Evaluating the Geology and Ground Water Hydrology of Deep Basin Lignite in the Wilcox Group of East Texas

Lignite resources in Texas are currently estimated at 58 billion short tons (755 quadrillion British thermal units or Quads [Q] of energy) (Kaiser and others, 1980), constituting just over one-fourth or 26 percent of the state's energy endowment of 2,915 Q. Resources of near-surface lignite, those at depths between 20 and 200 ft (6.1 and 61 m), are about 23 billion tons (300 Q), of which some 8.6 to 11.1 billion tons are exploitable by current surface-mining methods. Near-surface reserves are adequate to meet the demand for lignite in this century. Meeting the demand in the next century and beyond will require the recovery of deep-basin lignite, occurring between depths of 200 and 2,000 ft (61 and 610 m) below the surface. Resources of deep-basin lignite at these depths and in seams greater than 5 ft (1.5 m) thick are about 35 billion tons (455 Q) or 16 percent of the state's energy endowment. These resources occur mainly in East Texas north of the Colorado River (about 70 percent) in two geologic units, primarily in the lower Eocene Wilcox Group (55 percent) and secondarily in the upper Eocene Jackson Group (15 percent).

Deep-basin lignite is not economically recoverable at this time; however, large tonnages are potentially recoverable by deep-surface mining and underground, or in situ gasification. Small tonnages are now technically exploitable by in situ gasification, whereas deep mining on a routine basis remains to be demonstrated. Few details are known about deep-basin lignite in Texas. Therefore, a two-year program, funded by the Texas Energy and Natural Resources Advisory Council (TENRAC), was begun in September 1981 to collect, at the regional level, geologic, hydrologic, and chemical data about deep-basin lignite in the Wilcox Group to ultimately stimulate private exploration and exploitation of deep lignite.