directional drilling — Oil & Gas Glossary

What Is Directional Drilling?

Directional drilling steers a wellbore along a planned non-vertical path using a combination of mud motors, rotary steerable systems, and measurement-while-drilling tools. Operators apply directional drilling to develop horizontal shale wells in the Permian and Montney, multilateral wells in the Middle East, extended-reach wells at BP's Wytch Farm and ExxonMobil's Sakhalin-1, and offshore wells from clustered subsea templates in the Norwegian Continental Shelf and Australian Carnarvon Basin.

Key Takeaways

Directional drilling deliberately deviates a wellbore from vertical to reach a specific subsurface target, the foundational technology enabling horizontal shale development, extended-reach drilling, and multilateral wells.
Rotary steerable systems (RSS), mud motors with bent housings, MWD tools, and LWD tools form the directional drilling toolkit, with modern RSS tools holding wellbore placement within 0.5 m (1.6 ft) over 3,000 to 5,000 m (9,843 to 16,404 ft) laterals.
Operators, drilling contractors, and investors track directional drilling performance through rate-of-penetration, dogleg severity, and directional-control accuracy, all of which drive cycle time and cost per foot drilled.
Regulatory frameworks for directional surveying include AER Directive 059 in Alberta, Texas Railroad Commission survey requirements for Permian horizontals, Sodir directional reporting on the Norwegian Continental Shelf, and NOPSEMA survey-accuracy requirements for Australian Commonwealth offshore wells.
ExxonMobil's Sakhalin-1 Chayvo Z-42, drilled in 2013 to 12,700 m (41,667 ft) measured depth with 11,739 m (38,514 ft) horizontal departure, stands as the benchmark extended-reach well record.

How Directional Drilling Works

A directionally drilled well begins as a vertical hole from surface. At the kickoff point (KOP), the driller deploys a directional assembly that creates a controlled deviation from vertical. Two primary technologies generate the steering force: the positive displacement motor (PDM) with a bent housing, and the rotary steerable system (RSS). Both sit in the bottomhole assembly just above the bit, instrumented with MWD tools that transmit real-time inclination, azimuth, and tool-face data to the surface via mud-pulse or electromagnetic telemetry.

A PDM is a downhole motor powered by circulating drilling fluid. The bent housing creates an angular offset of roughly 1 to 3 degrees between the motor axis and the drill-string axis, so when the drill pipe is held stationary and the motor rotates the bit, the hole advances at that angle. Alternating between sliding (motor-only rotation) and rotating (full drill-string rotation) allows the directional driller to build angle, drop angle, or drill straight ahead. PDMs dominate onshore directional drilling for shale plays because they are cost-effective and reliable.

A rotary steerable system applies side force at the bit through servo-controlled pads (push-the-bit) or an offset internal shaft (point-the-bit), while the entire drill string rotates continuously. RSS eliminates sliding time, improves rate-of-penetration, and reduces tortuosity in the completed wellbore. Schlumberger's PowerDrive, Halliburton's Geo-Pilot, Baker Hughes's AutoTrak, and NOV's Vector family are the dominant RSS platforms. Modern high-build-rate RSS tools, introduced from 2018 onward, execute build rates above 15 degrees per 30 m (100 ft) while maintaining full rotation, enabling shorter build sections and longer reservoir contact.

Directional Drilling Across International Jurisdictions

Every major producing country regulates directional surveying to verify that wells stay within leased mineral rights, maintain offset distances from adjacent wells, and respect regulatory boundaries. In Canada, AER Directive 059 Well Drilling and Completion Data Filing Requirements prescribes directional survey reporting for every Alberta well, including gyroscopic or MWD survey data at prescribed intervals. The BCER and Saskatchewan's Ministry of Energy and Resources apply equivalent requirements for Montney, Horn River, Bakken, Viking, and Lloydminster wells.

In the United States, the Texas Railroad Commission's Rule 11 requires directional surveys on all horizontal wells in Texas, with specific accuracy thresholds tied to offset-well distance and lease boundaries. The NDIC, the Colorado Energy and Carbon Management Commission, the Pennsylvania DEP, and BSEE 30 CFR 250 all specify survey intervals, tool accuracy, and reporting formats. Federal BLM wells on public lands follow BLM Instruction Memoranda that track API Bulletin K2 accuracy standards.

Norway's Sodir enforces strict survey accuracy on the Norwegian Continental Shelf, particularly for wells drilled from fixed platforms where multiple wells share common wellheads. NORSOK D-010 references the Industry Steering Committee on Wellbore Survey Accuracy (ISCWSA) error models as the baseline. Operators at Troll, Johan Sverdrup, Snøhvit, and Ekofisk submit directional surveys to Sodir as part of standard well filings. Australia's NOPSEMA requires directional survey data in Well Operations Management Plans submitted by Woodside, Santos, INPEX, Chevron Australia, and other operators in Commonwealth waters covering Browse, Carnarvon, and Bass Strait basins.

Middle East operators apply API and ISCWSA survey standards supplemented by company-specific requirements. Saudi Aramco's Maximum Reservoir Contact (MRC) wells in Ghawar and the deep gas Jafurah project use multilateral configurations with multiple branches from a single parent wellbore, demanding particularly precise directional work. ADNOC's extended-reach wells in the UAE offshore, Kuwait Oil Company's multilateral Burgan developments, and QatarEnergy's North Field wells all rely on RSS and high-accuracy MWD to meet their subsurface targets.

