en zh es ja ko pt

Volume 18, Number 1January/February 1967

In This Issue

Back to Table of Contents

To Pull The Cork

"As you need a corkscrew to get at the wine, so you need a drill to get at the oil."

Written by Keith Carmichael
Photographed by Burnett H. Moody
Additional photographs by A. L. Yusif and V. K. Antony

Some people think that drilling for oil is like opening a bottle of wine—drill the hole, pull the cork and out bubbles the oil. And in a certain sense they are right: as you need a corkscrew to get at the wine, so you need a drill to get at the oil.

But otherwise drilling is not nearly so simple. Drillers can't just twist their "corkscrew" into the ground and pull out a "cork." If they did they might blow themselves, their rig, their drills and several miles of steel pipe into limbo. Drillers, furthermore, don't just "drill" a well; they build it. Deep in the earth, in carefully planned stages, they construct a series of tapered, concentric shafts of steel and cement that usually go down about 7,000 feet but have gone down more than four miles—farther below the surface than Alaska's Mount McKinley is above it. In addition they must prepare the drilling site, build roads, bring in supplies, set up shops and move and erect drilling rigs. It is an operation requiring squads of experienced craftsmen, scores of machines and mountains of materials.

Some months ago in Saudi Arabia, on a stretch of desert 12 miles from the oil town of Abqaiq, just such an operation was getting underway. As it often is in that area, it was blazingly hot. Little flies dived and weaved in whining spirals of sound. A wind, moving at the speed of a cavalry troop, charged across the sands toward a cluster of sweating men who were leveling a site for a drilling rig and digging a cellar, a pit 10 feet square and four feet deep over which the workers later would set up a drilling derrick.

The scene looked more like the preparation of a missile launching pad than the site of an oil derrick. Bulldozers, their huge convex blades extended stiffly before them, leveled rolling mounds of sand to provide a track connecting with the nearest road. Crews of workmen laid and joined sections of long thin water-pipe. Earthmovers shuttled back and forth carrying what seemed to be megatons of sand. Others pulled in and out with loads of marl—a hard, chalky clay used to surface the track.

Elsewhere, other phases of the project were also getting underway. At Abqaiq, the headquarters for the drilling operations of the Arabian American Oil Company (Aramco), the transport section was assembling an armada of vehicles to transport enormous quantities of cement, water, chemicals, drill pipe, steel casing and tools. At another site, where a drilling crew had completed a well and the engineer in charge had just released the drilling rig, the foreman responsible for moving the rig was getting ready to start it on its way toward the new site.

Moving a drilling rig was once a slow process. Twenty years ago Aramco workers spent many days breaking down a rig and its components into pieces small enough to be loaded on trucks, then moving and reassembling them. A drilling engineer then had a bright idea: why not fit wheels to the rig itself and move it in one piece? This posed problems, of course, since its weight and dimensions were huge. But the principle was sound. Today the rig is broken down into just three units—the derrick, the draw works and engines, and the pump—each of which is mounted on dollies so that the units can be pulled across the desert like trailers. Over the years Aramco has perfected this into such a well-organized routine that moving a rig now takes only one to four days depending on the distance.

"The key to this," explained the foreman, "is that there is very little dismantling. Everything is put onto its own wheels. Even the biggest and heaviest equipment—the derrick, the draw works and the engines, and the pumps—can be each put on wheels. Hydraulic jacks lift these units so that we can. fit dollies underneath. The dollies are just steel frames fitted with clusters of low-pressure tires. In this way we make three trailer units of the drilling rig. Of course they're heavy—the derrick trailer weighs over 100 tons—but the 30 wheels of the dollies spread the weight out so it doesn't bog down in the sand."

During that move, fortunately, no problems developed, partially because of good advance planning. "One of my crew," the foreman said, "scouted the terrain a couple of weeks back and picked a route that avoided steep slopes. Otherwise the derrick might topple over. It's 140 feet high, remember. On the steeper sand hills we had to slow down and we had to use all five Caterpillar tractors for towing, but still we managed a speed of four miles an hour. We started at sunrise and about 5 p.m. we lowered the rig over the cellar. Rigging down and up took just one day. That's a short move. And the rest of the equipment—the water tanks, the generators, the workshops, and the office—moves even faster because they are never taken off the wheels."

