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41.
A review and analysis of post-stack time-lapse time-shifts has been carried out that covers published literature supplemented by in-house datasets available to the authors. Time-shift data are classified into those originating from geomechanical effects and those due to fluid saturation changes. From these data, conclusions are drawn regarding the effectiveness of post-stack time-shifts for overburden and reservoir monitoring purposes. A variety of field examples are shown that display the range and magnitude of variation for each class of application. The underlying physical mechanisms creating these time-shifts are then described, and linked to a series of generic and field-specific rock physics calculations that predict their magnitudes. These calculations serve as a guide for practitioners wishing to utilize this information on their own datasets. Conclusions are drawn regarding the reliability of this attribute for monitoring purposes, and the extent to which further development is required and how it should be reported by authors. 相似文献
42.
K. H. Hamed A. E. Hassan 《Stochastic Environmental Research and Risk Assessment (SERRA)》2000,14(6):428-448
An efficient numerical solution for the two-dimensional groundwater flow problem using artificial neural networks (ANNs)
is presented. Under stationary velocity conditions with unidirectional mean flow, the conductivity realizations and the head
gradients, obtained by a traditional finite difference solution to the flow equation, are given as input-output pairs to train
a neural network. The ANN is trained successfully and a certain level of recognition of the relationship between input conductivity
patterns and output head gradients is achieved. The trained network produced velocity realizations that are physically plausible
without solving the flow equation for each of the conductivity realizations. This is achieved in a small fraction of the time
necessary for solving the flow equations. The prediction accuracy of the ANN reaches 97.5% for the longitudinal head gradient
and 94.7% for the transverse gradient. Head-gradient and velocity statistics in terms of the first two moments are obtained
with a very high accuracy. The cross covariances between head gradients and the fluctuating log-conductivity (log-K) and between velocity and log-K obtained with the ANN approach match very closely those obtained by a traditional numerical solution. The same is true for
the velocity components auto-covariances. The results are also extended to transport simulations with very good accuracy.
Spatial moments (up to the fourth) of mean-concentration plumes obtained using ANNs are in very good agreement with the traditional
Monte Carlo simulations. Furthermore, the concentration second moment (concentration variance) is very close between the two
approaches. Considering the fact that higher moments of concentration need more computational effort in numerical simulations,
the advantage of the presented approach in saving long computational times is evident. Another advantage of the ANNs approach
is the ability to generalize a trained network to conductivity distributions different from those used in training. However,
the accuracy of the approach in cases with higher conductivity variances is being investigated. 相似文献
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46.
Groundwater origins and mixing pattern in the multilayer aquifer system of the Gafsa-south mining district: a chemical and isotopic approach 总被引:3,自引:2,他引:1
Younes Hamed Lassaad Dassi Meriem Tarki Riadh Ahmadi Khalid Mehdi Hamed Ben Dhia 《Environmental Earth Sciences》2011,63(6):1355-1368
Major ion geochemistry and environmental isotopes were used to identify the origins and the mineralisation processes of groundwater
flowing within the three aquifer levels of the multilayer system of the Gafsa-south mining district (Southwestern Tunisia).
It has been demonstrated that groundwaters are characterised by a Ca–Mg–SO4 water type. Geochemical pattern is mainly controlled by the dissolution of halite, gypsum and/or anhydrite as well as by
the incongruent dissolution of dolomite. δ18O and δ2H values are much lower than the isotopic signature of regional precipitation and fall close to the meteoric water lines,
indicating that groundwaters have not been significantly affected by evaporation or mineral–water reactions. The distribution
of stable and radiogenic isotopes (δ18O, δ2H, δ13C and 14C) within the aquifer levels suggests that the deep confined aquifer receives a significant modern recharge at higher altitudes,
while, the shallow unconfined aquifer has been mainly recharged under cooler paleoclimatic condition, likely during Late Pleistocene
and Early Holocene humid periods. However, waters from the intermediate confined/unconfined aquifer have composite isotopic
signatures, highlighting that they are derived from a mixture of the two first end-members. 相似文献
47.
