Geophysics Enters the Fray
Contributed by Mark Mau and Henry Edmundson
Until the 1920s, drilling for oil and gas was still very much hit and miss. Geology provided some clues in terms of anticlines and salt domes, but otherwise it was follow your nose or see what your successful neighbor was doing. It took more science to provide the first crude pictures of the subsurface and increase the odds of an oil strike. Four techniques in particular revolutionized exploration for locating the next big oilfields. Together, they signaled the beginnings of exploration geophysics.
The First Geophysical Methods
Magnetics, the first technique, was based on the fact that some rocks, generally those containing iron, have a relatively high natural magnetism. This causes minute local effects on the intensity and direction of the earth’s magnetic field at the surface. These effects can be measured, and the resulting map of magnetic anomalies can be related to structure below the surface. In the early 1920s, prospectors began using a simple magnetometer invented by Swedish engineers Thalén and Tiberg in 1870 to locate iron ore deposits. In its simplest form, a magnetometer measures azimuth, the horizontal direction, and dip, the vertical inclination, of the earth’s magnetic field. For ten years or so, the magnetometer became a favorite for mapping potential oil structures. Especially in South Texas, oil operators had some success using the magnetometer because it reacted to basaltic plugs often associated with oil. However, the magnetometers produced only rather crude maps of the subsurface and were mainly used as a reconnaissance tool. Their use declined beginning in the early 1930s when other, more precise geophysical methods came into play.
Detecting variations in gravity on the surface was the second technique. Since the density of rocks varies quite widely, gravity surveys reacting to these density differences promised an alternative view for the explorationist. The earliest gravity measurement, actually of the gravitational constant, was made by Henry Cavendish in 1797 using a variant of the so-called torsion balance invented 20 years earlier by French scientist Charles-Augustin de Coulomb, the celebrated French 18th century polymath. The torsion balance comprises balanced masses suspended from a thin fiber. The fiber acts as a very weak torsion spring and twists when for any reason the masses are disturbed. As the fiber twists, an optical system indicates the angle of deflection, which translates to the force of gravity acting on the masses.
Baron Roland von Eötvös, a Hungarian professor of experimental physics at the University of Budapest, was the first to use the torsion balance to interpret subsurface geologic structure. Eötvös studied law, but in a letter to his father in 1867, he announced, “I was born with ambition and a sense of duty not only to one nation but towards the whole of humanity. In order to satisfy these urges and to retain my own individual independence, my aim in life will be best achieved, as far as I can see at present, if I follow a career in science.” In 1901, Baron Eötvös took his torsion balance on the frozen Lake Balaton in Hungary, and was able to map the irregular surface of the lake bottom. He also mapped the subsurface extension of the Jura Mountains in France. By this time, the Baron was becoming known internationally. He even had a mountain named after him in the Italian Dolomites. But it was the director of the Hungarian Geological Survey, Hugo de Böckh, an Eötvös contemporary, who was the first to use gravity to look for anticlines and salt domes, in the early 1910s in Transylvania, Romania.
About this time in the US, a young man named Everette Lee DeGolyer began his own journey in oil exploration. DeGolyer liked to learn everything from scratch. While a mining student at the University of Oklahoma, where he began his studies in 1905, he earned money during the summer break working as a cook at a local US Geological Survey (USGS) camp. Mixing with the geologists, he picked up enough geology to delay his graduation for a couple of years and instead join the Mexican Eagle Oil Company as a field geologist. For some years the company had been exploring up and down Mexico without success. DeGolyer was asked to pick the next drilling location, and in 1910 Mexican Eagle struck oil at what became the famous Potrero del Llano no. 4 well near Tampico on the Mexican east coast. The well came in a raging monster and would later record 100,000 barrels per day. A year later, a revolution in Mexico would result in the nationalization of foreign-owned companies and drive out their foreign personnel, including DeGolyer.
DeGolyer moved back to the US, set up a geologic consultancy business in New York City and became interested in the new geophysics. In early 1914 he learned of Eötvös’s torsion balance and immediately ordered one from Hungary. With the outbreak of World War I, however, the instrument never made it, and the commercial application of gravity surveying by the US oil industry was delayed by almost a decade. Meanwhile, petroleum companies in Europe continued to use the tool successfully. Deutsche Erdöl AG surveyed prospective salt domes in the North German Plain from 1916 to 1918. Some of their structural interpretations were corroborated by drilling after the war. Shell also carried out successful gravity surveys in Egypt, Borneo and Mexico between 1919 and 1922.
In 1919, DeGolyer formed his own oil company, Amerada Petroleum Corporation, and in November 1922 he was finally delivered two sets of torsion balances and immediately tested them at Spindletop. More tests followed, and then in 1924 he surveyed a prospect at Nash in Brazoria county, Texas, and found a salt dome. Drilling started in December 1924, and on January 3, 1926, Amerada struck oil. Some of the secrets of DeGolyer’s success may be found in his love for books. He was a prolific and meticulous collector of rare books and in the course of his lifetime would buy nearly 90,000 volumes, not only in science and technology but also business, history and literary classics. Once, while in San Francisco, DeGolyer purchased a small but valuable pamphlet from book dealer Lew Lengfield and told him to mail it to his home in Dallas. “It’s small,” said Lew, “Why don’t you stick it in your pocket and take it with you?” “Oh, no,” replied DeGolyer, “I don’t want anything to happen to it as I’m going by plane you know.”
