Abstract: Accurate Reservoir Evaluation from Borehole Imaging Techniques and Thin Bed Log Analysis: Case Studies in Shaly Sands and Complex Lithologies in Lower Eocene Sands, Block III, Lake Maracaibo, Venezuela

Carolina Coll, Luis Rondon

Computer-aided signal processing in combination with different types of quantitative log evaluation techniques is very useful for predicting reservoir quality in complex lithologies and will help to increase the confidence level to complete and produce a reservoir.

The Lower Eocene Sands in Block III are one of the largest reservoirs in Block III and it has produced light oil since 1960. Analysis of Borehole Images shows the reservoir heterogeneity by the presence of massive sands with very few shale laminations and thinnly bedded sands with a lot of laminations. The effect of these shales is a low resistivity that has been interpreted in most of the cases as water bearing sands. A reduction of the porosity due to diagenetic processes has produced a high-resistivity behaviour.

The presence of bed boundaries and shales is detected by the microconductivity curves of the Borehole Imaging Tools allowing the estimation of the percentage of shale on these sands. Interactive computer-aided analysis and various image processing techniques are used to aid in log interpretation for estimating formation properties. Integration between these results, core information and production data was used for evaluating producibility of the reservoirs and to predict reservoir quality. A new estimation of the net pay thickness using this new technique is presented with the consequent improvement on the expectation of additional recovery. This methodology was successfully applied in a case by case study showing consistency in the area.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela