Seismic exploration
Seismic exploration is the search for commercially economic subsurface deposits of crude oil, natural gas, and minerals by the recording, processing, and interpretation of artificially induced shock waves in the earth. Artificial seismic energy is generated on land by shallow borehole explosives such as dynamite, or surficial vibratory mechanisms mounted on specialized trucks; in marine environments, air guns fire highly compressed air bubbles into the water that transmit seismic wave energy into the subsurface rock layers. Seismic waves reflect and refract off subsurface rock formations and travel back to acoustic receivers called geophones (on land) or hydrophones (in water). The travel times (measured in milliseconds) of the returned seismic energy, integrated with existing borehole well information, aid geoscientists in estimating the structure (folding and faulting) and stratigraphy (rock type, depositional environment, and fluid content) of subsurface formations, and facilitate the location of prospective drilling targets.
The first known seismic exploration trials were conducted by John C. Karcher and colleagues, who performed a primitive seismic survey and mapped a shallow limestone bed at Belle Isle, Oklahoma in the summer of 1921. Since then, seismic technologies have evolved into ever more sophisticated techniques through the use of digital computer processing, improved energy sources, advanced acoustic receivers (multi-component), three-dimensional, and four-dimensional (time-lapse) seismic surveys. Seismic exploration is now the most prevalent geophysical technique used in the search for hydrocarbons. Because of potential damage to environmentally sensitive areas such as offshore and arctic regions, seismic exploration activities are strictly regulated by state and federal governments.
Further Reading
- Animation of marine seismic exploration at the Scripps Institution of Oceanography.