A few days later the new site was transformed. From far off, the drilling rig, 15 stories high, loomed against the sky like an obelisk. Nearer, it looked like a small replica of the Eiffel Tower. Around its base were clustered six large water tanks, row upon row of neatly stacked pipes, a mobile crane, dynamos, compressors, pumps, diesel engines, silver trailers, orange trucks and one sparkling white automobile. On the rig itself were gathered the men who would oversee the drilling: the foreman, called a "toolpusher," who supervises all the mechanical operations; the petroleum engineer, who sees that the objectives of the well are achieved, and the drilling crew. Nearby, three diesel engines each as big as a locomotive, growled noisily. On the rig drillers, moving with the rhythm of a topflight acrobatic team, swiftly joined a new length of pipe to the upright shaft that turned the drilling bit into the strata of the earth, far below the ground.

On the first day, the day the rig was moved in, the drillers had immediately "spudded-in" the well, their way of saying they had drilled the first couple of feet. What they had also done was start an operation that would probably go on for the next 15 days, 24 hours a day, seven days a week. In that time three shifts of drillers, each eight men strong, would pour and pump up to 2,000 barrels of drilling fluid or "mud", about 5,000 bags of cement and nearly 2,500,000 gallons of water. They also would connect and disconnect, stack and unstack more than a mile of steel pipe and install more than 200 tons of steel casing. Most important of all, they would determine whether Aramco was going to bring in another producing oil well, or not.

Roughly speaking, oil wells in Saudi Arabia resemble a bottle thrust into the ground neck down. But instead of glass the "bottle" is made of cement.

At the beginning, the bit passes easily through the soft layers of sand. Then it hits firm rock and the petroleum engineer stops the drilling and orders the installation of the first length of steel casing. This entails hauling up the drill pipe, the long jointed shaft that turns the drilling bit, then lowering casing into the hole. Casing is simply a lining of steel pipe. The first section, called surface casing, is lowered into the hole until it is lodged solidly on the rock bed—solidly enough to support the successive lengths of additional casing that will be fitted inside it as the well gets deeper.

Engineers then fill the casing with cement and, quickly, before the cement sets, put a disc (actually a rubber plug with sealing cups) on top of the cement and begin to pump drilling mud on top of the disc. Drilling mud is a viscous fluid used among other things to lubricate the drilling bit and as it is pumped onto the disc, it forces the disc down into the casing. The disc in turn pushes the cement ahead of it. Squeezed out at the bottom of the casing and with nowhere to go but up, the cement flows back up toward the surface between the well hole and the outside of the casing. When the cement hardens, the drill pipe is lowered into the well through the casing, roughly like a fountain pen into its cap. Then drilling is resumed.

As the bit reaches successive depths drillers repeat the casing operation as often as necessary. In a well 7,000 feet deep, Aramco usually cements three concentric columns of steel casing. The shortest and largest is at the top. The longest and smallest extends the full 7,000 feet to the bottom. This arrangement of successively smaller diameter and longer tubes nested one within the other eventually comes to look something like a with giant telescope opened to its full length, the eyepiece buried in a stratum that, hopefully, bears oil.

Even at this stage there are still doubts about the well's potential. Although the petroleum engineer and Aramco's laboratories regularly check drill cuttings and cores, no one can be quite certain how much oil the well contains until specialists have opened channels from the oil sands into the well. One way of doing this is to lower a casing perforator down through the mud-filled production casing string and fire bullets through the casing and the cement lining at a point opposite the oil sands. Another way is to lower a packet of explosive charges and set them off. Either way they perforate the casing and the cement and open channels from the sands into the well.

The next step is to install still another string of tubing in the well. This tubing is relatively small—three to five inches—and extends from the surface down through the mud-filled casing to just below the perforations. The tubing has many functions, but mainly it can be used to fill the well with water or mud, if it should be necessary to "kill" the well to make repairs.

Now the final stage is at hand. The crewmen bolt into place on the surface the piping and central valves that make up what is known as the Christmas tree, open the valves and glue their eyes to the dials. With the pressure from above removed, whatever was fighting to come up, now comes up, pushing the head of water before it. At first there is just gas, rich with the familiar smell of rotten eggs. Then, usually, traces of petroleum appear in the water. Much later the proportion of oil to water increases. Then, at last, pure crude oil, as thick and shiny as butterscotch pudding, ready for processing and shipment to consumers around the world.

An oil well is like a space missile. Neither gets moving without lengthy research and calculation, careful planning, large expenditures on preparatory operations and logistical support. And all of it must be done, and most of the money must be spent, before the well produces a dime's worth of oil or the missile moves an inch off the launching pad. To put it another way, you can't launch part of a missile or get the oil out of half of an oil well. It's all or nothing.

