Nanomechanics of organic-rich shales: the role of thermal maturity and organic matter content on texture

Despite the importance of organic-rich shales, microstructural characterization and theoretical modeling of these rocks are limited due to their highly heterogeneous microstructure, complex chemistry, and multiscale mechanical properties. One of the sources of complexity in organic-rich shales is the intricate interplay between microtextural evolution and kerogen maturity. In this study, a suite of experimental and theoretical microporomechanics methods are developed to associate the mechanical properties of organic-rich shales both to their maturity level and to the organic content at micrometer and sub-micrometer length scales. Recent results from chemomechanical characterization experiments involving grid nanoindentation and energy-dispersive X-ray spectroscopy (EDX) are used in new micromechanical models to isolate the effects of maturity levels and organic content from the inorganic solids. These models enable attribution of the role of organic maturity to the texture of the indented material, with immature systems exhibiting a matrix-inclusion morphology, while mature systems exhibit a polycrystal morphology. Application of these models to the interpretation of nanoindentation results on organic-rich shales allows us to identify unique clay mechanical properties that are consistent with molecular simulation results for illite and independent of the maturity of shale formation and total organic content. The results of this investigation contribute to the design of a multiscale model of the fundamental building blocks of organic-rich shales, which can be used for the design and validation of multiscale predictive poromechanics models.     

Seasonal circulation and mass flux estimates in the western Sicily Strait derived from a variational inverse section model

Seasonal hydrographic conductivity–temperature–depth surveys and moored current meter measurements have been analysed using an inverse approach in order to highlight the main features of the circulation in the western Sicily Strait during 2003. The variational inverse section model combines different types of constraints to seek for a continuous flow field satisfying data and physical assumptions within prescribed prior error bars. It is based on a finite element discretization that allows an appropriate resolution of very irregular topography. The corresponding results, consistent with data and dynamics, are providing new insight into the circulation of the surface and intermediate layers in conjunction with transport and formal error estimates during five hydrographic cruises. In the upper layer, these insights include the southward Atlantic Tunisian Current (ATC) off the Cap Bon Coasts, its high variability at short time-scales and its recirculation during October. For the Levantine Intermediate Water (LIW) regime, a detailed view of the circulation in the western Sicily Strait is given evidencing its recirculation at the western sill during the same period. Transports for both ATC and LIW are computed and found to be maximum in spring and decrease in summer and fall.     

Embryo dune development drivers: beach morphology,growing season precipitation,and storms

For development of embryo dunes on the highly dynamic land–sea boundary, summer growth and the absence of winter erosion are essential. Other than that, however, we know little about the specific conditions that favour embryo dune development. This study explores the boundary conditions for early dune development to enable better predictions of natural dune expansion. Using a 30 year time series of aerial photographs of 33 sites along the Dutch coast, we assessed the influence of beach morphology (beach width and tidal range), meteorological conditions (storm characteristics, wind speed, growing season precipitation, and temperature), and sand nourishment on early dune development. We examined the presence and area of embryo dunes in relation to beach width and tidal range, and compared changes in embryo dune area to meteorological conditions and whether sand nourishment had been applied. We found that the presence and area of embryo dunes increased with increasing beach width. Over time, embryo dune area was negatively correlated with storm intensity and frequency. Embryo dune area was positively correlated with precipitation in the growing season and sand nourishment. Embryo dune area increased in periods of low storm frequency and in wet summers, and decreased in periods of high storm frequency or intensity. We conclude that beach morphology is highly influential in determining the potential for new dune development, and wide beaches enable development of larger embryo dune fields. Sand nourishment stimulates dune development by increasing beach width. Finally, weather conditions and non‐interrupted sequences of years without high‐intensity storms determine whether progressive dune development will take place. Copyright © 2017 John Wiley & Sons, Ltd.     

Optimal Location of Wells for Storage and Recovery of Surplus Desalinated Water in Coastal Aquifers

Storage of water in aquifers using injection wells is an efficient way for utilizing excess desalinated water in arid regions. In this investigation we estimate the benefits of optimally recharging seasonal surplus desalinated water into a strategic coastal aquifer already benefitting from natural recharge of flash-floods water by a recharge dam. Since, usually the buyers of desalinated water commit to purchase surplus desalinated water under take-or-pay contracts, any attempt in utilizing the paid water is beneficial. Coastal cities are observing an increased urbanization leaving limited space for aquifer recharge infrastructure. In order to determine the optimal location of wells and maximize the use of surplus desalinated water available in winter period, a decision tool combining a numerical groundwater flow simulation model (MODFLOW) with an optimization model is developed. The results of this study show that increasing the number of wells from the existing 45 wells to 173 would allow storing 31.4 million cubic meter per year of excess desalinated water into the aquifer that can be used during later during summer months. The net benefit would reach US$55 million/year while the cost of drilling the new wells is US$5.11 million.     

Comparison of sequential extraction and principal component analysis for determination of heavy metal partitioning in sediments: the case of protected Lagoon El Kelbia (Tunisia)

A sequential extraction procedure applied to surface sediments from El Kelbia Lagoon determined the partitioning of Ba, Co, Cr, Cu, Ni, Sr, V and Zn among evaporites, carbonates, Fe–Mn oxides, organic matter and silicates. To validate the procedure, the sequential extraction results (SER) were compared to principal components analysis (PCA) using major and trace element concentrations and mineralogical quantitative data of surface sediments. SER showed that a part of Sr was highly mobile; Cu, Sr, and Zn and a part of Co and Ni were mobile depending on pH conditions; Cr and V were strongly bound to silicate phases; Co and Ni were partitioned between carbonates, oxides and silicates, and a great part of Ba and Sr were bound to organic matter or sulfides. An agreement was found with PCA in terms of partitioning among minerals for most trace elements. Moreover, the absence of correlation between Ca concentrations and the abundances of calcite, gypsum or dolomite could be explained by an important fraction of Ca bound to organic matter. Also, unexpected negative correlations between abundances of smectite and illite could be explained by a transformation of illite into smectite. Thus, SER and PCA were mostly convergent, which enabled: (1) validation of the extraction procedure used, and (2) refinement of interpretations of the origin and relations between minerals.     

