MEXICO CITY (Reuters) - Mexican billionaire investor Carlos Slim's team and state energy company Pemex are discussing substantial changes to a deal to develop the country's first deepwater natural gas field, five sources familiar with the matter told Reuters.

Slim's Mexican holding company Grupo Carso signed a deal last year to partner with Pemex to develop the Lakach field in the Gulf of Mexico, seeking to revive a project the state company had abandoned twice due to high costs.

Since then, Mexico's relationship with the U.S. has come under increased strain from U.S. President Donald Trump's threats of tariffs, mass deportations and military strikes on cartels.

In response, Mexican President Claudia Sheinbaum's government has redoubled its efforts, which began under her predecessor during the first Trump presidency, to wean the country off gas imports from the United States.

Representatives of Pemex and Grupo Carso have discussed different schemes to make Lakach profitable, at a lower gas price than they had initially projected, the sources said.

Grupo Carso wants to add two nearby fields with similar expected resources, Piklis and Kunah, to increase the potential profitability of the venture, four of the sources said.

It was unclear how much the addition of the two fields, which two sources said was close to being finalized, would raise the price for an investment that sources said would earn Slim substantial political clout.

Pemex did not immediately respond to a request for comment. A spokesman for Slim declined to comment.

The sources asked not to be named because they were not authorised to speak publicly on the issue.

In recent years, Slim has been increasing his investments in the energy sector, with stakes in shallow-water fields Zama, Ichalkil and Pokoch.

Piklis and Kunah, each of which has two wells drilled, were declared strategic priorities by Sheinbaum's government last year as Pemex aims to increase overall gas production to 5 billion cubic feet per day (cfd), up from around 3.7 billion cfd.

Slim's team also floated the possibility of putting the venture on ice or pulling out, three sources said, in what one of them added was a negotiation strategy for a better deal.

Earlier development plans for the field were for a startup in 2026 and a relatively short production span of eight years, according to official records. That timeline looks unlikely, the sources said.

The field, located some 90 kilometers (56 miles) from the Gulf port of Veracruz, holds an estimated 900 billion cubic feet of gas.

Lakach needs a lot more investment, added another source, who reviewed development plans. Pressure is low at the existing well there, making production a challenge.

Another seven wells drilled since 2007 were abandoned because they did not produce any gas, official records show.

So far, Pemex has spent $1.4 billion on it and was authorized by the regulator to spend another $400 million.

A fall in gas prices has added to the challenge of making the investment profitable.

The benchmark Henry Hub Natural Gas Spot Price is about $3 per million Btu, down about a third from a year ago and well below the $6 per million Btu initially assumed for the project, one of the sources said.

DEEP FREEZE

Apart from the prospect of Trump's comeback reshaping ties between the two neighbors, Mexico has other reasons to seek energy independence.

Supplies from the north have been disrupted. In 2021, energy outages in Texas caused by a deep freeze extended for a week. Republican Governor Greg Abbott directed its natural gas providers not to ship outside the state.

Exports of gas to Mexico via pipeline fell by about 75%.

But developing Mexico's own resources is not straightforward.

Pemex wants to develop the offshore field using a service contract where partners finance projects upfront, a mechanism used prior to the country's energy sector liberalization, which was curtailed by Sheinbaum's resource nationalist predecessor.

Developing Lakach will require both resources and expertise from private companies, whose participation the government has sought to limit in recent years.

A lack of infrastructure to pipe the gas away is another issue, the sources said.

Plans to produce gas from the field were first shelved in 2016, and then again after previous partner New Fortress Energy pulled out in 2023.