Only four examples of
shallow, basin margin gas accumulations are described here. They are major
plays that are fairly well documented in the literature. None of these
four are in Cretaceous units and all are outside of the Rocky Mountains
ANADARKO BASIN--NORTHEASTERN MARGIN
The giant Hugoton Gas Field in southwestern Kansas is one of the largest
in North America. Nonassociated thermogenic gas is produced from Permian
clastics and carbonates. As described in the Ideas section
of this website, the Hugoton Gas Field is the archetype for thermogenic
gas that has migrated up to shallow depths on the basin margin. The Kansas
Geological Survey has an ongoing study of the accumulation (www.kgs.ukans.edu/Hugoton/).
The trap is complex, including a stratigraphic pinch out to the north
and west, local fluid compartments controlled by faults, and a possible
hydrodynamic component. Depths are generally 2000-3000 ft. More than 23
TCF has been produced from an area of over 4100 sq mi.
The Hugoton Gas Field was discovered in the 1920s and the initial
production was locally consumed. Subsequent development supported a pipeline
infrastructure to the upper Midwest. During the 1980s, state authorized
in-fill drilling greatly increased production.
MICHIGAN BASIN--NORTHERN MARGIN
On the northern margin of the Michigan Basin, natural gas is produced
from fractured Antrim Shale (Devonian). This area in the northern part
of Michigans Lower Peninsula is the archetype for late generation
biogenic gas. The gas was generated in the relatively recent geologic
past and is in young ground water that is flowing down the basin margin,
away from subcrops beneath glacial drift. The Gas Research/Technology
Institute has funded several studies by University of Michigan people
Attempts to extend the play to other margins of the basin have met with
only limited success. The western margin seems to show the best potentials.
ILLINOIS BASIN--EASTERN MARGIN
The New Albany Shale in the Illinois Basin is similar to the Antrim. On
the eastern basin margin in western Indiana, biogenic gas has been produced
in a setting similar to the Michigan play. The late generation biogenic
gas has large amounts of co-produced water. The Gas Research/Technology
Institute has also funded research in the Illinois Basin (Walters and
others, 2000, GasTips).
APPALACHIAN BASIN--NORTHWESTERN MARGIN
Shallow gas has been produced from the historic Lake Shore Fields located
on the northwestern basin margin. The gas is either biogenic or migrated
thermogenic gas. The hosting rocks are silty and sandy beds in black shales
(Devonian/Mississippian) with low thermal maturity (Milici, 1993). These
accumulations have not received much modern attention. Most of the exploration
activity has been directed toward thermogenic gas in the basin center.