54 research outputs found
Application of Image Analysis for the Identification of Prehistoric Ceramic Production Technologies in the North Caucasus (Russia, Bronze/Iron Age)
The recent advances in microscopy and scanning techniques enabled the image analysis of archaeological objects in a high resolution. From the direct measurements in images, shapes and related parameters of the structural elements of interest can be derived. In this study, image analysis in 2D/3D is applied to archaeological ceramics, in order to obtain clues about the ceramic pastes, firing and shaping techniques. Images were acquired by the polarized light microscope, scanning electron microscopy (SEM) and 3D micro X-ray computed tomography (Β΅-CT) and segmented using Matlab. 70 ceramic sherds excavated at Ransyrt 1 (Middle-Late Bronze Age) and Kabardinka 2 (late Bronzeβearly Iron Age), located in in the North Caucasian mountains, Russia, were investigated. The size distribution, circularity and sphericity of sand grains in the ceramics show site specific difference as well as variations within a site. The sphericity, surface area, volume and Euler characteristic of pores show the existence of various pyrometamorphic states between the ceramics and within a ceramic. Using alignments of pores and grains, similar pottery shaping techniques are identified for both sites. These results show that the image analysis of archaeological ceramics can provide detailed information about the prehistoric ceramic production technologies with fast data availability
Experimental Investigation on Static and Dynamic Bulk Moduli of Dry and Fluid-Saturated Porous Sandstones
Knowledge of pressure-dependent static and dynamic moduli of porous reservoir rocks is of key importance for evaluating geological setting of a reservoir in geo-energy applications. We examined experimentally the evolution of static and dynamic bulk moduli for porous Bentheim sandstone with increasing confining pressure up to about 190 MPa under dry and water-saturated conditions. The static bulk moduli (K-s) were estimated from stress-volumetric strain curves while dynamic bulk moduli (K-d) were derived from the changes in ultrasonic P- and S- wave velocities (similar to 1 MHz) along different traces, which were monitored simultaneously during the entire deformation. In conjunction with published data of other porous sandstones (Berea, Navajo and Weber sandstones), our results reveal that the ratio between dynamic and static bulk moduli (K-d/K-s) reduces rapidly from about 1.5 - 2.0 at ambient pressure to about 1.1 at high