BP contracted Parker Drilling to construct the rig, which involved a total cost of $215m.
http://www.offshore-technology.com/projects/liberty-project/
The rig is 240ft high.
The Liberty rig will be fitted with eight 2,640hp engines and powered by natural gas. The top drive of the rig will be 105,000ft / lbs of torque. The rig will have the capacity to accommodate 84 people.
The u-ERD technology used to develop the field will extend the reach of the wells to world-record distances of 34,000-44,000ft.
The wells will follow a vertical path beneath the drilling rig and then turn to a horizontal position in the direction of the field. The well will again bend into a vertical position and penetrate into the field reservoir. The length of the wells will require fluid pressures of about 7,500lb / in² to pump oil from the reservoir.
The first well of the Liberty oilfield was discovered by BP in May 1997. BP presented a development programme for the field in February 1998 to the US Minerals Management Service (MMS).
In 2002, the US MMS disapproved the plan due to environmental concerns. As a result, development of the field was put on hold. Following BP’s decision to use ultra-extended-reach drilling, development began in 2005.
One would think there’s some risk of accumulated gasses on an enclosed structure like that.