Rotary Steerable Systems
Rotary steerable systems (RSS) represent a relatively new form of directional drilling technology in which specialized downhole equipment replaces conventional directional tools such as mud motors (Figure 1: Rotary steerable system). They are generally programmed by the MWD engineer or directional driller, who transmits commands from the surface by means of fluid pressure fluctuations in the mud column or variations in the drill string rotation . The tool receives these commands and gradually steers in the desired direction. Thus, unlike a mud motor, which works in a “sliding” mode (i.e., without drill string rotation), the RSS is designed to drill directionally with continuous rotation from the surface.
The advantages of this technology are many for geoscientists & drillers
- The flow of drilled cuttings past the BHA is enhanced because annular bottlenecks are not created in the wellbore. This results in improved transport of drilled cuttings to the surface, which in turn brings about better hydraulic performance and superior hole cleaning.
- Continuous rotation of the drill string eliminates the need to slide a steerable motor. This results in reduced drag and decreases the risk of sticking.
- Continuous rotation of the drill string improves penetration rates because there are no stationary components to create friction and reduce efficiency
- Continuous rotation also provides better weight transfer. This allows for the drilling of more complex wellbores, along with reduced wellbore tortuosity due to utilizing a more steady steering model. Well geometries are therefore less aggressive, and borehole walls are smoother than those drilled with mud motors. This is particularly beneficial for geoscientists, because it provides for higher quality measurements of formation properties.
Rotary steerable systems are available from a number of vendors, including :
- Baker Hughes Inc.
- Calmena Energy Services
- Cathedral Energy Services
- General Electric Oil & Gas
- Gyrodata
- Halliburton
- Jindal Drilling & Industries Limited
- Key Energy Services
- Leam Drilling Systems LLC
- Nabors Industries Ltd.
- National Oilwell Varco
- Schlumberger Limited
- Scientific Drilling International
- Weatherford International Ltd.
Rotary steerable systems allow operators to plan complex wellbore geometries, including horizontal and extended-reach wells, which could not be drilled efficiently or effectively with conventional drilling methods. RSS accomplish this by enabling full directional drilling control in three dimensions. The BHA directs the well path in the desired direction while keeping the orientation of the drilling trajectory separate from its rotation and the rotation of the drill pipe above it (Figure 2).
Rotary steerable systems are of two types – push-the-bit systems and point-the-bit systems. Both systems utilize complex working mechanisms to effect independent 3D directional control. Push-the-bit systems steer the bit by applying a side load that forces the bit laterally in the direction of the desired curve (Figure 3). Point-the-bit systems steer the bit by tilting the bit in the direction of the desired curve (Figure 4).
