Lower mill spaced cutting ring structure

摘要

The cutting structure on the lower mill is arrayed in rows that are preferably parallel. The cutting structure in each row is made sharper and more durable than prior designs with the objective of cutting the window higher than where the window mill started the window. The use of the rows increases the contact stress of the inserts on the casing inside wall because at any given time fewer and sharper inserts are cutting the casing wall to lengthen the window. As a row wears down the next row takes over to continue the cutting where the previous row was active and to further penetrate the casing wall. The cutout angle can also increase as this occurs. As a result a decreased insert density results in more effective casing wall cutting to extend the window to allow larger tools to exit into the window off the whipstock.

主权项

1. A window milling assembly for making a tubular exit at a subterranean location, comprising:
a whipstock supported in the tubular; a window mill having a longitudinal axis and rotatably mounted to a delivery string while advancing on a ramp of said whipstock and initiate the forming of the window; a lower mill connected to said window mill by a mandrel having an outside dimension smaller than a peripheral surface of a plurality of blades on said lower mill for tandem movement therewith with respect to said whipstock, said blades extending generally in in the direction of a longitudinal axis of said lower mill, with said outer peripheral surfaces of said blades further comprising more than two axially spaced rows of cutters with said rows comprising multiple cutters oriented substantially perpendicularly to said longitudinal axis of said lower mill with said rows extending in circumferential alignment among said plurality of blades.