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Title: Interpretation of drill cuttings from geothermal wells

Abstract

Problems in interpreting drill cuttings, as opposed to drill cores, and methods to solve these problems are outlined. The following are covered: identification of lithology; recognition of faults and fractures; interpretation of hydrothermal alteration; geochemistry; sample collection; sample preparple examination; and sample storage. (MHR)

Authors:
;
Publication Date:
Research Org.:
Utah Univ., Salt Lake City (USA). Research Inst.
OSTI Identifier:
5776354
Report Number(s):
DOE/ID/12079-36; ESL-57
ON: DE82003947
DOE Contract Number:
AC07-79ID12079
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
15 GEOTHERMAL ENERGY; DRILL CORES; DATA ANALYSIS; GEOTHERMAL WELLS; GEOCHEMISTRY; GEOLOGIC FAULTS; GEOLOGIC FISSURES; HYDROTHERMAL ALTERATION; LITHOLOGY; SAMPLE PREPARATION; SAMPLING; CHEMISTRY; GEOLOGIC STRUCTURES; WELLS; Geothermal Legacy; 150303* - Geothermal Exploration & Exploration Technology- Exploratory Drilling & Well Logging

Citation Formats

Hulen, J.B., and Sibbett, B.S. Interpretation of drill cuttings from geothermal wells. United States: N. p., 1981. Web. doi:10.2172/5776354.
Hulen, J.B., & Sibbett, B.S. Interpretation of drill cuttings from geothermal wells. United States. doi:10.2172/5776354.
Hulen, J.B., and Sibbett, B.S. Mon . "Interpretation of drill cuttings from geothermal wells". United States. doi:10.2172/5776354. https://www.osti.gov/servlets/purl/5776354.
@article{osti_5776354,
title = {Interpretation of drill cuttings from geothermal wells},
author = {Hulen, J.B. and Sibbett, B.S.},
abstractNote = {Problems in interpreting drill cuttings, as opposed to drill cores, and methods to solve these problems are outlined. The following are covered: identification of lithology; recognition of faults and fractures; interpretation of hydrothermal alteration; geochemistry; sample collection; sample preparple examination; and sample storage. (MHR)},
doi = {10.2172/5776354},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jun 01 00:00:00 EDT 1981},
month = {Mon Jun 01 00:00:00 EDT 1981}
}

Technical Report:

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  • Drill cuttings from geothermal and mineral exploration boreholes, by contrast with those from most petroleum wells, commonly are derived highly fractured and faulted, hydrothermally altered igneous and metamorphic rock sequences, and are likely to be severely contaminated. Characterization of a subsurface resource from cuttings thus requires not only especially careful sample collection, preparation, storage and examination, but also a thorough knowledge of drilling technology, local geology and the full range of potential borehole contaminants. Accurate identification of lithology from cuttings is critical for recognition and correlation of rock types likely to selectively host the desired commodity. However, many of themore » rocks encountered in geothermal and mineral exploration boreholes (such as gneisses and granitic rocks) can resemble one another closely as cuttings even though dissimilar in outcrop or core. In such cases, the actual rock type(s) in a cuttings sample generally can be determined by comparison with simulated cuttings of representative surface rocks, and with various geophysical and other well logs. Many other clues in cuttings, such as diagnostic metamorphic mineralogy, or sedimentary rounding and sorting, may help identify subsurface lithologies. Faults and fractures commonly are the dominant physical controls on geothermal and mineral resources. Faults occasionally can be recognized directly in cuttings by the presence of slickensiding, gouge, or other crushed material. More commonly, however, the ''gouge'' observed in cuttings actually is pseudo-gouge created beneath a bit during drilling. Since most faults and all fractures produce no direct evidence apparent in cuttings, they are best recognized indirectly, either by commonly associated hydrothermal alteration, or by responses on appropriate geophysical well logs. Hydrothermal alteration, useful for locating and defining a geothermal or mineral resource, is far more difficult to recognize and interpret in cuttings than in core or outcrop. Alteration textures and paragenetic relationships can be obscured or obliterated as cuttings are produced. Less resistant alteration (and rock-forming) minerals can be disaggregated during drilling and lost from cuttings during sampling or washing. Relict and contemporary alteration can be indistinguishable, and a wide variety of borehole contaminants can closely resemble natural alteration products encountered during drilling. These contaminants also can produce confusing geochemical signatures.« less
  • This compendium lists the repositories holding geothermal core and well cuttings from US government-sponsored geothermal wells. Also, a partial listing of cores and cutting from these wells is tabulated, along with referenced reports and location maps. These samples are available to the public for research investigations and studies, usually following submission of an appropriate request for use of the samples. The purpose of this compilation is to serve as a possible source of cores and cuttings that might aid in enhancing rock property studies in support of geothermal log interpretation.
  • Test hole USW UZ-13 is the fourth of a series of shallow unsaturated-zone test holes drilled in and near the southwestern part of the Nevada Test Site, Nye County, Nevada, in cooperation with the US Department of Energy. All of these test holes are a part of the Yucca Mountain Project to identify the suitability of the site for the underground storage of high-level radioactive wastes. This report contains a description of the methods used in drilling and coring of test hole USW UZ-13; a description of the methods used in the collecting, handling, and testing of test-hole samples; lithologicmore » information from the test hole; and water-content, water-potential, bulk-density and grain-density data for the test hole. 14 refs., 5 figs., 10 tabs.« less
  • The objective of this study was to develop a method of converting drill cuttings from gas shale wells into high strength proppants via flame spheroidization and devitrification processing. Conversion of drill cuttings to spherical particles was only possible for small particle sizes (< 53 {micro}m) using a flame former after a homogenizing melting step. This size limitation is likely to be impractical for application as conventional proppants due to particle packing characteristics. In an attempt to overcome the particle size limitation, sodium and calcium were added to the drill cuttings to act as fluxes during the spheroidization process. However, themore » flame former remained unable to form spheres from the fluxed material at the relatively large diameters (0.5 - 2 mm) targeted for proppants. For future work, the flame former could be modified to operate at higher temperature or longer residence time in order to produce larger, spherical materials. Post spheroidization heat treatments should be investigated to tailor the final phase assemblage for high strength and sufficient chemical durability.« less