Imaging a salt dome flank using surface-to-borehole traveltime tomography

The arrival times of energy generated by a surface source, traveling through a salt dome and recorded in down hole receivers can be used to calculate the location and shape of a salt dome's flank (Gardner, L. W. 1949). This is known as the salt proximity method and has been used quite successfully to image salt dome flanks. The theory and experiment we discuss here improves upon the salt proximity method by using energy from multiple surface sources recorded by multiple downhole receivers. This results in numerous travels paths whose travel times can be reduced to a salt flank image using tomographic techniques. The picked and measured first-arrivals times through the salt are used in a Generalized Linear Inverson (GLI) algorithm (Cooke and Schneider, 1983) to solve for the salt dome's location and velocity. Unlike the salt proximity solution's multiple aplanatic surfaces, the tomographic method requires no interpretation. The tomographic method also generates a surface and borehole consistent error analysis. We present an example data set from a Gulf of Mexico salt dome for which the proximity solution, the tomographic solution and their comparison with well control are discussed.