Method and apparatus for accurate milling of windows in well casings

A downhole assembly comprising:

• a deflecting tool adapted for selective static positioning within a well casing;
• a milling tool adapted to mill a window in the well casing, the milling tool comprising a pilot mill, the pilot mill secured to the deflecting tool during deployment of the assembly;
• and
• a first retaining mechanism and a second retaining mechanism,
• the first retaining mechanism securing the rear end of the pilot mill to the deflecting tool,
• the second retaining mechanism comprising a retaining member securely attached to the deflecting tool and adjacent the pilot mill front end,
• the retaining member having a general ring shape.

A downhole assembly comprising:

• a deflecting tool adapted for selective static positioning within a well casing;
• a milling tool adapted to mill a window in the well casing, the milling tool comprising a pilot mill, the pilot mill secured to the deflecting tool during deployment of the assembly;
• and
• a first retaining mechanism and a second retaining mechanism,
• the first retaining mechanism securing the rear end of the pilot mill to the deflecting tool,
• the second retaining mechanism securing the front end of the pilot mill to the deflecting tool,
• the second retaining mechanism comprising a drillable material plug.

A downhole assembly comprising:

• a deflecting tool adapted for selective static positioning within a well casing;
• a milling tool adapted to mill a window in the well casing, the milling tool comprising a pilot mill, the pilot mill secured to the deflecting tool during deployment of the assembly;
• and
• a first retaining mechanism and a second retaining mechanism,
• the first retaining mechanism securing the rear end of the pilot mill to the deflecting tool,
• the second retaining mechanism securing the front end of the pilot mill to the deflecting tool,
• a protection mechanism located intermediate the pilot mill and the second retaining mechanism;
• and
• the protection mechanism protecting abrasive inserts on the pilot mill from hitting the second retaining mechanism.

A method for deploying an assembly comprising a deflecting tool adapted for selective static positioning within a well casing and a milling tool adapted to mill a window in the well casing, the method comprising:

• securing the milling tool to the deflecting tool with a securing mechanism;
• deploying the assembly downhole;
• commencing the milling operation by rotating at least one portion of the milling tool;
• and
• releasing the securing mechanism by action of rotation of the at least one portion of the milling tool.

A method for deploying an assembly comprising a deflecting tool adapted for selective static positioning within a well casing and a milling tool adapted to mill a window in the well casing, the method comprising:

• securing the milling tool to the deflecting tool;
• deploying the assembly downhole;
• commencing the milling operation;
• and
• the securing step comprises attaching a first retaining mechanism to secure the rear end of a pilot mill of the milling tool to the deflecting tool and a second retaining mechanism to secure the front end of the pilot mill to the deflecting tool.

A method for deploying an assembly comprising a deflecting tool adapted for selective static positioning within a well casing and a milling tool adapted to mill a window in the well casing, the method comprising:

• securing the milling tool to the deflecting tool;
• deploying the assembly downhole;
• commencing the milling operation;
• and
• protecting abrasive inserts of the milling tool from being damaged during the deploying step,
• the securing step comprises attaching a retaining mechanism to secure the front end of a pilot mill of the milling tool to the deflecting tool;
• and
• the protecting step comprises inserting a protection mechanism intermediate the pilot mill and the retaining mechanism.

A string comprising:

• a deflecting tool;
• a milling tool having a pilot mill adapted to mill a window within a well casing;
• and
• a releasable securing mechanism adapted to secure the deflecting tool and the milling tool during deployment of the string,
• at least a portion of the securing mechanism adapted to be broken by milling action of the pilot mill.

A downhole assembly comprising:

• a milling tool having a pilot mill;
• a deflecting tool having a deflecting surface adapted to deflect the pilot mill;
• and
• a securing mechanism adapted to releasably attach the milling tool and the deflecting tool during deployment,
• the securing mechanism having a generally ring-shaped retainer proximal a forward end of the milling tool and a second retainer engaged to a second portion of the milling tool.

A downhole string for use in a wellbore comprising:

• a milling tool having a pilot mill and a shaft attached to a rear portion of the pilot mill;
• a deflecting tool adapted to deflect the pilot mill;
• and
• a retainer mechanism adapted to releasably attach the milling tool and the deflecting tool during deployment into the wellbore,
• the retainer mechanism comprising a first retainer member engaged to a front portion of the pilot mill, and a second retainer member engaged to the rear portion of the pilot mill.