Borehole Carbon Corrections Enable Accurate TOC Determination from Nuclear Spectroscopy
- Jeffrey Miles (Schlumberger) | Rob Badry (Schlumberger)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- June 2014
- Document Type
- Journal Paper
- 219 - 228
- 2014. Society of Petrophysicists & Well Log Analysts
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- 300 since 2007
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The modern combination of inelastic and capture spectroscopy enables the standalone measurement of total organic carbon (TOC). The use of oil-based mud presents a challenge in that the carbon in the borehole must be accurately resolved from the organic carbon of the reservoir. Previous publications demonstrated the accuracy of TOC in multiple oil-based mud examples; in these cases, the boreholes were in good condition and a constant correction for borehole carbon produced good results. However, the correction is sensitive to variations in borehole size, borehole shape, and other environmental effects.
Monte Carlo modeling is a valuable technique for understanding the measurement sensitivity to elements in the borehole. Unfortunately, the mud composition in the field is rarely known with enough accuracy to allow a pure modeled correction. In this paper, we describe a better solution in which modeling is combined with in situ empirical data to customize a correction for each well. The method is automated in software to provide a robust correction that varies level-by-level according to environmental conditions. The most pressing application is to correct the TOC measurement when hydrocarbons are present in the borehole, but the method is theoretically applicable to any mineral element in the borehole.
We demonstrate the performance of the self-calibrating borehole correction in four wells drilled with oil- and water-based muds. Core and cuttings measurements show that the new correction is essential for obtaining an accurate log of formation TOC when the borehole contains organic carbon and has variable size.
|File Size||603 KB||Number of Pages||10|