FACTBOX-BP moving ahead on containment cap, other options

June 3 (Reuters) - BP Plc's (BP.L) (BP.N) underwater robots used huge shears on Thursday to slice through a pipe connected to seabed equipment at the site of a massive oil leak in the Gulf of Mexico.

The move was part of British energy giant's latest effort to contain the leak that has been spewing crude for six weeks. The next step is to put a containment cap on the lower marine riser package, or LMRP, which would cover what is left of the sawed-off riser pipe to capture most of the oil.

Here is an explanation of how the LMRP cap is supposed to work, as well as other technologies BP is employing to attempt to bring the broken well under control.

LMRP CAP

* BP's underwater robots used giant shears to slice through the main pipe from which the oil is leaking, called a riser, which extended from the lower marine riser package. The LMRP sits atop a failed blowout preventer at the seabed.

* BP used the shears when a diamond-tipped saw failed to cut all the way through the pipe to provide a smooth surface over which to place the cap.

* BP aims to lower a containment cap with a grommet seal over the jagged remnant of the pipe, which is jutting from the LMRP at a 10-degree angle. That slight slant will also complicate the capping effort. The leak will continue gushing from the top of the LMRP during the process.

* The containment cap is intended to capture about 80 percent of the oil and gas. The rest is expected to escape.

* The cap is connected by pipe to a drillship at the water's surface a mile (1.6 km) above the well.

* The captured oil and gas is expected to be channeled to the ship, where the oil will be stored to bring ashore later for processing and the gas will be flared.

* BP monitored pressure data from the failed blowout preventer during a previous, failed "top kill" operation, and determined that cutting off the pipe at the top of the LMRP would not have significant impact on the oil flow. Dispersants are being sprayed at the site during the capping operation.

* U.S. government scientists estimated the flow could temporarily increase by as much as 20 percent.

* The cap effort is, in theory, similar to a much larger 98-ton containment dome that was placed at the end of the broken pipe in early May. That dome also was connected to the ship by pipe and was intended to corral and channel oil and gas to the surface.

* In that effort, too much seawater got inside, mixed with natural gas at high pressure and cold temperatures, and formed ice-like hydrates that blocked oil from flowing up the pipe to the ship.

* The smaller cap and seal are designed to exclude seawater and avoid the hydrate problem. BP also aims to pump methanol down the pipe during the operation to keep the oil warm and combat possible hydrate formation.

BACKUP CAPS/DOMES

* If the first containment cap doesn't work, BP has several backup caps with and without seals of varying sizes at the seabed, on the way or being manufactured.

ENHANCEMENT TO LMRP CAP PLAN

* BP will use seabed equipment installed to conduct the top kill to enhance the containment cap system.

* The top kill involved pumping heavy drilling fluid into the failed blowout preventer to try to smother the leak. Mud was pumped from a ship to a service rig, down to a manifold, which routed the fluid to "choke and kill" hoses connected to the blowout preventer.

* BP will try to reverse direction and pull oil and gas from the blowout preventer through the hoses and manifold to a vessel at the water's surface.

*That system is expected to be ready by mid-June.

HURRICANE PREPAREDNESS

* BP also is planning a system to allow the drillship connected by pipe to the containment cap to suspend operations and move if a hurricane approaches.

* BP will install a pipe that extends about 300 feet below the drillship. Then a hose would connect the pipe to the containment cap.

* Described by BP as a "long-term option," the system would allow BP to disconnect the hose from the pipe and move the ship out of a storm's path, then return when weather calms to resume the operation.

* BP has not yet worked out how it would cap or corral the leak while the storm passes and the hose is disconnected from the pipe.

* The system is expected to be implemented in late June or early July.

* The Atlantic hurricane season began June 1.

THE RELIEF WELLS

* Drilling continued on a relief well begun May 2 intended to intercept and cap the leaking well beneath the seabed. Drilling was been suspended last week on a second relief well, begun May 16, while the top kill was in progress, but that rig resumed drilling on Sunday. Both wells are expected to be finished in August.

BOP ON BOP:

* BP suspended drilling of the second well so that rig's blowout preventer could be on standby to place atop the failed blowout preventer and plug the well if the containment cap system fails. BP said June 1 that option has been sidelined "at the moment" because the company lacks sufficient information about the state of the failed blowout preventer. (Reporting by Kristen Hays; Editing by Doina Chiacu)