Method of seismic prospecting with very high resolution in horizontal boreholes

Claim 1

A method of seismic prospecting with very high resolution in horizontal boreholes drilled in a geological medium formed of stratified layers separated by interfaces, wherein the method comprises the steps of: placing within a substantially horizontal bore a measuring tool having at least three transducers for transmitting and receiving acoustic waves and a length at most equal to the distance between the bore hole and the most distant interface of interest of a zone of the medium; generating acoustic waves from a least one of the transmitting transducers the wavelength of said acoustic waves being within the range of a few centimeters to a few meters; at least one of the receiving transducers receiving on the one hand waves refracted from the borehole wall and from the geological strata located in the immediate vicinity of the bore hole and on the other hand waves reflected from geological strata located at a distance from the borehole; recording the refracted waves and reflected waves in the form of electrical signals; recording the instants of generation of the transmitted acoustic waves; processing the recorded signals in order to determine at least the average propagation velocities of the refracted waves and reflected waves respectively; determining at least one time-section from the signals corresponding to the reflected waves; converting at least the time-section to a depth-section by means of the average propagation velocities of the reflected waves so as to constitute a depth section from which is determined the position of the interfaces located within the geological zone traversed horizontally by said borehole.

Claim 2

A method of seismic prospecting with very high resolution in horizontal boreholes drilled in a geological medium formed of stratified layers separated by interfaces, wherein the method comprises the steps of: placing within a substantially horizontal bore a measuring tool having at least three transducers for transmitting and receiving acoustic waves and a length at most equal to the distance between the bore hole and the most distant interface of interest of a zone of the medium; generating acoustic waves from a least one of the transmitting transducers the wavelength of said acoustic waves being within the range of a few centimeters to a few meters; at least one of the receiving transducers receiving on the one hand waves refracted from the borehole wall and from the geological strata located in the immediate vicinity of the bore hole and on the other hand waves reflected from geological strata located at a distance from the borehole; recording the refracted waves and reflected waves in the form of electrical signals; recording the instants of generation of the transmitted acoustic waves; processing the recorded signals in order to determine at least the average propagation velocities of the refracted waves and reflected waves respectively; determining at least one time-section from the signals corresponding to the reflected waves; converting at least the time-section to a depth-section by means of the average propagation velocities of the reflected waves so as to constitute a depth section from which is determined the position of the interfaces located within the geological zone traversed horizontally by said borehole.