Grant Prideco, Inc.

Camco International (UK) Limited

Steven James Hart

Graham Watson

Graham R Watson

A method to design a bi-center drill bit designed to drill out the cement and other material in the casing and then proceed to drill out the full gauge drilling diameter borehole with a diameter greater than the inside of the casing. The bi-center drill bit has a pilot section on the end of the bit body, an eccentric reamer section and a plurality of cutting elements on the pilot section. The design method comprises the steps of: defining a first center of rotation of the pilot section about the longitudinal axis, defining a radius of rotation R of the drill bit about the first center of rotation, defining a second center of rotation of the pilot section spaced apart from the first center of rotation by a distance D, defining a radius of rotation R of the drill bit about the second center of rotation, and setting the relationship between D, R and R such that R is less than the sum of R and D.

Design method for drillout bi-center bits

The present invention is a bi-center drill bit designed to drill out the cement and other material in the casing and then proceed to drill out the full gauge drilling diameter borehole with a diameter greater than the inside of the casing. The bi-center drill bit is configured with non-drilling bearing elements that contact with the casing when the bit is drilling the cement without allowing the gauge cutting elements of the bi-center drill bit to contact the casing. The bi-center drill bit also has a cutting element configuration which prevents reverse scraping of the cutting elements when drilling both the cement and the formation.

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Bath, United Kingdom

Steven James Hart