But if the companies cannot avoid risks, they can lessen them. For one thing they try to improve the odds against finding a well by constantly improving the methods used in the initial phase: the search above the ground for geological features that indicate potential oil traps. This is not a certain science by any means, but it is of great help. As one geologist put it, "Geology and geophysics indicate the structural and stratigraphic locations where oil might be found. What they can do is lead you to a point on the surface where odds favor oil."

What companies can also do—and have done—is increase the output. Companies also have improved their overall efficiency so that they drill more wells in less time, thus reducing the cost. When Aramco, for example, mounted its rigs on wheels and cut the moving time between drilling sites from 30 days to less than one day, it saved considerable sums of money. The same approach was invoked with regard to technology and management. Drilling bits, for example, are the spearheads of drilling. To supply bits for just one well costs 56,000. Improvement of the bits, obviously, would be reflected in the whole drilling operation. And that's just what happened. "More drilling progress was made in the past 10 years through jet bit hydraulics than through any other single technique in the rotary drilling process," an engineer said. "In 1948 we used to change the bit every 50 to 200 feet. Now, through a better understanding of hydraulics at the bit face—different densities and pressures of mud for various substructures—and improvements in design, we use a bit for a depth of over 500 feet and sometimes up to 2,000 feet. As a result we save much time and money in less frequent changes of the worn-out bit. Also we can turn the bit much faster."

Or take more fundamental aspects for the operation. In the early 1960's an analysis of the overall drilling operation produced evidence that if certain time-consuming habits and activities could be changed, Aramco could drill more wells each year with the same equipment and increase the footage per rig at less cost per foot. The recommended changes were made.

The cumulative effect of the improvements—the jet bit hydraulics, better organization of crews, and many others—has been impressive. Only six years ago Aramco took an average of 35 days to drill and complete a 7,200-foot well on land. If drilling were held up for any reason it could take 60 days and sometimes even longer. Now a similar well—takes an average of only 15 days from spudding-in to completion. In 1965 the company recorded a 39 per cent increase in footage drilled compared with 1964, and notched a drilling record of just over nine days for a land well 6,584 feet deep. And although prices of vital materials have been spiraling upward like sand devils, over the last six years Aramco has succeeded in pulling down, by 40 per cent, the dollar cost per foot, the oil world's ultimate yardstick of efficiency.

Aramco, of course, like all Middle East companies, has special problems with costs. Compared, for example, with the United States, the average Middle East wells go down 2,500 feet more—a factor that boosts drilling costs appreciably. Others include the difficulty of getting water, which is fairly plentiful in the United States, but so scarce in many parts of the Middle East that it has to be brought in by tankers; the need to import basic tools and materials—bits, casing, mud and cement; the time and cost of transporting tools, materials, men, food, shops and living quarters sometimes hundreds of miles into the desert. The results? The Middle East cost per foot is at least four times as high as that of the United States.

"Comparisons, however, are always tricky, and with regard to the United States and the Middle East they are as deceptive as mirages. The cost per foot comparison does not take into account the different production rates. For instance, 1965 was a record year for the Middle East; its production rate topped that of the United States. But only about 1,900 wells supplied all the oil, compared to about 625,000 in the United States. According to figures from the Oil & Gas Journal, the average well in the Middle East produced, in 1965, an average of 4,300 barrels per day of crude oil, compared with only 14 barrels per day in the United States.

It is obvious, then, that the Middle East has advantages as well as disadvantages. Not the least of them is the opportunity to develop fields in the most economical and efficient way. In the United States, a landowner's property rights cover the petroleum and minerals which lie beneath the surface of the earth. As a result, hundreds of wells may be drilled on land of different owners in the development of one field. For many reasons, this is uneconomic and inefficient. In the Middle East, governments grant concessions which permit development of large areas as units. This gives oil companies the opportunities to achieve the ideal described by an engineer as the aim of proper field development: "To get the greatest economic benefit from the reservoir with the optimum number of wells."

At Berri, for example, a Saudi Arabian oil field 40 miles northwest of Aramco's marine terminal at Ras Tanura, the "wildcat" well—the first well—struck oil in June, 1964, and immediately became the "discovery" well. This shift of phraseology reflects an important change in the degree of risk. For although there was still risk involved, specialists, armed with solid facts provided by the discovery well, could move from speculation to calculation. The geologist, analyzing cuttings, cores and electric and radioactive logs, could begin to map the substructure with a much greater degree of accuracy. The reservoir engineer, concentrating on how much oil is down there and how it flows through the rock, could begin to plan how to maintain natural pressures as long as possible. The production engineer could begin to figure how to get the oil out of the ground and into the lines and tanks as economically as possible. And then, when they had made those calculations, they could decide where to drill the next wells—the wells for delineation of the field and the wells for production

Delineation wells by which oilmen try to determine the shape and size of an oil field, are not as risky as wildcat wells, but the odds of the delineation well striking the boundary of the oil field are still slim. For it is virtually impossible for a geologist to be precise about the outline of a field on the basis of data from just one well. Thus, if the discovery well indicates a field that might be commercially attractive, then more information must be assembled, despite the risk of drilling even more dry holes.

