Mars, Gulf of Mexico, USA

Mars is located in the Gulf of Mexico about 130 miles southeast of New Orleans, USA. The discovery well was drilled on Mississippi Canyon block 763 using the drillship Discoverer Seven Seas.

Data from four other wells and six sidetrack wells was used, together with 3D seismic work, in order to make the necessary decisions about development. Shell Deepwater Production is the operator and has 71.5% interest. The remaining 28.5% interest is held by BP Amoco (now known as BP).

Mars field development

The initial development was designed to recover about 500 million barrels of oil equivalent. The cost of the development for the initial project phase was approximately $1bn.

Out of the total project cost, 55% was expended on fabrication and installation of the hull, deck facilities and pipelines. The remaining 45% was spent on drilling and completion of the wells.

Around ten tension leg platform (TLP) development wells were predrilled with George Richardson, a semisubmersible rig from Sonat. H&P 201 (a contract rig) installed on the TLP was used to drill rest of the wells.

Tension leg platform

The TLP is 3,250ft high from the seafloor to the crown block of the drilling rig, and its steel weight is approximately 36,500t. The TLP was designed to withstand hurricane force waves of 71ft and winds of 140mph, simultaneously.

The hull comprises four circular steel columns, which are 66.5ft in diameter and 162ft high, and four pontoons, 27ft wide and 24ft high, which connect the bottoms of the four columns. It weighs approximately 15,650t. The fabrication of the hull was completed by Belleli SpA of Taranto, Italy.

The deck is composed of five modules: the wellbay, living quarters, processing, power and drilling. It has an open-truss framing design, which is 245ftx245ftx45ft and weighs approximately 7,200t. The fabrication of the modules was completed by McDermott.

The platform was closed temporarily in the first quarter of 2005 due to planned replacement of flexjoints on both its oil and natural gas export lines. The TLP was also affected by Hurricane Katrina and production was stopped temporarily in 2005. Production resumed in April 2006.

Tendons / piles

There are 12 tendons, three per corner, each with a 28in diameter and a wall thickness of 1.2in. Each tendon is approximately 2,852ft long and the total weight for the 12 tendons is 6,150t.

The tendons are connected directly to piles in the seafloor. There are 12 piles about 84in in diameter and 375ft long, weighing 260t each. Both piles and tendons were fabricated by Aker Gulf Marine, at its yard in Ingleside, Texas, USA.

Drilling and production topsides

There are 24 well slots and additionally, a subsea well is tied back to the TLP, which includes complete separation, dehydration and treatment facilities. The accommodation module houses 106 people, along with a control room and an emergency-response centre.

Integration and installation

The integration contract was awarded to Aker Gulf Marine of Ingleside, Texas. This included module setting and interconnecting steel, piping, electrical and instrumentation.

The integration was completed during the second quarter of 1996. The contract for the installation of the TLP was awarded to Heeremac in May 1996.

Mars production

The daily production from Mars (the largest Gulf of Mexico discovery in over 25 years) averages about 21,000 barrels of oil and 25 million square feet of natural gas.

Oil is transported 116 miles to the shore in the $135m Mars Pipeline system, which was initially capable of handling 250,000bopd, with expansion plans of up to 500,000bpd.

The Mars Pipeline system consists of an 18in line, extending from the TLP, about 40 miles to West Delta block 143, where it connects with a 24in line that comes ashore 55 miles away in Fourchon, South Louisiana.

From there, the line parallels the Louisiana Offshore Oil Port (Loop) pipeline about 29 miles to Loop's Clovelly storage facilities, where the oil will go into a dedicated 3 million barrel salt dome cavern, which can feed any of five major interconnecting pipelines serving the national refining market.