 
     FIG. 2 illustrates the hammer in contact with the soil to form a case opening. 
     FIG. 3 illustrates retraction of the hammer from the case opening. 
     FIG. 4 illustrates automatic insertion of a geophone in the case opening. 
     FIG. 5 illustrates a sleeve coupled between a geophone and the soil. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention contains a powerful~hammer for driving a preformed metal die into soil to provide a compressed indentation formed to receive a geophone. As defined herein, the term “soil” means the top layer of the Earth, which can comprise dirt, clay, unconsolidated aggregate, bedrock, marsh, organic material, and other materials having different compositions and hardness. 
     Referring to FIG. 1, chassis  10  is portable and can be moved across the survey region. Chassis  10  can include an independent power supply or can be towed by another vehicle (not shown).Chassis  10  can be sufficiently stable to perform additional functions without movement, or can be stabilized with outrigger pads or other mechanical or hydraulic devices (not shown). Frame  12  is engaged with chassis  10  and includes an orientation device such as gimbal  14  for permitting vertical orientation of frame  12  regardless of the chassis  10  orientation. Gimbal  14  provides unrestrained movement of frame  12  to a vertical position, then gimbal  14  or frame  12  is secured to retain such vertical orientation. Hammer  16  is moveably engaged with frame  12  and is reciprocable along the longitudinal axis of frame  12 . Hammer  16  is initially retained at an elevated position relative to frame  12  and is releasable along frame  12  to contact soil  18 . Hammer  16  can comprise different shapes and configurations for accelerating toward soil  18 . The acceleration may be accomplished with gravity or with a motive force powered by hydraulics, compressed gas, elongated elastic members or gun powder actuated devices. 
     Hammer  16  can include removable head  20  for contacting soil  18 . In a preferred embodiment of the invention, head  20  is interchangeable to provide different configurations and indentations in soil  18  depending on the soil conditions and geophone requirements. Head  20  can have a flat or shaped bottom depending on the soil hardness and composition, and can be solid or hollow. As shown in FIG. 2, head  20  has tapered bottom  22  to facilitate piercing and compaction of soil  18 . By providing such flexibility, hammer  16  is adaptable to different sizes and configurations of geophones. In unconsolidated soils, the penetration of head  20  compacts soil  18  to form the perimeter of case opening or hole  24 , thereby providing a hardened boundary more conducive to transfer of seismic energy from soil  12  to a geophone planted within case hole  24 . When a geophone is planted into case hole  24 , thee hardened boundary effectively entends the geophone case size by directly coupling the geophone to a larger surface area. 
     A template such as plate  26  contacts the upper surface of soil  18  as hammer  16  drives head  20  into soil  18 . For loose and unconsolidated soil  18 , plate can prevent upward deformation of soil  18 . This feature of the invention significantly increases the compaction of soil  18  by controlling the direction of compaction, thereby increasing the effectiveness of the hardened boundary surrounding case hole  24 . Alternatively, plate  26  can be lowered into contact with soil  18  after head  20  is driven into soil  18  so that as head  20  is retracted to clear case hole  14 , plate  26  retains the upper layer of soil  18  in position so that soil  18  surrounding case hole  24  is, not disturbed by withdrawal or retraction of head  20 . In this manner, the integrity of each case hole  24  indentation is retained so that more effective coupling between geophones and soil  18  is obtained after the geophones are planted in the case holes  24 . 
     Because frame  12  is accurately oriented in a vertical direction, case hole  24  is automatically oriented vertically. After case hole  24  is created in soil  18  and head  20  is retracted as illustrated in FIG. 3, geophone  28  can be inserted into case hole  24 . Such insertion can be performed manually or automatically. Frame  12  can be adapted to automatically guide geophone  28  into case hole  24 . The configuration of case hole  24  automatically orients geophone  28  to vertical, thereby eliminating the need to manually verify this orientation. In a preferred embodiment of the invention, geophone  28  is automatically orientated so that a selected compass heading is maintained as geophone  28  is inserted into case hole  24 . By providing for such orientation upon insertion, subsequent manipulation of geophone  28  tending to loosen the connection with soil  18  can be avoided. An impact force or a pushing force can be exerted on the top of geophone  28  to secure geophone with soil  18  so that solid contact is made. Although geophone  28  can be positioned into case hole  24  with frame  12  to facilitate automation of such installation, geophone  28  can be inserted into case hole  24  manually or with another vehicle or device trailing chassis  10 . 
     After case hole  24  is formed, chassis  10  is transported to the next geophone location and is stabilized for generation of the next case hole  14 . Global positioning (“GPS”) equipment  30  is attached to chassis  10  and records data regarding the precise location and attitude of each case hole  24 . Alternatively, GPS equipment  30  can broadcast the frame  12  location and attitude to a remotely located control station (not shown). 