At Berri, as it happened, Aramco drilled four delineation wells and all struck oil, thus providing enough information so that planners could get on with the refinement of initial cost estimates and tie them in with the many other factors which must be considered before decisions on production can be completed. The main one was the demand for the specific type of crude oil that was to be found in Berri. What would it be in the next three, five or even 10 years? Other factors considered were the long-range growth plans of Aramco; the number of years the field could produce oil efficiently without expenditures on pumps or on gas or water injection plants to keep the oil flowing; the number of production wells that would be required; the pipelines that would have to be laid; and the gas-oil separator plants, pumps and other installations that would be needed.

As the planners must consider a mathematically significant number of sets of all these variable factors, it was time for the computers to start humming—to see if and when, considering those and other factors, the per-barrel cost of placing a field on production was in balance with the cash realities of the market. This moment was the climax—the apex of a whole pyramid of decisions, for now Aramco management could make the final and major decision whether or not to "bring in the oil field." They had spent millions on geological and geophysical surveys, on wildcat and delineation wells. Now it was a question of balancing the demand for the Berri crude against the costs of such installations as pipelines, gas-oil separator plants and pumps, and of deciding if Berri prospects were as attractive as other potential fields in Saudi Arabia. Since the balance seemed favorable the decision was in the affirmative: "Bring it in."

It is a long road, obviously, from the exploration of a promising locality to putting an oil field "on stream." It is a road with many risks. It is a road without shortcuts. To find oil you have to have oil wells and to have wells you have to drill. There are no alternatives.

Keith Carmichael has published one novel, contributed articles to The Geographical Magazine, the Illustrated London News and several newspapers and is now researching a book on ancient trade between the Middle East and the Far East.

"A Rig Is A Rig, Is A ..."

Modern rotary drilling rigs vary in shape, size, power and mobility, but their essential functions are the same: to turn a bit deep in the earth; to raise and lower the drill pipe, a long jointed shaft that turns the bit; to control the flow of drilling mud, a special compound that lubricates the bit and washes out drilling cuttings. Powerful, efficient and modern, they are the end products of experimentation and improvement that began some 17 centuries ago.

A Chinese scribe first mentioned drilling in the 3rd century A.D.—for salt water to provide salt. It isn't known what methods were used, but whatever they were they evolved, by A.D. 1100, into a surprisingly modern technique: the use of a bit hung from the end of a springboard and jerked up and down by relays of men bouncing on the springboard. Going up and down like a yo-yo, the bit pounded its way into the ground, sometimes to a depth of 3,500 feet. This system was the forerunner of the "cable-tool" method which was used by Colonel Drake in 1854 to drill America's first oil well and give birth to the petroleum industry.

In 1901, the cable-tool method gave way to a radically different drilling system called the "rotary method." The rotary method proved its worth for the first time at the fabulous Spindletop oil field in Texas. It also revolutionized drilling to such an extent that, there have been no significant changes since. Although the familiar wooden derrick with its primitive hoist and steam engine has given way to steel framing, pneumatic and hydraulic controls and diesel engines, the rotary drilling rig has remained virtually unchanged.

The spearhead of the modern rotary drilling rig is the bit, an arrangement of tough, sharp rotating teeth which gnaw their way through rock. The usual type of bit has three cones fitted with wedge-shaped teeth which, turning at between 76 and 250 revolutions per minute. The bit is turned by the drill pipe, a thin shaft of steel pipe made up of sections of pipe joined together at the surface one after the other as the hole grows deeper. The bit is forced downward by the weight of the drill collars, heavy-walled joints of pipe which are placed just above the bit in the drill string. The weight is considerable, as high as 50,000 pounds, and imposes on the bit a punishing load. But then all the stresses on a drilling rig are enormous.

The action of a drill—i.e. the turning and pushing—is similar to that of a corkscrew in the cork of a wine bottle but because of the extraordinary proportions of a drill pipe, the strain is almost overwhelming. If a scale model of a drill pipe 7,500 feet long and 4½ inches in diameter, were made, and the diameter chosen for the model were about the same as that of a corkscrew—about 1/16 of an inch—the length of the "corkscrew" would be 130 feet. Furthermore, the pipe must be strong enough to bear its own weight yet relatively as flexible as a fishing rod since the upper end may have to make several revolutions before the bit itself catches up and starts to turn. Thus materials and workmanship have to meet exacting standards.

