Frac plug mill bit

Abstract

A fixed cutter bit for milling a frac plug includes a body and a face. The face includes a base surface and a plurality of cutter support structures extending from the base surface. Each cutter support structure has a peripheral portion and an inner portion disposed radially internal of the peripheral portion. At least one first-type cutter is supported by each peripheral portion; at least one second-type cutter is supported by each inner portion. The first type cutter is adapted to mill a harder material than the second-type cutter, and the first-type is different from the second-type.

What is claimed is: 
     
         1 . A fixed cutter bit, comprising:
 a body; and   a face, comprising:
 a base surface; 
 a plurality of cutter support structures extending from the base surface, each cutter support structure having a peripheral portion and an inner portion disposed radially internal of the peripheral portion; 
 at least one first-type cutter supported by each peripheral portion; and 
 at least one second-type cutter supported by each inner portion, the first-type cutter adapted to mill a harder material than the second-type cutter, the first-type being different from the second-type. 
   
     
     
         2 . The bit of  claim 1  wherein the plurality of cutter support structures form a generally concave cutting portion of the face. 
     
     
         3 . The bit of  claim 2  wherein each cutter support structure includes an inclined surface having an angle of at least 30 degrees from a horizontal. 
     
     
         4 . The bit of  claim 1  wherein the base surface is generally convex and the peripheral portions include peripheral surfaces that are generally perpendicular to a rotational axis of the bit. 
     
     
         5 . The bit of  claim 1  wherein the first-type is selected from a group consisting of: polycrystalline diamond cutters, cubic boron nitride cutters, cutting tool grade carbide cutters, and mill capped polycrystalline diamond cutters. 
     
     
         6 . The bit of  claim 5  wherein the second-type is either tungsten carbide cutters or polycrystalline diamond cutters. 
     
     
         7 . The bit of  claim 1  wherein the peripheral portions extend between 0.5 and 1.5 inches from a gage surface of the bit. 
     
     
         8 . The bit of  claim 1  wherein the cutter support structures are blades. 
     
     
         9 . The bit of  claim 1  wherein the first-type cutters supported by the peripheral portions and the second-type cutters supported by the inner portions are set such that the bit is force balanced when milling a slip having a thickness between 0.5 and 1.5 inches. 
     
     
         10 . The bit of  claim 9  wherein the cutters supported by the peripheral portions are more densely set than the cutters supported by the inner portions. 
     
     
         11 . The bit of  claim 1  wherein the peripheral portions collectively support at least six cutters. 
     
     
         12 . A fixed cutter bit for milling a frac plug, comprising:
 a body; and   a face having a peripheral portion and an inner portion disposed radially internal to the peripheral portion, the peripheral portion supporting a plurality of first-type cutters and the inner portion supporting a plurality of second-type cutters, the first-type being different from the second-type;   the second-type cutters adapted to mill a plug body material; and   the first-type cutters adapted to mill a slip material, the slip material having a greater compressive strength than the plug body material.   
     
     
         13 . The bit of  claim 12  wherein the first-type cutters and the second-type cutters are individually set. 
     
     
         14 . The bit of  claim 12  wherein the first-type cutters and the second-type cutters are supported by blade-type cutter support structures. 
     
     
         15 . The bit of  claim 14  wherein the blade-type cutter support structures each include a gage portion and an arcuate shoulder portion, the gage portions and the shoulder portions supporting the first-type cutters. 
     
     
         16 . The bit of  claim 12  wherein the bit has a flat profile. 
     
     
         17 . The bit of  claim 12  wherein the bit has a concave profile. 
     
     
         18 . The bit of  claim 12  wherein the first-type is selected from a group consisting of: polycrystalline diamond cutters, cubic boron nitride cutters, cutting tool grade carbide cutters, and mill capped polycrystalline diamond cutters. 
     
     
         19 . The bit of  claim 12  wherein the second-type is either tungsten carbide cutters or polycrystalline diamond cutters. 
     
     
         20 . The bit of  claim 19  wherein the second-type are scribe-shaped cutters. 
     
     
         21 . A fixed cutter bit for milling a frac plug, comprising:
 a body; and   a face having a peripheral portion and an inner portion disposed radially internal to the peripheral portion, the peripheral portion supporting a plurality of first-type cutters and the inner portion supporting a plurality of second-type cutters, the first-type being different from the second-type;   the second-type cutters adapted to mill a plug body material;   the first-type cutters adapted to mill a slip material, the slip material having a greater compressive strength than the plug body material;   wherein the first-type is selected from a group consisting of: polycrystalline diamond cutters, cubic boron nitride cutters, cutting tool grade carbide cutters, and mill capped polycrystalline diamond cutters;   wherein the second-type is either tungsten carbide cutters or polycrystalline diamond cutters; and   wherein the first-type cutters and the second-type cutters are set such that the bit is force balanced when milling a slip having a thickness between 0.5 and 1.5 inches.