Computation of Optimized Arrays for 3-D Electrical Imaging Surveys

Three-dimensional surveys and inversion models are required to accurately resolve structures in areas with very complex geology where 2-D models might suffer from artifacts. Many 3-D surveys use a survey grid where the number of electrodes along one direction (x) is much greater than in the perpendicular direction (y). Frequently, due to limitations in the number of independent electrodes in the multi-electrode system, the surveys use a roll-along system with a small number of parallel survey lines aligned along the xdirection. The 'Compare R' array optimization method previously used for 2-D surveys is adapted for such 3-D surveys. Offset versions of the inline arrays used in 2-D surveys are included in the number of possible arrays (the comprehensive data set) to improve the sensitivity to structures in between the lines. By using PCs with modern graphics cards incorporating a fast Graphics Processing Unit (GPU) and using an improved single-precision 'Compare R' algorithm, the 3-D optimized arrays can be calculated within a reasonable time despite the comprehensive data set possibly have millions of arrays. A comparison with data sets using inline measurements made using conventional arrays show that structures located between the lines are much better resolved with the optimized arrays.