Horizontal Drilling, How Directional Drillers Drill Oil Wells Sideways

What Is Horizontal Drilling?

Horizontal drilling, also called directional drilling, is the science of drilling a gas or oil well horizontally as opposed to how vertical wells as have been drilled in the past.

Horizontal drilling is opening up new frontiers in domestic natural gas and oil by enabling oil companies to drill through and expose a bigger payzone of a rock formation such as the Barnett shale, Marcellus Formation or the Bakken Shale.

Because horizontally drilled wells can aid in releasing more of the oil and gas held in tight rock formations such as shale, it has caused geologists to completely revise their estimations of how much recoverable natural gas and oil there is in the United States.

The Marcellus formation, which covers a huge swath of Appalachia and across into Canada holds as much as 500 trillion cubic feet of clean natural gas which can be used to power our power plants, homes and even vehicles.

How It's Done

The first step of the process is that a vertical well is drilled with traditional technology down to a depth where the oil company's geologist has chosen divert the well sideways with horizontal drilling technology. Next the oil company may set a cement plug or steel whipstock, which will be used to deflect the drilling assembly from vertical to an angle.

There are a couple of ways that a well can be drilled horizontally. They are rotary steerable, which uses a special device utilizing "kick pads" which deflect the rotating drilling assembly in a certain direction, and using a traditional mud motor type assembly, which does not rotate when building angle. Rotary steerable technology is somewhat more complex and because the companies that provide this equipment often charge higher rates, it is mostly used on the higher end wells where lots of money can be saved by shaving off costly rig time.

The way a mud motor works in drilling a directional well is that an actual motor, with a rotor and stator, at the very end the drill pipe, is powered by the force of the drilling mud or fluid that is pumped at high pressure down the drill pipe from the rig on the surface.

The drilling fluid causes the motor to turn, which in turn powers an oil well drill bit. The difference in this kind of drilling is that instead of the entire string of drill pipe turning from the surface on down to the bit, only the mud motor moves.

Because the mud motor has a bend in it, the driller can leave it in a certain position and allow it to eat away at the rock while the drill pipe slides along following it.

Because the driller has a readout up on the surface, displaying information from direction measuring instruments below, called MWD or LWD (measure while drilling) or (logging while drilling), he can know which way to slide the mud motor to achieve a "build" or increase in inclination upward.

Once the motor and bit reach a certain inclination, such as eighty degrees or more, the rig will pull out the entire section of drill pipe and mud motor and replace the mud motor with one that has less of a bend in it to drill the horizontal section of the hole.

Then they will "go to bottom" or trip in the hole with the new motor and finish drilling the well at ninety degrees. They may drill several hundred or even thousands of feet horizontally out from the original vertical well.

Directional drilling or horizontal drilling is definitely the way of the future in the oilfield. Drilling with this technology is occurring in the massive Marcellus Shale in the northeast US (for natural gas), as well as the newly discovered Eagle Ford shale oil play in Texas. The Eagle Ford shale may hold several billion barrels of recoverable oil. Because horizontal drilling for oil and gas is so effective, the U.S. is now for the first time in years beginning to see domestic production increasing. For more information on how wells are drilled horizontally try the links below.

For a better understanding of how oil and gas wells are drilled I recommend the book "A Nontechnical Guide Petroleum Geology, Exploration and Production".