Downhole assembly, tool and method

A downhole assembly comprising a bottom hole assembly for drilling a borehole, the bottom hole assembly comprising:

• a housing including a drilling tool disposed at a distal end;
• and
• a reaming tool comprising:
• a body having a longitudinal axis and an upper end opposite a lower end;
• and
• a plurality of blades located on said body, each blade comprising:
• a reaming surface having three or more reaming inserts arranged on at least a portion of the reaming surface in a number N of rows extending substantially parallel to a longitudinal axis of said reaming surface, wherein N is greater than two, the rows being laterally spaced from each other by a predetermined distance R, wherein the shortest distance along said longitudinal axis of said body between any two nearest inserts in two adjacent rows and between any two nearest inserts in two opposing outer rows is a predetermined value Y such that substantially equal load is applied on the reaming inserts in the longitudinal and circumferential directions;
• and
• a cutting surface having cutters disposed on at least a portion thereof, wherein radial distances between an outermost portion of all of said cutters and said longitudinal axis of said body are less than or equal to radial distances between an outermost portion of said reaming inserts and said longitudinal axis of said body.

A method of reaming a borehole comprising the steps of:

• providing a downhole assembly attached to a drillstring, wherein the downhole assembly comprises:
• a housing including a drilling tool disposed at a distal end;
• and
• a reaming tool comprising:
• a body having a longitudinal axis and an upper end opposite a lower end;
• and
• a plurality of blades located on said body, each blade comprising:
• a reaming surface having three or more reaming inserts arranged on at least a portion of the reaming surface in a number N of rows extending substantially parallel to a longitudinal axis of said reaming surface, wherein N is greater than two, the rows being laterally spaced from each other by a predetermined distance R, wherein the shortest distance along said longitudinal axis of said body between any two nearest inserts in two adjacent rows and between any two nearest inserts in two opposing outer rows is a predetermined value Y such that substantially equal load is applied on the reaming inserts in the longitudinal and circumferential directions;
• and
• a cutting surface having cutters disposed on at least a portion thereof, wherein radial distances between an outermost portion of all of said cutters and said longitudinal axis of said body are less than or equal to radial distances between an outermost portion of said reaming inserts and said longitudinal axis of said body;
• drilling a pilot borehole until the downhole assembly reaches a target depth beneath the surface;
• and
• moving the drillstring within the borehole while rotating the reaming tool of the downhole assembly.