Bi-Center Bits

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5th Generation Bi-Center Technology

• Optimized pilot cutting structure that will drill out and drill ahead in a single run
• Patented geometric balancing
• Reduced imbalance to conventional PDC bit levels

Patented Mid-Reamer Design

• Centralizes pilot providing it with full gauge contact for superior hole quality
• Improves bit stabilization with over 180 degrees of gauge contact
• Increases wear resistance with more cutters opening the pilot hole
• Reduces rock cutting loads on the reamer

Steerable Bi-Center bits are also available for applications using point-the-bit rotary steerable systems.

 

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تاریخچه مزایا و معایب bi center Bit

تاریخچه مزایا و معایب bi center Bit

useful data about the bicenter bits. Their features,advantages, problems, special BHA requirements




The first Bicenter core bits and drill bits were first manufactured in 1957-58 by the late Edward B. Williams, Jr (Williams Bit & Tool Co., Greenville, Texas). With the patent granted in 1960 (2953354). Williams was bought by Hycalog in 1974 and so went the patent.

BiCenter drill bits with natural diamonds have been used in many applications since then (Lagoven / Eastern Venezuela 1977 and Lake Maracaibo 1978).

The first BiCenter PDC bit that I know of was run in 1981 for Lagoven, also in Lake Maracaibo.

Current day state of the art has yielded at least one iteration of BiCenter PDC bit from all major bit companies and most offer three basic types:
1. A unitized pilot and eccentric that is short coupled to be used in high DLS steering applications.
2. A unitized bit with pilot and eccentric spaced apart somewhat to effect a more stable running condition.
http://www.nov.com/Downhole/Drill_Bits/F....ter_Bits.aspx3. A separate eccentric that can be run with a pilot bit of choice.
http://www.bakerhughesdirect.com/cgi/hel....D2_brochure.pdf
Currently the BiCenter concept is being applied to PDC, Diamond, and Diamond-Impreg drill bits… thru-tubing mills (in cement & scale)…and core bits.

In all Bicenters the basic component sizes are determined by BHA size (bottom 30 feet or so) in that the pilot bit portion cannot be smaller than the immediate BHA diameter. The difference between the pilot and drift diameter x 2 added to the pilot size is the maximum size the eccentric will cut if held on threaded center by the pilot.

The offsetting force created by the eccentric is not usually a factor in softer formations, but in medium to hard targets the side force can force the pilot off of its intended axis and the bit can “founder” which results in undersized drilled hole and uneven bit wear.

Generally, conventional Bicenter bits cannot be used to enlarge an existing borehole because the pilot must seat firmly in place to be able to hold the eccentric on center.

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