pressure under dry conditions and from about 2.0 - 4.0 to about 1.5 under water-saturated conditions, respectively. We interpret such a pressure-dependent reduction by closure of narrow (compliant) cracks, highlighting thatK(d)/K(s)is positively correlated with the amount of narrow cracks. Above the crack closure pressure, where equant (stiff) pores dominate the void space,K-d/K(s)is almost constant. The enhanced difference between dynamic and static bulk moduli under water saturation compared to dry conditions is possibly caused by high pore pressure that is locally maintained if measured using high-frequency ultrasonic wave velocities. In our experiments, the pressure dependence of dynamic bulk modulus of water-saturated Bentheim sandstone at effective pressures above 5 MPa can be roughly predicted by both the effective medium theory (Mori-Tanaka scheme) and the squirt-flow model. Static bulk moduli are found to be more sensitive to narrow cracks than dynamic bulk moduli for porous sandstones under dry and water-saturated conditions
Obtaining of oxidizers using physical fields
ΠΠ΅Π³Π°ΡΠΈΠ²Π½ΡΠ΅ ΠΏΠΎΡΠ»Π΅Π΄ΡΡΠ²ΠΈΡ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΡ Ρ
ΠΈΠΌΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΉ Π΄Π»Ρ ΠΎΡΠΈΡΡΠΊΠΈ ΠΏΡΠΈΡΠΎΠ΄Π½ΡΡ
ΠΈ ΡΡΠΎΡΠ½ΡΡ
Π²ΠΎΠ΄ ΠΏΠΎΡΠ»ΡΠΆΠΈΠ»ΠΈ ΡΠΎΠ»ΡΠΊΠΎΠΌ Π΄Π»Ρ ΡΠ°Π·Π²ΠΈΡΠΈΡ Π±ΠΎΠ»Π΅Π΅ ΡΠΈΡΡΡΡ
ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΉ. ΠΡΠ΅ ΡΠ°ΡΠ΅ ΠΈΡΠΏΠΎΠ»ΡΠ·ΡΡΡΡΡ ΡΠΈΡΡΡΠ΅ ΠΎΠΊΠΈΡΠ»ΠΈΡΠ΅Π»ΠΈ (ΠΎΠ·ΠΎΠ½, ΠΏΠ΅ΡΠΎΠΊΡΠΈΠ΄ Π²ΠΎΠ΄ΠΎΡΠΎΠ΄Π°) Π² ΡΠΎΡΠ΅ΡΠ°Π½ΠΈΠΈ Ρ ΡΠΈΠ·ΠΈΡΠ΅ΡΠΊΠΈΠΌΠΈ ΠΌΠ΅ΡΠΎΠ΄Π°ΠΌΠΈ. ΠΠ°ΠΈΠ±ΠΎΠ»Π΅Π΅ ΡΠΈΡΠΎΠΊΠΎ ΠΏΡΠΈΠΌΠ΅Π½ΡΠ΅ΡΡΡ ΠΎΠ±ΡΠ°Π±ΠΎΡΠΊΠ° Π²ΠΎΠ΄Ρ ΡΠ»ΡΡΡΠ°ΡΠΈΠΎΠ»Π΅ΡΠΎΠ²ΡΠΌ ΠΈΠ·Π»ΡΡΠ΅Π½ΠΈΠ΅ΠΌ. ΠΡΡΡ ΠΌΠ½ΠΎΠ³ΠΎ ΠΏΡΠ±Π»ΠΈΠΊΠ°ΡΠΈΠΉ ΠΎΠ± ΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΠΈ ΠΎΠΊΠΈΡΠ»ΠΈΡΠ΅Π»Π΅ΠΉ ΠΏΡΠΈ ΠΎΠ±ΡΠ°Π±ΠΎΡΠΊΠ΅ Π·Π°Π³ΡΡΠ·Π½Π΅Π½Π½ΠΎΠΉ Π²ΠΎΠ΄Ρ ΡΠ»ΡΡΡΠ°Π·Π²ΡΠΊΠΎΠΌ ΠΈ Π³ΠΈΠ΄ΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΊΠ°Π²ΠΈΡΠ°ΡΠΈΠ΅ΠΉ. Π Π΄Π°Π½Π½ΠΎΠΉ ΡΡΠ°ΡΡΠ΅ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π»ΠΎΡΡ ΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΠ΅ ΠΎΠΊΠΈΡΠ»ΠΈΡΠ΅Π»Π΅ΠΉ ΠΏΡΠΈ Π²ΠΎΠ·Π΄Π΅ΠΉΡΡΠ²ΠΈΠΈ ΡΠΈΠ·ΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΏΠΎΠ»Π΅ΠΉ (ΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎΠ΅ ΠΏΠΎΠ»Π΅ ΠΏΠΎΡΡΠΎΡΠ½Π½ΡΡ
ΠΌΠ°Π³Π½ΠΈΡΠΎΠ², ΡΠ»Π΅ΠΊΡΡΠΎΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎΠ΅ ΠΏΠΎΠ»Π΅ ΡΠ»ΡΡΡΠ°ΡΠΈΠΎΠ»Π΅ΡΠΎΠ²ΠΎΠ³ΠΎ ΠΈΠ·Π»ΡΡΠ΅Π½ΠΈΡ, Π°ΠΊΡΡΡΠΈΡΠ΅ΡΠΊΠΎΠ΅ ΠΏΠΎΠ»Π΅ ΡΠ»ΡΡΡΠ°Π·Π²ΡΠΊΠΎΠ²ΡΡ
