SUBSURFACE MAPPING OF THE PRAIRIE EVAPORITE GROUP SALT DEPOSITS: ASSESSING SALT CAVERN QUALITY FOR COMPRESSED AIR ENERGY STORAGE

The Elk Point Group (EPG) consists of Givetian to Frasnian-aged sedimentary strata representing hypersaline lagoon and salt pan paleoenvironments. Extending from the Northwest Territories, Canada to North Dakota, USA, it represents a major source of halite and potash minerals. Salt caverns in the EPG have previously been used by the oil and gas industry to contain waste water and pressurized fuels. More recently, it has been assessed for energy storage from renewable sources with variable energy output, such as wind and solar power, in the form of compressed air in brine solution-mined salt caverns. The compressed air is subsequently released to drive turbines when power generation is otherwise low. Our research will expand the current extent of high-resolution subsurface mapping for the purpose of planning cavern development and assessing the geomechanical stability of the caverns during repeated pressuring – depressuring cycles.

We present preliminary data from two cores and 118 well logs from south-central Alberta that penetrate the Prairie Evaporite and Lotsberg Formations of the EPG. From these, it has been found that the Prairie Evaporite Formation contains on the order of 3-5 % siltstone and anhydrite as mud drapes and dissolution lenses, with no thick layers of anhydrite or mudstone. The Lotsberg is nearly pure halite, and is therefore more suited to solution mining operations despite having a thick dolomite and anhydrite layer at its stratigraphic center. Based on our preliminary results, we identify areas containing salt that may be economically brined. We also identify layers of anhydrite or mudstone that may cause damage to drilling equipment or incur extra drilling time; thick layers (>10m) can render a salt bed uneconomic to develop. To delineate those beds, we use drill cores and well logs to correlate inter-salt mudstone and anhydrite layers. This allows us to not only identify concerns for drilling but also large scale environmental cycles and sub basins.

Future work will involve collaboration with researchers from other disciplines such as mechanical, electrical, and civil engineering to plan cavern shape and placement.