Exxon's shale output per well slips as total production rises -report

* Exxon's per-well output falls to sixth from first in key basin

* Shale acreage doubled with plan to sharply increase oil output

HOUSTON, June 9 (Reuters) - Exxon Mobil Corp's oil wells in part of a marquee U.S. shale field generated fewer barrels per well as it ramped up overall spending and production, according to a new report that looks at data from 2018-2019.

A $6.6 billion acquisition in 2017 of New Mexico acres doubled Exxon holdings in the Permian Basin that spans west Texas and New Mexico. The Permian's New Mexico portion is among Exxon's priorities with a goal to boost shale output to 700,000 bpd by 2025.

Exxon's average liquids output over a well's first 12 months fell to 521 barrels per day (bpd) in 2019 in its Delaware basin holdings in New Mexico, down from an average of 635 bpd in 2018, according to IHS Markit data compiled by the Institute for Energy Economics and Financial Analysis (IEEFA).

It dropped to 6th from first on a per-well production basis among a group of large, publicly-trade producers, the data showed, behind Occidental Petroleum, EOG Resources , and others.

Full data for 2020 is not yet available and many wells across the basin were shut-in due to the pandemic, but initial findings of data that looks at the peak month of a well's production "suggest that the company's Delaware wells have continued to fall behind," said Clark Williams-Derry, an IEEFA analyst.

DRILLING MORE LAYERS

Exxon did not respond to a request for comment. In a March presentation to investors, Exxon reported steady per-well gains between 2018 and 2020, citing its "core New Mexico development."

Producers commonly drill their greatest prospects first.

In 2018, Exxon was focused on the best slice in the Delaware basin, which has a layer cake of oil-producing zones, said Raoul LeBlanc, analyst with consultants IHS Markit. It since has started to produce from other layers as well.

Exxon's declining output per well came as the basin's average improved about 5%, according to data released on Wednesday by IEEFA. U.S. shale production in the Permian rose sharply last decade but has slowed as oil companies focus on profit over output.

The Delaware basin's per well average overall rose to 478 bpd in 2019 from 454 bpd the year before. Initial results for 2020 show the average reaching 501 bpd, IEEFA said.

"They're inviting investors to judge them on the production of their wells," said IEEFA's Williams-Derry. "But their actual production is not living up to what they seem to be claiming," he said referring to the company's investor presentation.

Exxon also is active in the Midland portion of the Permian where it ranked 12th out of top 20 in 2019 on an output measure that normalizes for well length. Its average production for the first 12 months of a well improved between 2018 and 2019, though. (Reporting by Jennifer Hiller; editing by Gary McWilliams and Aurora Ellis)