3D borehole-to-surface and surface electromagnetic modeling and inversion in the presence of steel infrastructure

Abstract

<jats:p> The borehole-to-surface electromagnetic (EM) method is a viable imaging and monitoring tool for energy reservoirs, geologic storage, geothermal exploration, fault zones, and other subsurface targets. Data interpretation typically requires considering steel-casing effects, but it is difficult and impractical to directly discretize arbitrarily oriented hollow steel-cased wells in a 3D reservoir-scale earth model because of their extremely high electrical conductivity and long hollow geometry. We have considered a borehole-to-surface EM configuration in which an electric dipole source is placed below the bottom of a steel-cased well. To practically simulate the casing effects on EM measurements, we develop a novel 3D finite-element EM algorithm using an unstructured tetrahedral mesh. To avoid excessive use of fine grids for modeling a steel-cased well, the well is replaced with the combination of a short solid conductive prism and a long linewise perfect electric conductor. We find that this combined structure can approximate casing effects at a small fraction of the computational cost required for modeling a complete hollow casing because the linewise structure is volumeless and does not require an excessive number of small elements. We also find that steel-cased wells distant from sources and receivers can be modeled as simple linewise perfect electric conductors, further improving the computational efficiency. Using this approximation, the 3D EM algorithm presented here is well-suited to modeling many arbitrarily oriented steel-cased wells. After verifying the accuracy and efficiency of this approach using various examples, we performed a 3D borehole-to-surface/surface-to-borehole and surface EM inversion and determine that the inversion can image a deep localized target in the presence of steel infrastructure. </jats:p>

Land CSEM Simulations and Experimental Test Using Metallic Casing in a Geothermal Exploration Context: Vallès Basin (NE Spain) Case Study

“…To improve the accuracy of EM responses, we have applied a mesh refinement close to source and receiver locations based on the semi-automatic refinement strategy proposed by [9]. Further, we applied a power-law stretching to control and adapt the number of points near the casing and account for extreme element aspect ratios [32], [33], [37]. The resulting adapted and unstructured tetrahedral mesh consists of 840 385 elements and 138 573 nodes.…”

“…The analysis of these effects has gained traction recently, and many different approaches have been evaluated on different application contexts. Out of these applications, studies in the area of energy reservoir modeling [28]- [33], water flooding [34], [35], geological storage [36]- [38], geothermal exploration [39], [40], and fractures and fault zones [41], [42], stand out. Regardless of numerical methodology or application area, these works stress out the significant effects on EM responses generated by the presence of steel-cased wells and other metallic infrastructure.…”

Integrated simulation of vertical fracture propagation induced by water injection and its borehole electromagnetic responses in shale gas systems

“…In contrast, the crosswell method allows sources and receivers to be placed directly in deep depth and can be operated at higher source frequencies for higher resolutions. We can also consider a hybrid version of the two methods where sources are placed inside a single monitoring well and receivers are placed on the surface (Um et al, 2017a). In this study, we choose the crosswell EM method over the surface-based EM method since the primary goal of our numerical modeling is to examine the feasibility of the EM methods for monitoring fractures rather than to evaluate the cost effectivenss of the EM methods.…”

The structure and features of the software for geophysical geometrical 3D inversions

“…Ключевые слова: программные комплексы, 3D-инверсия, геометрические параметры, метод Гаусса-Ньютона, адаптивная регуляризация, вычислительная эффективность, обратные задачи геофизики, апробация на практических данных ВВЕДЕНИЕ Для решения трехмерных обратных задач геофизики различные исследователи пытаются применять самые разные методы и подходы. Их можно разделить на традиционные, основанные на классических методах минимизации функционалов [1][2][3][4][5][6], и новые, основанные, например, на использовании нейронных сетей [7]. Всплеск интереса к использованию нейронных сетей обусловлен возросшими вычислительными возможностями и доступностью многопроцессорных систем.…”