Seismic Refraction and Tomography Using Distributed Acoustic Sensing

The patent segments the velocity determination process into two distinct components: near-surface velocity (V0) and deep formation velocity (Vd). By separating these measurements and processing them independently, the system can account for seasonal surface variations without compromising deep formation analysis. The near-surface velocity is determined separately using surface seismic data, while deep formation velocities are derived from VSP data corrected using the V0 measurements.

The patent changes the approach to velocity determination by introducing a two-velocity model instead of a single velocity model. This parameter change allows the system to accommodate seasonal variations in surface conditions by treating near-surface velocity as a separate, variable parameter that can be independently measured and corrected, thereby improving the reliability of travel time measurements for deep formation analysis.

The patent merges two different seismic measurement approaches into a unified system: surface seismic refraction measurements and downhole VSP measurements. By combining these methods, the system obtains both near-surface velocity information from surface data and deep formation velocity information from VSP data, achieving comprehensive formation characterization in a single integrated operation rather than requiring separate measurement campaigns.

The patent creates a multi-functional measurement system that simultaneously serves multiple purposes: determining near-surface velocity, measuring deep formation velocities, correcting travel times, and identifying formation properties. This universal approach allows a single seismic survey to accomplish what previously required multiple separate operations, significantly reducing measurement time and resource requirements.