How Much Undiscovered Oil and Gas Lies in the Haynesville Formation? A USGS Assessment

The Haynesville Formation is a body of Jurassic rock buried beneath the Gulf Coast Basin. Oil was first produced from it in 1921, when oil-bearing sands were discovered near Haynesville, Louisiana, and exploration has continued ever since. More than 11,000 wells have targeted it onshore, finding 219 fields.

The U.S. Geological Survey last assessed its undiscovered resources in 2017. Since then more than 5,000 new Haynesville wells have been drilled and new liquefied natural gas facilities have opened in the basin, so the USGS made a fresh estimate of the undiscovered, technically recoverable oil and gas under the onshore United States and state waters.

How the formation formed

The Haynesville and rocks of the same age were laid down on top of the older Smackover platform during a marine transgression in the Kimmeridgian and early Tithonian ages that spread mudrock, sandstone, carbonate and evaporite across the basin. In eastern Texas and northern Louisiana, abundant nutrients and oxygen-poor bottom water preserved organic-rich mudstone. After deep burial and heating, that mudstone — together with the Smackover below — became the main source of the Haynesville’s gas.

Elsewhere, rivers carried sediment in from the north, northeast and east, building mostly sandy deposits with patches of carbonate shelf. Changes in rock type, the movement of underground salt, and faulting created traps in the conventional reservoirs, and the overlying Bossier Formation seals much of the area.

Six assessment units

The formation lies beneath parts of Texas, Oklahoma, Arkansas, Louisiana, Mississippi, Alabama and Florida. The USGS divided it into six assessment units, based on geology, petroleum-system elements and the technical limits of drilling.

The four conventional and two continuous assessment units. Image from the USGS fact sheet.

Four conventional units hold sandstone or carbonate reservoirs in structural and stratigraphic traps, charged from Smackover, Haynesville and possibly Bossier source rocks:

• the Eastern Shelf Sandstone unit, where sandstone reservoirs are common;
• the Eastern Shelf Carbonate unit, in southern Louisiana, Mississippi and Alabama;
• the Western Shelf Carbonate unit, with shelf carbonates in Texas; and
• the Western Slope Carbonate unit, with carbonate slope reservoirs in Texas and Louisiana.

Two continuous units are the organic-rich mudrock itself, in eastern Texas and northern Louisiana, which generates its own gas:

• the Sabine Uplift unit, the heart of the horizontal-drilling Haynesville play, where the rock is overpressured; and
• the North Louisiana Salt Basin unit, similar rock farther east where only a few wells have reached the formation and none has been completed — so it is far less certain.

The recent shale gas development on the western side of the East Texas Basin, which industry calls the “Western Haynesville,” was left out: well logs and seismic data show that those wells actually produce from rocks equivalent to the Bossier Formation.

The estimate

The range means there is a 95% chance of at least the lower figure and a 5% chance of at least the upper one.

Almost all of the gas is in the continuous units: a mean of 44,751 billion cubic feet, of which the Sabine Uplift holds 37,643 and the North Louisiana Salt Basin 7,108. The four conventional units together hold a mean of 3,131 billion cubic feet of gas and all 152 million barrels of the oil.

Sources

Based on Gardner R, Flaum JA, Birdwell JE, et al., "Assessment of undiscovered oil and gas resources in the Haynesville Formation within the onshore United States and State waters of the Gulf Coast Basin," U.S. Geological Survey Fact Sheet 2025–3054; a work of the United States government in the public domain.