Improving Rotary-Steerable Borehole Quality Using Innovative Imaging Techniques

Abstract

Borehole quality of point-the-bit rotary steerable systems (RSS) has been well documented in the industry. This type of system, using an extended passive-gauge polycrystalline diamond compact (PDC) bit and/or a full-gauge near-bit stabilizer to tilt the bit, is known to produce high-quality borehole due to the extra lateral stability added to the lower part of the bottomhole assembly (BHA), below the RSS deflection unit. Yet, extended-gauge PDC bits and full-gauge stabilizers are not suitable for every drilling environment, and a push-the-bit system may be more applicable in certain formations.On the other hand, borehole quality of push-the-bit RSS has not been extensively discussed in the past, partly because the PDC bit gauge length and profile are directly related to the directional response of the tool, and different gauge lengths may be used based on the application. This type of system may lack lateral stabilization between the bit face and steering unit, depending on the type of bits used and the steering mechanism. To increase the lateral stability and borehole quality of the system, in-depth analysis of PDC bit (gauge type and length) and BHA design is required. This paper describes the results of extensive downhole drilling tests conducted on a push-the-bit RSS. The controlled tests were conducted using various PDC bits drilling through different formations. Improvements in stability and borehole quality have been examined using vibration data and a unique near-bit 2-D/3-D caliper image. Visualization of the borehole, using 3-D caliper images and their spectrum analysis, reveals that borehole quality is highly dependant on the BHA components below the RSS steering unit.The test results show that progressive testing with innovative imaging techniques can systematically improve the performance of push-the-bit RSS and produce a better understanding of the interaction among the bit, formation, and RSS steering unit. Proper use of these techniques helps during the development of a field where troublesome formations are encountered and poor borehole quality leads to high torque and drag which limits the drilling performance.