Unique Pivot Stabilizer Geometry Advances Directional Efficiency and Borehole Quality With a Specific Rotary-Steerable System

Abstract

The geometry of a stabilizer, when it is used as a near-bit pivot within specific point-the-bit rotary-steerable bottomhole assemblies (BHAs), is critical to both stability and deflection to provide optimal directional response. This paper describes the testing of a rotary-steerable system (RSS) and unique ring gauge pivot stabilizer at a purpose-built, full-size drilling test facility. The extensive, systematic testing of a point-the-bit RSS with both full ring gauge and conventional pivot stabilizer has enabled a direct comparison of the directional response, hole quality, and drillstring vibration to be made for the various combinations tested. Aside from comparison of the ring gauge stabilizer against conventional pivot, the testing also evaluated the interaction between the gauge design of the bit and the pivot stabilizer. Test monitoring required use of a proprietary downhole dynamic data recorder (DDDR) in a specially modified housing. The DDDR was used to assess both lateral and torsional stability of the stabilizer geometries and their relationship with bit gauge style and length. Further to the laboratory testing, trial applications have been sought where severe vibration issues are problematic to efficient operation of the RSS. Use of full ring stabilization geometry with an RSS in these applications will advance the industry's understanding of downhole dynamics. Enhanced understanding, in turn, will enable more efficient drilling of better-quality directional wellbores, significantly reducing cost per foot. Introduction The introduction of RSS has given the industry the ability to successfully drill complex and challenging well profiles such as extended-reach and infill designer re-entry wells. In addition, the use of polycrystalline diamond compact (PDC) bits, combined with RSS, has drastically changed the economics of directional drilling by significantly decreasing the time taken to drill hole sections and improve the quality of wellbores drilled, thus increasing the chances of trouble-free wireline logging and running of completions. The improve-ment in economics is particularly relevant in this era of high rig rates. It is recognized that the selection of correct design of bit is crucial to the successful directional performance of an RSS. The stability and steerability of the bit are key features in matching a bit to the specific RSS, while matching the durability and aggressivity to the formation is of importance in achieving the optimal rate of penetration (ROP) and bit run life. Point-the-bit RSS can take advantage of longer passive gauge lengths to reduce hole spiraling and improve borehole quality because they rely less on side-cutting action from the gauge than do push-the-bit systems.1,2 Key focus is maintained on providing very stable bit cutting structures that resist lateral instability and provide low variance in reactive torque. Furthermore the interaction between the bit, the RSS, and the BHA elements is extremely important to the successful directional performance of the system. Maintaining wellbore quality, and in particular hole gauge, is crucial to the steering performance of point-the-bit RSS.3 One aspect of wellbore quality is the stability of the active BHA, as vibration will contribute to wellbore enlargement. BHA instability can have a significant detrimental effect on the directional performance of the RSS. Prior testing has focused only on optimization of the cutting structure and gauge geometry to maximize stability of the drill bit.4,5 This paper details the introduction and systematic testing of stabilizer geometries to further enhance stability, and thus steering efficiency, of RSS.

Delivering Steering Success in Problematic Soft Formation Directional Wells

“…Some of this non-commercial testing is already published and available for review 12 . Some of this non-commercial testing is already published and available for review 12 .…”