Thie Application Of Surficial Geophysics To Well Site Exploration And Wellhead Protection In Fracture Controlled Aquifers

Siting high capacity wells in fractured controlled aquifers is difficult due to the<br>unpredictable distribution of relatively narrow fracture zones. Geophysical methods can<br>be used to locate fracture zones and select favorable test well locations. Due to the<br>expense of rock drilling, it is common to estimate the parameters of fractured aquifers<br>without monitoring wells. Under these conditions, most interpreters assume an isotropic<br>porous media equivalent. This can lead to serious errors in defining the ground water flow<br>system.<br>This paper presents two case histories that illustrate how surficial geophysical<br>methods can be used to locate high capacity wells in fracture controlled areas. The cases<br>also demonstrate how the properties of fractured aquifers can grossly deviate from<br>isotropic porous media and the errors that can result from ignoring this fact. Geophysical<br>methods can be used to predict the trend of the axis of maximum transmissivity in the<br>aquifer, which can be used to efficiently site monitoring wells to accurately measure<br>aquifer properties. Accurate measurements of anisotropy are critical for defining<br>reasonable wellhead protection zones in fracture controlled aquifers.