Republished from Offshore Engineer.
By Jennifer Pallanich
Bass Lite changed hands in a number of farm-ins and farm-outs following its 2001 discovery in 6700ft of water. With the gas field now in production via a 56-mile tieback to the neighboring Devils Tower spar, Jennifer Pallanich talks to operator Mariner Energy about the Bass Lite project highlights and the independent’s deepwater ambitions.
With a five-year interval between discovery by the original joint venture and sanction by the eventual operator, and another two for development, Bass Lite went onstream with the distinction of being one of the longest subsea tiebacks in the Gulf of Mexico as well as being quite deep.
The gas field began producing in February through an early production system; it is expected to reach peak capacity by the end of the summer. Production in mid-May was 75mmcf/d, and system upgrades for the spar topsides facilities were under way to allow peak production of up to 120mmcf/d. The two well field is expected to produce for seven to eight years.
When Mariner Energy decided to develop Bass Lite, the independent had to select its production strategy. The company opted to produce the two-well subsea tieback to a local host.
‘The first challenge was a host platform,’ says Cory Loegering, Mariner Energy’s senior vice president, deepwater.
The 2006 sanction meant choosing Devils Tower, which went onstream in 2004, or Independence Hub, which didn’t go onstream until last year. Preferring to commit to the known, Mariner chose Devils Tower.
Once Mariner selected the Williams-operated Devils Tower in Mississippi Canyon block 773 in 5610ft of water to host the tieback, the company turned to the challenge of designing the flowline route.
‘There was actually a significant engineering effort that was under way to establish a flowline route to avoid a lot of subsurface features. There were some rock outcrops, there was some faulting, some steep slopes that we had to contend with,’ Loegering says.
Mariner conducted an initial ‘table top’ survey based on seismic data to map the seafloor and determine a rough route for the flowlines.
The company followed that up with an AUV survey to finetune the route. Seabed issues that emerged after the AUV survey led to a bit of deviation in the rough route, Loegering says. One factor was that the company strove to make sure the flowlines had a continuous climb from the well to the host platform to avoid slugging issues.
Once the route was established, the team could design the flowlines and umbilicals. The flowlines were lowpressure for the depth, Loegering notes, but 56 miles weren’t readily available. An order for the flowlines went to Tenaris.
The design work on the SCR for Devils Tower came around the time the US Minerals Management Service (MMS) was working on a notice to lessees stipulating stricter design criteria based on more severe storm conditions and subsequent motions requirements, so Mariner designed it under the more stringent criteria, which meant meeting motions for a 100-year storm.
‘The umbilical, although more simple, was a bit more of a challenge,’ Loegering says. Meeting MMS safety requirements meant that Mariner was going to have to move away from the tried-and-true copper umbilicals to fiber optics for its 56-mile tieback. ‘In this case we ended up with two fiber optic cables because we couldn’t get adequate response time through the copper wire,’ he adds. Making the switch from copper to fiber optics allowed the company to meet the MMS-mandated response time to close the subsea safety valves. Mariner awarded the order for the umbilicals to Oceaneering Multiflex.
Loegering says he can see use of fiber optics becoming standard operating procedure for the company because of its almost instantaneous response time and that it is less costly than copper. Mariner has already purchased another umbilical featuring fiber optics for shorter tieback, he adds.
AFL Telecommunications was the fiber optic component supplier to Oceaneering Multiflex. The fiber optic component design utilizes AFL’s patented optical fiber filled stainless steel tube with layers of armoring and encapsulation to provide the required ruggedness to be cabled with other components at Oceaneering Multiflex. The optical budget on this project, given its length, was of concern. The optical fiber was selected for its low loss characteristics and AFL was able to put it into the cable, in the long lengths required, with no impact to the attenuation characteristics of the fiber. The fiber optics performed better than expected.
At one point, it became fairly evident that the flowlines and umbilicals were probably going to be laid at the same time, he says.
‘We always try to avoid vessel clash.We try not to lay flowline and umbilicals at the same time,’ Loegering says. ‘In this case it got everybody’s attention because it looked like we were not going to be able to avoid it.’
Since Technip had both contracts, it managed the interfaces and both Mariner and Technip were involved in the planning. Technip’s Deep Blue laid the flowline, and its Apache mobilized from the North Sea to lay the umbilicals. All this work was done in November and December 2007. The campaign worked out well, Loegering says.
With an eye on the future, Mariner gave the tieback two potential tie-in points. If Mariner doesn’t use the tie-ins itself, other operators can, Loegering says. ‘That’s pretty significant infrastructure that’s now laying on the bottom of the Gulf.’
In addition, it has sensors to monitor pressure and temperature along the flow line.
‘It’s not just a piece of iron that we put down there. We put a bit of technology down there too,’ Loegering says.
Mariner used smart completions on both wells to optimize gas recovery from the reservoir, he notes.
Oceaneering provided the umbilical system; Dril Quip the control system; Astro Technologies the flowline sensors; Roxar the subsea wet gas meter; Cameron the subsea trees; Technip the flowline and umbilical installation; Tenaris provided the flowlines; and Williams provided the topsides facilities.
Partnership rests at operator Mariner with 42.2%, Ert with 19%, Eog with 17.5%, Deep Gulf with 15% and Eni with 6.3%.
A deep splashWhen Mariner Energy made its deepwater debut in the mid 1990s, the company learned not just about the capital intensive nature of deepwater but also the long lead-time between discovery and going onstream.
To take the edge off of that, the company opted to hold its deepwater acreage and to build up its shelf presence and exploit its onshore reserves. The company in March 2006 acquired Forest’s offshore assets and in January 2008 bought StatoilHydro’s shelf Gulf of Mexico assets.
It may have appeared to some that Mariner was getting out of deepwater, ‘but that’s not the case at all,’ Loegering says. The independent is now working on four deepwater projects, two of which it’s operating, including the Bass Lite field. Its other deepwater work right now includes Viosca Knoll block 821 in 1100ft of water, which Mariner operates but will hand over operations to Walter Oil & Gas once the well work is complete, and the W&T-operated Daniel Boone in Green Canyon block 646 in 4300ft of water.
Loegering says the company intends to continue growing in the deepwater GoM and Mariner has remained active in lease sales since acquiring 21 blocks in the October 2007 lease sale and submitting 19 apparent high bids in the March 2008 auction. Mariner likes to operate but also wants to be considered as a partner in deepwater projects, he adds.
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