ΠΈΠ·Π»ΡΡΠ°ΡΠ΅Π»Π΅ΠΉ) Π½Π° Π΄ΠΈΡΡΠΈΠ»Π»ΠΈΡΠΎΠ²Π°Π½Π½ΡΡ Π²ΠΎΠ΄Ρ. ΠΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½ΡΡ ΠΏΡΠΎΠ²ΠΎΠ΄ΠΈΠ»ΠΈΡΡ Π½Π° ΡΡΠ΅Π½Π΄Π΅, Π³Π΄Π΅ Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎ ΠΎΡΡΡΠ΅ΡΡΠ²Π»ΡΡΡ ΡΠ°Π·Π΄Π΅Π»ΡΠ½ΠΎΠ΅ ΠΈ ΡΠΎΠ²ΠΌΠ΅ΡΡΠ½ΠΎΠ΅ Π²Π»ΠΈΡΠ½ΠΈΠ΅ ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
ΠΊΠΎΠΌΠ±ΠΈΠ½Π°ΡΠΈΠΉ ΡΠΈΠ·ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π²ΠΎΠ·Π΄Π΅ΠΉΡΡΠ²ΠΈΡ. ΠΡΠΎΠ²Π΅Π΄Π΅Π½Π½ΡΠ΅ ΡΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½ΡΡ ΠΏΠΎΠΊΠ°Π·Π°Π»ΠΈ, ΡΡΠΎ Π² Π΄ΠΈΡΡΠΈΠ»Π»ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ Π²ΠΎΠ΄Π΅ ΠΏΠΎΠ΄ Π΄Π΅ΠΉΡΡΠ²ΠΈΠ΅ΠΌ ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
ΡΠ»Π΅ΠΊΡΡΠΎΠΌΠ°Π³Π½ΠΈΡΠ½ΡΡ
ΠΏΠΎΠ»Π΅ΠΉ ΠΈ ΠΏΠΎΡΡΠΎΡΠ½Π½ΠΎΠ³ΠΎ ΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎΠ³ΠΎ ΠΏΠΎΠ»Ρ Π½Π°Π±Π»ΡΠ΄Π°Π΅ΡΡΡ Π³Π΅Π½Π΅ΡΠ°ΡΠΈΡ ΠΎΠΊΠΈΡΠ»ΠΈΡΠ΅Π»Π΅ΠΉ. ΠΠΎ ΠΈΡ
ΠΊΠΎΠ½ΡΠ΅Π½ΡΡΠ°ΡΠΈΡ ΠΌΠ°Π»Π° (0,03-0.07 ΠΌΠ³/Π» Π² ΠΏΠ΅ΡΠ΅ΡΡΠ΅ΡΠ΅ Π½Π° ΠΏΠ΅ΡΠ΅ΠΊΠΈΡΡ Π²ΠΎΠ΄ΠΎΡΠΎΠ΄Π°) ΠΈ Π΄Π»Ρ ΠΈΠ½ΡΠ΅Π½ΡΠΈΡΠΈΠΊΠ°ΡΠΈΠΈ Π²ΠΎΠ·Π΄Π΅ΠΉΡΡΠ²ΠΈΡ ΡΠΈΠ·ΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΏΠΎΠ»Π΅ΠΉ Π½Π΅ΠΎΠ±Ρ
ΠΎΠ΄ΠΈΠΌΠΎ Π²Π½ΠΎΡΠΈΡΡ Π΄ΠΎΠΏΠΎΠ»Π½ΠΈΡΠ΅Π»ΡΠ½ΡΠ΅ ΡΠ΅Π°Π³Π΅Π½ΡΡ (ΠΏΠ΅ΡΠ΅ΠΊΠΈΡΡ, ΠΎΠ·ΠΎΠ½ ΠΈ Π΄Ρ.). ΠΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΎ, ΡΡΠΎ Π΄Π΅ΠΉΡΡΠ²ΠΈΠ΅ ΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎΠ³ΠΎ ΠΏΠΎΠ»Ρ Π½Π°Π±Π»ΡΠ΄Π°Π΅ΡΡΡ ΠΏΡΠΈ ΠΈΠ½Π΄ΡΠΊΡΠΈΡΡ
ΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎΠ³ΠΎ ΠΏΠΎΠ»Ρ: 80, 100, 240 ΠΈ 540 ΠΌΠ’Π», ΠΈ ΡΠΊΠΎΡΠΎΡΡΠΈ ΠΏΠΎΡΠΎΠΊΠ° Π²ΠΎΠ΄Ρ ΡΠ΅ΡΠ΅Π· Π·Π°Π·ΠΎΡ ΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎΠ³ΠΎ Π°ΠΏΠΏΠ°ΡΠ°ΡΠ° 1,1 ΠΌ/Ρ, 3,3 ΠΌ/Ρ ΠΈ 4,4 ΠΌ/Ρ. ΠΠ°ΠΊΡΠΈΠΌΠ°Π»ΡΠ½Π°Ρ ΠΊΠΎΠ½ΡΠ΅Π½ΡΡΠ°ΡΠΈΡ ΠΎΠΊΠΈΡΠ»ΠΈΡΠ΅Π»Π΅ΠΉ Π½Π°Π±Π»ΡΠ΄Π°Π»Π°ΡΡ: ΠΏΡΠΈ Π³ΠΈΠ΄ΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠΌ ΡΠ΅ΠΆΠΈΠΌΠ΅ (Π²ΡΠ΅ ΡΠ΅Π°ΠΊΡΠΎΡΡ ΠΎΡΠΊΠ»ΡΡΠ΅Π½Ρ, ΡΠ°Π±ΠΎΡΠ°Π΅Ρ ΡΠΎΠ»ΡΠΊΠΎ Π½Π°ΡΠΎΡ), ΠΏΡΠΈ Π²ΠΊΠ»ΡΡΠ΅Π½Π½ΠΎΠΌ ΡΠΆΠ΅ΠΊΡΠΎΡΠ΅ ΠΈ ΠΈΠ½Π΄ΡΠΊΡΠΈΠΈ 540 ΠΌΠ’Π»; ΠΏΡΠΈ ΡΠΎΠ²ΠΌΠ΅ΡΠ΅Π½Π½ΠΎΠΌ Π£Π+2Π£Π€ ΡΠ΅ΠΆΠΈΠΌΠ΅ ΠΏΡΠΈ ΡΠ°ΠΊΠΎΠΉ ΠΆΠ΅ ΠΈΠ½Π΄ΡΠΊΡΠΈΠΈ, Π½ΠΎ Π±Π΅Π· ΡΠΆΠ΅ΠΊΡΠΎΡΠ°. ΠΠΎΠ»ΠΈΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΎ ΡΠΎΠ΄Π΅ΡΠΆΠ°Π½ΠΈΠ΅ ΠΎΠΊΠΈΡΠ»ΠΈΡΠ΅Π»Π΅ΠΉ Π² ΡΠΎΠ²ΠΌΠ΅ΡΠ΅Π½Π½ΠΎΠΌ ΡΠ΅ΠΆΠΈΠΌΠ΅ Π½Π° 11,5 % Π²ΡΡΠ΅, ΡΠ΅ΠΌ Π² Π³ΠΈΠ΄ΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠΌ ΡΠ΅ΠΆΠΈΠΌΠ΅, Π° ΡΠ½Π΅ΡΠ³ΠΎΠ·Π°ΡΡΠ°ΡΡ ΠΏΡΠΈ ΡΡΠΎΠΌ Π²ΡΡΠ΅ Π½Π° 28 %. ΠΡΡΠ°ΠΆΠ΅Π½Π½ΡΠΉ ΡΠΈΠ½Π΅ΡΠ³Π΅ΡΠΈΡΠ΅ΡΠΊΠΈΠΉ ΡΡΡΠ΅ΠΊΡ ΠΏΡΠΈ ΡΠΎΠ²ΠΌΠ΅ΡΡΠ½ΠΎΠΌ Π΄Π΅ΠΉΡΡΠ²ΠΈΠΈ ΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎΠ³ΠΎ ΠΏΠΎΠ»Ρ, ΡΠ»ΡΡΡΠ°Π·Π²ΡΠΊΠ° ΠΈ ΡΠ»ΡΡΡΠ°ΡΠΈΠΎΠ»Π΅ΡΠΎΠ²ΠΎΠ³ΠΎ ΠΈΠ·Π»ΡΡΠ΅Π½ΠΈΡ Π½Π΅ ΠΏΠΎΠ»ΡΡΠ΅Π½. Π£ΡΡΠΎΠΉΡΠΈΠ²ΡΠΉ ΡΠ΅Π·ΡΠ»ΡΡΠ°Ρ ΡΠ²Π΅Π»ΠΈΡΠ΅Π½ΠΈΡ Π³Π΅Π½Π΅ΡΠ°ΡΠΈΠΈ ΠΎΠΊΠΈΡΠ»ΠΈΡΠ΅Π»Π΅ΠΉ Π² Π΄ΠΈΡΡΠΈΠ»Π»ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ Π²ΠΎΠ΄Π΅ ΠΏΠΎΠ»ΡΡΠ΅Π½ ΠΏΡΠΈ Π²ΠΎΠ·Π΄Π΅ΠΉΡΡΠ²ΠΈΠΈ ΠΌΠ°Π³Π½ΠΈΡΠ½ΠΎΠ³ΠΎ ΠΏΠΎΠ»Ρ Π² ΡΠΎΡΠ΅ΡΠ°Π½ΠΈΠΈ Ρ ΡΠΆΠ΅ΠΊΡΠΎΡΠΎΠΌ
