A general method for simulating reactive dissolution in carbonate rocks with arbitrary geometry     

Piyang Liu  Gary Douglas Couples  Jun Yao  Zhaoqin Huang  Wenhui Song  Jingsheng Ma 《Computational Geosciences》2018,22(5):1187-1201

The two-scale continuum model is widely used in simulating the reactive dissolution process and predicting the optimum injection rate for carbonate reservoir acidizing treatment. The numerical methods of this model are currently based on structured grids, which are not applicable for complicated geometries. In this study, a general numerical scheme for simulating a reactive flow problem on both structured and unstructured grids is presented based on the finite volume method (FVM). The convection and diffusion terms involved in the reactive flow model are discretized by using the upwind scheme and two-point flux approximation (TPFA), respectively. The location of the centroid node inside each control volume is moved by using an optimization algorithm to make the connections with the surrounding elements as orthogonal as possible, which systematically improves the accuracy of the TPFA scheme. Additionally, in order to avoid the computational complexity resulting from the discretization of the non-linear term, the mass balance equation is only discretized in the spatial domain to get a set of ordinary differential equations (ODEs). These ODEs are coupled with the reaction equations and then solved using the numerical algorithm on ODEs. The accuracy and efficiency of the proposed method are studied by comparing the results obtained from the proposed numerical method with previous experimental and numerical results. This comparison indicates that, compared with the previous methods, the proposed method predicts the wormhole structure more accurately. Finally, the presented method is used to check the effect of the domain geometry, and it is found that the geometry of the flow domain has no effect on the optimum injection velocity, but the radial domain requires a larger breakthrough volume than the linear domain when other parameters are fixed.  相似文献   

Geostatistical Modelling of Cyclic and Rhythmic Facies Architectures     

Thomas Le Blévec  Olivier Dubrule  Cédric M. John  Gary J. Hampson 《Mathematical Geosciences》2018,50(6):609-637

A Pluri-Gaussian method is developed for facies variables in three dimensions to model vertical cyclicity related to facies ordering and rhythmicity. Cyclicity is generally characterised by shallowing-upward or deepening-upward sequences and rhythmicity by the repetition of facies at constant intervals along sequences. Both of these aspects are commonly observed in shallow-marine carbonate successions, especially in the vertical direction. A grid-free spectral simulation approach is developed, with a separable covariance allowing a dampened hole-effect to capture rhythmicity in the vertical direction and a different covariance in the lateral plane along strata, as in space-time models. In addition, facies ordering is created by using a spatial shift between two latent Gaussian functions in the Pluri-Gaussian approach. Rapid conditioning to data is performed via Gibbs sampling and kriging using the screening properties of separable covariances. The resulting facies transiograms can show complex patterns of cyclicity and rhythmicity. Finally, a three dimensional case study of shallow-marine carbonate deposits at outcrop shows the applicability of the modelling method.  相似文献   

Calcium-aluminum-rich inclusion found in the Ivuna CI chondrite: Are CI chondrites a good proxy for the bulk composition of the solar system?     

David R. Frank  Gary R. Huss  Michael E. Zolensky  Kazuhide Nagashima  Loan Le 《Meteoritics & planetary science》2023,58(10):1495-1511

Cosmochemists have relied on CI carbonaceous chondrites as proxies for chemical composition of the non-volatile elements in the solar system because these meteorites are fine-grained, chemically homogeneous, and have well-determined bulk compositions that agree with that of the solar photosphere, within uncertainties. Here we report the discovery of a calcium-aluminum-rich inclusion (CAI) in the Ivuna CI chondrite. CAIs are chemically highly fractionated compared to CI composition, consisting of refractory elements and having textures that either reflect condensation from nebular gas or melting in a nebular environment. The CAI we found is a compact type A CAI with typical ¹⁶O-rich oxygen. However, it shows no evidence of ²⁶Al, which was present when most CAIs formed. Finding a CAI in a CI chondrite raises serious questions about whether CI chondrites are a reliable proxy for the bulk composition of the solar system. Too much CAI material would show up as mismatches between the CI composition and the composition of the solar photosphere. Although small amounts of refractory material have previously been identified in CI chondrites, this material is not abundant enough to significantly perturb the bulk compositions of CI chondrites. The agreement between the composition of the solar photosphere and CI chondrites allows no more than ~0.5 atom% of CAI-like material to have been added to CI chondrites. As the compositions of CI chondrites, carbonaceous asteroids, and the solar photosphere are better determined, we will be able to reduce the uncertainties in our estimates of the composition of the solar system.  相似文献   