Intervention scenarios to manage seawater intrusion in a coastal agricultural area in Oman

The Batinah coastal plain in northern Oman has experienced a severe deterioration of groundwater quality due to seawater intrusion as a result of excessive groundwater abstraction for agricultural irrigation. Upgrading all farms to fully automated irrigation technology based on soil moisture sensors may significantly reduce the water demand and lead to recovering groundwater levels. This study compares the effects of smart irrigation technology, recharge dams, and a combination of both on seawater intrusion in the coastal aquifer of the Batinah. A groundwater flow and transport model is used to simulate the effect of reduced pumping rates on seawater intrusion for various intervention scenarios over a simulation period of 30 years, and an economic analysis based on cost-benefit analysis is conducted to estimate the potential benefits. Results indicate that a combination of smart irrigation and recharge dams may prevent further deterioration of groundwater quality over the next 30 years. In conjunction with increased efficiency, this combination also generates the highest gross profit. This outcome shows that the problem of seawater intrusion needs to be tackled by a comprehensive, integrated intervention strategy.     

Past and future plant diversity of a coastal wetland driven by soil subsidence and climate change

On the island of Ameland (The Netherlands), natural gas has been extracted from a dune and salt marsh natural area since 1986. This has caused a soil subsidence of c. 1–25?cm, which can be used as a model to infer effects of future sea level rise. The aims of our study were (a) to relate the changes in the vegetation, and more specifically, in plant diversity, during the extraction period to soil subsidence and weather fluctuations, and (b) to use these relations to predict future changes due to the combination of ongoing soil subsidence and climate change. We characterised climate change as increases in mean sea level, storm frequency and net precipitation. Simultaneous observations were made of vegetation composition, elevation, soil chemistry, net precipitation, groundwater level, and flooding frequency over the period 1986–2001. By using multiple regression the changes in the vegetation could be decomposed into (1) an oscillatory component due to fluctuations in net precipitation, (2) an oscillatory component due to incidental flooding, (3) a monotonous component due to soil subsidence, and (4) a monotonous component not related to any measured variable but probably due to eutrophication. The changes were generally small during the observation period, but the regression model predicts large changes by the year 2100 that are almost exclusively due to sea level rise. However, although sea level rise is expected to cause a loss of species, this does not necessarily lead to a loss of conservancy value.     

The regional development process: A critique and case study from northern Nigeria

The necessity of a spatial or regional component in development planning is recognized in both theory and practice. Spatial structure, the physical arrangement of development institutions, and spatial processes, patterns of activity, are integral parts of development planning and its results. The spatial component of development is critically reviewed in the cotext of regional growth theory, growth centre, or growth pole theory, and development viewed as an innovation process. Preliminary data from studies of regional development in northern Nigeria suggest that substantial growth leakages occur, and that the greatest regional impact of industrial development has been in the supply of foodstuffs to urban areas.     

Investigation of seawater intrusion using stable and radioisotopes at coastal area south of Beirut,the Capital of Lebanon

In this study, field measurements were made and environmental isotopes and radiological properties were determined in six selected wells located in the coastal area south of Beirut, the capital of Lebanon. It is one of the many district areas in Lebanon, threatened by the penetration of seawater into aquifers. Two sampling campaigns were carried out to determine possible seasonal variations. High electrical conductivity was observed, ranging from 1080 to 7900 μS/cm. The total dissolved solids values ranged from 530 to 5600 mg/L. This is attributed to a seawater intrusion confirmed by high chlorine concentrations that ranged from 400 to 3500 mg/L. Isotope data for δ¹⁸O/δ²H showed enrichment that is relatively small at the end of wet season due to recharge by local precipitation and infiltration. Carbon-14 ages and ²³⁴U/²³⁸U ratios confirmed the presence of young water. No radiological hazard was observed as all values lay below the guidance levels of the WHO.     

Management options for a multipurpose coastal aquifer in Oman

Using MODFLOW 2005, this study numerically evaluated the effects of managed aquifer recharge (MAR) using treated wastewater (TWW) in managing the Al-Khawd coastal aquifer northeast of Oman. Our primary objective is to increase the urban water supply and to sustain the aquifer service with the lowest possible damage to the aquifer. A number of managerial scenarios were simulated and progressively developed to reduce seawater intrusion and outflow of the groundwater to the sea. An economic analysis was conducted to characterize the trade-off between the benefits of MAR and seawater inflow to the aquifer under increased abstraction for domestic supply. The results show that by managing irrigation wells and relocating public wells in conjunction with MAR practices, the abstracted volume for drinking purposes could be doubled. Even though injection of TWW is more expensive (due to the injection cost), it was observed to result in greater benefits. The results indicate that managing the aquifer would produce a net benefit ranging from $8.22 million (scenario 7) to $15.21 million (scenario 4) compared to $1.57 million with the current practice. In conclusion, MAR using TWW is a feasible solution to develop water resources in arid regions, and the best scenario depends on the decision maker’s preference when weighing the benefits of MAR and the level of damage to the aquifer. MAR could help manage stressed aquifer systems in arid zones to maximize the benefit of using the water for domestic purposes while minimizing the damage to the aquifer.