Why drill sideways?
A vertical well only contacts the few feet of reservoir directly beneath it. A horizontal well turns and runs thousands of feet through the pay zone, exposing far more reservoir to a single wellbore — essential in thin shale layers.
How it's done
The well is drilled vertically to a kickoff point, then deviated using mud motors, bent subs or rotary steerable systems. The driller builds angle until the wellbore is horizontal, then drills the lateral through the reservoir. Measurement-while-drilling (MWD) tools report the bit's position in real time.
Horizontal drilling plus hydraulic fracturing is the combination that made shale plays like the Permian and Bakken economic. As of 2021, about 85% of Permian wells were horizontal.
Measured depth vs true vertical depth
A horizontal well's measured depth (total length of hole) is much greater than its true vertical depth (straight-down depth). This distinction matters for pressure calculations — only the vertical column creates hydrostatic pressure.
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Frequently asked
The lateral is the horizontal section of a well that runs through the reservoir. Modern laterals can extend 10,000 feet or more from the vertical section.
The kickoff point is the depth at which a well begins to deviate from vertical to build angle toward horizontal.