'Cleaner' well test vessels improve flaring, recovery in Bay of Campeche

The Toisa Pisces is expected to attend 120 well service operations per year

.

Cora, the first of the new fleet, performed most of these duties on the Mexican shelf from 1997 through to end-2003. During this period, it visited on average 140 offshore locations per year and tested around 240 wells annually. However, it lacked the capability to receive and process flows from well completion and stimulation exercises. Also, its solids and chemicals reception and treatment equipment was somewhat limited.

From 2000 onward, PEP had been addressing these concerns with Maritima de Ecologia SA de CV (Marecsa), based in Ciudad del Carmen. The company assisted in defining needs for two new generation vessels, which also incorporated DP-2 dynamic positioning capability. Two years later, Marecsa tendered for the conversion and operation contracts. Both were awarded in 2003, with different operating partners. Both were conversions of existing vessels.

According to Gabriel Delgado-Salivar, managing director of Marecsa, "We chose to convert instead of commissioning newly built vessels for two main reasons. First, during the tender process, Pemex requested a name, hull number, and location for the proposed vessel. This ruled out use of 'non-existing' vessels. Second, the time granted for construction and fit-out of the two vessels – respectively 12 and seven months – would not have been sufficient for newbuildings."

In partnership with Sealion Shipping (UK) and Petro Marine/BCI (Houston), Marecsa began converting the first vessel in Gdansk, Poland in January 2003, with the work being completed in Galveston. The vessel was a cable-layer, formerly owned by France Telecom, that was purchased by Sealion and re-named the Toisa Pisces. The converted vessel was delivered to the Bay of Campeche last December, and following performance tests, began operating this March.

The Toisa Pisces is a 3,500-dwt ship, 103.5 m long, with a breadth of 23.2 m, a draft of 6.9 m, and a maximum transit speed of 13.5 knots. In line with Pemex's requirements, it was given an FPSO DP-2 class notation, approved by DNV. It also features two 15-ton cranes, each with 100-ft reach; a Bell 412 helideck; accommodation for up to 70 people; and 10 storage tanks, capable of holding up to 1,320 cu m of oily water, 3,300 cu m of stabilized crude, and 98 cu m of slops.

The Toisa Pisces is working for Pemex under a 50-month contract valued at over $65 million. Marecsa operates the topsides and provides 25% of the crew, the remainder being supplied by Sealion. According to Delgado, the vessel has so far assisted mainly in well completion and stimulation services, visiting around 10 locations per month in the Bay of Campeche. Recently, it was sent to help out with exploration drilling in Tampico in the north of the Mexican sector. In late-July, it was providing reception/testing services for production from newly drilled wells in the north of the Bay of Campeche.

Between March and July this year, the vessel had performed 33 services, 24 of which related to processing of fluids for well cleaning and stimulation. Two were well tests, the remainder concerning storage of crude for export and oily water reinjection into industrial waste wells. A total of 45,000 bbl of crude were recovered during this period, and almost 20,000 lb of oily water was re-injected. At this rate, an average of 120 services per year is expected. Downtime due to equipment adjustment and maintenance, since commissioning in March, has been only 2%.

Marecsa also tendered successfully for the second vessel conversion in November 2003, in partnership with Bourbon Offshore Norway. The second vessel was the Bourbon Opale, a UT-745E platform supply vessel built speculatively by Groupe Bourbon at the Aker Langsten shipyard in Tomrefjord, Norway. According to Christian Lefevre, managing director of Groupe Bourbon's offshore division in Marseille, the offer of a four-year charter from Pemex was too good to pass up. "The offered rate was also better than for a high-spec PSV, although this could have been offset by the risk exposure arising from the conversion," he says.

"The Bourbon Opale was originally ordered in 2002 as an advanced, comfort-class PSV with good deck space, and with diesel-electric propulsion, provided by two brand new Rolls-Royce Azipull thrusters. These are designed to provide greater thrust, lower fuel consumption, and more flexibility for DP operations," Lefevre says. It was a sister vessel of the Bourbon Jade, a DP-2 maintenance supply vessel built at the same yard, which was itself converted during construction to serve as a subsea light intervention unit. That vessel was recently on duty for Total on the Girassol field off Angola.

The seven-month timeframe for adapting the Bourbon Opale was unusually tight. "Aker Langsten had to re-build the central bulk tank compartment," Lefevre says. "In parallel, the topsides were ordered from The Expro Group in Reading, UK, while we handled engineering for the conversion, including rearrangement of the tank capacities and steelwork for the process packages."