A comparison of ancient deltaic shoreline progradation with modern deltaic progradation rates: Unravelling the temporal structure of the shallow-marine Blackhawk Formation,Upper Cretaceous Western Interior Seaway,USA     

Tore Aadland  Gary Hampson  William Helland-Hansen 《Basin Research》2023,35(2):825-841

Understanding how sedimentary rocks represent time is one of the significant challenges in sedimentology. Sedimentation rates retrieved from vertical sections are strongly timescale dependent, which means that we cannot use empirical rate data derived from vertical sections in modern environments to interpret the temporal structure of ancient sedimentary deposits. We use the Lower to Middle Campanian Blackhawk Formation deposits in eastern Utah and western Colorado as a natural laboratory to test a source-to-sink methodology circumventing this timescale dependence by relating modern progradation rates to the deltaic shoreline progradation of ancient siliciclastic rocks. Our objective is to quantify how much time is needed to account for the observed cumulative deltaic shoreline progradation recorded by the shallow-marine sandstone bodies of the Blackhawk Formation in terms of progradation rates derived from comparable modern deltaic systems. By making the simplifying assumption that the Blackhawk Formation rocks were deposited along a linear coastline that only grew by aggradation and progradation, it is possible to argue that the stratigraphic completeness of two-dimensional dip-oriented stratigraphic cross-sections through these deposits should be high. Furthermore, we hypothesise that delta progradation estimates capture a significant portion of the biostratigraphically and radiometrically constrained duration of the succession. By comparing the recorded progradation with modern progradation rates, we estimate that we need ca. 20% (median value, with minimum and maximum estimates of 2% and 300%) of the time available from biostratigraphic and radiometric dating to account for the progradation recorded by the sedimentary deposits. This indicates that long-term progradation rates averaged over the entire duration of the Blackhawk Formation were only a factor of five times slower than the modern progradation rates derived from observations over periods that are five to six orders of magnitude shorter. We conclude that a significant amount of time is represented by prograding deltaic shoreline deposits and that by considering the cumulative shoreline progradation, we could limit the effects of timescale dependence on the rate estimates used in our analysis.  相似文献   

Precipitation changes due to the introduction of eddy-resolved sea surface temperatures into simulations of the “Pasha Bulker” Australian east coast low of June 2007     

Christopher R. S. Chambers  Gary B. Brassington  Ian Simmonds  Kevin Walsh 《Meteorology and Atmospheric Physics》2014,123(1-2):1-15

Stratocumulus is often present offshore of Peru and northern Chile and exists at the top of a cool, moist and well-mixed marine boundary layer (MBL) under a marked temperature inversion maintained by large-scale subsidence. The subtropical MBL and stratocumulus has been the focus of many recent studies, but mid-latitude systems can exert a strong influence. However, this connection is not well established due to debatable model results and few in situ measurements south of 20°S. During a 2-week field campaign in August 2011 at Robinson Crusoe Island (~700 km offshore at 33.6°S), radiosondes were launched to observe the response of the MBL to mid-latitude synoptic forcing. During the observation period a broad, slow-moving cutoff low (COL) passed over the region. Other observations include COSMIC GPS, infrared satellite imagery, TRMM radar reflectivity, and operational radiosondes from the Chilean weather service. A numerical simulation is included to diagnose the synoptic features. The inversion prior to the COL was maintained and lifted above 5 km as the COL passed over the island. Soon after the COL center passed the island, the MBL top did not descend or reform near the surface and then deepen, but rather an inversion reformed at ~2.7 km. Using a variety of datasets, the height of the reformation of the inversion is related to the cloud top height of the scattered shallow cumulus convection under the COL, which coincides with the level of maximum convergence of the vertical velocity.  相似文献   

Large eddy simulations of two-dimensional turbulent convection in a density-stratified fluid     

