geology

Henry D. Rogers, (1808 – 1866) was one of the first professional U.S. geologists.

When crude oil burst onto western Pennsylvania’s marketplace as a major commercial opportunity following an 1859 well drilled by Edwin L. Drake, the art and science of petroleum geology was born.

The mining industry had long provided employment for geologists and the oil boom presented a new kind of mineral wealth for America and a new challenge for geologists. But Pennsylvania’s first oilmen soon found that hiring geologists didn’t significantly improve their chances of success in an already risky business.

Decades before the Civil War, the pursuit and mining of coal prompted many geological surveys, studies, and assessments of potential mineral resources. Railroads stretching westward needed good quality coal supplies and routes always considered the availability of nearby sources.

In search of high-quality bituminous coal, geologists had often reported oil seeps and the associated landforms, but mostly as a curiosity and in relation to their proximity to coal beds.

In Kentucky, Ohio, and the western part of what is now West Virginia, the salt business also gave geologists important insights into formations called “structural traps.”

Drilling commercial brine wells and salt manufacturing was a lucrative industry. Geologists’ surveys found that strata of sedimentary rock fractured, faulted, and folded, sometimes producing salt domes and valuable brine deposits.

Geologists also noted that oil and natural gas was occasionally trapped in porous deposits sandwiched between impermeable rock layers. Such contamination fouled commercial brine wells and was an unwelcome intrusion, but cottage industry entrepreneurs skimmed it off and sold it for patent medicine, lubrication, and other novel purposes.

geology

In Kentucky, Ohio and West Virginia, geologists studied landforms associated with salt brine and coal “structural traps.” These anticlinal traps held oil and natural gas because the earth had been bent, deformed or fractured. Unsuccessfully applying structural trap theories to Pennsylvania’s differing geology undermined early petroleum geologists’ credibility.

A pioneering Ohio physician and natural scientist named Samuel Hildreth examined and recorded details of the salt business in southeastern Ohio, noting structural traps as a geologic feature associated with brine, coal, and oil. In 1836, he published his extensive “Observations on the Bituminous Coal Deposit for the Valley of the Ohio, and the Accompanying Rock Strata.” It was America’s first petroleum geology primer.

Hildreth was a strong advocate for Ohio’s first geological survey and later served as the state geologist. His observations of the structural trapping of petroleum were later affirmed by Pennsylvania’s state geologist, Henry D. Rogers, who erroneously declared that Pennsylvania’s oilfields were likewise based on structural trapping of petroleum in anticline formations.

Pennsylvania’s oilfields were in fact found predominantly in another kind of formation altogether, the “sandstone stratigraphic trap,” but Rogers’ prestigious endorsement, circulated widely in an 1863 Harper’s Magazine article, convinced geologists to the contrary.

The frenzied search for oil prompted the first petroleum geologists to impose Hildreth and Rogers’ structural trapping theory on Pennsylvania’s differing geology. It didn’t work and their failures in Pennsylvania hindered the acceptance of petroleum geologists for decades.

Although structural trapping remains a dominant characteristic for many of America’s most prolific oil and natural gas fields, ironically it wasn’t so in Pennsylvania’s Oil Creek region, where the petroleum industry was born. As noted by author and geologist Ray Sorenson, “theories of trapping did not work in the absence of anticlines.”

geology

The dominant oil bearing feature in Pennsylvania’s oil region is a sedimentary geologic formation known as a “stratigraphic trap” and differs significantly from a structural trap. It is formed in place by erosion, usually in porous sandstone enclosed in shale. The impermeable shale keeps the oil and gas from escaping.

It took until the turn of the century before successful geologically driven discoveries in the Mid-Continent and Gulf regions encouraged exploration companies to use petroleum geologists.

Although the science of geology had revealed the 34-square-mile El Dorado oilfield in central Kansas in 1915, many companies still had little confidence in geologists.

James C. Donnell, president of the Ohio Oil Company (later Marathon Oil) proclaimed, “The day The Ohio has to rely on geologists, I’ll get into another line of work.” But after the company’s first geologist, C.J. “Charlie” Hares found 19 oil and natural gas fields, Donnell changed his mind and declared Hares to be “the greatest geologist in the world.”

Increasing understanding and acceptance of petroleum geology as a valued tool in exploration led to the 1917 formation of the Southwestern Association of Petroleum Geologists, precursor to today’s American Association of Petroleum Geologists. Since then, AAPG has fostered scientific research, advanced the science of geology, promoted technology, and inspired professional conduct amongst its more than 30,000 members.

Petroleum geology has come a long way since taking its first steps and stumbles in the Ohio River Valley and Pennsylvania’s early oilfields. Geologists today grapple with enormous amounts of data and technological innovations in pursuit of petroleum.
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