Bourbon Opale also has FPSO DP-2 notation. Its main dimensions are 90.7 m length, 18.8 m breadth, and 7.6 m depth. Transit speed is up to 12 knots, with accommodation for 54 people, and one 20-ft crane, with 100-ft reach. Maximum handling capacity of the process equipment is 10,000 b/d, compared with 15,000 b/d for the Toisa Pisces.

Crude is processed to a water percentage volume for export of 5% maximum. Recovered gas is separated for subsequent re-injection or flaring. Water is separated for re-injection or disposal.

Expro has been designing and manufacturing well test packages since the 1970s for onshore use and for fixed and floating installations. On Shell's Malampaya project in the Philippines, it adapted equipment for use on a supply boat for an extended well test. Generally, these installations are temporary, although in the case of the Bourbon Opale, the equipment will remain on the boat longer term and has been welded to the deck, says Alastair MacLean, sales and marketing manager at Expro's Production Solutions Group.

"This system differs from our conventional well testing equipment in that it can separate the produced crude for export," MacLean says. "Also, it is designed to handle a much wider than normal range of crudes, fluids, and temperatures.

"We were given 20 weeks to deliver the topsides. Nine months is more typical for an equipment supplier to complete a contract of this scope. But one of our skills is our ability to do this type of work quickly. This is primarily down to having a small team of experienced people, and getting the engineering phase done in parallel with the fabrication."

According to MacLean, the Opale's 250-ton topsides are very compact. "We worked very closely with Aker Langsten to develop the deck in a more space-efficient way. It was fairly full to start with, and numerous items were added as the project progressed."

Langsten also had to strengthen the rear of the boat to support the flare boom, supplied by Expro. "They provided the base, and we handled the installation. The flare boom only weighs 8 tons, but an 80-ft tall structure hanging over at an angle of 45° produces significant bending moments."

Expro's packages were assembled by Steel Services in Great Yarmouth, UK, then shipped directly to Aker Langsten on supply boats at the end of April. In June, the vessel sailed into the Bender Shipbuilding yard in Mobile, Alabama, for installation of import/ export winches and hoses, supplied by Wellstream. Wood Group in Oklahoma provided the export and re-injection pumps.

Following performance tests in the Bay of Campeche in June, the vessel was ready for its first assignments in July, assisting with well measurements and a new well completion in the Litoral Tabasco field in the Bay of Campeche, followed by well measurements. According to Delgado, the vessel's duties will likely be split 50/50 between well testing and measurement, and fluid reception/testing from well stimulation/completion.

Bourbon Opale was delivered this June to Galveston for final commissioning.

null

The contract value for the Opale, which is operated 100% by Marecsa, is $55 million, for a period of 50 months. Pemex estimates both vessels will reduce pollution levels by 70-80%, with each vessel recovering crude valued at around $10-15 million annually.

On completion of the two contracts, the charters for both the vessels may be renewed for a further 10 months. By mid-2007, PEP is expected to tender further long-term charters following an open tender process.

"There is no guarantee that our contracts will be renewed," Delgado says, "but it is important to note that these vessels are tailored specifically to Pemex's needs and specifications. There are only a few vessels of this type anywhere in the world, and it is unlikely that another ship owner would build under speculation new ships to compete against the Opale or the Pisces by the renewal date of 2008."

Process plant comparison

Toisa Pisces

• Separation, treatment, and metering for 15,000 b/d of products (crude oil, water, chemicals, and solids as well as associated gas)
• Separation, metering, and flaring of 31.83 MMcf/d of gas
• Crude density range 14-43° API
• NACE compliance (H2S)
• Max. temperature 130° C
• Max. input pressure 10,000 psi
• Max. processing pressure 1,412 psi.

Bourbon Opale

• Solids exclusion based on cyclonic separation and pumping as slurry into storage tanks for onward shipment to shore for disposal
• Separation, treatment, and metering for 15,000 b/d (10,000 b/d of oil and 5,000 b/d of water)
• Fiscal metering for 200 to 15,000 b/d
• Crude export back through Pemex's offshore pipeline systems at a pressure of 40 bar
• Separation, metering, and flaring of 26 MMcf/d of gas
• Crude density range 14-43° API
• NACE compliance (H2S)
• Max. temperature 148° C
• Max. input pressure 10,000 psi
• Max. processing pressure 1,300 psi.