United Kingdom: The motor/VGS combination comes of age ///

The introduction of rotary steerable systems (RSSs) has been heralded – especially by the major directional companies – as the beginning of a new directional drilling age, and in many ways it is. Keeping the assembly turning cleans the hole more efficiently, reduces the chance of sticking and, ultimately, allows drilling further than sliding with a downhole motor. These new tools allow the driller to make subtle corrections as he builds and drops angle, turning left and then right as he follows the geologist's requirements. The only real glitch is getting enough power to the bit from the surface to keep a reasonable ROP. Sometimes, running a motor is preferable. As ever, engineering is never as clear-cut as one might want. Usually, new tools come with compromises, and this is also true of rotary steerable systems. When working at peak performance in ideal formations for building angle, where excessive vibration, wear and temperature are not a problem, the RSS can perform admirably. With motors still seen as more reliable than RSSs, and some deepwater rigs costing $200,000 per day and more to operate, pulling out of hole from 15,000 ft because a drive shaft has snapped, a pad has fallen off or some other problem becomes an important decision. With RSS prices ranging from $10,000 to $25,000 per day and more, drilling engineers continue to look for cost-effective alternatives.

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