In thin bedded reservoirs high resolution borehole images are generally used to determine distribution of high quality, productive sands. Deep water Tertiary reservoirs of Krishna Godavari basin are generally very complex and heterogeneous, ranging from massive thick sands to highly laminated very thin sand/shale sequences with average bed thicknesses less than the vertical resolution of microresistivity-imaging tool. The image tool responds to the beds and features smaller than the vertical resolution but can not accurately determine laminar bed thickness which can be used as an integral part of lowresolution technique. In the absence of a well defined set of thin bed boundaries from image tools, an integrated of approach of forward modeling and inversion is also impractical for the accurate thin bed evaluation.A new approach of laminated shaly sand analysis is developed where laminar sand/shale estimation is based on generation of binary lithology on shale volume curve derived from micro-electrical resistivity. Formation beds as thin as the twice of the sampling interval can be generated through this technique in such a way that cumulative net sand fraction is restricted with integrated sand volume. Laminar shale volume from image tool calibrated to the LamCount core data has been considered to be the ground truth in the analysis. The volume of dispersed shale and the total and effective porosities of the laminar sand fraction are determined using a Thomas-Stieber volumetric approach. Water saturation is estimated from laminar sand-fraction resistivity derived from electrical anisotropy.Application of the methodology leads to an improved accuracy of reserve estimates and productivity predictions. Entire procedure is illustrated with an example of completely cored reservoir section. Results indicate that low resistive laminated reservoirs with very high shale fractions can be highly productive with reservoir quality equivalent or some times even better than massive thick beds.

Deep water Tertiary reservoirs of Krishna Godavari basin are generally very complex and heterogeneous, ranging from massive thick sands to highly laminated very thin sand/shale sequences beyond the vertical resolution of imaging tools. Verification of log-derived quantities in very thin reservoirs is frequently difficult because of bias and scatter introduced by non-uniform or incomplete plugging of the available over 750 meters of conventional cores. As laminar shale does not occupy or alter the intergranular sand porosity, the conventional way of validation of log derived porosity and water saturation with core data showing excellent correlation does not ensure the correctness of petrophysical evaluations. In this paper, it has been demonstrated that there are potential problems associated with the integration of petrophysical evaluation and core data. Sources of errors are mainly due to the use of different parametric systems viz. using of the terms shale volume and clay volume interchangeably and validating log derived shaliness with clay abundance from XRD core data. Shaliness derived from logs cannot be directly correlated with such core data because neither de-averaging of lithology on log analysis nor averaging of core data is possible for the effective core-log integration. Average hydrocarbon pore volume in laminated reservoirs is linearly related to the average cumulative net sand fraction or shaliness of the formation. Laminar sand porosity and water saturations are independent of shaliness or net sand. Excellent correlation of log derived deconvolved data sets like porosity and water saturation with core measurements does not validate the correctness of hydrocarbon pore volume estimation, which is linearly related to net sand. Accurate estimation of hydrocarbon pore volume requires an accurate calibration of laminar sand/shale volumes, which can be precisely validated only with lamcount data.

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