Patent EA-002048-B1 (EA)
Title: Downhole milling device
Inventor: AMORY MARC EMMANUEL
IPC: E21B27/02
Filed: 1999-06-09
Abstract: 1. A device for performing milling operations in an underground borehole, the device comprising a stator housing (1), a toppling head (2) which is pivotably secured to the housing (1) and equipped with one or more rotatable mills (3,4), a drive mechanism for rotating each mill (3,4) relative to the toppling head (2), and a pivot mechanism (3,4) for pivoting the toppling head relative to the housing about a pivot axis (5) between a contracted position in which each mill (3,4) is substantially aligned with the stator housing (1) and an extended position in which each mill (3,4) protrudes at an angle in a lateral direction away from the housing (1), wherein stator housing defines a longitudinal central plane of the device which is substantially orthogonal to said pivot axis (5), characterized in that the drive mechanism comprises a flexible drive shaft (9) which is rotatable about an axis of rotation located in said central plane and which forms an input shaft that is directly or indirectly connected to each output shaft (8) on which a mill (3,4) is mounted. 2. The device of claim 1, wherein the toppling head (2) is equipped with a pair of contra-rotatable mills (3,4) that are mounted on output shafts (8) that are rotatable about axes of rotation which are parallel to each other and located at substantially equal distances from the central plane of the device and which mills (3,4) comprise substantially cylindrical bodies on which helical cutting teeth (11) are mounted such that the helix angles of the cutting teeth (11) are identical but opposite to each other and the cutting teeth (11) of adjacent mills face each other at or near the central plane of the device. 3. The device of claim 1, wherein the toppling head (2) is equipped with a pair of contra-rotatable mills that are mounted on output shafts (8) which are rotatable about axes of rotation which intersect each other at a point of intersection located in said central plane and the mills have frusto-conical bodies on which intermeshing cutting teeth are mounted. 4. The device of claim 1, wherein the drive mechanism comprises a hydraulic motor having a rotor which is rotatably mounted within the stator housing (1) and which is secured to the flexible drive shaft (9). 5. The device of claim 4, wherein the hydraulic motor is a Moineau-type motor which is located at an upper end of the stator housing (1) and wherein the pivot mechanism comprises a hydraulic piston (15) which is slidably arranged within the stator housing between the outlet of the Moineau-motor and a slant upper surface (13) of the toppling head (2) such that in use the elevated pressure of the driving fluid discharged by the motor presses the piston against said slant upper surface of the toppling head thereby inducing the toppling head to pivot towards the extended position thereof. 6. The device of claim 4, wherein the hydraulic piston (15) is slidably arranged around the flexible shaft (9) and the flexible shaft (9) is made of a resilient material and exerts a residual torque to the toppling head (2) which torque induces the toppling head to pivot towards its contracted position in the absence of hydraulic pressure exerted to the piston (15). 7. The device of claims 2 and 5, wherein the device is suitable for milling a window in a well tubular and a cuttings collecting box (26) is secured to the housing beneath the mills (3,4) and in use the hydraulic driving fluid emerging from the motor flushes cuttings (25) from the mills (3,4) into the cuttings collecting box (26).