HYDROGEOLOGY OF THE INTERMEDIATE ZONE BETWEEN DEEPER ANTHROPOGENIC ACTIVITIES AND SHALLOW AQUIFERS

Characterizing the “intermediate” zone which occurs between zones of geothermal energy production, carbon capture and storage, disposal wells and oil and gas production and zones of potable groundwater resources is important for ensuring water security in many regions. These intermediate zones commonly contain brackish to saline water and uneconomic amounts of hydrocarbons but lack hydrogeological data. It is this lack of proper data that leads to uncertainty regarding the direction and magnitude of groundwater fluxes and potential for migration of deeper saline fluids across this interface to shallower aquifers.

This study examines the “intermediate” zone in Saskatchewan’s portion of the Western Canada Sedimentary Basin, along with the Mannville Group and the Viking Formation, which are often some of the uppermost units exploited by industry. In Saskatchewan, a total of around 812,500,000 m³ of water have been disposed of into the Mannville Group, while only 550,600,000 m³ of water has been produced, which means an excess of 261,900,000 m³ has been injected into the Mannville Group. This excess fluid has increased pressures and makes upward migration of fluid more likely.

To determine and outline these zones of shallow, deep, and intermediate fluids, Drill Stem Test (DST) were analyzed to estimate hydraulic heads. From this approach, it can be determined if there is an upward gradient from the Mannville Group through the “intermediate” zone into shallower formations, which is useful for evaluating potential for upward migration of saline waters and dissolved contaminants. These hydraulic gradient estimates were combined with existing porosity and permeability measurements from core analyses to estimate the groundwater velocities. A similar approach can be used to characterize the hydrologic behavior of the “intermediate” zones and security of overlying potable water in other regions of the world. Modeling formational flows and leaky well scenarios will also be investigated to determine how both effect the flows within the “intermediate” zone, while helping better outline the protection of our freshwater resources.