Abstract: In accordance with the invention, there is provided a system for determining the location of an acoustic impedance boundary within the earth. A seismic signal is generated at a first location and detected at a second location so that the signal travels from the source to the acoustic impedance boundary and from the acoustic impedance boundary to the sensor. In a first embodiment, the travel time from source to receiver and the direction, in three dimensions, of the arrival path of the signal at the sensor are determined. Utilizing the determined direction of travel to the sensor and known information regarding the velocity profile of the earth strata between the source and the acoustic impedance boundary and between the receiver and the acoustic impedance boundary, a calculated travel path from the source to receiver is determined over which the calculated travel time substantially equals the measured travel time.

Abstract: An inventive method for simultaneously collecting depth-of-focus vertical seismic profiling (VSP) data and three-dimensional surface seismic data is disclosed. At least one seismic sensor is deployed at a predetermined depth of a borehole and raised in increments determined by the survey. A seismic source and a plurality of seismic sensor may be deployed at the surface along a partial arc offset from the top of the borehole by a distance inversely proportional to the depth of the sensor in the borehole. The seismic source generates a seismic signal at a plurality of points in a circular path around the borehole. Once a circle has been completed, the borehole sensor is raised, and the seismic signal generator and sensors are moved to the next largest circular path and the process is repeated. The seismic signals are simultaneously recorded by the borehole sensor and the sensors deployed in the arcuate path.

Abstract: In a VSP survey, the subsurface coverage of the bounce points of primary reflections is limited to one-half the offset between a borehole and a seismic-source point. The subsurface coverage may be extended by use of selected multiply-reflected wavefield arrivals.