The rock samples (cores and cuttings) that have and that will be collected during the drilling and stimulation of wells at Utah FORGE are available for research purposes. These samples will be preserved and made available to the R&D community upon request via a dedicated portal on the Utah FORGE website. We anticipate that fluid samples that are obtained during well testing and flow back experiments will be available as well. This document provides an overview of the samples, and also of the Salt Lake City archive facilities where the research community can study and collect samples for detailed study. Note, small quantities of drill cuttings and cores are accessible through the online web portal. The figures and data shown below are summaries abstracted from the Phase 2B and Phase 2C reports which are available on line from the Geothermal Data Repository.
Drill Cuttings and Core Samples
Drill cuttings were routinely sampled at 3 m (10 ft) intervals in all wells drilled in Phases 2B and 2C (i.e., wells 58-32, 68-32, and 78-32; In addition, 22 feet of oriented drill core was obtained from two depth intervals in granitoid reservoir rocks in well 58-32. Mud logs prepared by wellsite geologists describe the rock types and stratigraphy encountered during drilling. Cuttings samples are being curated for storage and preservation at the EGI Sample Library where they have been washed (as needed), dried, and stored in labeled envelopes/bags (well name & depth).
Chipboards of wells 58-32, 68-32, and 78-32, showing changes in lithology, analyzed samples (yellow filled circles), top of basement contact, and the EGS reservoir. The sedimentary strata forming basin fill that overlies the basement contact consists of poorly sorted and poorly lithified alluvial material, whereas the basement consists equigranular plutonic rocks predominantly made of granite and diorite.
Supplementary information about the rock-forming minerals, hydrothermal alteration, and open-space fillings is provided by laboratory thin section and XRD analyses of samples of cuttings taken at minimum of 100-foot intervals within the granitoid and multiple samples from the ~22 ft of drill core. Drill core tests comprise triaxial shear strength, Brazilian and fracture toughness, and permeability/porosity measurements. All of these results have been published on GDR. These same sampling and analytical protocols will be applied to all the new rock materials obtained from drilling wells in Phase 3, including the two deep wells, plus the wells required for seismic and groundwater monitoring. The full range of analyses and tests are summarized below.
Based on thin section and X-ray diffraction analyses of cuttings and cores, the mineralogy of the basement plutonic crystalline rocks is predominantly made of plagioclase, K-feldspar, and quartz, with minor amounts of biotite, hornblende, clinopyroxene, apatite, titanite, zircon, and magnetite-ilmenite. The proportions of minerals were used to classify the igneous rock types, which are made of light-colored granite to quartz monzonite and dark-colored diorite. Illite and chlorite are the main clay minerals, but they constitute <5% of the rock. Other secondary minerals include carbonate and anhydrite, and factures in the cored intervals are locally lined with chlorite or epidote, and overall the evidence for hydrothermal alteration is minimal. The interlocking inter-grown crystals contributes to the rock strength and exceedingly low porosity.
A significant collection of cuttings and core samples (list below) from legacy wells are available for study at the Utah Core Research Center (UCRC) at the Utah Geological Survey and the EGI Sample Library. These include cuttings from the Acord-1 well, which are housed at the UCRC, and cuttings and core from more than two dozen shallow to deep gradient and exploration wells, which are housed at the EGI Sample Library.Fluid Samples
Fluid samples of groundwaters from shallow aquifers have been collected, analyzed, and the results are published on GDR. Most of these samples come from shallow wells designed to monitor or produce water for surface activities (mainly farm-related) in the area surrounding the Utah FORGE site. The samples were collected during pump tests since the water table is several hundred feet below the ground surface. During the drilling of 78-32, shallow ground water samples were collected during an aquifer test of the basin fill aquifer.
All the groundwater samples have been analyzed for a range of aqueous species and isotopes, which require different types of pretreatment (e.g., filtering, acidification) and bottle types (e.g., polyethylene, glass) for storage and shipping to the analytical laboratories. Aliquots of samples are being preserved for the life of the project in refrigerators at the EGI Sample Library.
As the reservoir rocks contain to no recoverable/producible pore water, the only fluid samples that can be acquired during future operations will be those that are injected during stimulation or flow testing. These samples will be obtained once testing commences, and updates of their availability are subject to notification via the Utah FORGE website.
Facilities for Curation of FORGE Samples
Both the UCRC and the EGI Sample Library will be accessible to researchers investigating samples from the Utah FORGE site. The UCRC is under the control and supervision of the curator, Mr. Peter Nielsen, at the Utah Geological Survey, whereas the EGI Sample Library is under the supervision of Mr. David Langton. All work at the repositories will need to be reserved ahead of time to ensure the proposed work does not conflict with other commitments. All activities will be subject to the safety and core handling policies of the repositories. Retrieval of material from the shelves will be carried out by staff members. Core and cuttings that arrive at the repositories will be logged in upon arrival and entered into the respective databases. A listing of the samples and other supporting data including photographs and logs will be accessible to the public through the GDR.
An established schedule of fees will be charged for use of the facilities, including access to the internet, use of visitor’s office, staff time setting up for workshops or display material, pulling and returning sample boxes to shelves, and use of in-house equipment such as microscopes (petrographic, binocular), cameras that interface with the microscopes for high-resolution images (14 megapixel images). The maximum access costs will be capped at $6000 per year, and these will be billed directly to individual researchers. The $6000 is equivalent to 30 days of use per year at the standard rate of $200 per day. Additional, more intense work on core or cuttings, such as core slabbing and plugging will be separately charged to the project.
Rock and fluid samples can be requested via the sample request portal on the Utah FORGE website. We strive to ensure fair and equitable access to the samples and to provide priority to those groups funded by the project. Both non-destructive and destructive testing of samples are expected. Researchers requesting core materials will need to justify their request in their application for material. All methods and resulting analytical data must be reported to Utah FORGE in a timely manner, and workers are strongly encouraged to publish their data in peer reviewed journals. In all cases, interim reports may be required. All unused sample must be returned to the sample repository with a description of the testing that was conducted.
In most cases, aliquots of existing fluid samples can be obtained when requested by the researchers, but where circumstances require new fluid samples, permission for site access and scheduling are required. Strict protocols will be followed to maintain a safe environment and only authorized personnel will be permitted to collect the samples. Researchers will be required to provide their own correctly prepared sample vessels. Researchers who wish to participate in on site rock or fluid sampling will be required to complete on site safety training.