共查询到20条相似文献，搜索用时 765 毫秒
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On the shape and velocity of fluid-filled fractures in the Earth 总被引：3，自引：0，他引：3
T. Dahm 《Geophysical Journal International》2000,142(1):181-192
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Numerical simulations of the propagation path and the arrest of fluid-filled fractures in the Earth 总被引：3，自引：0，他引：3
T. Dahm 《Geophysical Journal International》2000,141(3):623-638
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Hydraulic conductivities of fractured sandstone bore cores of 0.1 m in diameter are calculated using detailed characterization of the fracture geometry parameters determined using a resin casting technique. The accuracy of the measurements was about 0.25–1.25 μm with the image size used. The values of the effective fracture apertures vary between 10 μm and 50 μm. For modelling purposes the samples are sectioned serially, perpendicular to the flow direction along the cylinder axis. The hydraulic conductivity of individual slices is estimated by summing the contribution of the matrix (assumed uniform) and each fracture (depending on its length and aperture). Finally, the hydraulic conductivity of the bulk sample is estimated by a harmonic average in series along the flow path. Results of this geometrical upscaling compare favourably with actual conductivity measured in hydraulic and pneumatic experiments carried out prior to sectioning. This study shows that the determination of larger-scale conductivity can be achieved, based on the evaluation of fracture geometry parameters (e.g. fracture aperture, fracture width and fracture length), measured using an optical method, at least at the laboratory scale. 相似文献
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Effects of fractures on seismic-wave velocity and attenuation 总被引：1，自引：0，他引：1
The effects of fractures on the seismic velocity and attenuation of a rock are investigated using theoretical results and experimental data. Fractures in a rock mass influence the traveltimes and amplitudes of seismic waves that have propagated through them. The displacement discontinuity model, recently employed in fracture investigations, is modified to describe the effect of fractures on seismic-wave velocity and attenuation. This new model, the modified displacement discontinuity model (MDD), is formulated in a way analogous to transmission-line analysis. The fractures are treated as transmission lines for the passage of seismic waves. The MDD takes into consideration realistic fracture parameters which include the fracture length, the fractional area of a fracture surface in contact, and the nature of the infilling material. A single fracture of varying geometric and material properties is shown to affect dramatically the transmission properties of a propagating waveform, and hence the seismic velocity and attenuation. These effects have been shown to result in a frequency-dependent velocity and attenuation. The sensitivity of the fracture parameters to seismic-wave velocity and attenuation was investigated and interesting results were obtained. Fracture parameters used in designing experimental models consisting of synthetically manufactured cracks were fed into the MDD and a well-known crack model, Hudson's model, for comparison. Velocities as a function of the incident-wave angle were obtained from both numerical models and were compared with the results from the experimental modelling. For P waves, the MDD model results show better agreement with those of the experimental model for all crack densities investigated than those from Hudson's model. 相似文献
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James G. Berryman 《Geophysical Journal International》2007,171(2):954-974
Seismic wave propagation through the earth is often strongly affected by the presence of fractures. When these fractures are filled with fluids (oil, gas, water, CO2 , etc.), the type and state of the fluid (liquid or gas) can make a large difference in the response of the seismic waves. This paper summarizes recent work on methods of deconstructing the effects of fractures, and any fluids within these fractures, on seismic wave propagation as observed in reflection seismic data. One method explored here is Thomsen's weak anisotropy approximation for wave moveout (since fractures often induce elastic anisotropy due to non-uniform crack-orientation statistics). Another method makes use of some very convenient crack/fracture parameters introduced previously that permit a relatively simple deconstruction of the elastic and wave propagation behaviour in terms of a small number of crack-influence parameters (whenever this is appropriate, as is certainly the case for small crack densities). Then, the quantitative effects of fluids on these crack-influence parameters are shown to be directly related to Skempton's coefficient B of undrained poroelasticity (where B typically ranges from 0 to 1). In particular, the rigorous result obtained for the low crack density limit is that the crack-influence parameters are multiplied by a factor (1 − B ) for undrained systems. It is also shown how fracture anisotropy affects Rayleigh wave speed, and how measured Rayleigh wave speeds can be used to infer shear wave speed of the fractured medium in some cases. Higher crack density results are also presented by incorporating recent simulation data on such cracked systems. 相似文献
