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Rio de Janeiro, Brazil

de Magalhaes M.F.,Federal University of Fluminense | Martins J.L.,Coordenacao da Area de Geofisica
Revista Brasileira de Geofisica | Year: 2012

The workflow for an integrated well log analysis must incorporate physically-consistent models for rock properties prediction. Therefore, the selection of the conceptual model is a crucial step in deriving the petrophysical model under investigation. In this paper, we apply the parallel layers conceptual model to derive a petrophysical model for bulk density of complex lithologies. This conceptual model assumes the natural rock as a set of parallel layers with individual densities, incorporating the main factors affecting bulk density of sedimentary formations (i.e., the solid matrix, porosity and fluid content). The resulting petrophysical model shows the volumetric fractions of individual rock constituents as the key parameters for bulk density description. Further parameters of the dependence can be easily selected from petrophysical tables. In this way, evaluation of predefined volumetric fractions of rock constituents is a mandatory procedure for applying the investigated petrophysical model. We present results of calibration and estimation of bulk density well log measurements through turbiditic sediments forming the Namorado reservoir, Campos basin. In evaluating the facies-described volumetric fractions of main constituents of rocks at well surroundings, fundamental well log measurements represented the inputs for mineral volume analysis using the non-negative least-squares inversion method. The outcomes of both experiments exhibited the good performance of the petrophysical model in estimating bulk density with negligible absolute errors and high correlation coefficient. As a conclusion, the parallel layers conceptual model revealed enough robustness for construction of petrophysical models of other well log measurements. © 2012 Sociedade Brasileira de Geofísica. Source

de Oliveira J.S.,Coordenacao da Area de Geofisica | Martins J.L.,Coordenacao da Area de Geofisica
Revista Brasileira de Geofisica | Year: 2011

The P-wave elastic impedance (EI) concept is currently used as a complementary petrophysical parameter for the characterization of oil and gas reservoirs. In this paper, we construct maps representing the spatial variation of isotropic and anisotropic EI at a specific depth through a turbiditic oil-producing reservoir. EI is thus used here not for calibration and inversion of seismic data at farther offsets as firstly introduced, but as an original application of a novel petrophysical concept. As long as bulk density, seismic velocities and incidence angle are common variables in the isotropic and anisotropic EI formulas, we used geophysical measurements at the surroundings of 39 wells drilled through the reservoir formation in order to generate isotropic and anisotropic EI maps. The reservoir inner structure consists of fine layering, allowing us to approximate the formation to a transverse isotropic medium with vertical axis of symmetry (VTI medium) for anisotropic EI map construction. We then applied the Backus-averaging technique for estimating VTI elastic stiffness logs from the well log measurements through the reservoir formation. For the construction of the maps, we implemented an interpolation process incorporating a robust inverse-distance square-weighted interpolator into a search radius scheme. In this scheme, only control points inside a distance specified a priori are considered in the interpolation process. The resulting EI maps for incidence angles of 0°, 20° and 40°, at 3080 m depth, reveal zones of fine layering around certain wells. We observed that seismic anisotropy induced by fine layering is pronounced in these zones, coinciding with low oil-producing intervals. At the same selected depth of the reservoir formation, the remaining parts of the maps show a weak strength of VTI anisotropy. © 2011 Sociedade Brasileira de Geofísica. Source

de Souza Garcia L.,Coordenacao da Area de Geofisica | Martins J.L.,Coordenacao da Area de Geofisica | de Oliveira J.S.,Coordenacao da Area de Geofisica
Revista Brasileira de Geofisica | Year: 2014

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. © Sociedade Brasileira de Geofísica. Source

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