Proven Alternative Hull Designs for Surface Drilling/Production Systems
Authors: Bennett William 
Published: May 2013

THIRD GENERATION MinDOC DESIGNS (MinDOC 3)

The ATP TITAN is the first MinDOC Design to be constructed and put into service. Since the unit became operational in 2009, it has operated in both the drilling and production modes. The Drilling mode was accomplished with a unique riser system consisting of an under water subsea intervention device (SID), a presurized riser, a surface Blow Out Preventer (BOP) and top tensioning. Production mode continues with dry trees located on the production deck supported by the same tensioners used in the drilling mode. The tensioners are supported by the Riser Support Structure (RSS), a fixed platform like device attached to the MinDOC upper columns that also provides protection for the risers. MinDOC is often a bit difficult to compare with other floating production units as it shares features with most of them but in the end is truly unique.

The ATP TITAN hull is based upon the MinDOC patented hull form that combines the best features of two of the most common production floating units, the spar and the semisubmersible. It consists of three buoyant upper-columns and three smaller non-buoyant lower columns held in spatial relationship by upper pontoons and a lower raft. The spacing between the centerlines of each column is 150 feet. The hull is 485 feet high. The lower raft extends 20 feet Above Base Line (ABL) and is composed of a riser guide flat, riser guide tubes, a moonpool and several High Density Ballast (HDB) tanks, which serve to stabilize the structure and lower the Vertical Center of Gravity (VCG). The lower columns are each 20 feet in diameter and extend from the keel to 220 feet ABL.

The upper pontoons are 24 feet in width and 20 ft in height, and connect the upper columns are located 220 ABL and hold the columns in spatial relationship. Each of the upper pontoons consists mainly of large central free-flooding saltwater tanks. The upper columns have 52-foot diameters and extend thru the water plane to the column tops at 485 feet ABL. Each upper column is composed of stiffened shells supported by ring frames and is divided by watertight flats and various partial flats to segregate the ballast and storage tanks. Five chain lockers for each column are by non-tight bulkheads. The column tanks contain1,964 barrels of diesel oil, 2,000 barrels of liquid mud, 2,292 barrels of base-oil and 4,560 barrels of drill water. Outboard of each storage tank, a damage zone void is fitted in way of the waterline to isolate their contents in case of damage to the shell. The spaces located immediately below the column tops at 485 feet ABL are designated as machinery spaces.

Each column has a access trunk 20 feet in diameter that connect the base of the upper pontoons to the column tops. It serves multiple purposes providing access to all tanks, housing the piping systems and valve operators, and vertical caissons which house submersible pumps for the bilge and ballast systems. Access platforms and ladders in each trunk provides tank access without compromising the watertight integrity of other tanks.