Qiaoning Chen  Gary A. Glatzmaier 《地球物理与天体物理流体动力学》2013,107(5):355-375

Large eddy simulations (LES) of two-dimensional turbulent convection within the anelastic approximation are presented for Rayleigh number Ra?=?10⁹, Prandtl number Pr?=?1 with free-slip boundary conditions. Various subgrid-scale (SGS) models are investigated such as a similarity model, a dynamic similarity model, a dynamic eddy-viscosity model, a hyperdiffusion model and a hybrid model (dynamic similarity hyperdiffusion model). To study the effects of density stratification on the models, we have also carried out simulations for a Boussinesq flow. The SGS models are compared to direct numerical simulation (DNS) data on the basis of kinetic energy and entropy variance spectra, mean entropy profiles, r.m.s. entropy profiles and r.m.s. kinetic energy density profiles. The results show that for the Boussinesq flow, all the SGS models agree fairly well with the high resolution DNS data. However, for the strongly density-stratified flow, only the hyperdiffusion and the hybrid model show good performance.  相似文献   

Design and quantification of an extreme winter storm scenario for emergency preparedness and planning exercises in California     

Michael D. Dettinger  F. Martin Ralph  Mimi Hughes  Tapash Das  Paul Neiman  Dale Cox  Gary Estes  David Reynolds  Robert Hartman  Daniel Cayan  Lucy Jones 《Natural Hazards》2012,60(3):1085-1111

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Editorial     

Gary Huckleberry  Jamie Woodward 《Geoarchaeology》2012,27(1):1-1

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Multi-batch, incremental assembly of a dynamic magma chamber: the case of the Peninsula pluton granite (Cape Granite Suite, South Africa)     

Federico Farina  Gary Stevens  Arnaud Villaros 《Mineralogy and Petrology》2012,106(3-4):193-216

The S-type Peninsula Pluton (South Africa) exhibits substantial compositional variability and hosts a large variety of mafic and felsic magmatic enclaves with contrasting textures and compositions. Moreover, the pluton is characterized by mechanical concentrations of K-feldspar megacrysts, cordierite and biotite, generating a complex array of magmatic structures including schlieren, pipes, and spectacular sheeted structures. Chemical evidence indicates that the pluton is constructed incrementally by rapid emplacement of numerous magma pulses. Field, and textural data suggest that magmatic structures form by local flow at the emplacement level of highly viscous crystal-rich magmas (i.e. crystallinity up to 50?vol.%) through magma mushes assembled from older batches. At the time of arrival of relatively late magma batches, some areas within the pluton had achieved crystal fractions that allowed the material to act as a solid, whilst maintaining enough melt to prevent formation of sharp intrusional contacts. Magmatic structures represent “snapshots” of processes that operate in multiphase crystal-rich mushes and their genesis is due to mechanical and thermal instabilities in the crystal-rich magma chamber that are triggered by the emplacement of pulses of new magma derived from the melting of a compositionally variable metasedimentary source.  相似文献   

Patterns in the Landscape and Erosion of Cultural Sites Along the Colorado River Corridor in Grand Canyon,USA     

Joel L. Pederson  Gary R. O'Brien 《Geoarchaeology》2014,29(6):431-447

The geologic and geomorphic template of Grand Canyon influences patterns in the archaeological record, including sites where apparent increases in erosion may be related to Glen Canyon Dam. To provide geoarchaeological context for the Colorado River corridor and such issues, we explore first‐order trends in a database of field observations and topographic metrics from 227 cultural sites. The patterns revealed may be expected in other river‐canyon settings of management concern. The spatial clustering of sites along the river follows variations in width of the valley bottom and the occurrence of alluvial terraces and debris fans, linking to bedrock controls. In contrast, the pattern of more Formative (Ancestral Puebloan, 800–1250 A.D.) sites in eastern Grand Canyon and Protohistoric (1250–1776 A.D.) sites in western Grand Canyon does not follow any evident geomorphic trends. In terms of site stability, wider reaches with more terrace and debris fan landforms host a disproportionate number of sites with acute erosion. This links most directly to weak alluvial substrates, and the primary erosion process is gullying with diffusive‐creep processes also pervasive. Although Glen Canyon Dam does not directly influence these erosion processes, overall sediment depletion and the loss of major flooding leaves erosion unhampered along the river corridor.  相似文献