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1.
Fractures in elastic media add compliance to a rock in the direction normal to the fracture strike. Therefore, elastic wave velocities in a fractured rock will vary as a function of the energy propagation direction relative to the orientation of the aligned fracture set. Anisotropic Thomson–Haskell matrix Rayleigh-wave equations for a vertically transverse isotropic media can be used to model surface-wave dispersion along the principal axes of a vertically fractured and transversely isotropic medium. Furthermore, a workflow combining first-break analysis and azimuthal anisotropic Rayleigh-wave inversion can be used to estimate P-wave and S-wave velocities, Thomsen's ε, and Thomsen's δ along the principal axes of the orthorhombic symmetry. In this work, linear slip theory is used to map our inversion results to the equivalent vertically fractured and transversely isotropic medium coefficients. We carried out this inversion on a synthetic example and a field example. The synthetic data example results show that joint estimation of S-wave velocities with Thomsen's parameters ε and δ along normal and parallel to the vertical fracture set is reliable and, when mapped to the corresponding vertically fractured and transversely isotropic medium, provides insight into the fracture compliances. When the inversion was carried out on the field data, results indicated that the fractured rock is more compliant in the azimuth normal to the visible fracture set orientation and that the in situ normal fracture compliance to tangential fracture compliance ratio is less than half, which implies some cementation may have occurred along the fractures. Such an observation has significant implications when modelling the transport properties of the rock and its strength. Both synthetic and field examples show the potential of azimuthal anisotropic Rayleigh-wave inversion as the method can be further expanded to a more general case where the vertical fracture set orientation is not known a priori.  相似文献   

2.
Permeability, resistivity formation factor, and pore volume change were simultaneously measured on samples of Chelmsford granite subjected to confining pressure and pore pressure cycles. Using a technique described in a previous paper, the tangent coefficients of the effective pressure law for permeability k and for formation factor F were determined. k and F did not differ significantly from one another. They showed a strong stress history dependence as has already been observed for k in several crystalline rocks. According to the definition of the effective pressure law used here, two physical properties with identical 's must be related through a one-to-one functional relationship. Hence, the observation above suggests that such a relationship may be empirically found between permeability and formation factor. Indeed, analysis of the data revealed that, to a good approximation, permeability was inversely proportional to the formation factor. The same relation has previously been observed in other crystalline rocks. This relationship was included in a recent version of the so-called equivalent channel model. Using this model, the specific surface area of the cracksA c/VS, the standard deviation of the distribution of asperities heightsh and the hydraulic radiusm o were evaluated. The following values were respectively found: 850 cm–1, 0.008 m and 0.14 m. The specific surface area of the cracks was independently estimated on micrographs of polished sections using a standard quantitative stereology method. The result was in good agreement with the values estimated from the transport properties data.  相似文献   

3.
The permeabilities of fault rocks from the rupture of Wenchuan earthquake were measured by using nitrogen gas and distilled water as pore fluids under the confining pressure ranging from 20 to 180 MPa at room temperature. Experimental results indicate that both gas and water permeabilities decrease with increasing confining pressure, described by power law relationship, i.e., b = 0.2×10–3kl–0.557. The water permeability is about one order less than gas permeability and also half order smaller than the permeability corrected by the Klinkenberg effect, so-called intrinsic permeability. The differences in the permeabilies imply that the reduction of effective pore size caused by the adhesion of water molecules to clay particle surface and water-swelling of expandable clay minerals contributes to lessening the water permeability besides the Klinkenberg effect. Hence, the liquid permeability of fault rocks cannot be deduced by gas permeability by the Klinkenberg correction reliably and accurately, and it is necessary to use liquid as pore media to measure their transport property directly.  相似文献   

