At first, looking for a good place to dig for oil simply depended upon finding where it had bubbled to the surface. But because oil reservoirs can be buried deep in the earth, it’s not always obvious from the surface. And because it’s costly to set up a rig and dig a deep well, companies don’t like to waste their time and money on an unproductive spot. Eventually, geologists were brought in to find out where oil would likely be by studying surface rock formations, magnetic fields and even slight variations in gravity.
One of the most important innovations in oil exploration was 3-D seismic imaging. This relies on the idea that sound bounces off and travels through different materials in slightly different ways. In this process, an energy source such as a vibrator truck sends sound waves deep into the earth. Special devices called geophones are positioned on the surface, which receive the sounds that bounce back up and send the information to recorder trucks.
Engineers and geophysicists study the recorded sound waves (in the form of squiggly lines) to interpret what kinds of layers of rock formation lie in that location. This way, they can construct 3-D images of what lies under the surface (4-D imaging also accounts for the passage of time). Although this advanced technology helps reduce the number of holes drilled and makes for more productive wells, it isn’t foolproof: Engineers are lucky if they can accurately predict the location of oil reservoirs half of the time.