Fast Facts

BP's Wytch Farm onshore field in Dorset, England, set the extended-reach drilling benchmark of the 1990s. The M16 well, drilled in 1999, reached a measured depth of 11,275 m (36,992 ft), a horizontal departure of 10,275 m (33,712 ft), and a true vertical depth of only 1,628 m (5,340 ft), accessing reservoirs beneath Poole Harbour from surface locations far inland. The M-15 Wytch Farm well was drilled as a multilateral with two branches of 8,900 m (29,199 ft) and 6,700 m (21,982 ft), an early demonstration of multilateral extended-reach technology that subsequently informed Sakhalin-1, Saudi Aramco MRC wells, and Gulf of Mexico deepwater subsea programs.

MWD, LWD, and Geosteering

Measurement-While-Drilling (MWD) tools sit in the bottomhole assembly and transmit directional and drilling dynamics data to surface in real time. Core MWD measurements include inclination, azimuth, tool face, rotary speed, downhole vibration, and pressure-while-drilling (PWD). The driller uses inclination and azimuth to verify the well is advancing on the planned trajectory, while tool face indicates the direction of the bent housing for sliding operations with a mud motor.

Logging-While-Drilling (LWD) tools extend MWD with formation evaluation sensors: gamma ray, resistivity, density, neutron porosity, sonic, imaging, and magnetic resonance. LWD allows the directional driller to steer based on formation properties rather than only on geometric target coordinates, a practice called geosteering. Geosteering is standard in horizontal shale wells and thin-reservoir offshore wells where keeping the lateral inside a 3 to 10 m (10 to 33 ft) pay zone materially affects EUR.

Modern MWD/LWD systems from Schlumberger, Halliburton, Baker Hughes, and Weatherford combine high-speed telemetry (mud-pulse at 6 to 40 bits per second, electromagnetic at up to 100 bits per second, or wired pipe at up to 57,600 bits per second) with real-time data transmission to onshore remote operations centers in Calgary, Houston, Aberdeen, Stavanger, and Dubai. Decision-making on directional adjustments frequently happens within seconds of a downhole measurement reaching surface.

Tip: Investors and portfolio managers can track directional drilling efficiency by comparing days-per-foot and cost-per-foot across operators in the same basin. A leading Permian operator using high-build-rate RSS plus wired-pipe telemetry might complete a 4,500 m (14,764 ft) lateral in 6 to 8 drilling days, while a lagging operator with traditional RSS and mud-pulse telemetry takes 10 to 12 days. That gap compounds into USD 2 to 3 million per well and materially changes program-level free cash flow on large acreage positions.

Deviated drilling: older term for non-vertical drilling, still common in engineering specifications.
Horizontal drilling: the subset of directional drilling at 80 to 95 degrees inclination.
Extended-reach drilling (ERD): directional wells with horizontal displacement more than twice true vertical depth.
Slant well: a low-angle deviated well, typical of SAGD thermal oil sands development in Alberta.
Multilateral well: a well with multiple lateral branches from a single parent wellbore.
Sidetrack: a new wellbore kicked off from an existing well, frequently used to bypass a stuck bottom hole assembly or reach a new target.
Geosteering: real-time directional adjustment based on LWD formation data to stay inside a target reservoir.

Frequently Asked Questions

What is directional drilling in oil and gas?

Directional drilling is the practice of deliberately steering a wellbore along a planned non-vertical path. It uses mud motors, rotary steerable systems, and measurement-while-drilling tools to reach subsurface targets that cannot be accessed by a vertical well. Directional drilling enables horizontal shale development, extended-reach wells from onshore pads to offshore reservoirs, multilateral wells with multiple branches, and subsea developments with clustered wellheads.

How does directional drilling work?

Directional drilling uses either a mud motor with a bent housing or a rotary steerable system to deflect the wellbore from its current trajectory. MWD tools transmit inclination, azimuth, and tool face data to surface, allowing the directional driller to verify position and adjust steering. LWD tools provide formation data that enables geosteering, keeping the lateral inside the target reservoir rock.

What is the difference between a mud motor and a rotary steerable system?

A mud motor (positive displacement motor with bent housing) generates its steering force by offsetting the bit axis from the drill-string axis. The driller alternates between sliding (motor-only rotation, building or dropping angle) and rotating (full drill-string rotation, drilling straight) to steer. A rotary steerable system applies side force at the bit while the entire drill string rotates continuously, eliminating sliding and delivering faster, smoother wellbores. RSS costs more per day but typically finishes laterals faster.

Why Directional Drilling Matters in Oil and Gas

Directional drilling is the enabling technology behind nearly every form of modern oil and gas development. Shale plays across the Permian, Bakken, Marcellus, Montney, Duvernay, and Vaca Muerta depend on it. Extended-reach wells at Sakhalin-1, Wytch Farm, and Saudi Aramco's Manifa depend on it. Deepwater subsea tiebacks from the North Sea to the Gulf of Mexico to offshore Brazil depend on it. For the directional driller on a Midland Basin horizontal, the RSS engineer troubleshooting a PowerDrive in Abu Dhabi, the geosteering operator watching a Duvernay lateral in Calgary, and the portfolio manager tracking days-per-foot efficiency for an upstream valuation, directional drilling sits at the center of how the industry turns subsurface targets into surface production.

Directional Drilling: Definition, Tools, and Extended-Reach Records