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 for determining the position of a gas-saturated porous rock in the vicinity of a deep borehole in the earth. The apparatus includes a source of seismic waves of selected characteristic, positioned at a selected point in the borehole, with an array of geophones positioned on the earth in known positions around the borehole. These geophones are adapted to receive the seismic waves generated by the source in the borehole, after traveling downwardly through the earth to the formation and reflected from the formation, and to produce corresponding facsimile electrical signals. If the seismic waves from the source in their downward movement impinge upon a gas-saturated porous rock they will reflected, and therefore the signals from the geophones which are in path of the reflected waves will show a change of character. If the reflection is observed while 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 of reciprocity, the same measurements can be made by interchanging the positions of seismic source and receiving sensor.