Imagine you’re standing in your upstairs bedroom, you’re thirsty, and the only water in the house is a glass in the basement laundry room. To make the game fun, you can’t leave the room but you have a super-long bendable straw. So how do you get a drink? You run your straw out the door and down the hall, around the corner, down the stairs, through the living room and into the kitchen, around another corner, under the door, down the basement stairs, and across the basement to where the glass of water is standing. You slip the end of the straw into the glass and sip: problem solved, thirst quenched.
Sure, it sounds unreasonable, probably because there’s a faucet in the upstairs bathroom. If there isn’t a nearby faucet, though, and if the water in the basement is cool, pure, and plentiful; you might just accept the challenge. Oil companies accept a similar challenge every day: they drill deviated wells that follow crooked paths to reach oil and gas deep underground, just like you pushed your bendable straw around corners and down stairways to get the water.
A deviated well sounds simple: just drill sideways or at an angle instead of straight down. Though the concept is simple, execution isn’t; so high tech is now applied to the task. The oil industry has gotten so good at directional drilling that it’s possible to guide a well to a target the size of a two-car garage tens of thousands of feet away, passing through solid rock all the way.
Why drill deviated wells? Some wells are deviated because you can’t drill from straight above the target. Perhaps the land at the surface is a park or protected in another way. A well that starts to one side before curving underneath the protected area may be the only way to reach resources thousands of feet under the ground. For example, the shoreline near Long Beach, California, is dotted with wells that start out vertical and then bend west to tap fields under the Pacific, far below waters protected by environmental law.
Most wells are deviated so several wells can be drilled from one place. This is common offshore, where dozens of wells are drilled from one production platform, covering a large area around the giant structure. A platforms costs hundreds of millions of dollars to build, so it’s cheaper to drill deviated wells from a central location than to build a platform for every well. On-shore, companies drill deviated wells from a stable pad in a hostile environments like swamps, or permafrost on Alaska’s North Slope. Environmental regulations sometimes mandate use of pads, or they may be used for the same economic reasons as offshore wells.
Pads and platforms end up surrounded by dozens of directionally-drilled wells fanning out to cover many square miles. A map of all of the well paths around these platforms sometimes resembles the web of an inebriated spider. Such a map is called, for obvious reasons, a spider plot.
How are deviated wells drilled? The earliest deviated wells were drilled near lakes in hopes of reaching resources under the water. The technology only allowed drilling on dry land, so some clever wildcatter just tipped his derrick at an angle. The result was a straight hole, but a hole with a slant: slant drilling was born!
Modern directional drilling is much more complex– it must be to drill deviated wells that run for a mile horizontally or bend and curve throughout the subsurface to hit multiple reservoirs. Early directional wells used wedges and ramps in the wellbore to force the entire drillstring to bend in the desired direction. As more complex paths were needed, however, oilfield engineers developed a more versatile method.
Today, directional drilling uses a motor at the bottom of the well to turn the drill bit whenever a bend is desired. The drill pipe, which runs from the surface to a bit that does the actual cutting, is held stationary while a hydraulic pump driven by the mud (drilling fluid) drives the bit. An angled section of drill pipe just above the bit steers it in the direction desired. Once the turn is made, the driller turns off the mud motor and lets the entire string of pipe rotate to drive the bit. Since the bent section turns with the bit, everything moves in a straight line once more.
Reaching a specified target tens of thousands of feet away from the surface location requires careful planning. Drillers also need instruments to show the exact position and orientation of the bit and motor, and constantly communicate that information to the surface. Modern technology allows drillers to place a drill bit within just a few feet of a designated point in space miles from the surface location, a problem not unlike the game of drinking from a faraway glass with a long, bendable straw.