One of DeGolyer’s purchases was Conrad Schlumberger’s “Etude sur la Prospection Electrique du Sous-Sol,” describing a third geophysical technique. This publication explained how to map subsurface structure by making electrical resistivity measurements on the earth’s surface. Conrad Schlumberger, a physicist and professor at the Ecole des Mines in Paris, had conceived this idea in 1912 and conducted early experiments in the grounds of the family estate in Val Richer, Normandy, France. His brother Marcel proved a perfect collaborator, being a gifted engineer who was fixing his father’s car at the age of 14 and who knew how to make Conrad’s ideas work in the field.
In 1919, their father, a wealthy businessman and owner of a textile factory, realized his sons’s joint potential and made a covenant with them. He agreed to fund the brothers 500,000 francs, almost a million US dollars in today’s money, to develop a business for measuring underground rocks, but demanded at the same time, “The scientific interest in research must take precedence over financial interest.” At first, measuring the electrical resistivity of rock was assumed to have application only for finding ore deposits. But recognizing that salt was highly resistive, Conrad and his brother Marcel started looking for salt domes. In 1923, they successfully tested their new method at the prolific Ariceştii field near Ploesti, Romania.
Three years later, the Schlumberger brothers carried out a large electrical survey in Meyenheim, Alsace, outlining the crest of an elongated underground arch nearly seven kilometers long where the salt layer bowed up. These experiences encouraged Conrad and Marcel to found a company in Paris in July 1926 under the name Société de Prospection Electrique—the genesis of the Schlumberger company. Even though their electrical method was successful to a degree in the mid-1920s, its moment of glory was temporary and in particular, along with magnetics and gravity, failed to compete with the up-and-coming fourth geophysical technique, seismic exploration.
The Arrival of Seismic Exploration
Seismic exploration owes its origins to seismology, the recording of earthquake tremors. Through the ages, mankind has devised a variety of instruments for detecting earthquakes. The first recorded seismograph was constructed in the year 132 AD by the Chinese astronomer Zhang Heng. His so-called “frog seismograph” was a large bronze urn with eight dragon heads gazing outward in different directions. Each dragon held a ball in its mouth. A bronze frog, with mouth open, was located under each dragon around the base of the urn, and a delicate inverted pendulum was hidden inside the urn. When a seismic event occurred, the pendulum swung a little and tapped a mechanism that dislodged one of the balls. The ball fell from the mouth of the dragon into the mouth of the frog below, landing with a great clang that announced the earthquake. Knowing which frog had received the ball would indicate the direction of the earthquake.
The first modern device to detect earth movement was constructed in 1885 by John Milne, a British mining geologist and advisor to the government of earthquake-plagued Japan. Milne’s seismograph consisted of a heavy mass suspended like a pendulum from a frame firmly fixed in the ground. During an earthquake the framework moved with the earth, while the suspended mass remained relatively stationary. A pen fixed to the mass then drew the earthquake’s characteristic oscillating signature on a turning roll of paper that was attached to the frame.
During World War I, German mine surveyor Ludger Mintrop used a portable seismograph of his own design to locate Allied artillery firing positions. Mintrop detected earth movement using a highly sensitive carbon-grain microphone, a precursor of the modern geophone. Curiously, on the other side of the trenches, Captain of the French artillery Conrad Schlumberger and others were trying the same technique with some success and succeeded in locating “Big Bertha,” the 100-kilometer range gun that regularly fired on Paris. Their technique used three seismographs, spaced some distance apart from each other, facing the artillery. Triangulating the times that it took for the sound waves to reach the seismographs established the position of the enemy’s artillery.
The sound waves in this instance were refracted waves. This type of wave enters the earth at an angle but then changes direction at shallow strata and proceeds parallel to the earth’s surface to get picked up by a seismograph. After the war, Mintrop began applying the refraction method to petroleum exploration by using a dynamite explosion to create an artificial sound wave. In 1919, he applied for a patent called “Method for the Determination of Rock Structures” and in 1921 founded a company he named Seismos and was soon engaged by Gulf Oil to conduct seismic refraction surveys along the Texas coast line.
Key to success in the Gulf of Mexico was knowing the acoustic properties of salt. Seismic waves travel faster through salt than most sediments, so to locate the salt domes the Seismos crews started analyzing the recorded squiggles of their seismographs for particularly fast travel times. Mintrop’s fame peaked in June 1924 when a Seismos crew discovered the Orchard salt dome in Fort Bend County, Texas. This find was the first success using the new seismic method in the US and was spectacular enough to begin displacing magnetics and gravity.
