GULF OF MEXICO: Cantarell lift gas, nitrogen programs approaching 80% completion

60% of new production units ready

Th 6106osmex1
Th 6106osmex1
Mexico is 80% done with improvements to its new facilities and gas handling capacities.
Click here to enlarge image

The expansion and refurbishment of Mexico's Cantarell Field in the Bay of Campeche is nearly 80% complete. Construction of the two multi-platform production complexes is about 60% complete. In addition to the two production complexes, other features of the construction program include two riser platforms and two accommodation platforms.

The first new production complex will begin operation at the end of this year, while the second complex will begin production in 2002. Pemex (Petroleos de Mexico), Mexico's national oil company, plans to continue to produce 2 million b/d from the field throughout the remainder of this year.

Upgrades for the Cantarell reservoir are split into short- and long-term plans:

  • The short-term plan concentrates on upgrades of the Akal C, Akal J, and Nohoch A complexes and involves a new lift gas generation facility at Akal C to encourage oil production and decrease gas flaring.
  • The long-term plan focuses on additional lift-gas production capacity and oil production facilities, which consist of a new production complex at Akal B and Akal L, and 10 new satellite wellhead platforms to produce more oil.

Akal C lift gas

The Akal C complex will consist of 11 additional major platforms when completed. Pemex's original redevelopment plan for the Cantarell Field was to improve natural gas usage by decreasing gas flaring. To do this will require five compression platforms, one integral compression service, one gas-processing platform, 48 km of pipelines, and 45 pieces of compression equipment (500,000 hp).

Gas handling capacity is expected to work at about 2,200 MMcf/d, including spare equipment, according to one of four technical papers at the Offshore Technology Conference in Houston detailing Mexico's plans for its refining infrastructure.

After considering three options to generate additional lift gas, Pemex chose to install additional processing and compression facilities offshore because it was the safest and most frugal. Since Akal C had the capacity to handle a major share of total gas available for gas conditioning, the processing and compression facilities for lift gas generation were installed as part of the Akal C complex.

The gas-processing platform, which will condition 600 MMcf/d of natural gas to use in the lift gas network, is currently under construction. The platform is scheduled to begin operation at the end of this year. The platform will be built in three levels with 7,160 sq meters of deck within a footprint of 82 meters by 45 meters, and will consist of gas sweetening units, a propane dew-point control refrigeration system, and additional utility support systems. The platforms will be able to handle 900 MMcf/d of gas, producing 730 MMcf/d of lift gas.

The Akal C compression platform has a booster compression system, a high-pressure compression system, a dehydration system, a condensate-handling system, and a utility support system. Six levels surround 9,920 sq meters of deck area within a footprint of 90 meters by 45 meters of the platform. The platform comes online in August.

The integral compression services platform is part of a build-own-operate contract (BOO). The BOO contract involves an average supply of 1,200 MMcf/d of nitrogen over 15 years. Capacity to handle the gas is expected to reach 1,250 MMcf/d. One of the technical papers (referenced below) states that flare volumes will decrease to below 30 MMcf/d and will be completely handled when new vapor recovery compressors come online at the end of 2001.

Pemex executed 39 engineering-procurement-construction (EPC) contracts to assist with the Cantarell project. Intec, one of the companies to sign a contract with Pemex, brought in about 30 engineers and inspectors to work on the project. The $4 million contract went into affect in February of this year and will continue until August. Six of the 39 contracts were specifically associated with pipeline construction.

Pipeline contracts

Pemex has installed more than 400 km of new pipelines in the Cantarell field. About 25 km of pipelines of different sizes were built to transport a two-phase mixture of oil and gas from the new platforms and wells to Akal C, Akal J, and Nohoch A, where the three central processing complexes use separators to separate the oil and gas. A major pipeline was built to transport export oil for Akal J to a floating storage and offloading system (FSO).

The FSO Ta'kuntah provides permanent storage capacity of 2.3 million bbl for loading onto tankers. It can offload 800,000 b/d onto tankers. A new pipeline from Akal L connects to this line. Additionally, a new pipeline was created to connect from Akal B to one of the major lines, and from Akal J to Cayo de Arcas.

Some gas will remain offshore to be processed for lift gas, while the remaining gas will be sent onshore for processing and consumption. A total of 21 pipelines were built to transport the expected increase in produced quantity gas. The pipes also will transport gas to centralized processing facilities.

A new pipeline was built from Nohoch A, one of Cantarell's blocks, to onshore facilites at Atasta. The new lines added to the existing 90 km total will bring the field to 310 km of natural gas pipeline length.

When the entire Cantarell project is complete, lift gas will orginate offshore and be routed to injection wells through pipelines. The existing pipeline is 58 km long, but the new line will total 47 km, involving routing lift gas through a 20-in. diameter pipeline from Nohoch A to Akal L. The system also will consist of adding 14 new 12-in. feeder pipelines to six existing and eight new production platforms, and two interconnections. One of the interconnections will be between the existing line 156 and Akal L. The other will be between line 156 and Akal C.

A new 85-km, 36-in. diameter pipeline currently transports nitrogen from offshore to the Nohoch A complex, at which point the nitrogen is injected into the reservoir through nine injection wells. Forty-five pipelines with a combined length of approximately 328 km have been built, as of Dec. 31, 2000.

Nitrogen update

Akal is the Cantarell's largest field, with a reservoir of 32 billion bbl and an oil column thickness of about 1,200 meters. The gas-oil contact level moved up to its current position of 1,930 meters subsea in recent years, and the water-oil contact moved to 480 meters, from its original position of 3,200 meters.

As a result, a major project through nitrogen injection was applied and completed with a nitrogen generator plant capable of 1,200 MMcf/d. The project has an injection platform, which contains seven nitrogen injection wells and a network of 233 km of pipelines. The injection process works through seven wells drilled and completed within the gas cap atop the Akal field.

Tracer injection tests to determine the presence of nitrogen in the reservoir, which could result in negative long-term effects such as thermal convection or molecular diffusion, showed no signs of nitrogen after seven months when an analysis of associated gas effluents was implemented. Nitrogen used in this process costs $0.36/Mcf, based on the bidding services for nitrogen supply.

Pemex states that overall improvements and modifications have increased oil production by more than 25% to approximately 1.4 million b/d. Nitrogen injection alone is expected to increase production by 20%. Pemex estimates oil production to increase an additional 50%, with a 55% reduction in gas flaring. Oil production capacity is expected to increase to about 2.2 million b/d in 2002.

References

Límon-Hernández, T.; Garza-Ponce, G.; Lechuga-Aguiñaga, C., "Status of the Cantarell Field Development Program: An Overview," Petroleos Mexicano; OTC 13175; Offshore Technology Conference, Houston, 2001.

De León, J.; Argüelles, A.; Morales, R.M., "Cantarell Field: Modernization and Expansion of the Pipeline Network," OTC 13176, Offshore Technology Conference, Houston, 2001.

Kettles, R.; Kuo, J., Rubio, J.; "Cantarell's Akal C Complex: the World's Largest Offshore Gas Treating and Lift Gas Generation Platforms," OTC 13177, Offshore Technology Conference, Houston, 2001.

Rodríguez, F.; Ortega, G.; Sánchez, J.L; Jiménez, O., "Reservoir Management Issues in the Cantarell Nitrogen Injection Project," OTC 13178, Offshore Technology Conference, Houston, 2001.

More in Production