A parallel ensemble-based framework for reservoir history matching and uncertainty characterization

We present a parallel framework for history matching and uncertainty characterization based on the Kalman filter update equation for the application of reservoir simulation. The main advantages of ensemble-based data assimilation methods are that they can handle large-scale numerical models with a high degree of nonlinearity and large amount of data, making them perfectly suited for coupling with a reservoir simulator. However, the sequential implementation is computationally expensive as the methods require relatively high number of reservoir simulation runs. Therefore, the main focus of this work is to develop a parallel data assimilation framework with minimum changes into the reservoir simulator source code. In this framework, multiple concurrent realizations are computed on several partitions of a parallel machine. These realizations are further subdivided among different processors, and communication is performed at data assimilation times. Although this parallel framework is general and can be used for different ensemble techniques, we discuss the methodology and compare results of two algorithms, the ensemble Kalman filter (EnKF) and the ensemble smoother (ES). Computational results show that the absolute runtime is greatly reduced using a parallel implementation versus a serial one. In particular, a parallel efficiency of about 35 % is obtained for the EnKF, and an efficiency of more than 50 % is obtained for the ES.     

Earthquakes in Switzerland and surrounding regions during 2012

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2012. During this period, 497 earthquakes and 88 quarry blasts were detected and located in the region under consideration. With a total of only 13 events with M_L ≥ 2.5, the seismic activity in the year 2012 was far below the average over the previous 37 years. Most noteworthy were the earthquake sequence of Filisur (GR) in January with two events of M_L 3.3 and 3.5, the M_L 4.2 and M_L 3.5 earthquakes at a depth of 32 km below Zug in February and the M_L 3.6 event near Vallorcine in October. The epicentral intensity of the M_L 4.2 event close to Zug was IV, with a maximum intensity of V reached in a few areas, probably due to site amplification effects.     

Calcite uranium–lead geochronology applied to hardground lithification and sequence boundary dating

Hardground discontinuities within carbonate platforms form important stratigraphic surfaces which can be used at basin scale to correlate sequence boundaries. Although these surfaces are commonly used in sequence strati‐graphy, the timing and duration of hardground lithification and the crystallization of early cements remain unexplored. Here, early calcite cements were dated by U‐Pb geochronology for five Jurassic hardgrounds, interpreted as third‐order sequence boundaries, situated within a well‐constrained petrographic, sedimentological and stratigraphic framework. The consistency or the slight deviation between the age of the cements and the stratigraphic age of deposition of the formations illustrate that cementation occurred early in the diagenetic history. The ages obtained on dogtooth cements, replacing aragonite in gastropod shells and pendant cements in intergranular spaces, match those of the standard Jurassic biostratigraphic ammonite Zones, making calcite U‐Pb geochronology a promising method for dating third‐order sequence boundaries of depositional sequences and refining the Jurassic time scale in the future.     

Review: The distribution,flow, and quality of Grand Canyon Springs,Arizona (USA)

An understanding of the hydrogeology of Grand Canyon National Park (GRCA) in northern Arizona, USA, is critical for future resource protection. The ~750 springs in GRCA provide both perennial and seasonal flow to numerous desert streams, drinking water to wildlife and visitors in an otherwise arid environment, and habitat for rare, endemic and threatened species. Spring behavior and flow patterns represent local and regional patterns in aquifer recharge, reflect the geologic structure and stratigraphy, and are indicators of the overall biotic health of the canyon. These springs, however, are subject to pressures from water supply development, changes in recharge from forest fires and other land management activities, and potential contamination. Roaring Springs is the sole water supply for residents and visitors (>6 million/year), and all springs support valuable riparian habitats with very high species diversity. Most springs flow from the karstic Redwall-Muav aquifer and show seasonal patterns in flow and water chemistry indicative of variable aquifer porosities, including conduit flow. They have Ca/Mg-HCO₃ dominated chemistry and trace elements consistent with nearby deep wells drilled into the Redwall-Muav aquifer. Tracer techniques and water-age dating indicate a wide range of residence times for many springs, supporting the concept of multiple porosities. A perched aquifer produces small springs which issue from the contacts between sandstone and shale units, with variable groundwater residence times. Stable isotope data suggest both an elevational and seasonal difference in recharge between North and South Rim springs. This review highlights the complex nature of the groundwater system.     

