APPARATUS AND METHOD FOR DETERMINING THE POSITION OF A GAS-SATURATED POROUS ROCK IN THE VICINITY OF A DEEP BOREHOLE IN THE EARTH

摘要

APPARATUS AND METHOD FOR DETERMINING THE POSITION OF AGAS-SATURATED POROUS ROCK IN THE VICINITY OF A DEEP BORE-HOLE IN THE EARTHAbstract of the DisclosureApparatus for determining the position of a gas-saturatedporous rock in the vicinity of a deep borehole in the earth,drilled to a selected depth below the expected position ofthe porous rock. The apparatus includes a source of seismicwaves of selected characteristic, positioned at a selectedpoint in the borehole, with an array of geophones positionedon the earth in known positions around the borehole. Thesegeophones are adapted to receive the seismic waves generatedby the source in the borehole, after traveling upwardlythrough the earth, and to produce corresponding facsimileelectrical signals. If the seismic waves from the source,in their upward movement to the surface, pass through agas-saturated porous rock they will be attenuated, andtherefore the signals from the geophones which are in theshadow of this gas-saturated rock will show a change ofcharacter and/or an attenuation. If the shadow is observedwhile drilling at two or more known depths, the depth,azimuth, and radial position, from the borehole, of the gas-saturated rock can be determined. Using the principle ofreciprocity, the same measurements can be made by inter-changing the positions of seismic source and receivingsensor. A geophone lowered into an open borehole on awire line will receive signals from a surface seismicsource. Attenuations along certain downward ray pathsindicate the shadow zones from which the depth, size, andposition of a gas-saturated reservoir can be deduced.