Sampling and Interpretation of Drill Cuttings from Geothermal Wells

Hulen, Jeffrey B.; Sibbett, B.S.

doi:10.2172/897433

Cited by 4 publications

(6 citation statements)

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“…These factors are in turn controlled by drill bit type, rotation speed, weight-on-bit, and density and circulation rate of drilling fluid (Hulen and Sibbett, 1981). In non-vertical holes, cutting beds develop on the "hanging wall" of the borehole, and impacts to the beds from other cuttings result in increased disaggregation (Bar-Cohen and Zachny, 2009).…”

Section: Mixing Of Drill Cuttingsmentioning

confidence: 99%

“…Drill cuttings concentrate more resistant alteration mineral phases, which more readily survive grain impacts and more rigorous drilling parameters (Hulen and Sibbett, 1981).…”

Section: Implications Of Drill Cutting Preservation Bias For Inferrinmentioning

confidence: 99%

“…Less resistant alteration minerals are easily disaggregated and lost from cuttings during sample washing and collection (Hulen and Sibbett, 1981 (Lonker et al, 1993), and significantly contribute to LOI due to the structural hydroxyls. While there are no available analyses of Zn in Reykjanes chlorite or actinolite, Zn is known to rarely substitute into the chlorite and actinolite structures (Deer et al, 1992).…”

Section: Q15mentioning

confidence: 99%

“…An alternate Cr source is potential contamination by Cr-rich steel alloys, which are commonly used in drill bits, stabilizers, and drill collars (Hulen and Sibbett, 1981).…”

Section: Contamination By Drilling Equipmentmentioning

confidence: 99%

“…An explanation for these anomalous concentrations is contamination from down hole drilling equipment. Non-magnetic drill collars used to apply weight on bit are manufactured from Ni-Cu alloys (Hulen and Sibbett, 1981). Ta and Nb contamination potentially results from grinding samples in a tungsten carbide ring mill (Hickson and Juras, 1986).…”

Section: Contamination By Drilling Equipmentmentioning

confidence: 99%

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Geochemical bias in drill cutting samples versus drill core samples returned from the Reykjanes Geothermal System, Iceland

Fowler

Zierenberg

2016

Geothermics

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a b s t r a c tThe wholerock major and trace element composition of drill cutting samples are compared to drill core samples from adjacent depths in the seawater recharged Reykjanes geothermal system in Iceland. The first appearance of alteration minerals and lithologies in drill cutting samples is a useful tool for interpreting broad subsurface characteristics. However, use of drill cutting samples for determining igneous affinity and elemental exchanges during hydrothermal alteration is problematic. Samples recovered from immediately above and below the cored intervals in wells RN-17B and RN-30 demonstrate that drillcutting samples are biased towards preservation of least altered primary igneous minerals and more resistant alteration minerals, including albite, quartz, and epidote, with preferential loss of finer-grained and less resistant minerals including chlorite and actinolite. This selective recovery obscures elemental exchanges resulting from hydrothermal alteration processes. For some elements, compositional variations (enrichments and depletions) measured from 9.5 m of core exceeds that observed in ∼3000 m of cutting analyses. Concentration ratios of hydrothermally immobile elements including Zr, Nb, V, Y, HREE, Hf, Ta and Th in deep (>2245 m) spot drill core samples record bimodal, trace element-enriched and trace element-depleted precursor compositions similar to subaerial Reykjanes Peninsula basalts. The same elements in nearly 3000 m of drill cutting samples from well RN-17 overwhelmingly reflect the more common trace element-enriched igneous precursor, demonstrating that mixing of drill cutting samples obscures details of their igneous affinity. A new and different drill rig was used to deepen well RN-17 below 2266 m in a sidetrack hole (RN-17ST), which resulted in a change in drilling conditions, accompanied with an increased well deviation angle from ∼0• to ∼4• . Wholerock geochemical results for drill cutting samples from RN-17ST are homogenous for virtually every element; suggesting the change in drilling conditions resulted in extreme mixing of the drill cuttings. Anomalously high concentrations of Cu, Ni, Cr and Ta in some drill cutting samples likely reflects contamination of drill cutting samples by metal alloys used in drill bits and drill collars or more resistant spinel and sulfide phases.

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Section: Mixing Of Drill Cuttingsmentioning

confidence: 99%

“…Drill cuttings concentrate more resistant alteration mineral phases, which more readily survive grain impacts and more rigorous drilling parameters (Hulen and Sibbett, 1981).…”

Section: Implications Of Drill Cutting Preservation Bias For Inferrinmentioning

confidence: 99%

Section: Q15mentioning

confidence: 99%

“…An alternate Cr source is potential contamination by Cr-rich steel alloys, which are commonly used in drill bits, stabilizers, and drill collars (Hulen and Sibbett, 1981).…”

Section: Contamination By Drilling Equipmentmentioning

confidence: 99%

Section: Contamination By Drilling Equipmentmentioning

confidence: 99%

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