Injection-induced fault slip and associated seismicity in the lab: Insights from source mechanisms, local stress states and fault geometry
Probing source mechanisms of natural and induced earthquakes is a powerful tool to unveil associated rupture kinematics. The source processes of failure and slip instability driven by stress loading are affected by fault geometry, but the source ruptures of injection-induced seismicity in relation to fault structures and local stress states remain poorly understood. We have conducted a series of fault reactivation and slip experiments on sandstone samples containing faults with different surface roughness (smooth saw-cut fault and fractured rough fault). We impose progressive fluid injection to induce fault slip, and simultaneously monitor the associated acoustic emission (AE) activity. Using high-resolution AE recordings, we perform full moment tensor inversion of all located AE sources, and investigate the changes of AE source characteristics associated with induced fault slip and their relation to fault roughness. For the complex and rough fault, we observe significant non-double-couple components of AE sources and a high degree of focal mechanism heterogeneity. The temporal changes of AE mechanisms associated with injection-induced fault slip on the smooth fault reveal increasing proportions of double-couple components and decreasing variability of AE focal mechanisms when approaching the onset of slip events. The observed inconsistency between the nodal planes of AE sources and the macroscopic fault plane orientation is attributed to the development of secondary fracture networks surrounding the principal slip surface. We analyze changes in the magnitude-frequency characteristics and source mechanisms of AEs with fault-normal distance, showing that for the smooth (mature) fault, GutenbergβRichter b-value of on-fault seismicity is lower and focal mechanisms are less heterogeneous, compared to off-fault seismicity. Our results emphasize the important role of roughness-related changes in local fault geometry and associated stress heterogeneity for source mechanisms and rupture kinematics of injection-induced seismicity
Strain Partitioning and Frictional Behavior of Opalinus Clay During Fault Reactivation
