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Investigating the impact of stress & chemistry on fracture permeability for EGS development, using hydro-mechanical and hydro-chemical models, experimentation, and upscaling approaches. Includes data on fluid flow, friction experiments, and modeling fractured limestone. This project, led by Derek Elsworth at Penn State University, aims to enhance understanding of flow connections in critically stressed fractures through thermal, hydraulic, mechanical, and chemical processes. Results from experiments in hydro-mechanical and hydro-chemical reactors are discussed, along with numerical modeling for simulating permeability changes from hydraulic and chemical stimulation. The study's importance, challenges, and potential isotopic linkages are highlighted, with projections for future findings and publications.
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Stress- and Chemistry-Mediated Permeability Enhancement/Degradation in Stimulated Critically-Stressed Fractures DE-FG36-04GO14289, M001 October 1, 2004 – December 31, 2007 (3 years) Derek Elsworth, Penn State University, PI Avrami Grader (EGEE, PSU) Chris Marone (Geosciences, PSU) Phillip Halleck (EGEE, PSU), & Peter Rose, EGI, University of Utah
Purpose • Towards the engineering of “EGS”: • Long-lived • Low-impedance • High heat flow • Consistent understanding of the evolution of flow connections resulting from stimulation • Physical (effective stresses) • Chemical (dissolution/precipitation) • Critical influences of: • Mechanical Influences [THM] • Chemical Influences [THC] • Importance where fractures are “critically stressed” • Resolve anomalous observations THMC
Objectives “… a consistent view of the thermal, hydraulic, mechanical, and chemical processes that influence permeability enhancement….and to be able to apply these principles to EGS reservoir development.” Hydro-Mechanical Hydro-Chemical Constitutive Models Modeling/Upscaling
Plan and Approach Hydro-Mechanical Hydro-Chemical Constitutive Models Modeling/Upscaling
Qmass X-ray CT Qfluid=Constant Apparatus
Typical Response [Polak et al., GRL, 2003]
Slide-Hold-Slide Friction Experiments • Hold periods of 30 – 104 [sec] @20 degree-C, peak coefficient is independent of hold periods @65 degree-C, peak value increases with increase of hold period
Results • Hydro-Chemical Reactor • Hydro-Mechanical Reactor • Modeling
Fractured Limestone – Features of Response (predate this project) 0 hr 1462 hr 0 hr 1462 hr
Thresholded three-dimensional image of the fracture
Three-dimensional image of the large openings of the fracture
Three-dimensional combined image of the large aperture openings and the linking smaller apertures within the core.
3. Transport and Mechanical Modeling • Goal: • Construct a numerical model to simulate permeability enhancement caused by hydraulic and chemical stimulation – ultimately apply to stimulation at Coso • FLAC3D→ [High Peclet Number Flows] → ToughReact • → Fist step; Focus on a behavior of a single fracture • ─ Mass transport within a fracture • ─ Solve an advection-dispersion equation, complete with a reactive term • ─ FEM, FDM • ─ Accommodate a problem with high Peclet number (advection dominant)
Advection-dispersion equation with high Peclet number A Lagrangian-Eulerian Method Continuous injection
Replicate experimental result (Nova II) 1. Set initial aperture distribution 2. Apply I.C. and B.C. → Obtain velocity distr. in a fracture by solving Reynolds’ equation 3. Dissolution at contact area and free-face (reaction) → Obtain concentration distribution + Modify aperture distribution due to dissolution Iteration 4. Lagrangian-Eulerian method (Advection-diffusion) → Obtain concentration distribution within and out of domain
Replicate experimental result (Nova II) • Numerical model is capable of replicating experiment though prescribed multiplier for dissolution rate constant is relatively large. • Another mechanism instead of pressure solution may be active (mechanical creep?).
Replicate experimental result (Nova II) <Aperture and contact area distribution (after experiment)> CT image Model prediction The model cannot perfectly represent experiment, but predict changes in aperture and contact area distribution with time
Impact/Merit • Project recently initiated • Providing meager data/information that are not well understood, and linking with improved understanding • Stress- and chemistry-mediated influences are potent • High temperatures where few data exist • Current understanding lacking • Linkages and Dissemination • Closely tied to EGI parallel study incl. personnel transfer • Potential isotopic linkages for heat-flow areas (E. Sonnenthal) • Products • Elsworth, D., and Yasuhara, H. (2005) Short timescale chemo-mechanical effects and their influence on the transport properties of fractured rock. Submitted for publication. Earth and Planetary Research Letters. 40 pp. • GRC Meeting September
