Uncertainty Estimate in Resources Assessment: A Geostatistical Contribution   总被引：2，自引：0，他引：2  

de Souza  Luis Eduardo  Costa  João Felipe C. L.  Koppe  Jair C. 《Natural Resources Research》2004,13(1):1-15

For many decades the mining industry regarded resources/reserves estimation and classification as a mere calculation requiring basic mathematical and geological knowledge. Most methods were based on geometrical procedures and spatial data distribution. Therefore, uncertainty associated with tonnages and grades either were ignored or mishandled, although various mining codes require a measure of confidence in the values reported. Traditional methods fail in reporting the level of confidence in the quantities and grades. Conversely, kriging is known to provide the best estimate and its associated variance. Among kriging methods, Ordinary Kriging (OK) probably is the most widely used one for mineral resource/reserve estimation, mainly because of its robustness and its facility in uncertainty assessment by using the kriging variance. It also is known that OK variance is unable to recognize local data variability, an important issue when heterogeneous mineral deposits with higher and poorer grade zones are being evaluated. Altenatively, stochastic simulation are used to build local or global uncertainty about a geological attribute respecting its statistical moments. This study investigates methods capable of incorporating uncertainty to the estimates of resources and reserves via OK and sequential gaussian and sequential indicator simulation The results showed that for the type of mineralization studied all methods classified the tonnages similarly. The methods are illustrated using an exploration drill hole data sets from a large Brazilian coal deposit.  相似文献   

Petrogenesis of the Eocene and Mio–Pliocene alkaline basaltic magmatism in Meseta Chile Chico, southern Patagonia, Chile: Evidence for the participation of two slab windows     

Felipe Espinoza  Diego Morata  Ewan Pelleter  Ren  C. Maury  Manuel Su  rez  Yves Lagabrielle  Mireille Polv    Herv  Bellon  Joseph Cotten  Rita De la Cruz  Christelle Guivel 《Lithos》2005,82(3-4):315-343

The Meseta Chile Chico (MCC, 46.4°S) is the westernmost exposure of Eocene (lower basaltic sequence, LBS; 55–40 Ma, K–Ar ages) and Mio–Pliocene (upper basaltic sequence, UBS; 16–4 Ma, K–Ar ages) flood basalt volcanism in Patagonia. The MCC is located south of the Lago General Carrera-Buenos Aires (LGCBA), southeast from the present day Chile Triple Junction (CTJ), east of the actual volcanic gap between Southern South Volcanic Zone and Austral Volcanic Zone (SSVZ and AVZ, respectively) and just above the inferred location of the South Chile Ridge segment subducted at 6 Ma (SCR-1). Erupted products consist of mainly ne-normative olivine basalt with minor hy-normative tholeiites basalt, trachybasalt and basanite. MCC lavas are alkaline (42.7–53.1 wt.% SiO₂, 3–8 wt.% Na₂O+K₂O) and relatively primitive (Ni: 133–360 ppm, Cr: 161–193 ppm, Co: 35–72 ppm, 4–16.5 MgO wt.%). They have a marked OIB-like signature, as shown by their isotopic compositions (⁸⁷Sr/⁸⁶Sr_o=0.70311–0.70414 and εNd=+4.7–+5.1) and their incompatible trace elements ratios (Ba/La=10–20, La/Nb=0.46–1.09, Ce/Pb=15.52–27.5, Sr/La<25), reflecting deep mantle origin. UBS-primitive lavas have characteristics similar to those of the Eocene LBS basalts, while UBS-intermediate lavas show geochemical imprints (La/Nb>1, Sr/La>25, low Ce/Pb, Nb/U) compatible with contamination by arc/slab-derived and/or crustal components. We propose that the genesis and extrusion of magmas is related to the opening of two slab windows due to the subduction of two active ridge segments beneath Patagonia during Eocene and Mio–Pliocene.  相似文献   

On the numerical simulation of waterflooding of heterogeneous petroleum reservoirs     

Jim Douglas Jr.  Frederico Furtado  Felipe Pereira 《Computational Geosciences》1997,1(2):155-190

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A parallelizable method for two‐phase flows in naturally‐fractured reservoirs     

Jim Douglas Jr.  Felipe Pereira  Li‐Ming Yeh 《Computational Geosciences》1997,1(3-4):333-368

