PORTLAND – The two massive oil rigs and the construction jobs they created pumped new life into the economy. Their tall cranes and bright lights became a familiar marker in Portland Harbor, and residents watching their construction over the past 18 months grew used to and even fond of them.

But the deep-water berth that houses the semisubmersible drilling rigs soon will be empty. One of the red-and-battleship-gray rigs will leave by the end of October for sea trials, first in a 70-foot-deep water hole right in Portland Harbor, then 40 miles off the Maine coast. Both rigs will be headed for warmer waters by the first of the year, most likely to Brazil.

“It is emotional. I’m tremendously proud of our people and what they’ve accomplished,” said Peter Vigue, Cianbro president and chief executive officer.

It will be a bittersweet goodbye for Cianbro, the employee-owned company based in Pittsfield that wooed Brazilian-based Petrodrill for the right to outfit the structures. The project has provided Cianbro with a $100 million contract and steady jobs for more than 1,000 Cianbro employees and subcontractors.

“These are good-paying jobs with benefits,” said Jack Cashman, commissioner of the state Department of Economic and Community Development. “The impact has been enormous to the city of Portland and the whole area.”

This is the first offshore oil work undertaken by Cianbro, Maine’s largest construction firm. The company is better known for outfitting pulp and paper mill plants and fixing bridges.

It was a challenge to formulate a plan to transfer the skill set typically used by their workers into a marine environment. But Vigue was determined to find a project that would expand his company and keep his workers employed during an economic downturn.

It’s not easy pulling wire or welding pipes on a floating tin can, say workers. It’s bitter cold in the winter and hot in the summer. It’s cramped. And being high up on a rolling rig during nasty weather is, well, nasty.

A breakthrough during the first months of the project was the advent of hot coffee on deck, followed by plumbing and fresh water.

While they won’t miss trudging up 111 metal grate stairs to get to the top deck, there weren’t many complaints otherwise.

“I milked cows for two years before this job,” said Josh Farrington of Wilton, a general laborer who moved to Portland for the job.

Roland Gross of Searsport is an electrician who never had worked on a ship before, but he adapted his skills to install the rig’s refrigeration, heating, ventilation and air conditioning units. “I liked the challenge,” said Gross, who stays in a hotel during the week and drives home on weekends, like many on the project.

Local residents say they’re pleased that the former site of the Bath Iron Works dry dock is being maintained as a working shipyard, and adding to the local and state economy.

Cianbro renovated an 87,000-square-foot dilapidated state pier and a 140,000-square-foot warehouse for use on the project, and the company signed a $1 million annual lease with the city of Portland to use the site.

“We like seeing it down there because it is a working waterfront. This is marine industrial work. It fits,” said William Gorham, president of the Munjoy Hill Neighborhood Association. The residential area overlooks the shipyard.

The rigs are essentially elevated, square-shaped ships capable of staying at sea for years while searching for oil in up to 4,925 feet of water and drilling to a depth of 10,000 feet.

They are self-propelled and use global positioning systems, accurate within six inches, to chart their course and mark where oil is found.

The two rigs were brought to Portland from separate Gulf Coast yards in Orange, Texas, and Pascagoula, Miss., after the companies that were building them sank into bankruptcy.

Cianbro transported each rig’s pontoon assembly and deck boxes to Portland. Workers welded each rig’s 5,550-ton deck box and derrick onto pontoons, creating a structure the size of a football field that rises 319 feet from the bottom of the pontoons to the tip of its derrick.

At a Thursday ceremony touting 2 million “safe hours” by Cianbro workers, Amethyst 4, named Oil Rig 1828 by Cianbro, will be dubbed “Pride Rio De Janeiro.” Amethyst 5 or Rig 1829 will become “Pride Portland.”

With the success of this project, Vigue says he’s looking at bidding on other marine projects for Portland, including refurbishing cruise ships.

More marine projects are good news to Gorham.

“I look at those rigs and I see dollar signs,” he said. “It’s been a great boost to the city of Portland. We needed it.”