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Volume 12, Number 9November 1961

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Search Beneath the Sands

Even though they sometimes compare their work with peering through a keyhole into a dark room, Aramco geologists accurately map Saudi Arabia's subsurface.

The pilot raised his right hand to the ceiling of the cockpit and turned a knob to adjust the trim tabs on the wings of the gently quivering Beaver. Aramco N-730-A seemed to hang suspended in the stillness of time and space at 9,000 feet.

Below the plane, the "sand mountains"—giant dunes stippled with iron-oxide-coated sand grains—rose to heights of 200, 400, even 500 feet. Here in the eastern Rub' al-Khali, the majestic dune complexes, their knife-edge crests moving slowly under the wind in long sinuous patterns, began to draw together to form linked islands.

Far ahead on the vast elongated floor of a sabkhah that suddenly hove into sight, a line of white cubes stood minute and gleaming in the sun. The pilot snapped a toggle switch and lifted a small microphone to his lips. His voice could not be heard above the roar of the engine over the VHF radiotelephone as he talked to the shiny, white island ahead. Slowly the white cubes on the salt flat assumed the shapes of big house trailers. A runway was clearly delineated by the lighter coloring of the pulverized sabkhah crust which had been powdered by vehicle and airplane tires.

An orange wind sock stood out limply, and to the right of the runway a man waited, observing the landing and ready to take immediate safety action if necessary. The Beaver touched down and taxied to a parking place where the "party chief" of Aramco seismic exploration camp S-3 stood waiting.

In the small, self-contained world of S-3—a world of Saudi Arabs and Americans, of tents, trailers, trucks and equipment—the mission is to map the subsurface structure of the eastern Rub' al-Khali by creating tiny, man-made earthquakes. The voice of S-3, an aircraft radio beacon, can be heard across the sandy wastes of the desert and through the airianes. The camp depends entirely upon airlift for its food, its fuels and supplies, except utility water. Its heart-beat is a GM (a Jimmy) diesel that powers its generator. It is the base camp for a Geophysical Services, Inc. (GSI) seismic crew that commutes daily in the Beaver to and from the survey area where the exploration equipment is left behind overnight in what is known as a "spike camp."

The man in charge of the camp is an Aramco seismograph geologist. The GSI team works under its own party chief, and a Saudi Arab heads the camp's work crew.

The coffee pot at S-3 is kept hot from dawn until late evening. Although the camp is isolated, it has a steady daily traffic: the spike camp commuters leaving at sunrise and coming back in the late afternoon in the Beaver; the overnight man flown in each morning from his vigil at the spike camp landing strip; the silver DC-3 winging in nearly every day from the central supply base at Ubaila that serves all Aramco's Rub' al-Khali exploration operations; the radio servicemen who keep the desert voices audible; the man returning from a week off in Dhahran and the man heading for Dhahran after 21 consecutive days of duty; the exploration manager, a desert veteran, on a swing around the network of camps; and the inevitable unexpected visitor.

Barely has the visitor stepped down from the Beaver before he is drawn into an old oilfield custom—a hot cup of coffee. When the American oil man brought his always-hot coffee pot to the Arabian desert, he found that coffee hospitality was also an old ritual in Saudi Arabia.

In the diner the visitor stretches his legs beneath the common table that seats as many as 14 men. A door at one end of the dining trailer opens onto a metal ramp that leads to the kitchen trailer with its banks of stainless steel refrigerators and deep-freeze units, its electric stove, serving table, deep sinks and its day-long aromas. The diner is one of the camp's most popular sites.

The steel steps leading up to the side door of the diner had just been sprayed by Saudi Arab painters in the camp crew. Hub caps shone freshly blue on the trailer wheels. The compressor huffed rhythmically as the painters moved from trailer to trailer. Nearby, Saudi Arab mechanics nearly disappeared under the great hoods of the elephantine Kenworth prime movers that haul S-3's trailer caravan across the difficult dune country.

First in line in the parked caravan stands the power plant trailer. In its fore-part is the camp generator. Amidship in the trailer is the shop. In its stern are shower stalls and wash basins.

Next in line are the gangway-linked kitchen and air-conditioned dining trailers. Then come the air-conditioned camp headquarters, the office trailer with its desks, files, maps, drafting table, bulletin board, radio transmitters and receivers, and its nightly array of seismic "wet-wash" (the long, damp strips of photo-inscribed "traces" that provide the clues of S-3's underground mapping). Here the preliminary studies and computations are made that convert the records into useable knowledge: the substructure of a heretofore unmapped area of Saudi Arabia.

