Application of Rotary Steerable Systems (RSS) requires a value proposition that exceeds the conventional method of drilling the well. The most quoted value proposition is savings in time for drilling wells of complex geometry.
This time saving is achieved because drilling of geometrically complex wells requires oriented drilling with conventional motors. This in turn reduces the rate of penetration (ROP) significantly and increases the amount of time required to drill the section. Rotary Steerable Systems on the other hand can be used to drill these wells without stopping rotation and in turn maintaining the rotating ROP throughout the section.
The real value proposition of rotary steerable systems is however in allowing options that would otherwise be impractical i.e. precise control due to closed loop systems, extended drilling due to continuous rotation or ability to utilize components that may be difficult to use with conventional motors.
This paper compares the drilling performance with and without rotary steerable system in the 12 ¼" sections on client wells. It also describes the benefits achieved when a rotary steerable application enabled the use of Polycrystalline diamond compact (PDC) bit in drilling 12 ¼" section. This resulted in significant time savings for client by saving a bit trip which was always required when tri cone insert bits (TCI) were used. Additional benefit of higher ROP was also realized due to increased effectiveness of PDC bit in comparison with TCI bits.
This PDC bit was not favored for use with conventional drilling systems due to difficulty in maintaining tool face during oriented drilling operation. Even though the bit was effective in drilling the formation, its unsuitability with drilling system rendered it unusable until the full benefits were realized by incorporating it in a rotary steerable BHA.
The application of Rotary Steerable System with the PDC bit resulted in an average on bottom ROP improvement of 67% as compared to the wells drilled in the same field with conventional motor assemblies. During this run 3590 feet of hole section was drilled with a circulation time of 180 Hrs. In addition to improved ROP, trip time for changing the bit was also saved which at the given depths could be 8 to 10 hrs. of rig time.