Bi-Center Drill Bits and MWD/LWD Tools in a Horizontal Application Prove Effective in Reducing Well Costs and Increasing Liner-Size Capability
Authors: Parrish Rick , Fielder Coy , Ishmael Rod 
Published: December 2007

Bi-Center Drill Bits and MWD/LWD Tools in a Horizontal Application Prove Effective in Reducing Well Costs and Increasing Liner-Size Capability Rick Parrish,*,** Chevron Niugini Pty. Ltd., and Coy Fielder* and Rod Ishmael,* Diamond Products Intl. Inc.

Abstract
A horizontal drilling program at the Kutubu Project in Papua New Guinea (PNG) called for the use of bi-center drill bit technology to be applied with MWD/LWD tools in a drill-in fluid system. This was the first time that bi-center polycrystalline-diamond-compact (PDC) bits were utilized in a horizontal drilling application. Bit performance while drilling with MWD/LWD tools was enhanced through the use of a sized-salt biopolymer drill-in fluid system. The fluid system was being enlisted for the first time in PNG.
The tool combination was able to drill a larger 9 1/8-in. hole out of the 9 5/8-in.-OD casing, as opposed to the 8 1/2-in. holes in four previous horizontal wells (includes one sidetrack) drilled with conventional PDC bits. The larger hole drilled by the 8 3/8-by-9 1/8-in. bi-center bits allowed a 7-in. production liner to be run, instead of the 5 1/2-in. liners run in the previous horizontal wells. The larger liner permits installation of larger production tubing required to selectively produce the desired 8,000-bopd flowrate, as well as a packer/sliding-sleeve completion system.
In addition to the benefit of multizone-completion ability and increased flowrate capability, drilling time in the horizontal section was reduced by 13 days using the bi-center-bit/MWD-LWD combination. This reduction in drilling time alone amounted to more than a $ 1.56 million savings to the operator.
Bi-center drill bit applications can now yield predictable results in demanding directional environments. The ability to log-while-steering in a horizontal lateral while providing an enlarged hole diameter, without need for additional trips in and out of the hole, results in an extremely cost-effective drilling system.

Project background
Oil was discovered at the Kutubu Project in 1986 by the Iagifu 2X exploratory well in a remote location in PNG's Southern Highlands Province about 300 mi northwest of Port Moresby, Fig. 1. The petroleum development license (PDL) was approved in December 1990 and first commercial production began in June 1992. Average Kutubu production for 1996 was 107,000 bopd.
Before the PDL could be approved, extensive appraisal drilling was required. Including sidetracks, some 31 delineation wells were drilled in the Iagifu/Hedinia and Agogo fields to determine the extent of the Kutubu oil reserves. A large number of appraisal wells were needed due to the significant structural complexity in each well. Massive karsted limestone beds also covered the surface of much of the license area that made acquisition of useful seismic data virtually impossible.
Current Kutubu original oil-in-place (OOIP) estimates are slated at about 515 MMSTB based on information from appraisal and development drilling. This is a combined estimate for seven distinct reservoir blocks in two fields. About 80% of the total OOIP, or 420 MMSTB, is from the Toro formation and about 73% is contained in one fault block, the Main Block Toro in the Iagifu/Hedinia field.
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