Effects of Aquifer Interconnection Resulting from Underground Coal Gasification

Abstract

An investigation was conducted to evaluate the effects of aquifer interconnection caused by the collapse of cavities formed in coal seams by two small underground coal gasification experiments in the Powder River Basin, Wyoming. The main objective of the work was to assess the magnitude and extent of changes in the ground‐water flow patterns near the sites of the two experiments. Hydraulic head measurements in the three affected aquifers were used to calibrate a steady‐state ground‐water flow model of the interconnection zone at each site. Flow modeling and field measurements show that water from one or both of the upper aquifers enters the collapse rubble and flows down to the lowest aquifer (the gasified coal seam) where it flows away from the collapse zones. The hydraulic conductivity of the collapse rubble is less than that of the aquifers and provides only a very moderately permeable interconnection between them. A marked reduction in the hydraulic conductivity of the gasified coal seam near the collapse zones causes restriction of flow in the seam, away from them. Changes in hydraulic head and flow patterns caused by aquifer interconnection extend generally only 200–300 ft (60–90 m) away from the experiment sites. Flow in the uppermost aquifer at one of the sites may be influenced as far as 400 ft (122 m) away. At both experiment sites, aquifer interconnection allows water from the uppermost (sand) aquifer, which contains the poorest quality water of the three aquifers, to enter one or both of the underlying coal aquifers.

Contamination of groundwater due to underground coal gasification

“…Aquifer interconnection due to UCG process is investigated in Hoe Creek II and Hoe Creek III experiment in Wyoming (Stone et al, 1982). Aquifer interconnection would be happened when two coal seams are gasified in a column and a strata lies between them.…”

Modeling of Contaminant Transport in Underground Coal Gasification

“…The literature − also contains studies of the same issues, and good progress has been achieved. However, this research on groundwater contamination induced by underground gasification was limited to monitoring, general analysis, or simple mathematical description or simulation; an integrated and quantitative study is imperative.…”