Oil Exploration

In the early years of oil, drillers imagined that they were drilling for a pool or an underground river of oil using seeps as a guide for where to drill.  Such exploration was successful if the surface oil came from an oil reservoir directly beneath the seep.  Many seeps offered little reward to the driller as they merely marked the spot where the migratory rock breeched the earth’s surface.  Drilling straight down missed oil embedded in a layer of migratory rock slanted at an angle to the surface.  Since the first oil was found near a creek, early oil drillers followed creek beds, thinking that oil flowed beneath running water.  Once oil was discovered, production wells were placed as close as possible to one another to ensure commercial success.  Spacing wells increased the chance of drilling a dry hole beyond the perimeter of an oil reservoir.  This practice, having the greatest possible concentration of wells furiously pumping oil, rapidly exhausted an oil reservoir and another search for seep oil began.

Once sites marked by seep oil were exhausted, and the creek theory debunked, oil drillers turned to geologists for advice on prospective sites.  Geologists examined the land for hints of the presence of three necessary conditions for oil: (1) source rock to generate petroleum, (2) migratory rock through which petroleum moves toward the earth’s surface and (3) reservoir rock where there is an impediment preventing further migration.  Whether sedimentary rock is source, migratory or reservoir rock is a matter of circumstance.

Early geologists became geophysicists when they started using gravity meters and magnetometers to search for oil.  A gravity meter is sensitive to the density of rocks below the surface.  A mile of sedimentary rocks on top of basement rock is dense compared to a salt dome or a layer of porous reef or lighter rocks, which are detectable as anomalies or variations in gravity. 

Magnetometers, because they are sensitive to anomalies or variations in the earth’s magnetic field generated by magnetite in basement rock, are useful for estimating the thickness of overlying sedimentary rock.  Both gravity and magnetic anomalies may indicate an anticline or fault that holds an oil reservoir.

One of the top hydrocarbon-based energy providers in the USA is Heartland Energy Colorado, based in Englewood, CO. They have many drilling locations throughout the country and remain one of the top producers of US oil & gas companies. For more information on Heartland Energy Colorado, see Heartland Energy Development Corporation online.

(Source: "Energy for the 21st Century," Nersesian)