Reverse section milling method and apparatus

A section milling apparatus for milling of a downhole portion of casing in a well, comprising:

• a rotatable work string;
• a hydraulic tensioning device having an upper end and a lower end, said upper end being attachable to said work string, said tensioning device being adapted to selectively pull said lower end upwardly toward said work string;
• a section mill attachable to said lower end of said hydraulic tensioning device for rotation by rotation of said work string, said section mill having a plurality of arms adapted to pivot outwardly and upwardly, said section mill being adapted to hydraulically apply an upward force to pivot said arms outwardly to contact a casing in a cutting relationship;
• and
• a fluid flow path through said work string, said fluid flow path being adapted to supply hydraulic pressure to operate said hydraulic tensioning device, and to pivot said arms of said section mill;
• wherein said section mill is adapted to expand at a fluid pressure which is lower than a fluid pressure at which said hydraulic tensioning device is adapted to pull upwardly.

A section milling apparatus for milling of a downhole portion of casing in a well, comprising:

• a work string;
• a hydraulic tensioning device having an upper end and a lower end, said upper end being attachable to said work string, said tensioning device being adapted to selectively pull said lower end upwardly toward said work string;
• a section mill attachable to said lower end of said hydraulic tensioning device, said section mill having a plurality of arms adapted to pivot outwardly and upwardly, said section mill being adapted to hydraulically apply an upward force to pivot said arms outwardly to contact a casing in a cutting relationship;
• a fluid driven downhole motor mountable in said section milling apparatus above said hydraulic tensioning device;
• a hydraulically operable anti-torque anchor mountable in said section milling apparatus above said fluid driven motor and below said work string, said anti-torque anchor being adapted to expand into contact with a casing to be cut by said section mill, to prevent transmission of torque up said work string during operation of said fluid driven motor;
• and
• a fluid flow path through said work string, said fluid flow path being adapted to supply hydraulic pressure to operate said hydraulic tensioning device, to pivot said arms of said section mill, to rotate said fluid driven motor, and to expand said anti-torque anchor;
• wherein said section mill is adapted to expand at a fluid pressure which is lower than a fluid pressure at which said hydraulic tensioning device is adapted to pull upwardly;
• wherein said anti-torque anchor is adapted to expand at a fluid pressure which is higher than said fluid pressure at which said section mill is adapted to expand, but lower than said fluid pressure at which said hydraulic tensioning device is adapted to pull upwardly;
• and
• wherein said fluid driven motor is adapted to begin to rotate at a fluid pressure which is higher than said fluid pressure at which said anti-torque anchor is adapted to expand, but lower than said fluid pressure at which said hydraulic tensioning device is adapted to pull upwardly.

A method for section milling of a downhole portion of casing in a well, comprising:

• providing a work string, with a section mill and a hydraulic tensioning device attached thereto, said section mill being attached below a lower end of said tensioning device;
• lowering said work string, said section mill, and said tensioning device into a casing to be milled;
• pumping fluid through said work string to supply hydraulic pressure to said hydraulic tensioning device and said section mill;
• raising said hydraulic pressure to a first level at which an upward force is hydraulically applied within said section mill, to cause a plurality of arms on said section mill to pivot outwardly and upwardly to contact said casing in a cutting relationship;
• rotating said section mill to cut through said casing;
• raising said hydraulic pressure to a second level, higher than said first level, at which a lower end of said tensioning device is hydraulically pulled upwardly toward said work string, thereby pulling said section mill upwardly;
• and
• rotating said section mill to mill a window in said casing in an upward direction.