GROUNDWATER FLOW ACROSS THE INTERMEDIATE ZONE

Characterizing the “intermediate” zone occurring between oil and gas production and overlying potable groundwater resources is critical to ensuring water security in many regions. These 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 of groundwater flow and potential for migration of deeper 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, which is often the uppermost unit exploited by the oil and gas industry. In Saskatchewan a total of around 812,500,000 m³ of water have been disposed of into the Mannville, 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 natural system. To determine the possible risk to potable aquifers overlying the Mannville Group, 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 into shallower formations. 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.