Hamed Noori Hojat Karami Saeed Farzin Seyed Mostafa Siadatmousavi Barat Mojaradi Ozgur Kisi 《Natural Hazards》2018,91(1):221-238
Soil erosion due to surface water is a standout among the serious threat land degradation problem and an hazard environmental destruction. The first stage for every kind of soil conservation planning is recognition of soil erosion status. In this research, the usability of two new techniques remote sensing and geographical information system was assessed to estimate the average annual specific sediments production and the intensity erosion map at two sub-basins of DEZ watershed, southwest of Lorestan Province, Iran, namely Absorkh and Keshvar sub-basins with 19,920 ha, using Modified Pacific Southwest Inter-Agency Committee (MPSIAC) soil erosion model. At the stage of imagery data processing of IRS-P6 satellite, the result showed that an overall accuracy and kappa coefficient were 90.3% and 0.901, respectively, which were considered acceptable or good for imagery data. According to our investigation, the study area can be categorized into three level of severity of erosion: moderate, high, and very high erosion zones. The amount of specific sediments and soil erosion predicted by MPSIAC model was 1374.656 and 2396.574 m3 km?2 year?1, respectively. The areas situated at the center and south parts of the watershed were subjected to significant erosion because of the geology formation and ground cover, while the area at the north parts was relatively less eroded due to intensive land cover. Based on effective of nine factors, the driving factors from high to low impact included: Topography > Land use > Upland erosion > Channel erosion > Climate > Ground cover > Soil > Runoff > Surface geology. The measured sediment yield of the watershed in the hydrometric station (Keshvar station) was approximately 2223.178 m3 km?2 year?1 and comparison of the amount of total sediment yield predicted by model with the measured sediment yield indicated that the MPSIAC model 38% underestimated the observed value of the watershed. 相似文献
48.
针对目前基于机器学习的PM2.5预报模型无法充分利用研究区域内其他相关站点的数据问题,该文提出了一种区域时空点数据的表示方法,并在此基础上提出了基于卷积神经网络的PM2.5预报模型。该模型利用了区域内多站点的历史PM2.5实测数据以及相应的气象预报数据,对区域内任一站点PM2.5浓度进行预报。实验结果显示,该模型在京津冀区域内能对未来至少3d内的PM2.5浓度进行较高精度的预报。与基于单站点的前馈神经网络预报结果对比表明,对区域整体污染及气象状况建模的卷积神经网络模型预报精度更高。该模型对区域内所有站点的预测结果与地面实测值的分布基本一致,表明了该模型具有对区域内PM2.5浓度进行时空预报的能力。 相似文献
49.
Younes Hamed Samir Anwar Al-Gamal Wassim Ali Abederazzak Nahid Hamed Ben Dhia 《Arabian Journal of Geosciences》2014,7(3):1165-1177
Through the Late Cretaceous, the southern shore of the Tethys Ocean migrated north and south over short distances. These vicissitudes are documented in the Continental Intercalaire, a long series of mainly non-marine sediments deposited in which dinosaur or other reptiles tracks and floral fossils are common across southern Tunisia (North Africa). A combined taxonomic, climatological, and palaentological studies provides independent lines of evidence for reconstruction of palaeoenvironments. The Bou Hedma/Boulouha and Sidi Aïch/Douiret Formations from southern Tunisia span the later part of the Late Cretaceous. During the Late Cretaceous the Tunisian territory was an archipelago, thus a particularly suitable area for a more detailed study. We investigated the area’s plant palaeo-biogeography, using fossil wood, with information from both a literature survey and investigation of new samples. The presence of fossils at great depths and distances from the present coastline, without signs of abrasion and far from areas of fluvial discharges does indicate that these remains have not been transported from the continent to the shelf, but have been preserved directly on the area that today correspond to the continental shelf. The climate during the accumulation of Barremian-Albian deposits in this region is inferred to have been warm and humid. 相似文献
50.
Hydrochemistry and geothermometry of thermal groundwater of southeastern Tunisia (Gabes region) 总被引:1,自引:0,他引:1
Given the vital importance of water and energy in desert regions, we undertook a study dealing with the deep reservoirs in Gabes area, which is located in the southeastern part of Tunisia. Geothermal resources are taken from the Intercalary Continental [or Continental Intercalaire (CI)], known as the largest deep aquifer in Tunisia and are used in a number of applications, mainly in agriculture. Previous investigations performed on the thermal waters of this area focused on the genesis of the deep waters with regard to the thermal features of geothermal reservoirs. A more detailed investigation has been carried out, considering both deep and shallow waters. In order to estimate the potential temperatures of deep reservoir in the Gabes area, we developed a synthetic study including chemical geothermometers, multiple mineral equilibrium approach, and other approaches. Chemical types of the thermal waters and effects of mixing between shallow cold waters with deep thermal waters were also discussed. In fact, the application of Na–K–Mg diagram relative to deep geothermal reservoir capitulate estimated temperatures (about 90°C). In addition, the multiple mineral equilibrium approach submits a similar estimated temperature ranging between 65 and 70°C, showing a disequilibrium status which indicates a possibly mixing with surface water. Indeed, wells exploiting the CI aquifer in the south part of the studied area showed the same characteristics, corroborating the reliability of the applied methods. 相似文献