The office trailer is very near to the end of a long line of endeavor that starts in Dhahran, far to the north, and which involves a wide variety of professional and semi-professional expertise—geographical, geological, geophysical and logistical.

Three four-man sleeping trailers complete the straight-line caravan. They are air conditioned to ensure rest in the hot summer months after a day of work in the sun. And there are thick blankets for the cool, sometimes cold, winter nights.

S-3 sits near the middle of a sabkhah that is about ten miles long and three miles wide. It is closed in by sand mountains with entry and exit corridors through low dune passes at the far ends. Behind the seismic crew trailers, white pyramidal tents are deployed as additional personnel quarters.

Town hall, library, motion picture house, music hall, recreation center—such are the many uses of the dining trailer. On its shelves are pocket book detective stories crowded against Taps at Reveille by F. Scott Fitzgerald, and John Ciardi's How Does A Poem Mean. Magazines are read dog-eared. A tape recorder hums its electronically remembered music in the background.

The field season for S-3 begins September 15. By last mid-January it had surveyed 170 miles. Work started in a terrain where sabkhahs formed almost continuous salt flats. For a month the seismic crew was able to drive to and from camp, and S-3 moved its base at one to two-week intervals. As they moved on, they entered an area where travel, even with special vehicles, became virtually impossible. The sand mountains closed in around each sabkhah, and the seismic crew had to establish a daily spike camp away from its base. The Beaver was called into action. The trailer caravan of S-3 had to stay put.

An excellent steak was broiled outdoors over a savory fire of aromatic wood. "Absolutely the best steak I've ever eaten," the pilot said. The chef beamed. Dinner had ended.

A young geologist hauled the 16-mm. movie projector from the shelf at the end of the dining trailer. Outside the side door of the diner a screen materialized against a power wagon. 'What's the picture?" the surveyor asked.

"The Rise and Fall of Legs Diamond."

Chairs were put out on the sand. Lights were doused; the projector hummed and the speaker threw off some static. "Five . . . four . . . three . . . two . . . one," everyone counted along with the lead strip. Suddenly Bugs Bunny emerged in the desert night. And just as suddenly the cook was passing out popcorn. In a short while the saga of Legs Diamond spun and clicked—and ended. Critical voices murmured in the solemn desert quiet:

"I liked the night-club scenes," someone said. "All that 1920 stuff. And the old cars."

The floodlights along one side of the trailers gave S-3 the look of a desert "great white way." The seismic observer walked through the loose sand, a towel slung over his shoulder. At the foot of the office steps the party chief told the pilot, "The cook'll get you up a little before six."

About 80 yards from the sleeping trailers, the Beaver sat in the darkness. On one side of S-3's silent valley the graceful silhouette of the sand mountains rose against the moon; on the other side of the valley they were swathed in a milky mist.

At 6:15 A.M. the next morning the camp was awake; by 7 the Beaver was warming up and the camp went to work.

The surveyor and the assistant shooter stepped into the small cabin of the plane. The Beaver rolled out onto the runway, gathered speed and was suddenly airborne. In an hour the plane was back with the overnight man who had slept out at the spike camp landing strip (Aramco regulations require the presence of a senior staff man on the ground with a radio at all landings).

At 8:05 the Beaver was aloft once more with a geologist, the observer-shooter and the observer-recorder. As it climbed to cruising altitude its shadow raced away from the brick red light in the deep dunes. Minutes later the plane banked over a sahkhah where three power wagons were lined up (for radio repair), and two more were moving to opposite ends of the mile-long valley paying out a long orange seismic cable. Four day-glow markers stood at the corners of the runway.

This was the "spike camp" for S-3's seismograph survey party. (The origin of the term spike camp remains vague; some guess it's a remnant of the U.S. Cavalry's frontier days.) The seismograph survey party's spike camp is a day-by-day work site, always on the move, linked to S-3 by an aerial lifeline.

The spike camp team consists of a handful of men, assorted equipment and a few trucks. Each truck carries its own water supply, a compass, brown paper bags with sandwiches (in the bake-oven heat the men eat lightly through the day), a big insulated container for cold fruit juices and milk, and the ubiquitous radio transmitters and receivers. And no census would be complete without mention of the astonishing desert flies. "Lemme tell you," one of the shooters said, "these flies are really smart. They always know when you've got both hands busy. Then zoom."

