Challenging ESPs in open-water
Methane hydrate is a white, ice-like solid consisting of methane
molecules trapped in a cage-like lattice of ice. Methane is the chief
constituent of natural gas. If methane is warmed or depressurized, it changes
back to water and natural gas, with 1 m3 [35 cf] of methane hydrate
yielding approximately 160 to 170 m3 [5.65 to 6 Mcf] (at 0 degC [32
degF] and 1 atmosphere) of natural gas. Methane hydrate reservoirs probably
contain 2 to 10 times the currently known global reserves of conventional
natural gas.
An operator in Japan has been researching the development of methane
hydrate as a future energy source. The deposit of interest is located at the
seabed, 1,000 m [3,280 ft] below mean sea level in the Nankai-Trough, Japan. It
is a methane hydrate zone with a well temperature of 13 to 15 degC [55 to 59
degF]. A test in March 2013 used an ESP to reduce the hydrostatic pressure and
liberate the methane gas, achieving 6 days of continuous flow. A second
production test was planned for 2017 with the goal of extending the duration of
gas flow. The operator asked Schlumberger to design, engineer, manufacture, and
operate the upper completion.
This well completion presented several challenges:
- riserless deployment
- gas separation for high-GOR environment
- reservoir monitoring for methane production
- requirement of an ESP capable of operating at 0 degC [32 degF]
- harsh sand environment.