Device for use in geophysical survey of soil formations

摘要

A downhole seismic exploration device (7) comprises a seismic detector (44) such as a geophone and a magnetic clamp (51, 52), supported by O-rings (45, 46) in an open cradle carrier (39) which can be secured to a cable (64) linking several such devices (7) into an array. The array is lowered into a cased borehole (3) and the magnetic clamps (51, 52) are operated to clamp the devices temporarily to the casing (3). Seismic signals detected by the geophones (44) are transmitted to the surface via the cable (64), the O-ring supports (45, 46) acting to reduce or eliminate transmission of vibrations from the borehole fluid and the cable (64) via the carrier (39) to the geophone (44). The array is then unclamped and moved to another location in the borehole (2) and the operation repeated.