The most visible aspects of offshore field development are the major drillships, semis, platforms, FPSOs, subsea wellheads, tie-backs and pipelines that require large capital investment. I believe one relatively modest technology deserves recognition, because without it, the offshore industry could not exist. That technology is directional drilling.
Directional technology makes offshore production economic, by making it possible to develop an entire field from one platform.
Shoreline whipstocks. Directional drilling was used to reach offshore oil in California, even before the first platform was installed in the Gulf of Mexico in 1947. In the late 1920s, the harbors at Huntington Beach and Long Beach were clogged with wooden piers, topped with wooden derricks drilling vertically to hit oil beneath the seabed. These makeshift structures posed a hazard to ship traffic, so the practice was banned. Enterprising drillers, like H. John Eastman, developed ways to deflect wells drilled from rigs on the shoreline to reach the subsea targets in the coastal Wilmington field. Since 1965, hundreds of wells have been drilled directionally from the four THUMS islands in Long Beach Harbor as part of this continuing development effort.
The early directional driller used an openhole whipstock to kick off the well from vertical and rotary bottomhole assemblies, with stabilizers placed in various configurations to build angle, hold angle, or drop inclination, as needed. Eastman called his technique “controlled directional drilling,” because he could take surveys of the well’s position using single- or multi-shot instruments that photographed a magnetic compass and plumb bob, which were isolated from the steel drillstring inside a nonmagnetic drill collar.
Before calculators or computers, directional drillers plotted the well’s trajectory using a surveyor’s “red book” of trig functions and the “average angle” hand calculation method. At this point, directional drilling was as much an art as a science, and directional drillers typically had worked their way up from roughneck to driller, before gaining enough practical experience to become skilled at placing the bit in the proposed target.
Technology evolves. In the late 1950s, mud motors began to replace whipstocks as the preferred tools for deflecting wells and turning them. The drilling motor could turn the bit without drillstring rotation, and with the addition of a bent sub, an orienting device to provide “toolface,” and a single shot instrument, a well could be kicked off more accurately, more efficiently and at a higher build rate than when using a whipstock. By the mid-1970s, wireline steering tools were introduced to replace the single-shot instrument during kick-offs. New sensors and electronics, and real-time data on the well’s direction and inclination, as well as the bit’s toolface, improved efficiency and enabled drillers to compensate for the reactive torque created by the mud motor.
The product life cycle of the wireline steering tool was relatively short, however, because of the introduction of measurement-while-drilling (MWD) systems in the late 1970s. MWD systems incorporated the new sensor technology and used mud-pulse telemetry to transmit the data to the surface without a wireline, and without having to retrieve a camera-based instrument. Surface computing systems also improved accuracy and provided more data for engineered decision-making.
By the mid 1980s, steerable motor systems were introduced. These systems included a bend in the motor for orientation and an MWD system for guidance. New PDC drill bits enabled longer runs between bit trips. Unlike previous directional motor assemblies used only at kick-off, these systems were designed to remain in the wellbore for the entire hole section. When a kick-off or course correction was needed, the bend would be oriented, the drillstring would be held steady without rotation, and “slide drilling” would take place until the adjustment was made. To drill ahead in a straight course, the entire drillstring was rotated, with the motor providing additional drilling power, and the bent assembly creating a slightly over-gauge hole. Steerable motor systems greatly improved the accuracy of directional wells, and enabled complex well profiles and the quick adoption of horizontal drilling.
Rotary steerable revolution. In the late 1990s, rotary steerable systems brought another step change in directional drilling. These systems are designed to provide continuous directional control without interrupting drillstring rotation. Rotary steerable systems employ programmable stabilizer pads near the bit, which are hydraulically actuated to nudge the bit in the right direction. Mud-pulse telemetry is used for two-way communication, so engineers at the surface can command the system to adjust course. Logging sensors added to the MWD system provide formation evaluation data and also enable “geosteering,” so the drilling assembly can be guided to the best-producing intervals in the reservoir.
The combination of accurate rotary steerable systems and logging-while-drilling systems has enabled remarkable offshore field development globally. With this technology, operators have drilled wells with complex trajectories to navigate between existing wells in crowded North Sea fields, drill “uphill” to reach multiple targets offshore Brunei, efficiently drill to subsalt and pre-salt zones in the Gulf of Mexico and Brazil, and set successive extended-reach drilling records at Sakhalin Island and Qatar. Advanced directional drilling and geosteering also have enabled the impressive development of Troll field in Norway, using long multilateral wells to produce thin oil zones.
That’s my case for the importance of directional drilling to the offshore industry. I encourage World Oil readers to nominate other essential, but unsung technologies, for recognition in this column. 
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