But despite the highest standards, bits do wear out and do need frequent changing. This means that the entire drill pipe must be pulled up and taken apart.

"When I decide the bit needs changing—and by the way, there is no formula; experience is what tells—we pull out the entire pipe, break it down into sections and rack the sections vertically in 90-foot stands inside the derrick," said a drilling foreman. "As soon as the new bit is fitted, the pipe is screwed together again and the whole lot lowered length by length down the hole. That's what we call 'making a trip' or 'yo-yoing the pipe'."

Despite modern equipment and powerful machinery, it is still no easy job to pick up 3 length of 4½-inch steel pipe, standing 90 feet high and weighing more than 1,400 pounds, join it to the others and lower it into the upper part of the hole, all within 50 seconds. Even at that pace, "running" in 7.500 feet of pipe—a total weight of some 60 tons—takes at least 1½ hours. A "round trip" takes nearly four hours. It also takes a combination of hoisting machinery, cables and pulleys which is strong enough to not only lift and lower tremendous loads at high speeds but also keep them under careful control.

In the lifting functions of an oil rig, the oil derrick and the draw works are particularly important. Derricks today have to be tail-usually about 136 feet, about a fourth the height of the Washington Monument—to accommodate the lengths of pipe which are stood inside the derrick's framework. They must also be strong because they support not only the pipe but the machinery, cables and pulleys used to lift and lower the pipe—tike the "traveling block," a giant multiple pulley that is 12 feet high and weighs four to nine tons.

It is the draw works, however, the hoisting machinery, that provide the rig's muscle. Set on the derrick floor, the draw works not only lift pipes, but, through a system of pulleys and brakes, make sure they can't fall. This is not as easy as it sounds. Each time a drill pipe 7.500 feet long is run into the hole, the energy absorbed by the braking system equals about 2,500 horsepower. To insure that the great lengths of pipe don't get away, the cable that unwinds off a great spool and weaves through a complex of pulleys, has several speed settings and two sets of brakes: friction and hydraulic.

But lifting and lowering is only one of the rig's essential functions and the other two—turning the bit and circulating of mud—are equally demanding.

Turning a bit 7.500 feet underground from a platform on the surface requires an efficient series of links between the draw works and the bit. The first link, of course, is the pipe which extends from the bit up through a hole in the rig's platform. There the drillers join the kelly—a hollow square column of forged steel, about 40 feet long—to the top of the drill pipe section then emerging from the well. The kelly hangs from the swivel, which allows the kelly and drill pipe to turn freely. On the rig floor is a rotary table with a turntable, a rotatable disc running on roller bearings and driven by a chain drive from the draw works, which turns the kelly. the drill pipe and the bit, grinding far into the earth.

Then there's the circulation of drilling mud. Mud is a drilling fluid composed of barites and clay. It is pumped from large tanks through the kelly, down the hollow drill pipe to the bit where tt spurts out of nozzles in the bit. Its function is fourfold: to help cool and lubricate the bit which can get as hot as 350-400 degrees Fahrenheit—a temperature that would lock the bit beyond the power of rig to move it, should the mud coagulate; to carry to the surface, as it flows back up the well, the bit cuttings; and, on the way up, to seal cracks, loose shale or sand. The fourth function of the mud, one vital to the safe completion of a well, is to provide a counterweight to the pressures of gas or oil or water which might seep into the hole from porous formations. So the weight of the column of the mud in the well must at all times be greater than the pressure of any gas or oil encountered. Sometimes, the mud is pumped at a formidable pressure: up to 3,000 pounds per square inch (only 15 pounds per square inch is enough to expel a passenger out of a broken window of a high-flying airplane.)

To drive these systems, an enormous amount of power is required. Less than 20 years ago it was provided by steam, but today the demands are met by three or four 500-horsepower diesel engines, coupled together by a compound transmission, a system of clutches and chain drives. This ensures great flexibility, since the combined power of all the engines can be used to drive either the draw works, for heavy hoisting. or the pumps, or both.

A drilling rig, in brief, is not a single machine; it is several tightly interlocking machines and systems able to muster the power, speed, and precision required to put a bit into the precious oil strata deep in the earth.

This article appeared on pages 9-17 of the January/February 1967 print edition of Saudi Aramco World.


Check the Public Affairs Digital Image Archive for January/February 1967 images.