Analysis of Fluid Flow Pathways in the Mount Meager Volcanic Complex, Southwestern Canada, Utilizing AMT and Petrophysical Data

Defining the spatial distribution of geological structures and rock properties is important for understanding how fluid flow is controlled in a geothermal reservoir. Here, we present a procedure to examine the potential fluid pathways. By combining 3-D resistivity models derived from audio-magnetotelluric (AMT) data with available rock properties (porosity and permeability) and fluid sample data (fluid resistivity, salinity, and temperature), we investigated the relationship between electrical resistivity and fluid flow in an active volcanic system. Different petrophysical models and empirical relations are evaluated to determine the relationship between the fluid flow system at Mount Meager, British Columbia, and the resistivity model. In addition, we utilized porosity and permeability measured in the laboratory to define the porosity-permeability relationship. The porosity of the volcanic core samples showed a range of 2.6%-23.2% and the permeability was in a range of 0.001-5,186.57 mD. The results showed the potential of 3-D inversion of AMT data to map the fluid pathways at Mount Meager. These pathways are correlated with loss circulation zones in boreholes and can account for porosity up to 8.5%, which using the porosity-permeability relationship translates to permeability of the order 0.249 mD. Not only are the fault and fracture zones important for reservoir exploitation, but they also provide permeability for the circulation of meteoric water. Our studies suggest that a set of fractures with 0.1 m spacing and 20 mm aperture can keep 40% fluid in pores and transmit fluid with possible permeability of 666 mD.