The Influence of Curved and Angled Survey Lines on 2D Resistivity Surveys Employing the Wenner (α) Geometr

Multi-electrode resistivity systems, such as the Lund Imaging System, employ protocols that control switching between the various electrode pairs. The standard protocols used for 2D surveying assume that the survey lines are straight so that the various electrode pairs are collinear. However, due to the presence of infrastructure and other surface constraints it is not always possible to conduct 2D resistivity surveys along straight lines. When survey lines are curved/angled, the apparent resistivity values and assumed pseudo-depths are affected by the non-collinearity of the electrode pairs. In addition, the recorded apparent resistivity data may be representative of the subsurface conditions at positions laterally displaced from the survey line. For a curved survey line spanning an angle of less than π/2 radians, the errors in both the calculated apparent resistivities and assumed pseudo-depths are less than 3%. Similarly, for angled survey lines with angles smaller than π/4 radians, these errors remain below 6.5% and 4%. Although these errors are relatively small, it is possible that they may be propagated during the inversion process and result in distorted resistivity models. If the true positions of the electrodes along a curved/angled survey line can be measured, the error in the calculated apparent resistivity values may be compensated for by calculating the true geometric factors. Corrections to the pseudo-depths may be made by calculating the true median depth for each measurement position. The lateral displacement of the measurement position is a consequence of the survey geometry and cannot be compensated for.