Declines in Plant Productivity Drive Carbon Loss from Brackish Coastal Wetland Mesocosms Exposed to Saltwater Intrusion

Coastal wetlands, among the most productive ecosystems, are important global reservoirs of carbon (C). Accelerated sea level rise (SLR) and saltwater intrusion in coastal wetlands increase salinity and inundation depth, causing uncertain effects on plant and soil processes that drive C storage. We exposed peat-soil monoliths with sawgrass (Cladium jamaicense) plants from a brackish marsh to continuous treatments of salinity (elevated (~?20 ppt) vs. ambient (~?10 ppt)) and inundation levels (submerged (water above soil surface) vs. exposed (water level 4 cm below soil surface)) for 18 months. We quantified changes in soil biogeochemistry, plant productivity, and whole-ecosystem C flux (gross ecosystem productivity, GEP; ecosystem respiration, ER). Elevated salinity had no effect on soil CO₂ and CH₄ efflux, but it reduced ER and GEP by 42 and 72%, respectively. Control monoliths exposed to ambient salinity had greater net ecosystem productivity (NEP), storing up to nine times more C than plants and soils exposed to elevated salinity. Submersion suppressed soil CO₂ efflux but had no effect on NEP. Decreased plant productivity and soil organic C inputs with saltwater intrusion are likely mechanisms of net declines in soil C storage, which may affect the ability of coastal peat marshes to adapt to rising seas.     

Variability in soil-water retention properties and implications for physics-based simulation of landslide early warning criteria

Rainfall-induced shallow landsliding is a persistent hazard to human life and property. Despite the observed connection between infiltration through the unsaturated zone and shallow landslide initiation, there is considerable uncertainty in how estimates of unsaturated soil-water retention properties affect slope stability assessment. This source of uncertainty is critical to evaluating the utility of physics-based hydrologic modeling as a tool for landslide early warning. We employ a numerical model of variably saturated groundwater flow parameterized with an ensemble of texture-, laboratory-, and field-based estimates of soil-water retention properties for an extensively monitored landslide-prone site in the San Francisco Bay Area, CA, USA. Simulations of soil-water content, pore-water pressure, and the resultant factor of safety show considerable variability across and within these different parameter estimation techniques. In particular, we demonstrate that with the same permeability structure imposed across all simulations, the variability in soil-water retention properties strongly influences predictions of positive pore-water pressure coincident with widespread shallow landsliding. We also find that the ensemble of soil-water retention properties imposes an order-of-magnitude and nearly two-fold variability in seasonal and event-scale landslide susceptibility, respectively. Despite the reduced factor of safety uncertainty during wet conditions, parameters that control the dry end of the soil-water retention function markedly impact the ability of a hydrologic model to capture soil-water content dynamics observed in the field. These results suggest that variability in soil-water retention properties should be considered for objective physics-based simulation of landslide early warning criteria.     

A Framework for Quantitative Assessment of Impacts Related to Energy and Mineral Resource Development

Natural resource planning at all scales demands methods for assessing the impacts of resource development and use, and in particular it requires standardized methods that yield robust and unbiased results. Building from existing probabilistic methods for assessing the volumes of energy and mineral resources, we provide an algorithm for consistent, reproducible, quantitative assessment of resource development impacts. The approach combines probabilistic input data with Monte Carlo statistical methods to determine probabilistic outputs that convey the uncertainties inherent in the data. For example, one can utilize our algorithm to combine data from a natural gas resource assessment with maps of sage grouse leks and piñon-juniper woodlands in the same area to estimate possible future habitat impacts due to possible future gas development. As another example: one could combine geochemical data and maps of lynx habitat with data from a mineral deposit assessment in the same area to determine possible future mining impacts on water resources and lynx habitat. The approach can be applied to a broad range of positive and negative resource development impacts, such as water quantity or quality, economic benefits, or air quality, limited only by the availability of necessary input data and quantified relationships among geologic resources, development alternatives, and impacts. The framework enables quantitative evaluation of the trade-offs inherent in resource management decision-making, including cumulative impacts, to address societal concerns and policy aspects of resource development.     

