Effect of Bicenter Bit BHA Design on BHA Behavior
- Jennifer Lynne Taylor (Schlumberger) | Reisha Bouska (Schlumberger) | Michael K. Mckenty (Newfield Exploration Co.) | Roger Silva (NOV) | Ernest Prochaska (ReedHycalog)
- Document ID
- Society of Petroleum Engineers
- IADC/SPE Drilling Conference and Exhibition, 2-4 February, New Orleans, Louisiana, USA
- Publication Date
- Document Type
- Conference Paper
- 2010. IADC/SPE Drilling Conference and Exhibition
- 1.6.3 Drilling Optimisation, 1.5 Drill Bits, 5.1.2 Faults and Fracture Characterisation, 1.6 Drilling Operations, 1.4.1 BHA Design, 4.1.5 Processing Equipment, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.6.2 Technical Limit Drilling, 1.12.6 Drilling Data Management and Standards, 1.6.6 Directional Drilling, 1.10 Drilling Equipment, 1.1 Well Planning, 2.1.7 Deepwater Completions Design, 1.5.1 Bit Design, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6.1 Drilling Operation Management, 4.1.2 Separation and Treating
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The petroleum industry is continually pushing to safely drill deeper, longer, and faster sections. The use of bicenter drill bits has been a popular option since the mid 1990s for borehole enlargement while drilling. Borehole enlargement offers significant benefits allowing multi-diameter casing strings, additional contingent hole sections and reduced equivalent circulating density with a narrow mud-weight situations, allowing longer well profiles and larger hole diameters to reach deeper reservoir sections.
Bicenter bits are unique because of their eccentric design and the rules of use below a smaller diameter drift. Those with a pilot bit and reamer combination are different than a conventional full-hole concentric bit. Generally, the bicenter bits are longer and have cutting force challenges not shared by concentric full-hole bits. The ability of a bicenter bit to drill a larger hole below a smaller drift diameter requires slightly different BHA configurations to maintain consistent directional control. There are currently no published reference tables or programs to accurately predict the directional behavior of bicenter-bit bottom-hole assemblies (BHAs).
This paper presents a study of bicenter bit and BHA runs in the Gulf of Mexico (GOM) that evaluates and analyzes operating parameters, stabilizer placement and BHA type [positive displacement motor and point-the-bit rotary steerable system (RSS)]. Also included are documented results, techniques, and references for establishing guidelines for successful use of bicenter-bit BHAs in directional drilling applications.
In the past 10 years bicenter bits have become a popular tool to enlarge a bore-hole section beneath a section of a smaller diameter. In the mid 1990s bicenter bit design attracted attention from drill bit manufacturers as a solution to extend a well by sidetracking out of small-diameter casing and liners and providing a larger hole. As stated by Denham and Fielder (2000), deepwater drilling activity was also increasing during this period requiring multi-diameter casing strings. Bicenter bits enabled the operator to set multiple casing strings by providing a larger hole than conventional concentric bits. Geometric balancing, force balancing, and design features using chamfered cutters and rounded tungsten carbide inserts were used in bicenter-bit design to reduce lateral vibrations and improve directional steerability while increasing durability. In the late 1990s a bicenter bit capable of drilling a casing shoe was introduced, allowing the driller to drill-out inside of liner hangers and casing float equipment, eliminating the need of making a trip to drill out with a conventional bit and pick up a bicenter bit.
Current bicenter technology is in its fifth generation and a sixth generation is in development. Sizes range from 2.75 in. x 3 in. to 18 in. x 22 in. The sizes are usually defined as pass-through size by hole size. Pass-through size is defined as the outer diameter of the tool measured at maximum radii points, and hole size is defined as the maximum hole size the bit is designed to drill. Bicenter bits have been used in rotary and air drilling and on mud motors and point-the-bit rotary steerable tools. They are also commonly used with mud motors in vertical and directional wells, achieving doglegs with inclinations of 20+ deg/100 ft. In horizontal wells, small diameter bicenter bits have also been used with mud motors on coiled tubing.
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