Frictional properties of simulated shale-coal fault gouges: Implications for induced seismicity in source rocks below Europe's largest gas field

Liu, Jinfeng; Hunfeld, Luuk B.; Niemeijer, A. R.; Spiers, Christopher J.

doi:10.1016/j.coal.2020.103499

Cited by 2 publications

(3 citation statements)

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“…Pycnometric studies have shown that the volumetric density (ρ) of Tumlin sandstone is approximately 2.43 g/cm 3 with a porosity (n) not exceeding 8%. Uniaxial compression tests have shown that the compressive strength of this sandstone is in the order of 90 MPa, its Young's modulus is in the order of 24 MPa and the Poisson's ratio is in the order of 0.20.…”

Section: Test Subjectmentioning

confidence: 99%

“…One of these problems is the correct determination of the mechanical properties of rocks forming the rock mass from which natural gas is extracted. A good example of such studies were the results of research on the properties of rocks from the Groningen gas deposit, published in [3,4]. The facts cited above show that the extraction and storage of natural gas is still posing new and ever more complex problems, the solutions to which often require the employment of significant human and material resources.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Influence of Rate of Change in Confining and Pore Pressure on Values of the Modulus of Compressibility of the Rock Skeleton and Biot’s Coefficient

Nowakowski

2021

Energies

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This work discusses the results of a study of the influence of rates of change of confining pressure on the result of a drained compressibility tests intended to determine the modulus of compressibility of a rock skeleton Ks. A series of cyclical compressibility tests was performed on samples of sandstone soaked in kerosene, for various rates of compression and decompression of the pressure liquid filling the cell and the pore volume of the sample. The studies showed that the deformability of the tested sample was directly proportional to the rate of change of the confining pressure. As a consequence, the value of the Ks modulus and Biot coefficient α decreased with increasing sample load rate. This phenomenon should be attributed primarily to equilibration of the liquid pressure inside the high-pressure cell with the liquid pressure in the sample pore space, caused by filtration of the pore liquid. These phenomena prove that the filtration process impacts the values of the modulus of compressibility of the rock skeleton Ks and of Biot coefficient α determined on the basis of the experiment. This is significant in the context of the use of Biot equations as constitutive equations for a porous rock medium.

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Section: Test Subjectmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Influence of Rate of Change in Confining and Pore Pressure on Values of the Modulus of Compressibility of the Rock Skeleton and Biot’s Coefficient

Nowakowski

2021

Energies

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Frictional slip weakening and shear-enhanced crystallinity in simulated coal fault gouges at slow slip rates

et al. 2020

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Abstract. Previous studies show that organic-rich fault patches may play an important role in promoting unstable fault slip. However, the frictional properties of rock materials with nearly 100 % organic content, e.g., coal, and the controlling microscale mechanisms remain unclear. Here, we report seven velocity stepping (VS) experiments and one slide–hold–slide (SHS) friction experiment performed on simulated fault gouges prepared from bituminous coal collected from the upper Silesian Basin of Poland. These experiments were performed at 25–45 MPa effective normal stress and 100 ∘C, employing sliding velocities of 0.1–100 µm s−1 and using a conventional triaxial apparatus plus direct shear assembly. All samples showed marked slip-weakening behavior at shear displacements beyond ∼ 1–2 mm, from a peak friction coefficient approaching ∼0.5 to (nearly) steady-state values of ∼0.3, regardless of effective normal stress or whether vacuum-dry or flooded with distilled (DI) water at 15 MPa pore fluid pressure. Analysis of both unsheared and sheared samples by means of microstructural observation, micro-area X-ray diffraction (XRD) and Raman spectroscopy suggests that the marked slip-weakening behavior can be attributed to the development of R-, B- and Y-shear bands, with internal shear-enhanced coal crystallinity development. The SHS experiment performed showed a transient peak healing (restrengthening) effect that increased with the logarithm of hold time at a linearized rate of ∼0.006. We also determined the rate dependence of steady-state friction for all VS samples using a full rate and state friction approach. This showed a transition from velocity strengthening to velocity weakening at slip velocities >1 µm s−1 in the coal sample under vacuum-dry conditions but at >10 µm s−1 in coal samples exposed to DI water at 15 MPa pore pressure. The observed behavior may be controlled by competition between dilatant granular flow and compaction enhanced by the presence of water. Together with our previous work on the frictional properties of coal–shale mixtures, our results imply that the presence of a weak, coal-dominated patch on faults that cut or smear out coal seams may promote unstable, seismogenic slip behavior, though the importance of this in enhancing either induced or natural seismicity depends on local conditions.

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Frictional properties of simulated shale-coal fault gouges: Implications for induced seismicity in source rocks below Europe's largest gas field

Cited by 2 publications

References 58 publications

The Influence of Rate of Change in Confining and Pore Pressure on Values of the Modulus of Compressibility of the Rock Skeleton and Biot’s Coefficient

The Influence of Rate of Change in Confining and Pore Pressure on Values of the Modulus of Compressibility of the Rock Skeleton and Biot’s Coefficient

Frictional slip weakening and shear-enhanced crystallinity in simulated coal fault gouges at slow slip rates

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