NS35B-0383 - Clay Volume Estimation Using Electrical Resistivity Tomography Utilizing ResIPy
Presentation Information
TitleNS35B-0383 - Clay Volume Estimation Using Electrical Resistivity Tomography Utilizing ResIPy
Session Start2022-12-14 14:45:00 CST
Session End2022-12-14 18:15:00 CST
LocationMcCormick Place, Poster Hall, Hall - A
AuthorJohn
AbstractElectrical resistivity has been a reliable, and relatively inexpensive way to visualize the near surface earth. After field acquisition, it is often difficult to estimate the volume of anomalies in the post-processing stages away from the field with no direct measurements of the subsurface such as local borehole data. The software ResIPy (v3.3.3) allows for onsite processing with immediate images of electrical resistivity distribution of the near surface structures. For a groundwater exploration survey in Sentinel, OK, electrical resistivity was used. Processing the data using ResIPy showed possible groundwater and clay lenses locations in the study area. The groundwater zone was distinguished from clay lenses with its higher resistivity compared to the low resistivity pockets close to the surface. The water sample from a nearby well has a 22.5 ?.m resistivity value and the resistive groundwater anomaly zone lies at depth of 15m to 20m, consistent with data from a water well close to the survey site. Creek water near the survey area has a 6.22 ?.m resistivity. Nearby well data also shows clay lenses atop of a sandy layer at depths of 0m to 7m with an average thickness of 4m. Here we show how any anomaly�s volume can be calculated using the attributes of ResIPy�s meshing algorithm. Meshing usually discretizes the subsurface into small tetrahedrons with known volumes known as cells. The volumes of each cell can be calculated with simple volume equations for tetrahedra or any other shape specified by the user post inversion and used to estimate the sum of the anomaly volume that lies within a group of cells. We developed a simple GUI module and added that to ResIPy, so that the users can simply define a resistivity (or conductivity) threshold after the inversion and see the volume of the anomaly that appears within the defined threshold. In this study, we used this approach to estimate the volume of clay lenses that lie above the aquifer in the target area. Our findings show that an overall 858 m3 of clay with an average thickness of 7m (consistent with the well data) is available at the site.