Many contemporary hydrocarbon reservoirs are made of formations with widely and rapidly varying physical characteristics. Vertical resolution of logging measurements has become a critical parameter for evaluating these reservoirs. The dual detector compensated density log gives us today the most important measurement of rock porosity. The response of the compensated density log is dominated by the far detector, and thus the resulting vertical resolution is determined by the far detector spacing, which in most existing tools is between 1 and 1.5 ft. (In contrast, the near detector is usually spaced somewhat closer than 0.5 ft from the source.) In addition, statistical averaging, standard practice in the industry, further degrades the resolution. This means that beds thinner than about 2 ft cannot be properly evaluated. In this paper, we introduce a technique that utilizes a combination of the vertical information contained in the near detector response with the compensated response of the standard "spine-and-ribs" density. The resulting density log exhibits a vertical resolution of better than 6 in, while retaining the essential advantages of dual detector compensation. This technique is very different from deconvolution in that no assumption is made as to the expected bedding features, and no serious degradation in statistical uncertainty is introduced. Optimum results are obtained with data acquired at high depth sampling rate (0.lft). The technique has been successfully applied to a number of examples and demonstrates the potential of significant improvement in evaluating beds of thickness between 6 in and 2 ft. Comparisons with other high resolution measurements, such as the EPT electromagnetic propagation log and the Formation MicroScanner images, can demonstrate the validity of this technique.

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