Using Micro-Resistivity Imaging and Elemental Analysis Data to Identify Thin Organic-Rich Beds in the Williston Basin, North Dakota
- Treasure Bailley (Halliburton) | Robert Denton (Halliburton) | Flemming Mengel (Anschutz Exploration Corporation)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 56th Annual Logging Symposium, 18-22 July, Long Beach, California, USA
- Publication Date
- Document Type
- Conference Paper
- 2015. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
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Ordovician G. prisca kukersites provide a potential source for the Red River oil in the Williston basin of North Dakota; consequently, the identification of these intervals can be critical when planning completions. Although kukersites are very organic-rich [total organic content (TOC) up to 59% in the literature], identification of these beds using standard openhole logs is hindered because the kukersites generally occur only as thin laminae or beds of less than 1-ft thickness. This is well below the vertical resolution of most openhole tools. With a vertical resolution of approximately 0.10 in., microresistivity imaging tools can detect thin organic-rich beds; however resistivity alone cannot be used to accurately distinguish between an organic-rich bed and other resistive beds such as anhydrite.
Published literature suggests algal blooms associated with kukersite deposition would have slowed or stopped carbonate sedimentation; consequently, the first step in the identification of kukersites is to use microresistivity image data to identify thin beds or laminae with high resistivity in dolomitic intervals. After these initial candidates are identified, triple combination data is examined to rule out lithologies with similar resistivities but strong identifying signals, such as anhydrite, to reduce the number of potential kukersite candidates to approximately 20 beds. An elemental analysis tool was used to further investigate the likelihood the beds identified were kukersite. An Estonian study showed kukersites to contain approximately 1.5% total sulfur. Therefore, sulfur was used when solving for kerogen with the elemental analysis within the Red River Formation. When solving in this manner, the kerogen signals in the elemental analysis were found to correspond closely with many of the possible kukersites identified in the image data. Kukersite-rich intervals are likely to be found where the potentially organic-rich thin beds identified in both tools overlap. Sidewall cores collected in these intervals appear to have the same visual characteristics as kukersites described in published literature; however, the full analysis of these cores have not yet been completed.
This case study demonstrates how solutions to difficult problems can be provided by using an interdisciplinary approach that incorporates all available data as well as a fundamental knowledge of the geologic environment in which the problem exists.
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