Horizontal drilling is a technique where a well starts by going straight down like a traditional well, then gradually curves until the drill bit travels sideways through a rock formation. This allows the wellbore to stay within a thin, oil- or gas-rich layer for thousands of feet, making contact with far more of the resource than a vertical well ever could. It transformed the oil and gas industry by making it possible to extract hydrocarbons from tight shale formations that were previously uneconomical to produce.
How a Horizontal Well Gets Drilled
Every horizontal well begins as a vertical one. The drill bores straight down through surface rock until it reaches a predetermined depth, often several thousand feet below the surface. This vertical section is lined with steel casing and cemented in place to protect groundwater and stabilize the hole.
Once the vertical section is complete, the drill begins a gradual turn called the “build section” or “kickoff point.” The curvature is controlled so that over several hundred feet, the wellbore transitions from pointing straight down to pointing sideways. The angle change is typically measured in degrees per 100 feet of depth, and the turn rate is gentle enough that the drill string and casing can flex through it without breaking.
After the well reaches a roughly horizontal orientation, the drill continues sideways through the target formation. This sideways portion is called the lateral. In the Permian Basin’s Midland region, the average lateral length has increased by 58% since 2015. More than half of Midland wells completed in 2025 have laterals longer than 10,500 feet (about two miles), up from just 8% in 2018. The longest laterals now stretch over 21,000 feet, roughly four miles, according to data cited by the American Petroleum Institute.
Steering the Drill Underground
Drilling sideways through a rock layer that might be only 30 to 100 feet thick requires precise navigation. Operators rely on two key technologies mounted near the drill bit: Measurement While Drilling (MWD) and Logging While Drilling (LWD).
MWD tools track the well’s position underground, measuring the angle, direction, and depth of the drill bit in real time. LWD tools go a step further by reading the properties of the surrounding rock as the bit advances. They detect changes in density, porosity, and electrical resistance, which tell the operator whether the bit is still inside the oil- or gas-bearing “pay zone” or drifting into unproductive rock above or below it.
This real-time data feeds into a process called geosteering, where operators adjust the well’s path to keep it centered in the most productive part of the formation. Modern geosteering can be partially automated. Platforms evaluate formation changes in real time and adjust the trajectory within predefined parameters, reducing the risk of steering the well out of the target zone. Operators can also optimize drilling speed, the weight applied to the bit, and mud flow rates based on continuous downhole telemetry.
The drill bit itself is steered using either a bent motor (a downhole motor with a slight angle built in) or a rotary steerable system, which can change direction while the entire drill string keeps rotating. Rotary steerable systems allow smoother, more consistent wellbores and are standard on most modern horizontal wells.
Why Horizontal Drilling Produces More
A vertical well passes through a productive formation at a right angle, so its contact with that layer is limited to the thickness of the rock, perhaps 50 to 100 feet. A horizontal well, by contrast, can run through the same layer for two miles or more. That dramatically increases the surface area of rock exposed to the wellbore, which means more oil or gas can flow into it.
This matters most in tight formations like shale, where oil and gas are trapped in rock with very low permeability. The hydrocarbons don’t flow easily through the rock on their own, so increasing the contact area between the wellbore and the formation is essential. Horizontal drilling is almost always paired with hydraulic fracturing, which creates small cracks radiating outward from the lateral to further increase flow. The combination of a long lateral and multiple fracture stages along its length is what made the U.S. shale revolution possible.
Smaller Surface Footprint
Because horizontal wells can reach resources spread across a wide underground area, multiple wells can be drilled from a single surface location called a pad. A typical drilling pad today may host five to ten wells, each drilled horizontally in a different direction from the same spot. This replaces what would otherwise require numerous individual well sites scattered across the landscape.
The practical benefit is a much smaller surface disturbance. Instead of clearing land, building access roads, and installing equipment at dozens of separate locations, operators concentrate activity on one pad. This reduces the impact on farmland, wildlife habitat, and nearby communities. It also makes operations more efficient, since equipment, water, and pipelines serve multiple wells from a single location.
Where Horizontal Drilling Is Used
The most prominent application is in shale oil and gas production. Formations like the Permian Basin, the Bakken, the Eagle Ford, and the Marcellus Shale are all developed almost exclusively with horizontal wells. These tight rock formations would produce little to nothing from a vertical well alone.
Horizontal drilling is also used in conventional oil and gas reservoirs to boost recovery, in geothermal energy projects to access hot rock layers, and for installing underground utility lines and pipelines through a related technique called horizontal directional drilling, or HDD. HDD uses similar principles but on a smaller scale, typically to run cables or pipes under rivers, roads, or buildings without digging trenches.
Costs and Trade-Offs
Horizontal wells cost significantly more than vertical ones. The specialized drill bits, downhole steering tools, longer casing strings, and additional drilling time all add to the price. A horizontal shale well can cost several million dollars more than a comparable vertical well in the same area.
The higher cost is justified by the dramatically higher production. A single horizontal well with a two-mile lateral can produce as much as several vertical wells combined, which means the cost per barrel of oil or per unit of gas is often lower despite the higher upfront investment. The trend toward longer laterals is driven partly by this math: extending the lateral adds incremental cost, but each additional foot of contact with the pay zone adds more production.
There are physical limits, though. Friction between the drill string and the wellbore increases with lateral length, making it harder to push the bit forward and rotate the string. Casing and completion equipment also become more difficult to install in extremely long laterals. As the industry pushes past three and four miles, these engineering challenges intensify, and each operator has to weigh whether the added production justifies the added complexity and risk of a longer well.