Results from Systematic Rotary-Steerable Testing with PDC Drill-Bits Depict the Optimal Balance between Stability, Steerability, and Borehole Quality

Abstract

There is significant discussion concerning what type of Rotary Steerable System (RSS) provides the best-quality hole, and which key characteristics of the drill bit, along with a particular RSS, will produce the optimal balance between stability and steerability in directional wells. Although some evidence can be drawn from field performance with various tools and customized drill bits, these results can often be inconclusive due to the large variance in factors involved with commercial drilling.This paper describes an extensive series of test wells drilled in a controlled and non-commercial environment, allowing single step changes in both the drill bit features and Rotary Steerable (RS) configurations. The testing is unique in that the specific RSS works in shop-configurable point-the-bit and push-the-bit modes. Between two distinct RSS operation modes, consistency in stiffness, weight, force applying capability, and control systems lead to a direct comparison of bit performance. A unique sensor system, integrated into the specific RSS, provided real-time measurement of near-bit borehole caliper and near-bit stick-slip and vibration. This feature allowed real-time evaluation of bit and BHA stability and borehole quality. After each test run, memory data was retrieved and used for more detailed assessment of bit performance.Drill bit tests were systematically structured in a controlled environment so that the relationship between gauge geometry and configuration could be examined without alteration of the cutting structure. As a result, comparison between stability, dogleg capability, torque and drag, and borehole quality was solely dependent upon gauge length and geometry. Further, the systematic testing led to the conclusion that a specific gauge design related to effective side cutting and gauge stabilization is crucial for optimized RS drilling in both point-the-bit and push-the-bit configurations.

The Use of the Industry's First 3-D Mechanical Caliper Image While Drilling Leads to Optimized Rotary-Steerable Assemblies in Push- and Point-the-Bit Configurations

“…Bit B with the undergauge sub did not produce high DLS due to the extra length of the sub, but the toolface control was the best. In this test, a tapered gauge bit with the ledge trimmer (Bit B) produced 4.0 DLS, whereas in the prior test 13 , the same combination produced 5.4 DLS. This reduction in DLS (≈ 1.4 °/100ft) is caused by the extra 1-foot length between a bit and the pads.…”

“…push-the-bit RSS had been optimized for touch-point spacing during initial development 13 . However, in the previous tests, a special ledge trimmer (a separate undergauge sub) was run with the active gauge, tapered gauge, and partialring gauge bits to increase lateral stability.…”

“…push-the-bit RSS, it was discovered that the combination of an active gauge bit and a ledge trimming sub produced the highest DLS (5.8°/100ft) while providing excellent bit, BHA stability and highquality borehole 13 . Active gauge bits provide maximum side cutting for demanding DLS (or hard formation) applications and the ledge trimming sub keeps the hole on gauge to allow the assembly to pass through.…”

“…This extra 1-foot spacing is expected to reduce the DLS capability of the system. In prior bit testing 13 , an integrated ledge trimming sub was used, and it did not add any length to the spacing. Bit C has the shortest passive gauge length, whereas Bit D has the longest passive gauge length.…”

Integrated Approach to Rotary-Steerable Drilling Optimization Using Concurrent Real-time Measurement of Near-bit Borehole Caliper and Near-bit Vibration

“…The build rate with a point-the-bit configuration was 10.0°/100ft while the push-the-bit configuration produced 11.4°/100ft. More detailed test results are described by Jones et al in other literature [8].…”