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The Advantages of Horizontal Drilling Technique Over Other Methods of Drilling

Oil and gas wells that finish with a section running horizontally are not a new development in the petroleum industry, but in recent years they have become more widely used. Like a conventional well, a horizontal well begins drilling from the surface with a vertical section. At a point above the target horizon, the well begins to curve until it results in a well running sideways, away from its surface location.

Advantages
- A conventional well passes through the oil- or gas-bearing zone, or reservoir, vertically or at a steep angle. The short distance penetrated limits the portion of the reservoir that can drain to the well. This is especially restrictive where a reservoir is only a few feet to a tens of feet thick. A horizontal well that follows such a thin reservoir for thousands of feet laterally exposes a much greater amount of the reservoir to the well, with a resulting increase in production. Drillers originally used horizontal wells to intersect multiple natural fractures, but the technique has also found wide use in reservoirs with conventional permeability.
Disadvantages
- The technology necessary to drill a horizontal well increases both the duration and cost of drilling. The average overall cost of a horizontal well is approximately two times the cost of a vertical well, and some wells reach a cost of three times that of a conventional vertical well.
Use in Shale
- Shale oil and shale gas operators drill many horizontal wells, often combining the technique with hydraulic fracturing. Hydraulic fracturing, or "fracking," creates man-made cracks or fractures in the reservoir rock, which are then held open by sand grains injected along with fluids under extreme pressure. The fractures increase the permeability of the reservoir, allowing more oil and gas to reach the well.
Method
- The oil industry drills straight wells with rotary drilling rigs, which rotate a string of pipe running the full length of the hole to spin a bit at the bottom. The lateral sections of horizontal wells are drilled with a mud motor. Instead of turning the whole length of pipe to drive the bit, mud motors rotate only the bit. This allows drillers to position an angled section of the drill string immediately above the bit to steer the well in a specified direction. Once the well is pointed in the right direction, the driller locks the motor and bit and the rig spins the drill string once again from the surface. Without the influence of that eccentric section, the bit continues to run in the direction in which it is pointed.

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