Industrializing nature,knowledge, and labour: The political economy of bioprospecting in Madagascar

This article provides a new way of analyzing and defining contemporary bioprospecting under emerging frameworks of neoliberal conservation. I document how bioprospecting has changed over time on the island-nation of Madagascar due to shifts in environmental governance. The most significant change includes efforts to speed up and industrialize the production of new drugs derived from nature. This has been accomplished through the switching over to rational collection strategies that employ new geo-referencing technologies, global networks of herbarium archives, and high-technology rapid screening methods. Results show that nature is re-constituted, traditional knowledge is rendered inefficient, and labour is mechanized within sites of production. This study demonstrates how changes in bioprospecting alter the way Malagasy scientists and local resource users participate in the practice and diminish their decision making power over natural resources. These developments, in turn, cause some Malagasy scientists, researchers and administrators to question their participation in bioprospecting projects and reveal that current natural resource policies of extraction, commercialization and benefit-sharing face many challenges.     

侏罗纪末至白垩纪非海相介形类生物地层学:回顾与展望

以非海相介形类为依据而建立的侏罗纪末至白垩纪的生物地层学,尤其是欧洲所谓"Purbeck-Wealden层段"(提塘阶顶部至巴列姆阶/阿普特阶底部)和全球同期沉积层的生物地层学建立已久,但这一生物地层学存有很多问题与局限性。本文对中生代晚期(聚焦于早白垩世)的非海相介形类生物地层学的基本原理、历史、目前进展、存在问题和前景进行了综述。因为介形类的繁殖、扩散与成种机制已有比较成熟的研究,所以介形类的生物地层学的应用潜力被认识已久。然而,全球不同地区中生代晚期的非海相介形类众多的研究积累已构成了一个丰富但常常混乱和矛盾的文献库。这些问题不仅存在于介形类的分类鉴定中,也见于关于古环境和系统发育的解释中。虽然地区性的盆地内的介形类生物地层学研究已产生了好结果,并可能能够用于局部地区的高精度对比。但是在进行地区间(盆地间至全球)的对比时,其实用性广遭怀疑。在过去的二十年间,许多学者采用了将今论古的古生物学研究方法,努力修订和更新中生代晚期的非海相介形类的生物地层学与古环境意义,从而促进了地区间生物地层学研究和对比的发展。古生物学家认识到,对于许多非海相介形类动物来讲,它们的分布和扩散不仅仅局限于单个的水系或较小的地理区域,而是和现生的非海相介形类一样,晚侏罗世至白垩纪的非海相介形类动物和它们的卵可被较大的动物或风长距离搬运,跨越迁移的屏障,进行扩散。鉴于以上事实,地区间的对比必须涉及两大内容:分类学的应用与古环境背景。缺乏适用于地区—全球的稳定和一致的分类学系统是进行正确对比的重要障碍。由于大量地方性分类命名、地方性特有动物的假设、与壳体特征相关的分类和生态型认识的混乱,以及对种内变异尺度的统一认识的缺乏,导致了对生物分异度的过高或过低的估量。非海相白垩纪介形类的地层记录受到诸多因素的影响:分类单元的演化与灭绝、扩散事件、当地的环境变化和地区性至全球的气候变迁。在生物地层学的应用中,我们可以通过不同手段去把握同时代的Cytheroidea,特别是Cypridoidea中具重要地层意义的Cypridea属及其亲近者(即CypridoideaMartin,1940)的分类单元的形态变异度。解释种内变异时需要格外谨慎。区分生物自生(内因)导致的变异(遗传的和形态的变异)和环境(外因)导致的变异(生态表型)是一大难题。比较保守的分类学观念(分类单元很少,但变异极大(分类单元中包含了多种生态表型))有助于不同古环境间的(生物地层)对比。另一方法是运用随着时间的古环境变化及其对介形类组合的组成的影响来进行(生物地层)对比。古生物工作者已在利用受环境控制的周期性介形类组合变化建立对比关系方面进行了大量有意义的尝试,但这些工作仍处在争议中。建立全球生物地层学方法,建立统一而持久的分类概念这一目标可以达到,但不可能在短期内实现。用现代的思想(概念)理解和研究非海相介形类的古生物学和古生物地理学及新资料将有助于修订工作的进展。尽管我们对中生代的非海相介形类的演化和分布的认识还很不全面,但目前我们已取得了可喜的进展。盆地间至大陆间的对比是否可行,早已不是问题。目前和未来的指导原则无疑是发展以介形类为基础,并与其他的年代地层学和地质年代学资料及方案相结合的从地区至全球范围的地层对比系统。因为我们正在迈向一个非海相晚中生代介形类生物地层学的重新解释和应用的新时代,我们必须承认我们还有许多东西需要学习。