Method and apparatus to remove shifting balls from frac sleeves in oil and gas wells

Abstract

A process to drill through a spherical frac shifting ball in an oil well utilizes an improved mill, rotates drill pipe at one hundred to five hundred rpm, circulates drilling fluid such that the velocity of said fluid upwardly over said exterior of the drill pipe is in the range of three hundred to four hundred and seventy five feet per minute, and applies one thousand to three thousand pounds of slack off weight.

1 . A process to drill through a frac plug in an oil well, the frac plug including
 an exterior sleeve structure, and   a spherical frac shifting ball mounted in the sleeve structure,   the process including the steps of   (a) providing an elongate mill including
 (i) an elongate axis, 
 (ii) an exterior, 
 (iii) a distal end, 
 (iv) a proximate end, 
 (v) a plurality of spaced apart primary rows of carbide inserts
 extending axially along said exterior from said proximate end to said distal end, and 
 tapering inwardly at said distal end, 
 
 (vi) a plurality of spaced secondary rows of carbide inserts, said secondary rows each intermediate and spaced apart from a pair of said primary rows of carbide inserts, 
 said mill shaped and dimensioned to drill said spherical frac shifting ball while leaving at least a portion of said exterior sleeve structure; 
   (b) providing drill pipe having an exterior, a distal end and a proximate end;   (c) attaching said mill to said distal end of said drill pipe;   (d) inserting said mill and said distal end of said drill pipe in the oil well until said mill contacts the top of the frac plug;   (e) engaging said proximate end of said drill pipe and
 (i) rotating said pipe and said mill at one hundred to five hundred rpm, 
 (iii) circulating drilling fluid such that the velocity of said fluid upwardly over said exterior of said drill pipe is in the range of three hundred to four hundred and seventy five feet per minute, and 
 (iii) applying one thousand to three thousand pounds of slack off weight.