Geologists and geophysicists begin their search for natural gas by integrating all available surface and subsurface information. This includes looking at rock and core samples, reviewing seismic data, and surface mapping.
Over the last few years you may have seen convoys of uniquely shaped seismic-survey trucks crawling along our local roads. Every few feet they lower the truck's heavy frame to the road and vibrate deep rumbling sounds into the earth. Monitors arranged some distance away track the sound waves and their reflections as the vibrations pass through underground layers and formations. Powerful computers process the data to reveal a cross-sectional slice through the earth (known as a 2D view) that can be interpreted by geologists and geophysicists.
Once a target location is identified, another more expensive study called a 3D-seismic survey is sometimes done to look for recognizable rock features that are often seen near gas deposits. In a 3D-seismic survey, a network of sensitive "geophone" receivers track the wave-paths of vibrations from a grid of controlled explosions. This produces a much clearer "picture" of the rock structures, and identifies optimum points to drill.