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A mechanical-statistical model is presented that aims to help to understand the history and geometry of the process of formation of fracture zones along oceanic ridges. It uses ideas of statistical fracture theory used in engineering, namely the Weibull fracture model. The approximate parallelism of the fracture zones along ridges makes it possible to use a one-dimensional point process model with points along the ridge axes, which represent the transform faults. The ratios of the lengths of the corresponding fracture zones to the ocean width are used to obtain a rough estimate of the Weibull modulus, which is an important material parameter in fracture theory. The theory is refined by introducing a hard-core point process model. The corresponding positive minimum distance between subsequent fracture zones results from stress relaxation in the vicinity of a given fracture zone. 相似文献
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Acceleration of buoyancy-driven fractures and magmatic dikes beneath the free surface 总被引：3，自引：0，他引：3
By performing buoyancy-driven fracture experiments in brittle gelatin we observe that the ascent velocity of a fracture containing a finite volume of fluid increases when approaching the free surface. We theoretically describe this free-surface effect and quantify it by introducing an effective depth-dependent fracture toughness and developing an ascent model on the basis of linear fracture mechanics. We develop a successful inversion approach and resolve the actual and critical fracture length and the ascent velocity far away from the free surface from the observation of the fracture tip migration alone. Other parameters, as the fluid volume included in the fracture and the in situ fracture toughness, can be derived. Applying the model and inversion to the 1998 eruption at Piton de la Fournaise, Reunion Island, reveals estimates of the length and critical length of the feeding magma batch, the magma batch volume and the in situ fracture toughness. It further indicates that the ascent velocity of the magma batch was probably much smaller at greater depths and that the batch might have been initiated several months or years before the eruption. 相似文献
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Y.Y. Kagan 《Geophysical Journal International》1994,117(2):345-364
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本文运用断裂力学的原理和方法,分析了斜坡破坏过程中后缘开裂、滑动面的形成和结构面连通的机理,以及破坏中所遵循的轨迹。通过模拟实验、数值分析和应用,证明断裂力学方法是一种分析斜坡破坏机理的有效方法。 相似文献
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Anindita Samsu Alexander R. Cruden Mike Hall Steven Micklethwaite Steven W. Denyszyn 《Basin Research》2019,31(4):782-807
Complex arrays of faults in extensional basins are potentially influenced by pre‐existing zones of weakness in the underlying basement, such as faults, shear zones, foliation, and terrane boundaries. Separating the influence of such basement heterogeneities from far‐field tectonics proves to be challenging, especially when the timing and character of deformation cannot be interpreted from seismic reflection data. Here we aim to determine the influence of basement heterogeneities on fault patterns in overlying cover rocks using interpretations of potential field geophysical data and outcrop‐scale observations. We mapped >1 km to meter scale fractures in the western onshore Gippsland Basin of southeast Australia and its underlying basement. Overprinting relationships between fractures and mafic intrusions are used to determine the sequence of faulting and reactivation, beginning with initial Early Cretaceous rifting. Our interpretations are constrained by a new Early Cretaceous U‐Pb zircon isotope dilution thermal ionization mass spectrometry age (116.04 ± 0.15 Ma) for an outcropping subvertical, NNW‐SSE striking dolerite dike hosted in Lower Cretaceous Strzelecki Group sandstone. NW‐SE to NNW‐SSE striking dikes may have signaled the onset of Early Cretaceous rifting along the East Gondwana margin at ca. 105–100 Ma. Our results show that rift faults can be oblique to their expected orientation when pre‐existing basement heterogeneities are present, and they are orthogonal to the extension direction where basement structures are less influential or absent. NE‐SW to ENE‐WSW trending Early Cretaceous rift‐related normal faults traced on unmanned aerial vehicle orthophotos and digital aerial images of outcrops are strongly oblique to the inferred Early Cretaceous N‐S to NNE‐SSW regional extension direction. However, previously mapped rift‐related faults in the offshore Gippsland Basin (to the east of the study area) trend E‐W to WNW‐ESE, consistent with the inferred regional extension direction. This discrepancy is attributed to the influence of NNE‐SSW trending basement faults underneath the onshore part of the basin, which caused local re‐orientation of the Early Cretaceous far‐field stress above the basement during rifting. Two possible mechanisms for inheritance are discussed—reactivation of pre‐existing basement faults or local re‐orientation of extension vectors. Multiple stages of extension with rotated extension vectors are not required to achieve non‐parallel fault sets observed at the rift basin scale. Our findings demonstrate the importance of (1) using integrated, multi‐scale datasets to map faults and (2) mapping basement geology when investigating the structural evolution of an overlying sedimentary basin. 相似文献
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Micro and macroscopic models of rock fracture 总被引：8，自引：0，他引：8
Donald L. Turcotte William I. Newman Robert Shcherbakov 《Geophysical Journal International》2003,152(3):718-728