4.
Fracturing and hydrothermal alteration in normal fault zones   总被引：9，自引：0，他引：9  
Large normal fault zones are characterized by intense fracturing and hydrothermal alteration. Displacement is localized in a slip zone of cataclasite, breccia and phyllonite surrounding corrugated and striated fault surfaces. Slip zone rock grades into fractured, but less comminuted and hydrothermally altered rock in the transition zone, which in turn grades abruptly into the wall rock. Fracturing and fluid flow is episodic, because permeability generated during earthquakes is destroyed by hydrothermal processes during the time between earthquakes.Fracture networks are described by a fracture fabric tensor (F). The permeability tensor (k) is used to estimate fluid transport properties if the trace of F is sufficiently large. Variations in elastic moduli and seismic velocities between fault zone and wall rock are estimated as a function of fracture density (). Fracturing decreases elastic moduli in the transition zone by 50–100% relative to the country rock, and similar or even greater changes presumably occur in the slip zone.P-andS-wave velocity decrease, andV p /V s increases in the fault zone relative to the wall rock. Fracture permeability is highly variable, ranging between 10–13 m2 and 10–19 m2 at depths near 10 km. Changes in permeability arise from variations in effective stress and fracture sealing and healing.Hydrothermal alteration of quartzo-feldspathic rock atT>300°C creates mica, chlorite, epidote and alters the quartz content. Alteration changes elastic moduli, but the changes are much less than those caused by fracturing.P-andS-wave velocities also decrease in the hydrothermally altered fault rock relative to the country rock, and there is a slight decrease inV p /V s , which partially offsets the increase inV p /V s caused by fracturing.Fracturing and hydrothermal alteration affect fault mechanics. Low modulus rock surrounding fault surfaces increases the probability of exceeding the critical slip distance required for the onset of unstable slip during rupture initiation. Boundaries between low modulus fault rock and higher modulus wall rock also act as rupture guides and enhance rupture acceleration to dynamic velocity. Hydrothermal alteration at temperatures in excess of 300°C weakens the deeper parts of the fault zone by producingphyllitic mineral assemblages. Sealing of fracture in time periods between large earthquakes generates pods of abnormally pressured fluid which may play a fundamental role in the initiation of large earthquakes.  相似文献   

5.
The pressure dependence of P- and S-wave velocities, velocity anisotropy, shear wave splitting and crack-porosity has been investigated in a number of samples from different crustal rock types for dry and wet (water saturated) conditions. At atmospheric pressure, P-wave velocities of the saturated, low-porosity rocks (< 1%) are significantly higher than in dry rocks, whereas the differences for S-wave velocities are less pronounced. The effect of intercrystalline fluids on seismic properties at increased pressure conditions is particularly reflected by the variation of the Poisson's ratio because P-wave velocities are more sensitive to fluids than S-wave velocities in the low-porosity rocks. Based on the experimental data, the respective crack-density parameter (), which is a measure of the number of flat cracks per volume unit contained within the background medium (crack-free matrix), has been calculated for dry and saturated conditions. There is a good correlation between the calculated crack-densities and crack-porosities derived from the experimentally determined volumetric strain curves. The shear wave velocity data, along with the shear wave polarisation referred to a orthogonal reference system, have been used to derive the spatial orientation of effective oriented cracks within a foliated biotite gneiss. The experimental data are in reasonable agreement with the self consistent model of O'Connell and Budiansky (1974). Taking the various lithologies into account, it is clear from the present study, that combined seismic measurements ofV p andV s , using theV p V s -ratio, may give evidence for fluids on grain boundaries and, in addition, may provide an estimate on the in-situ crack-densities.  相似文献   

6.
During geothermal power production using a borehole doublet consisting of a production and injection well, the reservoir conditions such as permeability k, porosity φ and Skempton coefficient B at the geothermal research site Gross Schoenebeck/Germany will change. Besides a temperature decrease at the injection well and a change of the chemical equilibrium, also the pore pressure p p will vary in a range of approximately 44 MPa ± 10 MPa in our reservoir at ?3850 to ?4258 m depth. This leads to a poroelastic response of the reservoir rocks depending on effective pressure p eff (difference between mean stress and pore pressure), resulting in a change in permeability k, porosity φ and the poroelastic parameter Skempton coefficient B. Hence, we investigated the effective pressure dependency of Flechtinger sandstone, an outcropping equivalent of the reservoir rock via laboratory experiments. The permeability decreased by 21% at an effective pressure range from 3 to 30 MPa, the porosity decreased by 11% (p eff = 6 to 65 MPa) and the Skempton coefficient decreased by 24% (p eff = 4 to 25 MPa). We will show which mechanisms lead to the change of the mentioned hydraulic and poroelastic parameters and the influence of these changes on the productivity of the reservoir. The most significant changes occur at low effective pressures until 15 to 20 MPa. For our in situ reservoir conditions p eff = 43 MPa a change of 10 MPa effective pressure will result in a change in matrix permeability of less than 4% and in matrix porosity of less than 2%. Besides natural fracture systems, fault zones and induced hydraulic fractures, the rock matrix its only one part of geothermal systems. All components can be influenced by pressure, temperature and chemical reactions. Therefore, the determined small poroelastic response of rock matrix does not significantly influence the sustainability of the geothermal reservoir.  相似文献   

