The effects of groundwater abstraction on lateral gas migration in the Milk River Formation, Alberta

In Southeast Alberta, Canada the Milk River Aquifer and Medicine Hat Gas Field are separated by approximately 15km of interbedded low permeability sediments and confined by the overlying Pakowki Shale underlying Colorado Group. A steady state groundwater model was used to calculate the hydraulic head level of the Milk River Aquifer and was validated with historic and modern head maps. Abstraction scenarios were run at low medium and high pumping rates and the maximum drawdown found at the edge of the Milk River Aquifer closest to the Medicine Hat Gas Field was 62 meters. This drawdown was converted into a water pressure and used as an input into a STOMP multiphase flow model designed to assess the effects of water pressure, permeability and gas pressure on the vertical and lateral flow of gas. A sensitivity analysis on the permeability input within a two zone column allowed for the estimate of a seal strength. At a gas pressure of 3200kPa a permeability of 0.0001md restricted the vertical flow of gas. Increasing gas pressure within the system allowed for the increased mobility of gas through lower permeability materials. 2D STOMP models were developed to observe the simultaneous gas movement both laterally and vertically. Their results suggested that increasing gas pressure and decreasing water pressure enabled gas the ability to move further from its source in the lateral direction and more rapidly in the vertical direction