Mapping subsurface fractures using nonlinearity measurements

Abstract

This Patent describes a method for determining the location and orientation of the open natural fractures in an earth formation by analyzing the interaction of the two seismic signals. One is a low frequency signal transmitted from the earth's surface and the other a high frequency signal transmitted from a wellbore. The compressional and the rarefaction cycles of the lower frequency signal are used to modulate the width of the open fractures, which changes their transmission characteristics. As a result, the amplitude of the high frequency signal gets modulated as it propagates through the open fractures. The result of the interaction of the high and low frequency seismic signals is recorded in another wellbore. The spectral analysis of the modulated signal that is recorded during compression and rarefaction cycles of the lower frequency surface generated signal is used to determine the location and the orientation of the open natural fractures.

Dependencies are inferred from the claim text.