7.
Equilibrium water uptake and the sizes of atmospheric aerosol particles have for the first time been determined for high relative humidities, i.e., for humidities above 95 percent, as a function of the particles chemical composition. For that purpose a new treatment of the osmotic coefficient has been developed and experimentally confirmed. It is shown that the equilibrium water uptake and the equilibrium sizes of atmospheric aerosol particles at large relative humidities are significantly dependent on their chemical composition.List of symbols A proportionality factor - a w activity of water in a solution - c p v specific heat of water vapour at constant pressure - c w specific heat of liquid water - f relative humidity - l w specific heat of evaporation of water - M i molar mass of solute speciesi - M s mean molar mass of all the solute species in a solution - M w molar mass of water - m 0 mass of an aerosol particle in dry state - m i mass of solute speciesi - m s mass of solute - m w mass of water taken up by an aerosol particle in equilibrium state - m total molality=number of mols of solute species in 1000 g of water - m i molality of solute speciesi - m k total molality of a pure electrolytek - O(m 2) remaining terms being of the second and of higher powers ofm - p + standard pressure - p total pressure of the gas phase - p pressure within a droplet - p 1,p 2,p 3 coefficients in the expansion of M - p 1i, p2i, p3i specific parameters of ioni - p s saturation vapour pressure - p w water vapour pressure - R w individual gas constant of water - r radius of a droplet - r 0 equivalent volume radius of an aerosol particle in dry state - T temperature - T 0 standard temperature - T 1 temperature of the pure water drop in the osmometer - v w specific volume of pure water - z i valence of ioni - i relativenumber concentration of ioni in a solution - correction term due to the adsorption of ions at liquid-solid interfaces - activity coefficient of solute speciesi in a solution, related to molalities - I bridge current - T temperature difference between solution and pure water drop in the osmometer - exponential mass increase coefficient - w specific chemical potential of water vapour - w specific chemical potential of water - 0 w specific chemical potential of pure water vapour - 0 w specific chemical potential of pure water - 0 density of an aerosol particle in dry state - w density of pure water - surface tension of a droplet - 0 surface tension of pure water, i.e., at infinite dilution of the solute - osmotic coefficient - k osmotic coefficient of a solution of a pure electrolytek - k osmotic coefficient of a solution of a mixed solute - M fugacity coefficient of water vapour - s i=1 i z 2 i This work is part of a Ph.D. thesis carried out at the Meteorological Institute of the Johannes Gutenberg-Universität, Mainz.  相似文献   

