The impact of 3D tilted resistivity anisotropy on marine CSEM measurements

Abstract

Marine CSEM modeling and data-interpretation algorithms currently used by the E&P industry are based on application of vertical transverse isotropic (VTI) resistivity models, which in many practical cases cannot adequately describe complex tilted anisotropic geologic structures typical for accumulation of hydrocarbons (e.g., syncline or anticline types). Use of VTI models is a serious limitation of CSEM technology and might be one of the core reasons for some false-positive and false-negative outcomes of marine CSEM surveys. To investigate this phenomenon in more detail and assess the impact of arbitrary tilted resistivity anisotropy on CSEM data, we performed simulations for a set of 3D tilted transverse isotropic (TTI) and VTI benchmark models. The 3D modeling results show that ignoring the TTI effect, if it is present, might lead to incorrect assessment of the feasibility of a potential CSEM survey as well as erroneous assessments and/or mispositioning of hydrocarbon targets during interpretation of field data and, in turn, might compromise the reliability of marine CSEM technology. Therefore, there is a strong practical need to start using TTI models, which provide more accurate descriptions of complex anisotropic resistivity structures than VTI models do. Application of 3D TTI modeling will improve the reliability of CSEM technology and its derisking potential.