Computation of optimized arrays for 3-D electrical imaging surveys

Abstract

S U M M A R Y3-D electrical resistivity surveys and inversion models are required to accurately resolve structures in areas with very complex geology where 2-D models might suffer from artefacts. Many 3-D surveys use a 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 x-direction. 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. The array geometric factor and its relative error are used to filter out potentially unstable arrays in the construction of the comprehensive data set. Comparisons of the conventional (consisting of dipole-dipole and Wenner-Schlumberger arrays) and optimized arrays are made using a synthetic model and experimental measurements in a tank. The tests show that structures located between the lines are better resolved with the optimized arrays. The optimized arrays also have significantly better depth resolution compared to the conventional arrays.

Data acquisition, processing and filtering for reliable 3D resistivity and time‐domain induced polarisation tomography in an urban area: field example of Vinsta, Stockholm

“…The array sequence 3D‐CD included cross‐line perpendicular and diagonal (with an angle above 60° against the parallel lines) nested array measurements taken with the current electrodes on the outer lines (Lines A and F) and the potential electrodes on the centre lines (Lines C and D). This could be referred to as quadrupleline offset configurations (Loke et al ).…”

“…Geophysical methods can produce large and laterally continuous 2D/3D images of the subsurface properties at reasonable cost, but they are limited by resolution and ambiguities in the interpretation. The combination of geotechnical probing and geophysical imaging can lead to a comprehensive overview of the underground structures, the distribution of lithologies, and the properties of materials (Cavinato et al ; Danielsen and Dahlin ; Rønning et al ). The building of a reliable engineering‐geological conceptual model can reduce the risk of encountering unexpected geological conditions, and consequently minimise delays and extra costs in the construction works.…”

“…Archeological pre‐investigations in cities can be carried out through ERT techniques (Tsokas et al ; Papadopoulos et al ). The characterisation of rock masses, aiming for discontinuities and weak zones, in support of underground constructions (i.e., tunnelling) can be accomplished also via geoelectrical measurements (Ganerød et al ; Danielsen and Dahlin ; Bellmunt et al ; Rønning et al ).…”

Optimized arrays for 2-D resistivity survey lines with a large number of electrodes

“…Another area of current investigation is the use of 10 optimized pole-dipole arrays to obtain a deeper depth of investigation (Bloome et al, 2011). As 3-D 11 effects can be a significant factor in some areas, research is being conducted to adapt these techniques to 12 optimized arrays for 3-D surveys (Loke et al, 2014c). We are also studying the possible improvement in 13 the performance of the optimized arrays by incorporating known topography and non-homogeneous 14 subsurface resistivity distributions.…”

Modeling of Three-Dimensional Magnetotelluric Fields by Vector Finite Element Method Using GPU

“…Например, в (Sommer et al 2013) используется GPU для ускорения расчетов трехмерных электромагнитных полей в задаче морской электроразведки при использовании МКР. Использование GPU для решения задач электроразведки было успешно применено в (Gundogdu et al 2016, Loke et al 2013) и многих других работах. При решении разреженных систем уравнений, к которым приводит использование МКР и МКЭ, наиболее затратной является операция умножения разреженной матрицы на вектор (Grossman et al 2016).…”