Patent GB-1385971-A (GB)
Title: Seismic detector conveyances
IPC: G01V1/16
Filed: 1972-04-13
Abstract: 1385971 Seismic detectors WESTERN GEOPHYSICAL, CO OF AMERICA 13 April 1972 [3 May 1971 1 June 1971 16 Aug 1971] 17180/72 Heading H4J A seismic dectector conveyance has separately operable dector units spaced apart along and supported by a flexible structure which can be placed in a substantially flat condition. The flexible structure supports a multiconductor cable composed of pairs connected only to respective ones of a plurality of the units. These plurality of units can be utilized simultaneously but with independent recording of their signals at a seismic recording station. A seismic detector conveyance 10 (Fig. 1) is towed over the earth's surface by a tow line 16 attached to a hitch 18. A snowplough or other surface conditioner 20 may be employed. The conveyance 10 is several thousand feet long and is preferably made up of sections joined by coupling elements 20 (see also Fig, 3, not shown), or by cementing. The supporting element 30 of the conveyance is a band-shaped belt which does not tend to twist and is made of fabric, rubber or plastics (e.g. polyurethane), leather or combinations thereof, e.g. plies of cotton duck impregnated with rubber compound or neoprene. In the detectors are hydrophones and/or geophones and may be of dynamic, variable reluctance, solid state or pressure responsive type. The detector 32 (Fig. 5) has wires connecting it to a multiconductor cable 38 (see also Fig. 1) which is stapled to the belt or moulded within the belt material and which channels output signals from all detectors 32 to a utilization device 39 including a recorder. Plug and socket connections (not shown) are provided for cable sections. The detectors 32 are geophones in an array which extends over a portion or an entire section of the conveyance or over two or more sections. Each illustrated detector 32 may represent a cluster of geophones. Single-fold reflection, commondepth-point reflection or refraction profiling techniques may be used. The conveyance 10 carries relatively inexpensive "vertical" geophones. The detectors 32 (Fig. 5) snugly fit into a two-part housing 42, 44 between which the belt is clamped. A flat surface 46 achieves optimum seismic coupling and an inclined surface 48 allows housing 40 to ride smoothly over an irregular terrain. The lower half housing 44 may be weighted. The upper half housing 42 is shaped to minimize wind resistance. The two parts 42, 44 are clamped together by bolts (62) Fig. 6 (not shown). Each housing 40 (Fig. 7) may be mounted on a tongue 70 cut from the belting material to assist acoustic coupling with the terrain and acoustically isolate the housing 40 from the remainder of the belt. In another arrangement the housing 40 is mounted at the centre of an annular, flexible membrane (80) Fig. 9 (not shown), the membrane itself being bolted to the rim of an opening in the belting. This membrane (80) permits the housing to move vertically up and down to assist coupling with the terrain. Another embodiment (Fig. 11) has a detector housing 40 at the bottom of an armature 90 forming the core of a solenoid assembly 92. A spring 98 normally maintains the housing in an upward position. Upon energization of a coil 94 the armature 90 is caused to move downwardly to establish a repulatable and firm coupling between the housing 40 and terrain. When the detector is used on snow or ice the housing 40 may be provided with an electric heater (100) Fig. 12 (not shown) energized by the cable 38 to enable the housing 40 to be "welded" into the snow or ice. The detector may have a switch 102 (Fig. 13) which, on contacting the ground, removes a short circuit to a coil 108 so that any signal induced in coil 108 will be transmitted to the detector's output leads 36, 37. A mercury tilt switch 112 is provided to short circuit the coil 108 if the housing 40 tilts by a sufficient angle. For seismic prospecting in shallow waters a conveyance 120 (Fig. 14) supporting hydrophones 122 rests on the bottom 124. The hydrophones 122 are mounted by a plate (138) (see Figs. 17, 18, 19, not shown) between two plies 152, 154 (Fig. 16) of the belt. Preferably signal cable 130 also extends between the plies 152, 154, which are stapled together. Slack may be introduced into the cable 130. The conveyance 120 is preferably divided into sections provided at their ends with mechanical and electrical connections (Fig. 19, not shown). An additional ply (176) Fig. 19 (not shown) may be added as reinforcement where the hydrophones 122 are mounted.