Mirror-like Surfaces (MSs) are ultra-polished fault surfaces widespread in carbonate seismic terrains, but their formation process is still debated. We deformed gouge samples from exposed fault surfaces hosted in bituminous dolostone rocks in a rotary shear apparatus (SHIVA) at seismic slip rates (1 m/s). By changing the water availability (water-pressurised and room-humidity conditions) and the organic matter/dolomite content (> 35%, dark gouge DG; < 30% bright gouge BG) we investigated the mechanical behaviour leading to MSs formation in fault gouges. We run tests at 15 MPa effective normal stress, 2 MPa confinement and 1 MPa pore pressure for the water-pressurised experiments and a total displacement of 0.13 m. Mirror-like fault surfaces were obtained in all successful experiments; mirrors were more developed under room-humidity conditions. Bituminous dolostones under room-humidity conditions had a slip neutral behaviour with a low friction (0.3). Bituminous dolostones under water-pressurised conditions showed a slip weakening behaviour with an initial peak effective friction μp = 0.65, followed by a drop to effective friction μss DG than in BG (i.e., μss of 0.25 vs 0.28). Future work will focus on the microstructural analysis of the experimental products and the investigation of the slip behaviour of bituminous dolostones at sub-seismic slip rates for a complete study of the slip behaviour spectra.
This publication results from work conducted under the national open access action at SHIVA (Slow to High Velocity Apparatus) - HP-HT laboratory of experimental Volcanology and Geophysics (INGV, Roma 1 section) supported by WP3 ILGE - MEET project, PNRR - EU Next Generation Europe program, MUR grant number D53C22001400005.
Here we report the raw data of the friction experiments carried out on basalt-built simulated faults defined by rock-on-rock contacts and powdered gouge. The experiments were specifically designed to investigate the role of fault microstructure on the frictional properties of basalts and the fault slip stability, and were conducted with the rotary-shear apparatus (SHIVA) and the biaxial deformation apparatus (BRAVA), hosted at the National Institute of Geophysics and Volcanology (INGV) in Rome.
Simulated faults were sheared at constant normal stress from 4 to 30 MPa. In SHIVA experiments, we deformed samples at constant slip velocity of 10 μm/s up to 56 mm net slip. In BRAVA tests we performed a sequence of velocity steps (0.1 to 300 μm/s), followed by slide-hold-slide tests (30-3000 s holds; V=10 μm/s slides).
Our main results highlight the frictionally strong nature of basalt faults and show opposite friction velocity dependence upon the velocity upsteps: while fault gouges exhibit velocity weakening behavior with increasing normal stress and sliding velocity, bare rock surfaces transition to velocity strengthening behavior as we approach higher slip velocities. The experiments setup and data are further described in the manuscript “Frictional properties of basalt experimental faults and implications for volcano-tectonic settings and geo-energy sites” to which these data are supplementary material.
To understand the physical mechanisms governing fluid-induced seismicity at field-scale fluid injection projects, we conducted fluid-induced fault slip experiments in the laboratory on critically stressed saw-cut sandstone samples with high permeability using different fluid pressurization rates. The data archived here acts as supplementary material to Wang et al. (2020; https://doi.org/10.1029/2019GL086627).Experiments were conducted at room temperature using a servo-hydraulic tri-axial deformation apparatus (MTS) equipped with a pore pressure system (Quizix pumps) at Experimental Rock Deformation Laboratory, GFZ. To investigate the correlation between fault slip and fluid pressure, we applied two different fluid injection schemes (hereafter tests “SC1” and “SC2”, respectively). ‘TestSC1’ refers to the fluid-induced fault slip experiment performed at fluid pressurization rate of 2 MPa/min while ‘TestSC2’ indicates the fluid-induced fault slip experiment performed at fluid pressurization rate of 0.5 MPa/min. The other boundary conditions for both experiments are similar. In addition, to simultaneously record acoustic emission (AE) events induced by artificial fault slip, 16 piezoelectric transducers (PZTs, resonance frequency ~1 MHz) contained in brass cases were directly mounted to the surface of samples, ensuring full azimuthal coverage for AE events. AE waveforms were amplified first by 40 dB using preamplifiers equipped with 100‐kHz high‐pass filters and then recorded at a sampling rate of 10 MHz with 16‐bit amplitude resolution. Each experiment lasted for about 4 hours. Throughout the experiment, mechanical data (measured by MTS) and hydraulic data (measured by Quizix pump) were all synchronously monitored with a sampling rate of 10 Hz whereas acoustic emission data were recorded with a sampling rate of 10 MHz. All results shown are recorded as a function of experimental time.The data are provided in tab-separated ASCII-Format (.txt). 2020-002_Wang-et-al_TestSC1.zip and 2020-002_Wang-et-al_TestSC2.zip are composed of 7 txt files and 8 txt files, respectively, as described below in Table 1. The first column represents time in second and the subsequent columns are indicated by the corresponding header at the first row. The second row indicates the unit for each column data. The raw data was processed with MATLAB. The algorithms we implemented include the moving average method, statistical regression and our developed MATLAB-based codes.
Pore pressure reduction in sandstone reservoirs generally leads to small elastic plus inelastic strains. These small strains (0.1 – 1.0% in total) may lead to surface subsidence and induced seismicity. In current geomechanical models, the inelastic component is usually neglected, though its contribution to stress-strain behaviour is poorly constrained.To help bridge this gap, we performed deviatoric and hydrostatic stress-cycling experiments on Slochteren sandstone samples from the seismogenic Groningen gas field in the Netherlands. We explored in-situ conditions of temperature (T = 100°C) and pore fluid chemistry, porosities of 13 to 26% and effective confining pressures (≤ 320 MPa) and differential stresses (≤ 135 MPa) covering and exceeding those relevant to producing fields. The findings of our work are outlined in the corresponding paper. The data presented here are the measured mechanical tabular data and microstructural data (stitched mosaic of backscatter electron images) provided as uncompressed jpg images. In addition, for one sample we include chemical element maps obtained through Electron Dispersive X-ray spectrometry (EDX).
Hydrocarbon or groundwater production from sandstone reservoirs can result in surface subsidence and induced seismicity. Subsidence results from combined elastic and inelastic compaction of the reservoir due to a change in the effective stress state upon fluid extraction. The magnitude of elastic compaction can be accurately described using poroelasticity theory. However inelastic or time-dependent compaction is poorly constrained. We use sandstones recovered by the field operator (NAM) from the Slochteren gas reservoir (Groningen, NE Netherlands) to study the importance of elastic versus inelastic deformation processes upon simulated pore pressure depletion. We conducted conventional triaxial tests under true in-situ conditions of pressure and temperature. To investigate the effect of applied differential stress (σ1 – σ3 = 0 - 50 MPa) and initial sample porosity (φi = 12 – 25%) on instantaneous and time-dependent inelastic deformation, we imposed multiple stages of axial loading and relaxation.The obtained data include:1) Mechanical data obtained in conventional triaxial compression experiments performed on reservoir sandstone. In these experiments, we imposed multiple stages of active loading, each followed by 24 hours of stress relaxation.2) Microstructural data obtained on undeformed and deformed samples.