8.
Stable isotope paleoaltimetry has provided unprecedented insights into the topographic histories of many of the world’s highest mountain ranges. However, on the Tibetan Plateau (TP), stable isotopes from paleosols generally yield much higher paleoaltitudes than those based on fossils. It is therefore essential when attempting to interpret accurately this region’s paleoaltitudes that the empirical calibrations of local stable isotopes and the relations between them are established. Additionally, it is vital that careful estimations be made when estimate how different isotopes sourced from different areas may have been influenced by different controls. We present here 29 hydrogen isotopic values for leaf wax-derived n-alkanes (i.e., δDwax values, and abundance-weighted average δD values of C29 and C31) in surface soils, as well as the δD values of soil water (δDsw) samples (totaling 22) from Mount Longmen (LM), on the eastern TP (altitude ~0.8–4.0 km above sea level (asl), a region climatically affected by the East Asian Monsoon (EAM). We compared our results with published data from Mount Gongga (GG). In addition, 47 river water samples, 55 spring water samples, and the daily and monthly summer precipitation records (from May to October, 2015) from two precipitation observation stations were collected along the GG transect for δD analysis. LM soil δDwax values showed regional differences and responded strongly to altitude, varying from?160‰ to?219‰, with an altitudinal lapse rate (ALR) of?18‰ km?1 (R 2=0.83; p<0.0001; n=29). These δDwax values appeared more enriched than those from the GG transect by ~40‰. We found that both the climate and moisture sources led to the differences observed in soil δDwax values between the LM and GG transects. We found that, as a general rule, ε wax/rw, ε wax/p and ε wax/sw values (i.e., the isotopic fractionation of δDwax corresponding to δDrw, δDp and δDsw) increased with increasing altitude along both the LM and GG transects (up to 34‰and 50‰, respectively). Basing its research on a comparative study of δDwax, δDp, δDrw(δDspringw) and δDsw, this paper discusses the effects of moisture recycling, glacier-fed meltwater, relative humidity (RH), evapotranspiration (ET), vegetation cover, latitude, topography and/or other factors on ε wax/p values. Clearly, if ε wax-p values at higher altitudes are calculated using smaller ε wax-p values from lower altitudes, the calculated paleowaterδDp values are going to be more depleted than the actual δD values, and any paleoaltitude would therefore be overestimated.  相似文献   

9.
The deformation of movable boundaries under the action of an applied turbulent shear stress is well known. The resulting bed forms often are highly organized and nearly two-dimensional, which makes them an intriguing focus of study considering that they are generated in both steady and oscillatory turbulent flows. Many past studies share a common approach in which an infinitesimal perturbation is prescribed and the resulting growth or decay patterns are examined. In this approach, the bed forms are usually sinusoidal and the perturbation analysis does not provide a theoretical prediction of equilibrium bed-form geometry. An alternative approach is suggested here in which the forcing terms (pressure and stress) are prescribed parametrically and the governing equations are solved for the flow velocity and the associated boundary deformation. Using a multilayered approach, in which the bottom boundary layer is divided into a discrete, yet, arbitrary number of finite layers, analytical solutions for the horizontal current and bed profile are derived. The derivations identify two nondimensional parameters, p0/u02 and 0/kh0u02, which modulate the amplitude of the velocity fluctuations and boundary deformation. For the case of combined pressure and stress divergence anomalies, the magnitude of the front face and lee slopes exhibit an asymmetry that is consistent with observed bed forms in steady two-dimensional flows.Responsible Editor: Jens Kappenberg  相似文献   

10.
Analysis of Thomsen parameters for finely layered VTI media   总被引：2，自引：0，他引：2  
Since the work of Postma and Backus, much has been learned about elastic constants in vertical transversely isotropic (VTI) media when the anisotropy is due to fine layering of isotropic elastic materials. Nevertheless, there has continued to be some uncertainty about the possible range of Thomsen's anisotropy parameters ε and δ for such media. We use both Monte Carlo studies and detailed analysis of Backus' equations for both two- and three-component layered media to establish the results presented. We show that ε lies in the range ?3/8 ε ½[〈v2p〉〈v?2p〉?1], for finely layered media; smaller positive and all negative values of ε occur for media with large fluctuations in the Lamé parameter λ in the component layers. We show that δ can also be either positive or negative, and that for constant density media, sign (δ) = sign (〈v?2p〉 ? 〈v?2s〉〈v2s/v2p〉). Monte Carlo simulations show that among all theoretically possible random media, positive and negative δ are equally likely in finely layered media. (Of course, the δs associated with real earth materials may span some smaller subset of those that are theoretically possible, but answering this important question is beyond our present scope.) Layered media having large fluctuations in λ are those most likely to have positive δ. This is somewhat surprising since ε is often negative or a small positive number for such media, and we have the general constraint that ε ? δ > 0 for layered VTI media. Since Gassmann's results for fluid-saturated porous media show that the mechanical effects of fluids influence only the Lamé parameter λ, not the shear modulus μ, these results suggest that small positive δ occurring together with small positive ε (but somewhat larger than δ) may be indicative of changing fluid content in a layered earth.  相似文献   