Naturally, this led to an extensive campaign of refraction shooting, with competitors such as Petty Geophysical Engineering from San Antonio, Texas, joining the fray. By 1930, most of the shallow domes on the Gulf Coast had been discovered. The following year, Seismos ended its refraction operations, although the technique continued to be offered by other companies and in 1956 was instrumental in the discovery of the Hassi Messaoud field, Algeria’s largest. In 1934, Seismos reorganized itself and began offering the services of another even more promising seismic technique called reflection seismics.
This technique owes its origins to the sinking of RMS Titanic when it collided with an iceberg in the North Atlantic, resulting in the loss of more than 1,500 lives. The famous disaster inspired Reginald Aubrey Fessenden, a Canadian inventor who had been working for Thomas Edison, to construct a device that would detect icebergs by emitting a sound wave and timing the return of the reflected echo. In January 1913, Fessenden filed a patent and on April 27, 1914, aboard the US Coast Guard cutter, Miami, in the North Atlantic, was able to demonstrate that his device could detect icebergs up to 12 miles away.
But his inventive mind didn’t stop there. In the spring of 1913, Fessenden and his assistants began experimenting near Framingham, Massachusetts, and succeeded in detecting both refracted and reflected waves from the subsurface. These tests resulted in another Fessenden patent in September 1917 entitled “Method and Apparatus for Locating Ore Bodies.” The news of Fessenden’s work quickly spread through the growing US geoscience community.
Meanwhile, the US government had also been sponsoring research to use sound waves in artillery detection and sent physicist John Clarence Karcher from the US Bureau of Standards’s Sound Section in Gaithersburg, Maryland, to the front lines in France to investigate. Returning to the US, Karcher had another look at Fessenden’s patents and started discussing with his colleague William Peter Haseman, a physics professor on leave from the University of Oklahoma, the idea that sound waves generated by explosions and reflected by the subsurface might be used for identifying petroleum-bearing structures.
Over the next two years, the Sound Section of the Bureau of Standards prepared for tests and on April 12, 1919, obtained the first seismic reflections from strata beneath a Maryland rock quarry. Encouraged by these results, Karcher and others from the University of Oklahoma formed the Geological Engineering Company in April 1920. A year later, in June 1921, Karcher and his Geological Engineering colleagues conducted a reflection experiment at Belle Isle in Oklahoma City and obtained a clear reflection from the interface between two known strata, the Sylvan Shale and the Viola Limestone, a hard limestone cap rock under which producers later discovered several major oil reservoirs.
But Geologic Engineering soon folded due to a collapse in the price of oil, and engineers still had work to do to resolve problems detecting the weak reflected signals. However, a number of innovations in the mid-1920s improved the reflection method considerably. Mechanical seismographs were superseded by a variety of electric geophones, the most popular being the moving-coil electrodynamic type. The development of vacuum-tube amplifiers made it possible to strengthen the reflected signals, and electronic filters were developed to eliminate extraneous vibrations. It also became possible to record on the same strip of photographic paper the vibrations from a number of seismographs set up at different points on the surface.
In 1925, oil prices had rebounded, and DeGolyer, still in charge of Amerada, decided to create a research arm called the Geophysical Research Corporation (GRC) and asked Karcher to lead it. Karcher’s first move was to acquire Fessenden’s patent and services as a consultant, but his main task was to improve the reliability of the reflection seismic method. In 1930, GRC used the reflection technique at Seminole, Oklahoma, to discover three reservoirs, securing its place as the most efficient and practical method for hydrocarbon exploration. Although the older refraction method remained well suited for finding salt domes, the reflection seismic technique generated more precise observations over complex geologic structures and could pinpoint the location—or at least provide clues—of a potential oil pool.
By the 1930s, four companies were offering reflection seismology: Geophysical Service Incorporated (GSI), formed in 1930 by spinning off GRC from Amerada, run by DeGolyer and Karcher; Compagnie Générale de Géophysique (CGG), set up in 1931 by Conrad and Marcel Schlumberger jointly with the French government and another French geophysical company, Société Géophysique de Recherches Minières; Seismograph Service Corporation, also set up in 1931, by electrical engineer William G. Green who had previously worked in both GRC and GSI with Karcher; and finally Western Geophysical, created in 1933 by Henry Salvatori who worked for Karcher in GSI but left to establish his own company. All these founding fathers would acquire great wealth over the next few decades, some became philanthropists, and some went into politics such as Salvatori.
Reflection seismology convinced the industry that geophysics had arrived, and on March 11, 1930, thirty geophysicists met at the University Club in Houston to cement this coming of age and to found what would be later become the Society of Exploration Geophysicists (SEG). At first, their technical meetings were held alongside those of the American Association of Petroleum Geologists (AAPG) that DeGolyer and friends from Tulsa, Oklahoma, had launched in 1917. Both professional societies would grow from a handful of members at their founding to many thousands today.
This entry is based on Groundbreakers: The story of oilfield technology and the people who made it happen, by Mark Mau and Henry Edmundson. You can find the book at www.fast-print.net/bookshop/1791/groundbreakers.