Novel System and Method for Cryogenic Core Collection (C3)
Figure 1. Drilling and sampling sequence
At A Glance
Researchers at Colorado State University have developed a patented system and method for soil core collection that enables practical in situ cryogenic freezing to capture material that is otherwise lost in traditional methods of soil coring. The approach is referred to as C3, ″cryogenic core collection”.
Critical elements associated with the C3 method include the use of (1) HSA drilling techniques, (2) liquid nitrogen as the cryogenic coolant, (3) insulation to focus cooling into the core, and (4) core collection systems that can freeze sediments below the auger cutting head, thereby reducing the likelihood of flowing sand.
The effectiveness of the C3 method in preserving the distribution of pore contents (i.e., water, LNAPL, and gases) both above and below the water table has been successfully tested and evaluated on frozen cores collected from various contaminated field sites.
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Reference No.: 16-021
Collection of cores from unconsolidated subsurface media is common to many disciplines, including geotechnical engineering, mining, and subsurface remediation. Common approaches include hollow-stem auger (HSA) and direct push (DP) drilling techniques. Successful core collection requires effective recovery of sediment core from the targeted interval and preservation of the critical core attributes, including contaminant concentrations, fluid saturations, hydraulic conductivity, and biogeochemical conditions.
Collection of high-quality sediment cores can be challenging. This is particularly true for saturated, cohesionless sediments (e.g., sands and gravels) as these commonly fall out of coring systems during withdrawal of the core from the borehole. A common remedy for losses during core withdrawal is to place a “catcher” at the base of the coring system; unfortunately, catchers can be ineffective in preventing losses.
A second challenge in saturated cohesionless sediments (i.e., below the water table) is “flowing sand.” During withdrawal of coring tools to the surface, unbalanced stresses can lead to flow of sediments and fluids into the HSAs, which can compromise the quality of cores from deeper intervals. Fluids (e.g., drilling mud) can be added to coring systems to control flowing sediments; however, addition of fluids can be complicated and may compromise critical attributes of cores.
Lastly, during core withdrawal and post recovery, pore fluids commonly drain from cores and are replaced by atmospheric gases. Loss of pore fluids and invasion of atmospheric gases can bias (1) estimates of fluid saturations (i.e., water, nonaqueous phase liquid [NAPL], and gas), (2) estimates of contaminant concentrations (due to losses of pore fluids and volatile compounds), (3) analyses of reactive minerals, and (4) evaluations of microbial ecology.
The limitations of core collection using conventional HSA and DP drilling techniques have led to the exploration of alternatives.
- Utilization of liquid nitrogen reduces freeze times (and limits downhole locking/entrapment of sample/drill system)
- Novel design limits cooling losses (e.g., insulated conductor lines, dual wall barrel, etc.)
- Continuous contact between cooling system and the soil sample
- Able to collect flowing sands and sediments that traditional methods cannot
- Characterization of sites in support of remediation
- Conventional Geotechnical soil studies
- Quantifying sand and gravel resources
- Sampling of sediment below water
Kiaalhosseini, Saeed, et al. “Magnetic Resonance Imaging of Nonaqueous Phase Liquid Distribution in Unconsolidated Soils Using Discriminatory Freezing.” National Groundwater Association, John Wiley & Sons, Ltd, 1 Apr. 2019, ngwa.onlinelibrary.wiley.com/doi/abs/10.1111/gwmr.12323.
Kiaalhosseini, Saeed, et al. “Cryogenic Core Collection (C3) from Unconsolidated Subsurface Media.” National Groundwater Association, John Wiley & Sons, Ltd, 11 Nov. 2016, ngwa.onlinelibrary.wiley.com/doi/abs/10.1111/gwmr.12186.
Sale, Tom, et al. “Third Generation (3G) Site Characterization: Cryogenic Core Collection and High Throughput Core Analysis – An Addendum to Basic Research Addressing Contaminants in Low Permeability Zones – A State of the Science Review.” Defense Technical Information Center, 2015, apps.dtic.mil/sti/citations/AD1022599.
Last updated: June 2021