What Is Horizontal Drilling?

Horizontal drilling or directional drilling is the science of drilling a gas or oil well horizontally as opposed to 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 or Marcellus Formation.

Because horizontal wells can release so much of the gas in a rock formation it has caused geologists to completely revise their estimations of how much recoverable natural gas lies beneath our country.

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

There are a couple of ways that a well can be drilled horizontally. They are rotary steerable and using a traditional mud motor.

First a vertical well is drilled with traditional technology down to a depth where the oil company will divert the well with horizontal drilling technology.

Horizontal drilling is done with a device called a mud motor.

The way a mud motor works in drilling a directional well is that it is an actual motor, with a rotor and stator, at the end of all that drill pipe down in the ground, 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 a regular oil well drill bit. The difference in this kind of drilling is that instead of the whole drill pipe turning from the surface 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 at the surface from direction measuring instruments below called MWD or measure while drilling tools, 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 motor and replace the motor with one with less of a bend in it.

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 thousand feet horizontally out from the original vertical well.

Rotary steerable is a newer technology that uses much the same process except that the drill pipe can be rotated as well, achieving faster drilling time. The way this is done is also with MWD technology showing which way the hole is going but in this case the motor has a kick pad which deflects the mud motor in the desired direction.

Rotary steerable technology is more complicated and because the companies that do it charge higher rates it is only used on the higher end wells where lots of money can be saved by shaving off costly rig time.

Directional drilling or horizontal drilling is definitely the way of the future in the oilfield. Drilling is just beginning in the massive Marcellus Shale in the northeast US and it holds promise of supplying us with much of the natural gas that we need. 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".