11.
Summary An explicit solution is obtained for the system of equations describing the spheroidal motion in a homogeneous, isotropic, gravitating, elastic medium possessing spherical symmetry. This solution is used to derive the Green's dyad for a homogeneous gravitating sphere. The Green's dyad is then employed to obtain the displacement field induced by tangential and tensile dislocations of arbitrary orientation and depth within the sphere.Notation G Gravitational constant - a Radius of the earth - A o =4/3 G - Perturbation of the gravitational potential - Circular frequency - V p ,V s Compressional and shear wave velocities - k p =/V p - k s =/V s - k p [(2.8)] - , [(2.17)] - f l + Spherical Bessel function of the first kind - f l – Spherical Hankel function of the second kind - x =r - y =r - x o =r o - y o =ro - x =r k s - y =r k p - x o =r o k s - y o =r o k p - =a - =a - [(5.17)] - m, l   相似文献   

12.
In granite aquifers, fractures can provide both storage volume and conduits for groundwater. Characterization of fracture hydraulic conductivity (K) in such aquifers is important for predicting flow rate and calibrating models. Nuclear magnetic resonance (NMR) well logging is a method to quickly obtain near-borehole hydraulic conductivity (i.e., KNMR) at high-vertical resolution. On the other hand, FLUTe flexible liner technology can produce a K profile at comparable resolution but requires a fluid driving force between borehole and formation. For three boreholes completed in a fractured granite, we jointly interpreted logging NMR data and FLUTe K estimates to calibrate an empirical equation for translating borehole NMR data to K estimates. For over 90% of the depth intervals investigated from these boreholes, the estimated KNMR are within one order of magnitude of KFLUTe. The empirical parameters obtained from calibrating the NMR data suggest that “intermediate diffusion” and/or “slow diffusion” during the NMR relaxation time may occur in the flowing fractures when hydraulic aperture are sufficiently large. For each borehole, “intermediate diffusion” dominates the relaxation time, therefore assuming “fast diffusion” in the interpretation of NMR data from fractured rock may lead to inaccurate KNMR estimates. We also compare calibrations using inexpensive slug tests that suggest reliable KNMR estimates for fractured rock may be achieved using limited calibration against borehole hydraulic measurements.  相似文献   

13.
The distributions of permeability and porosity are key factors that control airflow and gas phase transport in unsaturated formations. To understand the behavior of flow and transport in such formations, characterization procedure is a typical approach that has been widely applied to laboratories and fields. As is recognized by most investigations, this approach relies on accurate measurements, and more importantly, an adequate tool to interpret those measurements from experiments. This study presents a pneumatic inverse model that is capable to estimate the distributions of permeability (k) and porosity () with high resolution in heterogeneous unsaturated formations. Based on the concept of sequential successive linear estimator (SSLE), the developed model accounts for compressibility and density of air and estimates the geologic parameters using air pressure measurements from sequential cross-hole pneumatic pumping or injection tests. Four synthetic examples, including a one-dimensional well-posed, a horizontally two-dimensional, and two three-dimensional problems, are used to evaluate the developed model in estimating the distributions of permeability and porosity in unsaturated formations. Results of the numerical experiments are promising. The developed pneumatic inverse model can reconstruct the property (i.e., permeability and porosity) fields if the well-defined conditions are met. With a relatively small number of available measurements, the proposed model can accurately capture the patterns and the magnitudes of estimated properties for unsaturated formations. Results of two complex three-dimensional examples show that the proposed model can map the fracture connectivity using a small number of subsurface pressure measurements and estimate k and in shallow soil layers using spatial variations of barometric pressure.  相似文献   

14.
We used hydrogeologic models to assess how fault-zone properties promote or inhibit the downward propagation of fluid overpressures from a basal reservoir injection well (150 m from fault zone, Q = 5000 m3/day) into the underlying crystalline basement rocks. We varied the permeability of the fault-zone architectural components and a crystalline basement weathered layer as part of a numerical sensitivity study. Realistic conduit-barrier style fault zones effectively transmit elevated pore pressures associated with 4 years of continuous injection to depths of approximately 2.5 km within the crystalline basement while compartmentalizing fluid flow within the injection reservoir. The presence of a laterally continuous, relatively low-permeability altered/weathered basement horizon (kaltered layer = 0.1 × kbasement) can limit the penetration depth of the pressure front to approximately 500 m. On the other hand, the presence of a discontinuous altered/weathered horizon that partially confines the injection reservoir without blocking the fault fluid conduit promotes downward propagation of pressures. Permeability enhancement via hydromechanical failure was found to increase the depth of early-time pressure front migration by a factor of 1.3 to 1.85. Dynamic permeability models may help explain seismicity at depths of greater than 10 km such as is observed within the Permian Basin, NM.  相似文献   

