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AAPG Southwest Section Annual Convention

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Assessing Organic Richness of Source Rocks through Integration of Microresistivity Images and Acoustic Logs

Abstract

Accurate evaluation of source rock thickness and organic richness are key components to estimating the hydrocarbon potential of a basin and identifying target zones in self-sourcing shale plays. The millimeter-scale variability in mineralogy and organic matter concentrations in source rocks can make petrophysical quantification problematic when relying on the resolution of standard well logs. Integrating microresistivity images with other well log data can improve bed-boundary definition while generating more meaningful information than their separate results. Previous research has shown that organic-rich sediments have higher electrical resistivity and acoustic slowness than organic-lean source rocks. Petrophysical methods have been developed that successfully use these anomalous properties to assess organic richness. Our method differs from previous methods by using oriented microresistivity images composed of 176 circumferential resistivity measurements that provide a 360° high-resolution picture of the borehole wall. The calibrated resistivity image data are transformed with respect to the acoustic slowness data through multilinear regression to generate a synthesized image. Additional processing is performed on the acoustic data to improve vertical resolution prior to this transformation process. A final oriented image is generated from the difference between the transformed image and enhanced acoustic slowness to highlight zones of excess resistivity and reveal anomalous properties related to organic richness. In this presentation, the validity of the method is assessed by comparing the results with standard well log -derived solutions for total organic carbon. Excellent correlation between the image results and petrophysical solutions is observed. Comparison to laboratory results is ongoing.