The Opalinus Clay (OPA) formation is considered a suitable host rock candidate for nuclear waste storage. However, the sealing integrity and long-term safety of OPA are potentially compromised by pre-existing natural or artificially induced faults. Therefore, characterizing the mechanical behavior and microscale deformation mechanisms of faults and the surrounding rock is relevant for predicting repository damage evolution. In this study, we performed triaxial tests using saw-cut samples of the shaly and sandy facies of OPA to investigate the influence of pressure and mineral composition on the deformation behavior during fault reactivation. Dried samples were hydrostatically pre-compacted at 50Β MPa and then deformed at constant strain rate, drained conditions and confining pressures (pc) of 5β35Β MPa. Mechanical data from triaxial tests was complemented by local strain measurements to determine the relative contribution of bulk deformation and fault slip, as well as by acoustic emission (AE) monitoring, and elastic P-wave velocity measurements using ultrasonic transmissions. With increasing pc, we observe a transition from brittle deformation behavior with highly localized fault slip to semi-brittle behavior characterized by non-linear strain hardening with increasing delocalization of deformation. We find that brittle localization behavior is limited by pc at which fault strength exceeds matrix yield strength. AEs were only detected in tests performed on sandy facies samples, and activity decreased with increasing pc. Microstructural analysis of deformed samples revealed a positive correlation between increasing pc and gouge layer thickness. This goes along with a change from brittle fragmentation and frictional sliding to the development of shear zones with a higher contribution of cataclastic and granular flow. Friction coefficient at fault reactivation is only slightly higher for the sandy (Β΅β~β0.48) compared to the shaly facies (Β΅β~β0.4). Slide-hold-slide tests performed afterβ~β6Β mm axial shortening suggest stable creeping and long-term weakness of faults at the applied conditions. Our results demonstrate that the mode of fault reactivation highly depends on the present stress field and burial history
Authorsβ Reply to the Discussion by Crisci et al.Β (2021) on βExperimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions Mechanical Properties and the Influence of Rock Fabricβ
This is a repond to the comments raised in CrisciΒ΄s et al. paper βDiscussion on βExperimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions
