Geophysical Prospecting doi: 10.1111/j.1365-2478.2012.01073.x Rock physics interpretation of heterogeneous and anisotropic turbidite reservoirs Pavel Golikov, 1∗ Per Avseth 2 , Alexey Stovas 1 and Ran Bachrach 3 1 Department of Petroleum Engineering and Applied Geophysics, NTNU S.P.Andersens vei 15A, 7491 Trondheim, Norway 2 Odin Petroleum, Bergen, Norway. 3 Tel Aviv University, Tel Aviv, Israel Received June 2011, revision accepted February 2012 ABSTRACT In this paper, we create rock physics templates for heterogeneous and anisotropic thin- bedded sand-shale intervals as a function of group angle, net-to-gross, saturation and porosity as variable parameters. These templates are basically cross-plots of acoustic impedance versus P- to S-velocity ratio. We apply these templates to interpret well log data from a vertical and a deviated well, respectively, in a North Sea turbidite system. We are able to infer the shale anisotropic elastic moduli and Thomsen parameters by comparing the measured velocities in a deviated well with the velocities in an adjacent vertical well. Our modeling captures the observed trends in the data as we go from a vertical well to a deviated well through a heterogeneous reservoir saturated with light oil and water. We can clearly see how the reservoir properties changes due to the presence of anisotropy. We also perform an AVO sensitivity study as a function of heterogeneity and hydrocarbon saturation. Key words: Modeling, Reservoir characterization, Rock physics. INTRODUCTION Shale anisotropy is important to consider during rock physics analysis and/or correction of well log data from deviated wells or in areas with dipping stratigraphy. It is also important during amplitude variations with offset (AVO) analysis, as both cap-rock shales and heterogeneous reservoir rocks can be anisotropic. The sonic velocity measurement from the wells with dif- ferent inclinations gives powerful tool for rock formation anisotropy quantification. One of the earliest observations of shale anisotropy from the well-logs and comparison with surface seismic was done in Banik (1984). He found that the reflection depth anomalies in the North Sea reservoirs were observed due to the presence of anisotropic shales above the target reflection. Nowadays, anisotropy quantification from the well-log data is a common practice (Walsh et al. 2007; Bre- ∗ E-mail: pavel.golikov@ntnu.no vik et al. 2007) and it provides a good link between laboratory core measurements (Sondergeld and Rai 2011), geomechanics (Dewhurst et al. 2011) and surface seismic (Tsvankin et al. 2010). Despite the fact that the well-log measurement provides the information about rock properties, very often it is not easy to interpret the well-logs. In this case, the rock physics templates (Ødegaard and Avseth 2004) can help. The well-log data plotted on the crossplot acoustic impedance versus P- to S-velocity ratio can be divided into the clusters corresponding to different rock formations. The model trends added to the rock physics templates is a powerful tool for elastic properties inversion and interpretation. More detailed background about the rock physics templates is presented by Avseth et al. (2005). In this paper, we create rock physics templates for het- erogeneous and anisotropic thin-bedded sand-shale intervals. We believe that this sand-shale mix can be assumed as a model for vertically heterogeneous turbidite reservoir. We cre- ate template models as a function of group angle, net-to-gross ratio, fluid saturation and porosity as variable parameters, C  2012 European Association of Geoscientists & Engineers 1