The seismic team at the spike camp represents one of the most valuable tools in geophysical exploration. Geologists like to say that underground mapping is like looking through a keyhole into a dark room. Nevertheless, seismic exploration is based on the precise application of principles adapted in part from seismology (the study of earthquakes), optics, mathematics, radio, and kindred sciences and technologies. In itself, seismic exploration is a very complex technology. It enables the men at the S-3 spike camp to look through the keyhole of a sahkhah into the dark room that lies below.

S-3 was using a system of seismic exploration called reflection. With the help of Saudi Arab workmen, a cable was spread out almost the full length of the mile-long sabkhah. Every 200 feet a string of geophones was tapped into the cable. These geophones or "jugs," ultra-sensitive energy detectors, were spaced out 15 feet apart.

Small rotary drills were used to sink three holes about seven feet deep at one end of the cable. Then three holes were dug at the other end of the line and three in the middle. The charge of ammonium nitrate was lowered into each hole and tamped down; then lines were run from the first set of charges to a hand-blaster.

The observer-shooter tested the leads with fingertips and thumbs that were cross-hatched from twisting thousands of wire ends. He knelt in the sand above his box and gave the dynamo crank a couple of extra turns and read the voltage level.

"Ready anytime," he said.

"Okay," the observer-recorder called from his doghouse. The shooter pressed a button. The shots all went off as planned. The earth humped up over each hole. Shock waves rippled across the sahkhah as the elastic waves of the explosion drove into the earth and returned to the surface. The waves were picked up by the geophones, amplified and transmitted to the observation truck where they were recorded.

What happened underground was more complicated. It has been compared to mapping an ocean floor where sounds are bounced off the bottom and captured by a fathometer on the rebound. The seismic explosion created an elastic wave that drove almost straight into the earth. It struck various layers (strata) underground and was bounced (reflected) back to the surface. There it was picked up as a very weak ground movement by the "jugs."

How long does it take from the time of the explosion until the elastic energy wave bounces back to the surface and activates the geophones? That's what the geologists want to know. If an observer bouncing signals off the ocean floor gets them back in five seconds in one place and seven seconds in another, it stands to reason that the ocean floor is deeper at the second location. The "time lag" in seismic exploration tells the geologist whether the strata he is studying are rising or dipping, as well as providing clues helpful in identifying the kinds of material the energy wave passes through.

One more step remains.

The energy wave that returns to the surface is recorded both on a magnetic disc and on a continuous roll of photosensitive paper. The magnetic disc provides a permanent record of the character of the energy as it returns to the surface. The record can be played again and again through various filters. This is almost like re-shooting the area, under differing conditions. The record that is inscribed on the photo-sensitive paper by oscillographs ("light writers") shows a number of roughly parallel lines that wiggle. These are "traces" of the returning energy tremors, and they are the real clue to the underground terrain.

The foregoing description of S-3's geophysical work is an extreme simplification. Like all such reductions of complex technology and scientific theory, it runs the risk not so much of damaging the concepts involved but rather of minimizing the hard-won skills of the world fraternity of doodlebuggers, as the men in geophysical exploration are called. The nickname comes from doodlebug, a term used at one time to describe the many unscientific instruments used to devine metal, treasures, oil or water.

Aramco geologists have made extensive use of their own versatile adaptations of another seismic system, refraction. This system makes use of the same tools as reflection, but in a quite different way. Heavier charges of explosive are used—as much as 800 pounds, enabling one '"shot" to cover up to ten miles. It permits relatively precise mapping of vast areas of subsurface structures in a short time. But surface and subsurface conditions both have to be right to use this method of seismic reconnaissance.

Seismic "maps" are coordinated with other underground information, such as actual samples of the earth cut by a structure drill, from various subsurface strata. Ultimately, of course, Aramco will have to decide whether or not to drill a deep test well in a specific area. Despite the increasing light that seismic methods throw on the "dark room" below the Saudi Arabian sands and sabkhahs, nature still yields her liquid treasure grudgingly—or not at all.

The exploration "hunting season" in the Rub' al-Khali ends about the first of June. Then all the camps (seismic reflection, seismic refraction, structure drilling, stratigraphic drilling) are called in from the vast reaches of the desert. During the months when the sun turns the Empty Quarter into an oven, the seismic data is interpreted, reports are written, all equipment is repaired, and the men are restored by vacations.

But until that time, the men of S-3 will continue with their desert colleagues the painstaking search for new knowledge about the hidden structures under the great sweeps of Arabian sand and dune.

Then the radios will cease. Ancient time will settle in.

This article appeared on pages 3-7 of the November 1961 print edition of Saudi Aramco World.


Check the Public Affairs Digital Image Archive for November 1961 images.