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Can oil drilling bits possibly be steered by a computer?
Can oil drilling bits possibly be steered by a computer?

Well Drilling (oil/gas)

Andrew hit the mark. But, I'll give you a few more details about directional drilling. As an MWD field Engineer with a direction drilling team, I currently work in the field.

Wells can also be "steered" (or deviated). This is done by forcing the drill bits in the desired direction to increase or decrease the angle of the well. Dependent on the drilling assembly, wells can be diverted by as much as 30 to 35 degrees per 100 ft. Many companies use a 90 degree deviation to form horizontal holes that span anywhere from 1500 up to 20,000 ft.

There are two primary ways to steer a well away from the desired direction.

1. Drill a mixture of "rotary", "slide", and "slide" sequences with a bent-sub sub mudmotor.

A bent-submotor works much the same as a normal muzzle motor, but the motor has a bend at the bottom.

This bend helps facilitate the "sliding". The entire drill line (the segments of the drill pipe that connect to the bit) can be rotated. Because the bend distributes force evenly along the entire sidewall of the drillstring, it has little effect on the direction the string is being rotated.

Sliding refers to the fact that the rig stops turning the bit but keeps circulating fluid through the drillstring. Because the motor's bend is oriented in a specific direction, bits tend to drill at an angle relative with the existing wellbore.

The trick is to find the direction of the bend. This is where measurement-while-drilling (MWD) tools come into play. MWD instruments are tiny computers that are enclosed in cylindrical tubes of metal. These tubes are usually seated within pipes around 30 feet above (or below) the motor or 60 to 70 feet behind the drillbit. They can contain magnetometers (and accelerometers) to determine the orientations of the wellbore, as well the mud engine.

MWD tools have the function of determining the orientation of the "toolface," which is the position that the motor bends on the drill string. This information can help to point the bend in your desired direction. The directional driller is able to keep the desired angle while sliding in that same position.

MWD Instruments measure the inclination, up/down angle, and azimuth (left/right side) at regular intervals while the well is drilling. These measurements are called "deviation Surveys". Directional drillers combine this information with the measured ground depth to triangulate bit position, well path, and overall length in 3-D space.

MWD tools need data transmission to the surface so that they can be used to drill a well. They can do this using binary data encoded within one of several media.

One way to do this is to pass an electrical current through a portion of the earth formation to the engineer’s top equipment. Another option is to use special valves to temporarily limit mud flow through the drillpipe, creating small pressure spikes that can then be detected at ground level.

When high angles are required, the slide/rotate sequence can become slow. This is because drill string rotating provides a higher rate for penetration into earth formations. Therefore, rotation must be stopped before sliding.

While slide/rotate is a complicated process that can sometimes be frustrating, many companies see great returns from optimizing well placement.

2. To deviate the well and rotate, you can use a rotating steerable motor.

They are more sophisticated than bent-submotors and I don’t know as much. Rotary steerable motors have a higher tech edge than bent-submotors. I will however share what little I know.

These motors can be used to steer rotary rotors. They are not bent. Instead, they usually have three metal pads around the motor's circumference which are pushed against a wall of the formation by pistons.

The pads remain motionless if the motor drills straight. However, when the motor deviates in one direction, the pad are extended quickly so that each pad presses the motor to that side while rotating.

The motor has a computer within it that measures the rate and azimuth, as well as the inclination and azimuth. It can also perform MWD instrumentsation, it is obvious.

The rotary-steerable motor is controlled with the same process MWD tool use to communicate with surface machinery, but in reverse. The directional motor is controlled by the driller rotating at specific speeds and time intervals. The signal is received by the computer which decodes it and executes the instruction (e.g. "Seek 90.5 deg. inclination or 346.8 degrees. azimuth").

Rotor steerable motors have the advantage of being faster than bent-sub ones. They also offer a higher drilling speed thanks to constant rotation. Their increased cost is the biggest problem. These motors are not economically feasible for most companies. Large companies may find it more cost-effective to drill faster due to the fact that drilling costs are higher per day.

Other methods of well departure exist, but are rarely used and are only for situations that warrant it.

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