Well bore casing cutting tool having an improved blade structure and pad type stabilizers
A downhole cutting tool for cutting sections or “windows” in tubular strings in wellbores has rotating cutters and a lower stabilizer section, both actuated by a fluid operated mechanism. The stabilizer section keeps the downhole cutting tool centralized in the tubular string. The cutters may have a robust profile and structure which enhances the window cutting function and permits passage of an operating rod to operate the stabilizer section.
1. A downhole cutting tool, comprising:
a) a main body having a bore therethrough, and a fluid piston disposed in said bore and longitudinally movable therein, said piston having a bore therethrough;
b) a plurality of rotatably mounted blades mounted in said main body, movable from a first position retracted into said main body and a second position rotated outwardly from said main body;
c) a plurality of pairs of positioning arms rotatably mounted in said main body, and movable from a first position retracted into said main body and a second position rotated outwardly from said main body; and
d) a stabilizer pad mounted on each pair of positioning arms, whereby when said positioning arms are rotated outwardly said stabilizer pad is moved radially outward from said main body and held generally parallel to said main body;
wherein said fluid piston bears on said blades under the influence of fluid flow through said bore of said main body, thereby rotating said blades from said first position to said second position, and wherein said fluid piston further comprises an operating rod extension which bears on at least one of said pairs of positioning arms, thereby rotating said positioning arms from said first position to said second position and moving said stabilizer pads outwardly, said operating rod extension comprising a longitudinal bore therethrough, said longitudinal bore providing a fluid flow path for fluid flow to said positioning arms.
2. The downhole cutting tool of claim 1 , wherein said rotating arms and said stabilizer pads are dimensioned to position said stabilizer pads closely against an inner diameter of a casing string within which said cutting tool is positioned.
3. The downhole cutting tool of claim 1 , wherein said blades, when viewed end-on, from an end of said blades distal from one of said downhole cutting tools in which one of said blade is mounted:
comprise a main body having a rounded top surface conforming to the radius of said main body, when said blades are in said first position;
a leading cutting surface inclined at an angle to a longitudinal axis of said downhole cutting tool and in the direction of the cutting movement; and
a bottom cutting surface having a leading edge and a trailing edge and inclined at an angle to a line perpendicular to a longitudinal axis of said downhole cutting tool, such that the trailing edge of said bottom cutting surface is higher than the leading edge of said bottom cutting surface.
4. The downhole cutting tool of claim 3 , wherein said blades have a width, and further comprise a heel portion against which said operating rod extension bears, said heel portion having a dimension less than one-half of said width of said blade.
5. The downhole cutting tool of claim 3 , wherein said blades comprise a plurality of cutters mounted thereon, said cutters arranged in layers and embedded in a matrix of hardened cutting material.
6. A method of milling casing with a downhole cutting tool, said casing comprising a window section removed therefrom in a downhole location, said casing presenting an upward facing casing edge, comprising the steps of:
a. providing a downhole cutting tool comprising
a main body having a bore therethrough, and a fluid piston disposed in said bore and longitudinally movable therein, said piston having a bore therethrough;
a plurality of rotatably mounted blades mounted in said main body, movable from a first position retracted into said main body and a second position rotated outwardly from said main body;
a plurality of pairs of positioning arms rotatably mounted in said main body, and movable from a first position retracted into said main body and a second position rotated outwardly from said main body; and
a stabilizer pad mounted on each pair of positioning arms, whereby when said positioning arms are rotated outwardly said stabilizer pad is moved radially outward from said main body and held generally parallel to said main body;
wherein said fluid piston bears on said blades under the influence of fluid flow through said bore of said main body, thereby rotating said blades from said first position to said second position, and wherein said fluid piston further comprises an operating rod extension which bears on at least one of said pairs of positioning arms, thereby rotating said positioning arms from said first position to said second position and moving said stabilizer pads outwardly, said operating rod extension comprising a longitudinal bore therethrough, said longitudinal bore providing a fluid flow path for fluid flow to said positioning arms;
b) positioning said downhole cutting tool within said window section, said downhole cutting tool lowered on a tubular string;
c) pumping fluid through said tubular string and said downhole cutting tool, thereby rotating said blades to said second position and moving said stabilizer pads into proximity with an inner diameter of said casing string;
d) rotating said downhole cutting tool and lowering said downhole cutting tool until said blades contact said casing edge;
e) applying a desired amount of weight to said downhole cutting tool, while continuing pumping fluid and rotating said downhole cutting tool, thereby milling said casing, until a desired length of casing has been removed.