A parallelizable, semi‐implicit numerical method is proposed for the study of naturally‐fractured reservoir systems. It has proved to be computationally efficient in producing accurate numerical solutions for the dual‐porosity model for immiscible, two‐phase flow in such reservoirs. The method combines hybridized mixed finite elements, a new version of the modified method of characteristics, a sophisticated operator‐splitting procedure for separating the pressure calculation in the fractures from that of the saturation, another operator splitting to handle the interaction of the matrix blocks and the fractures, and domain decomposition iterative procedures for both the pressure and the saturation. It permits moderately long time steps for the pressure and the saturation in the fractures and matrix blocks by using short, inexpensive microsteps to treat the transport portion of the saturation equation in the fractures. This paper is devoted to the formulation of the method and a discussion of numerical results for five‐spot and vertical cross‐section examples.  相似文献   

Structure of the Mérida Andes, Venezuela: relations with the South America–Caribbean geodynamic interaction     

Felipe E. Audemard  Franck A. Audemard   《Tectonophysics》2002,345(1-4)

For over 50 years, several models based on diverse geologic concepts and variable quality of data have been proposed to explain the major structure and history of the Mérida Andes (MA), in western Venezuela. Lately, this chain growth and associated flexural basins deepening have been related to incipient type-A subductions of either polarity, accounting for the across-chain asymmetry. However, these recent models have not well integrated the present tectonically active setting driven by neighboring major plate interactions. At present, this chain exhibits ongoing strain partitioning where cumulative right-lateral slip along chain axis is as much as half of, or about the same, as the transverse shortening since late Miocene, thus implying that the NNE-directed Maracaibo block extrusion with respect to the South America (SA) plate is not a secondary feature. Consequently, this paper discusses some limitations exhibited by the SE-directed continental subduction models—Maracaibo crust underthrusting the Mérida Andes—in the light of available geological and geophysical data. Besides, it is herein proposed that the Mérida Andes structuration is related to a NW-directed, gently dipping, incipient type-A subduction, where chain growth and evolution are similar to those of a sedimentary accretionary wedge (i.e., Barbados), but at crustal scale and with ongoing strain partitioning. This continental subduction is the SE portion of a major orogenic float that also comprises the Perijá range and the Santa Marta block.  相似文献   

Geostatistical Simulation of Acoustic Log Data for Seismic Depth Conversion     

Vanessa Cerqueira Koppe  João Felipe Coimbra Leite Costa  Jair Carlos Koppe  Fernando Gambin  Gary Fallon  Nick Davies 《Natural Resources Research》2007,16(4):293-303

Seismic reflection methods measure the time a seismic wave takes to travel through the ground, from the user defined source to a series of signal monitoring sensors known as geophones. The measured times need to be depth converted to allow for integration with other geological data. In order to convert from time to depth, an estimate of the rock volume velocity field must be made. The velocity field estimate can be made by assignment of velocity estimates to a geological model independent of the seismic processing. This article presents the results of using the acoustic geophysical log data extrapolated via sequential Gaussian simulation to derive the velocity field. The uncertainties associated with the velocity estimates were significant and provided the means to assess confidence limits for the actual depth determination. The technique is assessed by application to a major coal deposit, approximately 2.1 m thick and 210 m deep. Considering only the uncertainty associated with estimating the velocity field, half of the confidence interval values showed approximately 1 m of uncertainty in depth. The application of sequential Gaussian simulation to model the 3D distribution of acoustic velocity can be extended to other geophysical log parameters or derived estimates.  相似文献   

Partial melt in the lowermost mantle near the base of a plume     

Zuihong Zou  Felipe Leyton  Keith D. Koper 《Geophysical Journal International》2007,168(2):809-817

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Modelling the effects of soil type and root distribution on shallow groundwater resources          下载免费PDF全文

