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Onset of Hydraulic Fracture Initiation Monitored by Acoustic Emission and Volumetric Deformation Measurements 总被引：2，自引：1，他引：1
Sergey Stanchits Aniket Surdi Patrick Gathogo Eric Edelman Roberto Suarez-Rivera 《Rock Mechanics and Rock Engineering》2014,47(5):1521-1532
In this paper, the results of laboratory studies of fracture initiation, early propagation and breakdown are reported. Three experiments were conducted on a low permeability sandstone block, loaded in a polyaxial test frame, to representative effective in situ stress conditions. The blocks were instrumented with acoustic emission (AE) and volumetric deformation sensors. In two experiments, fluids of different viscosity were injected into the wellbore, fluid injection was interrupted soon after the breakdown pressure had been reached. This allowed us to investigate hydraulic fracture initiation. In the third test, fracture initiation criteria were applied to stop hydraulic fracture propagation significantly earlier, prior to breakdown, and as it propagated a short distance from the wellbore. The analysis of AE results shows an increase in AE activity and a change in the AE spatial correlation, during the fracture initiation. This early stage of fracturing correlates strongly with the onset of rock volumetric deformation, and is confirmed by the analysis of ultrasonic transmission monitoring. The rock microstructure, after the test, was investigated by analysis of scanning electron microscope images. These indicated the development of leak-off zone near the wellbore and a dry hydraulic fracture at the farther distance from the wellbore. 相似文献
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Ultrasonic Velocities, Acoustic Emission Characteristics and Crack Damage of Basalt and Granite 总被引：2，自引：0，他引：2
Acoustic emissions (AE), compressional (P), shear (S) wave velocities, and volumetric strain of Etna basalt and Aue granite were measured simultaneously during triaxial compression
tests. Deformation-induced AE activity and velocity changes were monitored using twelve P-wave sensors and eight orthogonally polarized S-wave piezoelectric sensors; volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the
rock surface. P-wave velocity in basalt is about 3 km/s at atmospheric pressure, but increases by > 50% when the hydrostatic pressure is
increased to 120 MPa. In granite samples initial P-wave velocity is 5 km/s and increases with pressure by < 20%. The pressure-induced changes of elastic wave speed indicate
dominantly compliant low-aspect ratio pores in both materials, in addition Etna basalt also contains high-aspect ratio voids.
In triaxial loading, stress-induced anisotropy of P-wave velocities was significantly higher for basalt than for granite, with vertical velocity components being faster than
horizontal velocities. However, with increasing axial load, horizontal velocities show a small increase for basalt but a significant
decrease for granite. Using first motion polarity we determined AE source types generated during triaxial loading of the samples.
With increasing differential stress AE activity in granite and basalt increased with a significant contribution of tensile
events. Close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly.
A concomitant increase of double-couple events indicating shear, suggests shear cracks linking previously formed tensile cracks. 相似文献
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Sergei Stanchits Jerome Fortin Yves Gueguen Georg Dresen 《Pure and Applied Geophysics》2009,166(5-7):843-868
We investigated initiation and propagation of compaction bands (CB) in six wet and four dry Bentheim sandstone samples deformed in axial compression tests with strain rates ranging from 3.2 × 10?8 s?1 to 3.2 × 10?4 s?1. Circumferential notches with 0.8-mm width and 5-mm depth served to initiate CB at mid-sample length. Wet samples were saturated with distilled water and deformed at 195 MPa confining pressure and 10 MPa pore pressure. Dry samples were deformed at 185 MPa confining pressure. Twelve P-wave sensors, eight S-wave sensors and two pairs of orthogonally oriented strain-gages were glued to the sample surface to monitor acoustic emission (AE), velocities and local strain during the loading process. Nucleation of compaction bands is indicated by AE clusters close to the notch tips. With progressive loading, AE activity increased and AE hypocenters indicated propagation of a single CB normal to the sample axis. CB propagation from the sample periphery towards the centre was monitored. Microstructural analysis of deformed samples shows excellent agreement between location of AE clusters and CBs. In both dry and wet samples the lateral propagation of CBs was about 100 times faster than axial shortening rates. At the slowest displacement rate, AE activity during band propagation was reduced and CB nucleation in wet samples occurred at 20% lower stresses. This may indicate an increasing contribution of stress corrosion processes to the formation of the compaction bands. In dry and wet samples inelastic compaction energy per area ranged between 16 and 80 kJ m?2. This is in good agreement with previous estimates from laboratory and field studies. 相似文献
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本文用光弹性的方法记录岩石中诱发脉冲的自然振动场,并做频谱分析,这种方法可以测量波动的应力,用以显示在有限尺寸的非均匀固体或岩层结构中,由于破裂成核结构的形成而激发的声发射频谱。地声频谱方法的一个应用,是探测宏观破碎断裂面或不同岩性的断裂面。本文的结果,可导致对不同频率波的层析成像;可对矿山的岩体断层定位作出贡献,从而有助于预测矿井的灾害。在实验室中岩层破裂时声发射系列的频谱模式,可能转用于天然强震系列频谱作模拟类比。 相似文献
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Smirnov V. B. Ponomarev A. V. Stanchits S. A. Potanina M. G. Patonin A. V. Dresen G. Narteau C. Bernard P. Stroganova S. M. 《Izvestiya Physics of the Solid Earth》2019,55(1):124-137
Izvestiya, Physics of the Solid Earth - Laboratory experiments on studying the aftershock regime are carried out on sandstone specimens at different levels of axial loading and uniform compression... 相似文献
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Acoustic Emissions Monitoring during Inelastic Deformation of Porous Sandstone: Comparison of Three Modes of Deformation 总被引：4，自引：0，他引：4
Jerome Fortin Sergei Stanchits Georg Dresen Yves Gueguen 《Pure and Applied Geophysics》2009,166(5-7):823-841
In some reservoirs, large deformations can occur during oil or gas production because of the effective stress change. For very porous rocks, these production operations can be sufficient to cause inelastic deformation and irreversible damage. Rock formations can undergo deformation by different mechanisms, including dilatancy or pore collapse. In the laboratory, it has been shown that the inelastic deformation and failure mode of porous rocks are pressure sensitive. Indeed, when subjected to an overall compressive loading, a porous rock may fail by shear localization, compaction localization, or by cataclastic compaction. Acoustic emission (AE) records provide important information to understand the failure mode of rocks: the spatial evolution of damage as well as the source mechanisms can be followed using this technique. In this paper, we present three different laboratory axisymmetric compression experiments, performed on Bleurswiller sandstone, which enable us to compare the acoustic emission signature of these three modes of deformation. Our data show that compaction localization and cataclastic compaction are characterized by similar acoustic signatures (in terms of AE sources characteristics and evolution of AE number), in comparison to the acoustic signature from shear localization. This implies similar micromechanisms involved during compaction bands formation and cataclastic compaction. 相似文献
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