Integrated Sonic Study for Identification of Anisotropy Characterized by Effects of Natural Fractures and Horizontal In-Situ Stresses

The objective of this study is to identify acoustic anisotropy in a vertical well producing heavy oil through siliciclastic formations (Cretaceous turbidites). Several types of methods are available to analyze anisotropy in the borehole such as resistivity, sonic and seismic. In this study advanced sonic measurements such as compressional, shear and stoneley waves obtained through monopole and dipole sonic measurements, were used to quantify reservoir anisotropy. Advanced sonic anisotropic studies applied in wells to identify natural fractures and effects of horizontal in-situ stresses provide an exciting methodology which can be incorporated into reservoir characterization to aid in field development planning with aim to increase recovery factors. Advanced computational methods used for processing and sequential inversion of sonic waveforms were used to obtain the respective anisotropic indicators like monopole semblances, stoneley waveforms, energy differences in attenuated shear dipole waves, dispersion plots and fast shear wave direction. Results were compared with the anisotropic studies carried out in previous years in the same field. In addition, the sonic data were integrated during the final interpretation with processed and interpreted micro resistivity well image logs, showing good agreement and correlation. Understanding gained of the behavior of the natural fractures and horizontal in-situ stresses can be applied as a way forward into a coupled 4D geomechanical and dynamic model, with objective of quantifying e impact of anisotropic attributes on history matching and forecast.