Seyyedmaalek Momeni

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Experimental Investigation of Hydraulic Fracture Closure in a Porous Sandstone

Brice Tanguy Alphonse Lecampion, Guanyi Lu, Seyyedmaalek Momeni, Mohsen Talebkeikhah

Depending on the type of fracture propagation regime when the injection stops, the closure of the fracture may occur exactly after the injection ceases, in the case where the fracturing process is dominated by fracture energy, or the fracture propagate for a while due to the elastic energy stored in the rock, when fluid viscous dissipation dominates. In any cases, fluid losses in the surrounding porous media ultimately stops fracture growth and the fracture closes (on the proppant pack in practice). Some recent theoretical solutions have been reported for the recession and closure of a hydraulic fracture in the absence of proppant. These solutions are relevant in the context of micro hydraulic fracturing tests for in-situ stress determination. In this work, we report a laboratory hydraulic fracture experiments performed in sandstones with the aim to study experimentally fracture closure. In our experimental set-up, an extensive passive acoustic monitoring is performed and provide un-precedented spatio-temporal evolution of fracture development and closure.

Onepetro2022

Experimental investigation of hydraulic fracture growth in an anisotropic rock with pre-existing discontinuities under different propagation regimes

Brice Tanguy Alphonse Lecampion, Guanyi Lu, Seyyedmaalek Momeni

Laboratory experiments have been carried out to investigate the growth of hydraulic fracture (HF) in an anisotropic rock with pre-existing discontinuities such as bedding planes and veins. The experiments are designed in light of scaling relationships that enable investigation on the impact by the weak mechanical discontinuities on the HF growth under desired regimes (under either a toughness dominated or a lag-viscosity dominated regime based on the scaling analysis). According to our laboratory observations, planar HF growth is promoted in the experiments under the lag-viscosity regime, in which the radial HF is able to cross both the bedding planes and veins. In contrast, profound influence of the weak discontinuities is shown in the toughness dominated experiments, causing the HF to be diverted into, or arrested by the pre-existing weak planes. The test results suggest that the complexity of the fracture path is highly dependent on a dimensionless toughness, K𝑚. This laboratory study highlights the importance to account for the hydromechanical characteristics in the HF propagation in anisotropic rocks with pre-existing weak discontinuities.

2022

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Fault slip behavior and earthquake nucleation are often framed within the context of velocity-dependent friction, ranging from velocity-strengthening to velocity-weakening behavior. Previous studies have shown that fault roughness controls the fault slip behavior, with rougher faults having a greater tendency to be velocity-strengthening. However, it is not clear how the spontaneous transition from velocity-strengthening to velocity-weakening occurs nor what the role of roughness is. Using the High Strain TEmperature Pressure Speed (HighSTEPS) low to high velocity biaxial friction apparatus located at the EPFL in Switzerland, this transition has been investigated with load-controlled experiments. Creep in biaxial apparatuses has rarely been investigated, but this approach allows for a development of slip which is spontaneous and a loading which is more readily compared to natural seismicity. The investigation concerns bare surface norite samples with customized roughnesses. The samples were loaded to a normal stress of 20 MPa and then a shear stress of 8 MPa. The applied shear stress was held for 1000 seconds before the shear stress was increased in a step-wise fashion by 0.4 MPa, until the sample achieved a shear displacement of 25 mm (typically around 18 MPa). Typical mechanical data, such as the horizontal and vertical displacements and forces, were collected. The samples/sample holder were also equipped with 12 P-wave acoustic sensors. Smoother samples exhibited larger and more frequent stress drops than rougher samples, with reactivation at lower strength. Slip velocity was also observed to be higher for smooth samples. Localized acoustic emissions were used to assess the degree of localization and provide insight into the relative magnitude distributions for each roughness. These results highlight how local microscopic heterogeneities associated with surface roughness can influence the macroscopic stability of faults. They demonstrate roughness’ ability to result in stress barriers which can halt rupture.

2022