Apparatus for rotary drilling of wells using casing as the drill pipe

Claim 1

Apparatus for rotary drilling of wells using casing as the drill pipe, comprising in combination with a string of casing and means for rotating the same: a. a bit section bodily insertable and removable through the bore of the casing; b. cooperating means on the bit section and the lower end portion of the casing for landing the bit section in said lower end portion in nonrotative relation to the casing; c. said bit section comprising: I. a generally tubular body; II. radially movable anchor means mounted on the body for releasably anchoring the body to the casing; III. a pilot bit carried by the lower end of the body; IV, a plurality of angularly spaced underreamers mounted on the body for radial movement between extended positions for enlarging the diameter of the bore hole made by the pilot bit and positions fully within the perimeter of said body; v. piston means operably connected to said underreamers and reciprocable in the bore of the body between upper and lower positions respectively retracting and extending said underreamers; VI. sleeve means in said body reciprocable with said piston means between upper and lower positions respectively releasing and actuating said anchor means; and VII. means initially securing said sleeve means and said piston means to said body in said upper positions and releasable for movement to said lower position in response to fluid pressure applied to the piston means through the casing string whereby to actuate said anchor means and to extend said underreamers.