15.
Two equivalent permeability tensors are defined for 3D heterogeneous media, KpKp and KqKq, valid respectively for linear pressure and constant flux conditions at the block boundary. Both tensors are symmetric and positive-definite and the second one produces lower magnitude of directional permeability than the first one. These tensors only depends upon the internal block structure and 3D distribution of the local permeability values. On this basis, we develop first a straightforward method for evaluating the coefficients of the 2D tensor for the problem of flow through fracture traces in a cross-section, subject to linear pressure conditions. A quartzite rock mass is used as an example to illustrate this method. Then, an approximated method is proposed to build up the 3D permeability tensor of the fractured block from the ellipses within cross-sections in varied orientations.  相似文献   

16.
—The "dynamic" permeability k(ω) of heterogeneous networks of cracks, tubes and spheres, was determined by numerically simulating the harmonic flow of an interstitial fluid for a wide range of frequencies. For comparison with previous works, this procedure was applied to the 100 network realizations used in Bernabé (1995). In most cases, the calculated frequency dependence of the real and imaginary parts of k(ω) was consistent with the JKD model (Johnson et al., 1987), showing a transition from "viscous", macroscopic flow at low frequencies to "inertial" flow at high frequencies. The viscous skin depth δ c at the transition was found to be proportional to the critical capillary radius r c from a capillary invasion (Katz and Thompson, 1986). A simple explanation is that these two length scales arise from the same percolation problem. On the other hand, δ c was not well correlated with the JKD parameter Λ. The conclusion is that Λ and δ c (or r c ?) are two independent parameters, derived from two unrelated approaches (i.e., weighted averaging and percolation theory). Finally, an attempt was made to relax the initial assumptions of a rigid solid matrix and an incompressible fluid. It was observed that the effect of the fluid compressibility could occasionally be very large, especially when networks with large amounts of storage pore space were considered.  相似文献   

17.
The time required at a field site to obtain a few measurements of saturated hydraulic conductivity (Ks) will allow for many measurements of soil air permeability (ka). This study investigates if ka measured in situ (ka, in situ) can be a substitute for measurement of Ks in relation to infiltration and surface runoff modelling. Measurements of ka, in situ were carried out in two small agricultural catchments. A spatial correlation of the log‐transformed values existed having a range of approximately 100 m. A predictive relationship between Ks and ka measured on 100‐cm3 soil samples in the laboratory was derived for one of the field slopes and showed good agreement with an earlier suggested predictive Ks–ka relationship. In situ measurements of Ks and ka suggested that the predictive relationships also could be used at larger scale. The Ks–ka relationships together with the ka, in situ data were applied in a distributed surface runoff (DSR) model, simulating a high‐intensity rainfall event. The DSR simulation results were highly dependent on whether the geometric average of ka, in situ or kriged values of ka, in situ was used as model input. When increasing the resolution of Ks in the DSR model, a limit of 30–40 m was found for both field slopes. Below this limit, the simulated runoff and hydrograph peaks were independent of resolution scale. If only a few randomly chosen values of Ks were used to represent the spatial variation within the field slope, very large deviations in repeated DSR simulation results were obtained, both with respect to peak height and hydrograph shape. In contrast, when using many predicted Ks values based on a Ks–ka relationship and measured ka, in situ data, the DSR model generally captured the correct hydrograph shape although simulations were sensitive to the chosen Ks–ka relationship. As massive measurement efforts normally will be required to obtain a satisfactory representation of the spatial variability in Ks, the use of ka, in situ to assess spatial variability in Ks appears a promising alternative. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