Stefania Grimaldi  Felipe Orellana  Edoardo Daly 《水文研究》2015,29(20):4457-4469

Vegetated, shallow groundwater environments typically have high environmental and economic value. A sound understanding of the complex interactions and feedbacks between surface vegetation and groundwater resources is crucial to managing and maintaining healthy ecosystems while responding to human needs. A vegetated shallow groundwater environment was modelled using the software HYDRUS 2D to investigate the effects of several combinations of soil type and root distributions on shallow groundwater resources. Three rainfall regimes coupled to both natural and anthropogenically affected groundwater conditions were used to investigate the effect that combinations of four soil types and five root distributions can have on (a) groundwater level drops, (b) groundwater depletion, (c) groundwater recharge and (d) water stress conditions. Vegetation with roots distributed across the whole unsaturated zone and vegetation with dimorphic root systems (i.e. roots having larger concentrations both near the surface and the capillary fringe) behaved differently from vegetation growing roots mainly near the saturated zone. Specifically, vegetation with roots in the unsaturated zone caused water‐table drops and groundwater depletions that were half the amount due to deep‐rooted vegetation. Vegetation with a large portion of roots near the soil surface benefited from rainfall and was less vulnerable to water‐table lowering; as such, the fraction of the total area of roots affected by water stress conditions could be 40% smaller than in the case with deep‐rooted vegetation. However, roots uniformly distributed in the unsaturated zone could halve groundwater recharge rates observed in bare soils. Our analysis provided insights that can enable the formulation of site‐ and purpose‐specific management plans to respond to both human and ecosystem water requirements. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Application of the two-stage Markov chain Monte Carlo method for characterization of fractured reservoirs using a surrogate flow model     

Victor Ginting  Felipe Pereira  Michael Presho  Shaochang Wo 《Computational Geosciences》2011,15(4):691-707

In this paper, we develop a procedure for subsurface characterization of a fractured porous medium. The characterization involves sampling from a representation of a fracture’s permeability that has been suitably adjusted to the dynamic tracer cut measurement data. We propose to use a type of dual-porosity, dual-permeability model for tracer flow. This model is built into the Markov chain Monte Carlo (MCMC) method in which the permeability is sampled. The Bayesian statistical framework is used to set the acceptance criteria of these samples and is enforced through sampling from the posterior distribution of the permeability fields conditioned to dynamic tracer cut data. In order to get a sample from the distribution, we must solve a series of problems which requires a fine-scale solution of the dual model. As direct MCMC is a costly method with the possibility of a low acceptance rate, we introduce a two-stage MCMC alternative which requires a suitable coarse-scale solution method of the dual model. With this filtering process, we are able to decrease our computational time as well as increase the proposal acceptance rate. A number of numerical examples are presented to illustrate the performance of the method.  相似文献   

Downscaling projections of climate change in Sao Tome and Principe Islands,Africa     

Sin Chan Chou  Andr&#; de Arruda Lyra  Jorge Lu&#;s Gomes  Daniel Andr&#;s Rodriguez  Minella Alves Martins  Nicole Costa Resende  Priscila da Silva Tavares  Claudine Pereira Dereczynski  Isabel Lopes Pilotto  Alessandro Marques Martins  Lu&#;s Felipe Alves de Carvalho  Jos&#; Luiz Lima Onofre  Idal&#;cio Major  Manuel Penhor  Ad&#;rito Santana 《Climate Dynamics》2020,54(9):4021-4042

Sao Tome and Principe is a small insular African country extremely vulnerable to rising sea levels and impacts such as inundation, shore line change, and salt water intrusion into underground aquifers. Projections of climate change have considered coarse model resolutions. The objective of this work is to dynamically downscale the global model projections to 4-km resolution and to assess the climate change in the Sao Tome and Principe islands. The global climate projections are provided by the Canadian Earth System Model under two Representative Concentration Pathways greenhouse gas scenarios, RCP4.5 and RCP8.5. The downscaling is produced by the Eta regional climate model. The baseline period is taken between 1971 and 2000, and the future climate period is taken between 2041 and 2070. The 2-m temperature simulations show good agreement with station data. The model simulates temperature more accurately than precipitation. The precipitation simulations systematically show underestimation and delay of the rainy and the dry seasons by about 1 month, a feature inherited from the global climate model. In the middle of the 21st century, projections show the strongest warming in the elevated parts of the Sao Tome Island, especially in February under RCP8.5. Warmer nights and warmer days become more frequent in the islands when compared with those in the present. While under RCP4.5, precipitation increases in the islands; under RCP8.5, it decreases everywhere in both islands. Heavy precipitation rates should increase, especially in the south-southwestern parts of the Sao Tome islands. Detailed spatial variability of the temperature and precipitation changes in the islands can only be revealed at very high spatial model resolution. Implications for the potential energy production from two major river basins are assessed in this work.  相似文献