     Automated vertical control such as gimbal  14  is attached to frame  12  and is connected with computerized controller  32  linked with electronic inclinometer  34 . In other embodiments of the invention, gimbal  14  can be replaced with devices having mechanical means connected to controller  32  for controlling frame  12  orientation. In this embodiment controller  32  is responsible for achieving a precise vertical attitude and for detecting variations from such attitude. Controller  32  can automatically provide such vertical orientation so that operator control is not required. Controller  32  can also record such orientation to provide a record of any inclination errors experienced. If controller  32  determines that a vertical inclination is not achieved, operation of hammer  16  is restricted until the proper vertical inclination is achieved. 
     Controller  32  also monitors the orientation of each geophone so that the compass heading of each geophone is known. Alternatively, the shape of each geophone case can be marked or configured to provide orientation control. Controller  32  monitors the placement of each geophone, and variations in compass heading can be recorded for subsequent data correction. 
     Stop  36  can be attached to or integrated within frame  12  or hammer  16  to limit the downward movement of hammer  16 . In this manner, the precise depth of case hole  24  can be controlled so that the bottom of geophbne  28  contacts the bottom of case hole  24  as illustrated in FIG.  4 . In one embodiment of the invention, the diameter of case hole  24  is slightly less than the exterior diameter of geophone  28 . This difference in diameter provides a tight, controlled fit between geophone  28  and case hole  24 . By controlling such fit, the extent of coupling therebetween is also controlled so that variables in seismic energy detection are reduced. As shown in FIG. 4, geophone  28  can have vertical, longitudinal ribs  38  for enhancing the coupling effectiveness between geophone  28  and case hole  24 . 
     In another embodiment of the invention, controller  32  can automatically monitor the depth of case hole  24  formed with hammer  16 . If case hole  24  is not sufficiently deep, geophone  28  will not be effectively coupled to soil  18 . If soil  18  comprises bedrock, a single stroke of hammer  12  may not adequately create the desired case hole  24  depth. In such event, sensor  40  detects the position of hammer  16  and delivers a position signal to controller  32 . If the proper depth has not be achieved, controller  32  automatically retracts hammer and releases hammer  16  to impact soil  18  a second time. Such process is reiterated by controller  32  until the proper case hole  24  configuration is achieved. Such operation is accomplished without operator intervention, and can be overridden by an operator if sufficient progress is not accomplished. In such event, operator can change head  20  to another configuration or type, or can implement operation of another case hole  24  formation device. Controller  32  also records the steps required to generate each case hole  24 , which provides information regarding the soil  18  conditions local to each case hole  24 . Such information can be correlated with the seismic data recorded to permit data set adjustments in the processing of such data. This feature of the invention accounts for variations in the coupling effectiveness between geophones  28  and different soil conditions, and permits data correction for such variations. 
     FIG. 5 illustrates another embodiment of the invention wherein sleeve  42  is inserted into case hole  24 , and geophone  28  is coupled to sleeve  42 . Sleeve  42  is particularly useful for loose and unconsolidated soil  18  because sleeve  42  compacts and retains soil  18  from further movement. Sleeve  42  can be formed with plastic, metal, or with organic or inorganic materials and can be dedicated in place or can be removed for reuse at another location. Sleeve  42  can have ribs  44  or similar protrusions to prevent rotation of sleeve  42  within soil  18 . Additionally, the interior of sleeve  42  can be configured to mate with the exterior of geophone  28  to facilitate orientation, installation and coupling of geophone  28 . 
     By controlling the orientation and placement of each case hole  24 , accuracy of data detected by geophones  28  is increased. Accurate accounting for case hole  24  placement enhances recorded seismic data processing. Additionally, the initial plant of each geophone  28  is more effective, thereby eliminating the need to adjust or move geophones  28  after a geophone  28  is planted in a case hole  24 . This feature of the invention not only increases operating productivity by eliminating geophone  28  repositioning steps, but also provides higher quality seismic data by more accurately measuring the character of soil motion and the direction of movement transmitted through soil  18 . 
     The invention significantly increases soil/geophone coupling. The interface between conventional geophones and the soil is effectively eliminated, as the soil proximate to the geophone transforms into an extension of the geophone housing. Increased coupling and a lower profile significantly reduces signal noise. Case flexure and resonances in the horizontal plane are substantially eliminated, permitting deployment of a single geophone instead of multiple geophones conventionally deployed to address undesirable factors. Single sensor deployment reduces cost and increases overall survey productivity. Additionally, deployment of single sensor increases data processing control over the sensor positioning effects, thereby increasing finer resolution and enhanced data quality. 
     Although the invention has been described in terms of certain preferred embodiments, it will become apparent to those of ordinary skill in the art that modifications and improvements can be made to the inventive concepts herein without departing from the scope of the invention. The embodiments shown herein are merely illustrative of the inventive concepts and should not be interpreted as limiting the scope of the invention.