BP plc said Monday the Thunder Horse South Expansion project in the deepwater Gulf of Mexico has begun operations early, one year ahead of schedule and $150 million under budget, boosting output from the main platform by 50,000 boe/d gross.

Planned for 2017 but brought online early in December, the expansion was completed 11 months ahead of schedule. It adds a subsea production system roughly two miles to the south of the existing Thunder Horse platform, 25% owned by ExxonMobil Corp.

“Thunder Horse South Expansion — along with our recent approval of the $9 billion Mad Dog Phase 2 platform — demonstrates that the U.S. Gulf of Mexico remains a key part of our global portfolio today and for many years to come,” said CEO Bob Dudley.

“This project also marks the first of several major upstream start-ups expected before the end of this year and a major step toward our goal of adding 800,000 boe of new production by 2020.

“These new projects, coupled with a series of recent agreements we’ve reached around the world, reflect the growing momentum across BP and clear progress in building a strong foundation for the future.”

The Thunder Horse platform, which sits in more than 6,000 feet of water, initially began producing in June 2008. Gross production capacity is estimated at 250,000 b/d of oil and 200 MMcf/d of natural gas.

The expansion was completed more than 15% below budget by relying on “proven standardized equipment and technology rather than building customized components,” BP noted.

The first new well for the project tapped into the highest amount of hydrocarbon bearing sand seen to date at the Thunder Horse field, with drilling results confirming more than 500 feet of net pay.

The Thunder Horse system is a collection point for wells connected to the platform by two 11,000-foot flowlines installed on the seabed in late 2016. The facility continued to operate when the subsea production and pipeline system was installed.

The expansion project continues momentum for BP in the deepwater GOM, where last year the company started up a major water-injection project at Thunder Horse and approved the second phase of Mad Dog, which is set to come online in late 2021.

“The Thunder Horse South Expansion project, brought online ahead of schedule and under budget, proves that deepwater can be done in a cost-effective way, while keeping a relentless focus on safety,” said BP’s Richard Morrison, regional president of the GOM unit. “It also shows the effectiveness of our strategy in the Gulf, which is all about increasing production from within our existing asset base and large portfolio of undeveloped resources.

BP, which has about 400 lease blocks in the GOM, operates four large GOM production platforms in the U.S. deepwater besides Thunder Horse — Atlantis, Mad Dog and Na Kika. It also holds interests in four nonoperated hubs — Mars, Olympus, Ursa and Great White. Between 2013 and 2016, BP’s average production in U.S. GOM increased to 264,000 boe/d net from 189,000 boe/d net.