Dynamic Young Modulus Variation Through a Turbiditic Sedimentary Interval

Abstract

ABSTRACT. In reservoir development, the integration of results from distinct disciplines aims at increasing oil and gas production. In this context, geoscientists and engineers rely mainly on the records from geophysical well logging for controlling the spatial and depth variation of petrophysical properties of the formations.In this paper, we use geophysical well logging data through the turbiditic Namorado reservoir in Campos basin for calculating the spatial and depth variation of the isotropic Young modulus. The reservoir formation is mainly formed by subhorizontal thin layers of sandstones and shales. Such structural feature of the reservoir corroborated for approximating the sedimentary interval to a vertically transverse isotropic (VTI) medium using the Backus-averaging technique. We then calculated the correspondent Young moduli, in order to construct depth maps showing the spatial variation of VTI Young moduli in the reservoir formation. In the construction of the maps along depths selected a priori, an interpolation process was applied, which incorporates an inverse-distance square-weighted interpolator into a "search radius scheme". We evaluated the uncertainties in the interpolated maps by calculating statistical measures, revealing the robustness of the inverse-distance square-weighted interpolator coupled to the proposed "search radius scheme". For a selected depth, the resulting maps for the isotropic Young modulus show higher magnitudes if compared to the magnitudes of the VTI Young moduli (i.e., perpendicular and parallel) maps. This result confirms previous works which point out the importance of incorporating anisotropy in geomechanical studies, particularly in the analysis of in situ stresses in which use of elastic moduli is crucial. On the other hand, comparing the VTI Young moduli depth maps reveals that, in the Namorado reservoir, anisotropy induced by thin layers has weak influence on the calculation of Young modulus.Keywords: geophysical well logs, effective VTI elastic stiffnesses, Backus averaging, dynamic Young modulus, spatial interpolation, Namorado reservoir. RESUMO.No desenvolvimento de reservatórios, a integração de resultados de diversas disciplinas visa ao aumento da produção deóleo e gás. Nesse contexto, geocientistas e engenheiros contam principalmente com os registros de perfilagem geofísica de poços para controlar as variações espacial e em profundidade das propriedades petrofísicas das formações. Nesse artigo, usamos dados de perfilagem geofísica através do reservatório turbidítico de Namorado na bacia de Campos para calcular as variações espacial e em profundidade do módulo de Young isotrópico. A formação onde o reservatório se insereé composta principalmente por camadas sub-horizontais delgadas de arenitos e folhelhos. Tal feição estrutural do reservatório corroborou para aproximar o intervalo sedimentar a um meio transversalmente isotrópico vertical (TIV) usando a técnica de Backus. Calculamos então os módulos de Young correspondentes, a fim de construir mapas represen...