How does horizontal drilling work?

How does horizontal drilling work?

Horizontal drilling starts with planning. Reservoir engineers and geologists will identify the target reservoir structure and determine the horizontal length required for optimal drainage. Then it's up to the drilling engineer to design the well to meet that need.

The well will preferentially start vertically. A directional well path will be drawn with a build-up radius of no more than 5 degrees per 100 ft, but typically 3 degrees per 100 ft (to avoid excessive stress on the drill string and wear on the borehole) that ends at the start of the target. Before getting there, the casing string will be set as per normal in the competent formation above the reservoir.
 
Common tools used to achieve the high accuracy required for this well design would be Measurement Whilst Drilling (MWD) and a Bottom Hole Assembly (BHA), which includes some sort of steerable tool to start and maintain the required radius. They can be rotary tools or mud turbine tools, but typically they have a means of angleing the bit or adjustable stabilizers that can be controlled by surface mud pulse telemetry. By doing this and continuously monitoring the MWD results (again using mud pulse telemetry), the well path can be steered exactly where it is needed.
 
There are many other factors required to drill a successful horizontal well, too many to list. For example, if knowing anything about drilling oil wells, you'll know it requiring a BHA with heavy drill collars to provide Weight On the Bit (WOB) using gravity. When you're drilling horizontally you, can't apply WOB this way, so the drill string is designed with Heavy Weight Drill Pipe (HWDP) high up near the vertical section to be able to push down and provide WOB while drilling horizontally.

Therefore, it takes months of planning, the right equipment and operators, and a motivated crew to drill horizontally.