Β¬ Mechanical Properties and the Influence of Rock Fabricβ (2021). We are pleased to use the opportunity to clarify issues related to testing procedures and interpretation in more detail.Bundesministerium fΓΌr Bildung und Forschung
http://dx.doi.org/10.13039/501100002347Helmholtz-Gemeinschaft
http://dx.doi.org/10.13039/501100001656Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217
Creep and strain-dependent microstructures of synthetic anorthite-diopside aggregates
International audienc
Experimental Investigation on Static and Dynamic Bulk Moduli of Dry and Fluid-Saturated Porous Sandstones
Knowledge of pressure-dependent static and dynamic moduli of porous reservoir rocks is of key importance for evaluating geological setting of a reservoir in geo-energy applications. We examined experimentally the evolution of static and dynamic bulk moduli for porous Bentheim sandstone with increasing confining pressure up to about 190Β MPa under dry and water-saturated conditions. The static bulk moduli (Ks) were estimated from stressβvolumetric strain curves while dynamic bulk moduli (Kd) were derived from the changes in ultrasonic P- and S- wave velocities (~β1Β MHz) along different traces, which were monitored simultaneously during the entire deformation. In conjunction with published data of other porous sandstones (Berea, Navajo and Weber sandstones), our results reveal that the ratio between dynamic and static bulk moduli (Kd/Ks) reduces rapidly from about 1.5βββ2.0 at ambient pressure to about 1.1 at high pressure under dry conditions and from about 2.0βββ4.0 to about 1.5 under water-saturated conditions, respectively. We interpret such a pressure-dependent reduction by closure of narrow (compliant) cracks, highlighting that Kd/Ks is positively correlated with the amount of narrow cracks. Above the crack closure pressure, where equant (stiff) pores dominate the void space, Kd/Ks is almost constant. The enhanced difference between dynamic and static bulk moduli under water saturation compared to dry conditions is possibly caused by high pore pressure that is locally maintained if measured using high-frequency ultrasonic wave velocities. In our experiments, the pressure dependence of dynamic bulk modulus of water-saturated Bentheim sandstone at effective pressures above 5Β MPa can be roughly predicted by both theΒ effective medium theory (MoriβTanaka scheme) and the squirt-flow model. Static bulk moduli are found to be more sensitive to narrow cracks than dynamic bulk moduli for porous sandstones under dry and water-saturated conditions.Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217
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