Abstract: The side tracking system includes a window mill having a full diameter cutting surface and a reduced diameter tapered cutting surface and a whipstock having a ramp engaging the reduced diameter cutting surface. The materials of the whipstock have a first cutablity and the materials of the casing have a second cutability. The reduced diameter cutting surface contacts the whipstock ramp at a first contact area and the full diameter cutting surface contacts the wall of the casing at a second contact area. As weight is applied to the mill, there is a first contact stress at the first contact area and a second contact stress at the second contact area. A cutability ratio is the first cutability divided by the second cutability and a contact stress ratio is the first contact stress divided by the second contact stress. The mill cuts the casing rather than the whipstock by maintaining the product of the cutability ratio and the contact stress ratio less than one.

Abstract: The side tracking system includes a window mill having a full diameter cutting surface and a reduced diameter tapered cutting surface and a whipstock having a ramp engaging the reduced diameter cutting surface. The materials of the whipstock have a first cutablity and the materials of the casing have a second cutability. The reduced diameter cutting surface contacts the whipstock ramp at a first contact area and the full diameter cutting surface contacts the wall of the casing at a second contact area. As weight is applied to the mill, there is a first contact stress at the first contact area and a second contact stress at the second contact area. A cutability ratio is the first cutability divided by the second cutability and a contact stress ratio is the first contact stress divided by the second contact stress. The mill cuts the casing rather than the whipstock by maintaining the product of the cutability ratio and the contact stress ratio less than one.

Abstract: The milling and whipstock assembly includes a whipstock having a ramp portion for directing the milling assembly to cut a secondary borehole in an existing cased borehole. The milling assembly includes a shaft having rigid and flexible portions and an under gauge cutting tool disposed on the lower end of the flexible portion and a full gauge cutting tool disposed on the rigid portion. A third under gauge cutting tool is disposed on the flexible portion in between the full gauge and under gauge cutting tools. In operation, the milling and whipstock assembly is lowered into the borehole and then the milling assembly is detached from the whipstock assembly. As weight is placed on the milling assembly, the ramp portion places a side load on the lower under gauge cutting tool causing the flexible portion of the shaft to flex and pivot allowing the under gauge cutting tool to come into engagement with the wall of the casing allowing the under gauge cutting tools to cut a window in the cased borehole.

Abstract: The side tracking system includes a window mill having a full diameter cutting surface and a reduced diameter tapered cutting surface and a whipstock having a ramp engaging the reduced diameter cutting surface. The materials of the whipstock have a first cutablity and the materials of the casing have a second cutability. The reduced diameter cutting surface contacts the whipstock ramp at a first contact area and the fill diameter cutting surface contacts the wall of the casing at a second contact area. As weight is applied to the mill, there is a first contact stress at the first contact area and a second contact stress at the second contact area. A cutability ratio is the first cutability divided by the second cutability and a contact stress ratio is the first contact stress divided by the second contact stress. The mill cuts the casing rather than the whipstock by maintaining the product of the cutability ratio and the contact stress ratio less than one.

Abstract: A whipstock for guiding a cutting tool within a cased borehole. The whipstock having a guide surface for guiding engagement with the cutting tool. The guide surface having a first taper with the axis of the whipstock and a greater taper with the axis of the whipstock at the point that the center of the cutting tool reaches the inside diameter of the wall of the casing thereby more quickly moving the center point of the cutting tool across the wall of the casing.

Abstract: The mill assembly and whipstock assembly include a mill having a tapered end which engages a ramp of the whipstock assembly. The ramp includes a plurality of surfaces having different angles whereby the rate of deflection of the mill by the whipstock varies as the mill is lowered into the borehole. In particular, the ramp of the whipstock includes two surfaces having steep angles, one steep angled surface causing the mill to punch through the wall of the casing and the second steep angle surface moving the center of the mill across the wall of the casing.

Abstract: A hydraulic control sub assembly for actuating hydraulically operated downhole remedial tools, such as section mills or underreamers, is disclosed. The control sub features a drop ball mechanism to terminate the flow of drilling fluid to the hydraulic tool thereby inactivating the tool. The control sub also has a hydraulic rupture disc that permits drilling fluid circulation when tripping the drill pipe. The control sub further contains upwardly directed jet nozzles to enhance fluid flow in the well bore to help clear away debris. A float valve is also incorporated in the control sub to ensure there is no fluid under high pressure trapped in the hydraulic tool that may jam the tool.