18.
This study presents a new unsteady-state method for measuring two-phase relative permeability by obtaining local values of the three key parameters (saturation, pressure drop, and phase flux) versus time during a displacement. These three parameters can be substituted to two-phase Darcy Buckingham equation to directly determine relative permeability. To obtain the first two, we use a medical X-ray Computed Tomography (CT) scanner to monitor saturation in time and space, and six differential pressure transducers to measure the overall pressure drop and the pressure drops of five individual sections (divided by four pressure taps on the core) continuously. At each scanning time, the local phase flux is obtained by spatially integrating the saturation profile and converting this to the flux using a fractional flow framework. One advantage of this local method over most previous methods is that the capillary end effect is experimentally avoided; this improvement is crucial for experiments using low viscosity fluids such as supercritical and gas phases. To illustrate the new method, we conduct five CO2-brine primary drainage experiments in a 60.8 cm long and 116 mD Berea sandstone core at 20 °C and 1500 psi. In return, we obtain hundreds of unsteady-state CO2 and brine relative permeability data points that are consistent with steady-state relative permeability data from the same experiments. Due to the large amount of relative permeability data obtained by the new unsteady-state method, the uncertainties of the exponents in the Corey-type fits decrease by up to 90% compared with the steady-state method.  相似文献   

19.
Summary This paper considers an incompressible fluid flowing through a straight, circular tube whose walls are uniformly porous. The flow is steady and one dimensional. The loss of fluid through the wall is proportional to the mean static pressure in the tube. Several formulations of the wall shear stress are considered; these formulations were motivated by the results from Hamel's radial flow problem, boundary layer flows/and boundary layer suction profiles. For each of these formulations exact solutions for the mean axial velocity and the mean static pressure of the fluid are obtained. Sample results are plotted on graphs. For the constant wall shear stress problem, the theoretical solutions compare favorably with some experimental results.Notations A, B, D, E constant parameters - a, b constant parameters - Ai(z), Bi(z) Airy functions - Ai, Bi derivatives of Airy functions - k constant of proportionality betweenV andp - L length of pores - p,p mean static pressure - p 0 static pressure outside the tube - p 0 value ofp atx=0 - Q constant exponent - R inside radius of the tube - T wall shear stress - T 0 shear parameter - t wall thickness - U free stream velocity - ,u mean axial velocity - u 0 value ofu atx=0 - V,V mean seepage velocity through the wall - v 0 mean seepage velocity - x,x axial distance along the tube - z transformed axial distance - z 0 value ofz atx=0 - mean outflow angle through the wall - cos - density of the fluid - wall shear stress - dynamic viscosity of the fluid - over-bar dimensional terms - no bar nondimensional terms The National Center for Atmospheric Research is sponsored by the National Science Foundation  相似文献   

20.
Floods have become increasingly important in fluvial export of water, sediment and carbon (C). Using high-frequency sampling, the export of water, sediment and C was examined in the Wuding River catchment on the Chinese Loess Plateau. With groundwater as an important contributor to runoff all year round, floods were relatively less important in the export of water. However, large floods were disproportionately important in exporting sediment and inorganic C (DIC) and organic C (DOC and POC). The three largest floods in each year transported 53.6–97.3 and 41.4–77% of the annual sediment and C fluxes, respectively. An extreme flood in 2017 alone contributed 94.6 and 73.1% of the annual sediment and C fluxes, respectively, in just 7 days, which included 20.3, 92.1 and 35.7% of the annual DOC, POC and DIC fluxes, respectively. A stable carbon isotope (δ13C) analysis of POC indicated that modern soils and C3 plants were its primary source. Furthermore, floods greatly accelerated CO2 degassing due to elevated gas transfer velocity, although stream water CO2 partial pressure (pCO2) exhibited a decreasing trend with flow discharge. Although these results illustrated that increasing runoff diluted pCO2, the timing and magnitude of floods were found to be critical in determining the response of pCO2 to flow dynamics. Low-magnitude floods in the early wet season increased pCO2 because of enhanced organic matter input, while subsequent large floods caused a lower pCO2 due to greatly reduced organic matter supply. Finally, continuous monitoring of a complete flood event showed that the CO2 efflux during the flood (2348 ± 664 mg C m–2 day–1) was three times that under low-flow conditions (808 ± 98 mg C m–2 day–1). Our study suggests that infrequent, heavy storm events, which are predicted to increase under climate change, will greatly alter the transport regimes of sediment and C. © 2020 John Wiley & Sons, Ltd.  相似文献   

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