Horizontal Well

What it is

A horizontal well is a directional drilling technique in which the wellbore is steered to run nearly sideways through a reservoir—typically drilled at an angle of about 80 degrees or more from vertical. This approach lets operators access and produce oil or natural gas from formations that are thin, widely spread, or otherwise hard to reach from a conventional vertical well.

How it works

Modern horizontal drilling combines specialized downhole tools and real‑time monitoring:

• Mud motor: A downhole drilling motor driven by circulating drilling fluid (“mud”) that can be configured to steer the drill bit away from vertical.
• Measurement-while-drilling (MWD): Instruments that provide real‑time data on the drill bit’s orientation and subsurface conditions, enabling precise steering.
• Steerable/bendable bits and hydraulic jets: Tools that allow controlled changes in borehole direction during drilling.
• Computerized guidance and positioning: Software and location systems help guide the drill to the planned horizontal target.

Together these technologies allow the drill to kick off from a vertical or angled pilot hole and extend laterally through the reservoir for hundreds to thousands of feet.

Why it matters

Horizontal wells became especially important in the 2010s as improvements in drilling technology reduced costs and increased recovery from unconventional reservoirs. Key advantages include:

• Access: Reach reservoirs that are not accessible from directly above.
• Greater reservoir exposure: A single horizontal well can contact much more of a formation than a vertical well, improving production rates.
• Efficient field development: Multiple laterals can be drilled from one surface pad, reducing surface footprint and infrastructure.
• Relief wells and other uses: Horizontal drilling can be used to intercept and mitigate problem wells, or to route underground utilities beneath obstacles.

Relationship with hydraulic fracturing

Horizontal drilling is commonly paired with hydraulic fracturing (fracking) to produce oil and gas from low‑permeability formations such as shale. In a typical approach, operators drill horizontally through the target rock, then inject a high‑pressure fluid mixture (water, chemical additives, and proppant or gelling agents) to fracture the rock and create pathways for hydrocarbons to flow into the wellbore. The long lateral sections in horizontal wells expose more of the fractured rock to the well, significantly boosting recovery compared with vertical wells alone.

Key takeaways

• A horizontal well is a form of directional drilling that runs nearly parallel to reservoir layers to improve access and production.
• It relies on mud motors, steerable bits, MWD instruments, and computerized guidance for precision.
• Horizontal drilling expanded oil and gas production from unconventional reservoirs and is often used in combination with hydraulic fracturing.