Wyodak Coal
, Tongue River
Member of the Fort Union Formation, Powder River Basin, Wyoming: "No-
Coal
Zones"
and Their Effects on Coalbed Methane Production*
Click
to view presentation in PDF format.
The Powder River Basin contains more
than 80 percent of the state's coal
resources within the Tongue River Member of
the Fort Union Formation (upper Paleocene). The Fort Union Formation is divided
from older to younger into the Tullock, Lebo Shale, and Tongue River Members.
The coals of the Tongue River Member consist of approximately 32
coal
seams with
a combined thickness in excess of 300 ft. One of the major
coal
seams within the
Tongue River Member is the Wyodak
coal
.
The Tongue River Member of the Fort Union Formation
was deposited by a fluvial-deltaic system filling Lake Lebo. Extensive peat
deposits accumulated within poorly drained interdeltaic and deltaic swamps.
There are “no-coal
zones” within the Wyodak
coal
seam where the
coal
has been
replaced by sandstones and shales. The “no-
coal
zones” are distributary fluvial
channels that meandered throughout the swamps. Several methods have been
developed to predict the locations of the fluvial channels and avoid drilling
“no-
coal
zones.” Additionally, the relationship between adjacent
coal
seams may
imply a pattern of production.
Geologic map of Powder River Basin (after Flores and Bader, 1999), with study area
Depositional environment of Wyodak
coal
Click
to view sequence of six maps depicting or suggesting Wyodak coal
attributes
(structure, isopach, structure of overlying Big George
coal
(BGC), BGC structure
with “no-
coal
zones,” interval isopach, and interval isopach with “no-
coal
zones”).
Reference
R.M. Flores and L.R. Bader, 1999, Fort
Union Coal
in the Powder River Basin, Wyoming and Montana: A synthesis, in
1999 Resource Assessment
of Selected Tertiary
Coal
Beds and Zones in the Northern Rocky Mountains and
Great Plains region: U.S. Geological Survey Professional Paper 1625-A, Chapter
PS, p. i-iv, 1-71.