The primary Task E objective is to predict and quantify the importance of coupled THMC processes relating to the availability of heating, mechanical deformation, and water to flow into heated excavations in bedded salt. Increased brine flow from and through salt occurs due to increased porosity and permeability in the excavation damaged zone around room and borehole excavations (Kuhlman, 2020).
The task begins with historical unheated brine inflow data from boreholes drilled in bedded salt at the Waste Isolation Pilot Plant (WIPP), near Carlsbad New Mexico (USA). The task includes temperature, brine production, tracer transport, and composition data collected at WIPP as part of the ongoing Brine Availability Test in Salt (BATS), see Figure 1 (Kuhlman et al., 2020). In BATS, two similar arrays of horizontal boreholes (heated and unheated) in salt are monitored for temperature, electrical resistivity tomography, fiber-optic distributed strain and temperature, acoustic emissions, liquid brine samples, and cement/salt/brine interactions. Each array has a central borehole where borehole closure is monitored and N2 gas is circulated behind a packer to remove water flowing into the borehole. The gas stream coming off the central borehole is monitored in drift for gas composition; water isotope composition; and humidity, temperature, and pressure.
The focus on brine availability includes estimating two aspects of the salt:
1)The amount, type, and distribution of water in the salt
2)The pathways (i.e., porosity and permeability) that allow the water to flow to the central borehole, and their evolution during the tests.
The task is structured into four steps of increasing complexity and coupling between processes. During all the steps there is an interest in uncertainty quantification and sensitivity analysis. Step 0 begins with benchmark exercises, using unheated historical brine inflow data and heat conduction data from the first phase of the BATS test (January to March 2020; Figure 2). Step 1 increases the complexity of benchmarking, matching numerical models against an analytical solution for flow to a well driven by temperature and pressure gradients. The two-phase flow properties of salt (needed for the next step) are also considered explicitly in step 1. Step 2 then attempts to match numerical models to the possibly two-phase thermal-hydraulic-mechanical response of the BATS system, predicting brine inflow and tracer test data. One of the responses we hope to consider is the significant increase in brine flow at the end of heating (i.e., during cool-down). The final step includes additional advanced chemical process (i.e., cement/salt/brine interactions in seals, water isotopes, and evaporite mineral speciation) coupling or joint inversion of geophysical data (acoustic emissions and electrical resistivity tomography) with the brine production and temperature data.
Task E has participation from a US team (comprised of members form SNL, LANL, and LBNL), a German team (comprised of members from BGR and GRS), a Dutch team (COVRA), and a UK team (comprised of members from RWM and Quintessa).
For further information, please contact the task leader, Kristopher L. Kuhlman.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This is SAND2020-8776 O.