Method for capping a well in the event of subsea blowout preventer failure

1. A method for capping a subsea wellbore having a failed blowout preventer proximate the bottom of a body of water, comprising:

lowering a replacement blowout preventer system into the water from a vessel on the water surface, the replacement blowout preventer system including an hydraulic pressure source comprising at least one accumulator precharged to a selected operating pressure compensated for hydrostatic pressure disposed proximate well closure elements on the replacement blowout preventer system;

coupling the replacement blowout preventer system to the failed blowout preventer; and

operating the well closure elements on the replacement blowout preventer system by using a remotely operated vessel to operate valve controls proximate the well closure elements to conduct pressure from the at least one accumulator of the hydraulic pressure source to actuators for the well closure elements.

2. The method of claim 1 wherein the hydraulic pressure source comprises accumulators disposed on a skid coupled to the replacement blowout preventer system.

3. The method of claim 1 wherein the lowering comprises extending a cable from a winch disposed on the vessel.

4. The method of claim 1 wherein the vessel excludes equipment for drilling a wellbore.

5. The method of claim 1 further comprising moving a mobile offshore drilling unit or another vessel on the water surface proximate a geodetic location of the wellbore, coupling a pump to an hydraulic line in fluid communication with the wellbore below the replacement blowout preventer system, opening a valve to make hydraulic communication between the hydraulic line and the pump, and pumping sealing material into the wellbore below the replacement blowout preventer.

6. The method of claim 5 wherein the sealing material comprises cement.