Cantarell Oil Field, Gulf of Mexico, Mexico

The Cantarell field is Pemex Exploración y Producción’s large, heavy oilfield, located 100km off the coast of the Yucatan Peninsula, in the Gulf of Mexico. When it was built, in the early 1980s, it was the largest offshore development project in the world to date, with a total installed cost of more than $5bn.

The project consists of four fields – Akal (by far the largest), Nohoch, Chac and Kutz. The reservoirs are formed from carbonate breccia of Upper Cretaceous age, the rubble from the asteroid impact that created the Chicxulub Crater.

Crude oil from the field in the Bay of Campeche is transported via pipelines to tanker berths at Cayo de Arcas and to storage tanks onshore at Dos Bocas, where part of the production is exported and the balance is transported inland by pipeline.

Produced gas is sent onshore for treatment and consumption and the balance is returned offshore for gas lift.

The first field was discovered in 1976, and by 1981 the Cantarell complex was producing 1.16 million barrels a day. By 1995, however, production had dropped to a million barrels a day.

DESIGN AND DEVELOPMENT

In 1996, project managers Bechteland Pemex prepared a conceptual design study for the development of the Cantarell field. This identified a number of projects to remove short-term production bottlenecks and increase the long-term production of the field. The design, fabrication and installation of the facilities to accomplish these objectives was known as the Cantarell field development project.

The short-term debottlenecking projects, known as the short-term plan, included modifications to existing platforms to add new production separation facilities, pumps and compressors, and the installation of additional produced gas-compression facilities, interconnecting pipelines and a floating storage and offloading vessel.

The projects to increase the long-term production of the Cantarell field were known as the long-term plan. This plan consisted of several major components, including the installation of new wellhead platforms, riser and injection platforms, two new central processing complexes, accommodation platforms, bridges and flares, and interconnecting pipelines.

OIL PRODUCTION

One of the main reasons for Cantarell’s prolific oil production rate was the existence of a giant natural gas bubble that maintained pressure over the reservoir for the first 20 years or so of the field’s life. As reservoir pressure fell, however, Pemex decided to maintain it by injecting nitrogen, to increase the final reservoir recovery.

As gas is at a premium in Mexico, Pemex knew it could put the gas to better use by selling it. So Bechtel and Pemex studied other options, such as steam and water injection. Because of the oil field’s geological formation, neither of these turned out to be a viable solution. But nitrogen was. After six months of study, the team recommended that nitrogen be used to pressurise the reservoir and enhance production at Cantarell.

NITROGEN PLANT

The nitrogen-production facilities were built onshore as a private venture near the town of Atasta, and the nitrogen is sent offshore via pipeline for injection into the reservoir. The nitrogen production for pressure maintenance is about 1,200 billion standard cubic feet a day.

The nitrogen for the injection process is supplied by the largest nitrogen production plant in the world – ten times the size of the largest existing plant. The plant consists of five production lines, each consisting of an air separation unit powered by its own turbine generator, which is supplied with natural gas by Pemex.

The plant was built by a consortium including Empresas ICA of Mexico and Fluor Corp of the US; gas companies Linde and BOC Group; Westcoast Energy of Canada (a gas pipeline company later acquired by Spectra Energy); and Marubeni. The plant is owned and operated by a joint venture company which is majority-owned by BOC Group, which was itself acquired by Linde in 2006.

The injection project started operating in 2000, and boosted production from about a million barrels a day to 1.6 million barrels a day, then to 1.9 million barrels a day in 2002 and to a peak of 2.1 million barrels a day in 2004, at the time making Cantarell the second-fastest producing oil field in the world, behind Ghawar Field in Saudi Arabia.

However, Cantarell is now in relentless decline. As long ago as August 2004, Pemex announced that actual oil output from the field was forecast to decline steeply from 2006 onwards, at a rate of 14% a year.

In March 2006 it was reported that Cantarell had peaked, with a second year of declining production in 2005.

For 2006, the field's output fell by 13.1%, according to Pemex, which also predicted another decline of 15% for 2007. And in May 2008, Mexico's Energy Ministry said output had fallen a further 33% to 1.07 million barrels a day – the lowest output at the field since March 1996.

In order to try to maintain heavy crude production in the Bay of Campeche, Pemex is focusing its efforts on the development of the Ku-Maloob-Zaap complex in an adjacent area, which can be connected to the existing facilities of Cantarell. Ku-Maloob-Zaap is expected to produce 0.8 million barrels a day by 2010.