Mill out gate to 3 1/8 diameters on top master valve that is seized closed and freewheeling to accommodate wireline tools and installation of back pressure valve in tubing hanger. Bottom master valve previously milled out.
Well Information: 3 mPa water injection well
Procedure: Assemble hot tap equipment, start power pack and check all functions. Confirm no pressure above damaged valve, remove wireline cap and install crossover-work valve-Bop and hot tap equipment. Pressure test all components and connections to 7 mPa. Bleed pressure back to 5 mPa drill ¾ inch pilot hole. Retract drill above work valve, close, bleed off pressure, and change out bit to 3 inch cone mill. Rig up new assembly, equalize above work valve and open valve. Advance mill to gate, record measurements and confirm depth is correct. Commence milling, noting time for advancement gained. After advancing 2 inches through 2 ½ inch gate advancement slowed considerably. Retract cone mill above work valve, close valve and bleed off. Change out cone mill to 2 7/8 outside-in aggressive mill. Rig up hot tap equipment, equalize above work valve and open valve. Advance drill to gate, check measurements and resume milling. Monitor torque and distance travelled, double check measurements to confirm through gate. Retract mill above working valve, close valve and bleed off. Change out mill to 3 1/8 reamer re-install hot tap equipment, equalize and open work valve. Ream out gate valve, retract above work valve, close and bleed off. Change out reamer to wire brush, re-install equipment, equalize above work valve and open. Advance brush to threads in tubing hanger, check measurements and clean threads in hanger. Retract brush above work valve and close valve, bleed off and rig out hot tap equipment. Hand over well to wireline.
Time on location: 27 hours over three days