Hydraulic Modeling of Induced and Propagated Fractures: Analysis of Flow and Pressure Data From Hydromechanical Experiments in the COSC-1 Deep Borehole in Crystalline Rock Near Åre, Sweden

Journal Article · Tue Nov 09 00:00:00 EST 2021 · Water Resources Research

DOI:https://doi.org/10.1029/2020wr029484· OSTI ID:1898887

Basirat, Farzad ^[1]; Tsang, Chin‐Fu ^[2]; Tatomir, Alexandru ^[1]; Guglielmi, Yves ^[3]; Dobson, Patrick ^[3]; Cook, Paul ^[3]; Dessirier, Benoit ^[4]; Juhlin, Christopher ^[1]; Niemi, Auli ^[1]

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1. Uppsala University (Sweden)
2. Uppsala University (Sweden); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
3. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
4. Stockholm University (Sweden)

To characterize the coupled hydromechanical behavior of rock fractures, the step-rate injection method for fracture in-situ properties (SIMFIP) was conducted with a specialized downhole probe developed by Guglielmi et.al. In June 2019, a field campaign was carried out near Åre, Sweden, where the SIMFIP probe was applied in the Collisional Orogeny in the Scandinavian Caledonides-1 scientific borehole to understand the dynamics of injection-induced fracture initiation, fracture opening, and shearing due to water injection-withdrawal in a borehole interval isolated by two packers. Three intervals were investigated at ~500 m depth: (a) an unfractured section (intact rock), (b) a section with non-conductive fractures, and (c) a section with hydraulically conductive fractures. Pressure, injection flow rate, and borehole wall displacement were simultaneously measured during the tests. In the present study, the geometry of the induced fracture and deformation of existing fractures at different time stages of the tests are determined based on a hydrologic model by using the measured pressure and flow data during each time stage of the experiment. A numerical model for the fluid flow within the fracture and the packed-off borehole interval is implemented within COMSOL Multiphysics. By matching model simulations with observed data for all three sections, estimates of the induced and propagated fractures' radius and aperture at successive time stages have been obtained in each case. We could also determine the non-linear relationship between fracture aperture and pressure for values above fracture opening pressures. The model results provide insights for the understanding of pressure-induced fracture initiation and propagation in crystalline rock.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: Geological Survey of Sweden; USDOE Office of Nuclear Energy (NE); Uppsala University
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1898887
• Journal Information: Water Resources Research, Journal Name: Water Resources Research Journal Issue: 11 Vol. 57; ISSN 0043-1397
• Publisher: American Geophysical Union (AGU)
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES