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.     

Reliability framework for characterizing heat wave and cold spell events

Natural Hazards - Extreme weather events such as heat waves and cold spells affect people’s lives. This study develops a probabilistic framework to evaluate heat waves and cold spells. As...     

Three-parameter Radon transform in layered transversely isotropic media

Radon transform is a powerful tool with many applications in different stages of seismic data processing, because of its capability to focus seismic events in the transform domain. Three-parameter Radon transform can optimally focus and separate different seismic events, if its basis functions accurately match the events. In anisotropic media, the conventional hyperbolic or shifted hyperbolic basis functions lose their accuracy and cannot preserve data fidelity, especially at large offsets. To address this issue, we propose an accurate traveltime approximation for transversely isotropic media with vertical symmetry axis, and derive two versions of Radon basis functions, time-variant and time-invariant. A time-variant basis function can be used in time domain Radon transform algorithms while a time-invariant version can be used in, generally more efficient, frequency domain algorithms. Comparing the time-variant and time-invariant Radon transform by the proposed basis functions, the time-invariant version can better focus different seismic events; it is also more accurate, especially in presence of vertical heterogeneity. However, the proposed time-invariant basis functions are suitable for a specific type of layered anisotropic media, known as factorized media. We test the proposed methods and illustrate successful applications of them for trace interpolation and coherent noise attenuation.     

System dynamic modeling to assess the effect of subsurface drain spacing and depth on minimizing the environmental impacts

The excessive loss of soil nitrogen through drainage losses causes different environmental problems. The depth and spacing drain of drains play an important role in the quality and quantity of discharged drainage into the environment. In this paper, a simple but comprehensive model using system dynamic approach for water cycle and nitrogen dynamics was used to simulate the effect of drain depth and spacing on nitrate and ammonium losses in a sugarcane agro-industrial company. Twenty-four scenarios were modeled including the combination of four different drain depths and six drain spacing to compare the effect of drain depth and spacing on the nitrogen uptake by plant, denitrification, net mineralization, the amount of ammonium losses through runoff, nitrate and ammonium losses through drainage water, the sum of excessive water, the stress day index and the relative yield. The results indicated that optimal drainage system density is obtained in the depth of 1.1 m and spacing of 80 m, in a way that the total drainage losses would be reduced up to an acceptable level. The optimum designing of the drainage systems according to environmental criteria can control nitrogen pollution load at farm level and can therefore have appropriate results both in terms of economic and environmental considerations.     

Application of various methods for 2D inverse modeling of residual gravity anomalies

This paper presents a neural network approach to determine 2D inverse modeling of a buried structure from gravity anomaly profile. The results of the applied neural network method are compared with the results of two other methods, least-squares minimization and the simple method. Sphere, horizontal cylinder and vertical cylinder and their gravity effects are considered as the synthetic models and the synthetic data, respectively. The synthetic data are also corrupted with noise to evaluate the capability of the methods. Then the Dehloran bitumen map in Iran is chosen as a real data application. Anomaly value of the cross-section, which is taken from the gravity anomaly map of Dehloran bitumen, is very close to those obtained from these methods.     

Assessment of reference evapotranspiration across an arid urban environment having poor data monitoring system

Estimation of reference evapotranspiration (ET₀) in urban areas is challenging but essential in arid urban climates. To evaluate ET₀ in an urban environment and non-urban areas, air temperature and relative humidity were measured at five different sites across the arid city of Isfahan, Iran, over 4 years. Wind speed and sunshine hours were obtained from an urban surrounding weather station over the same period and used to estimate ET₀. Calculated ET₀ was compared with satellite-based ET₀ retrieved from the MOD16A2 PET product. Although MODIS PET was strongly correlated with the Valiantzas equation, it overestimated ET₀ and showed average accuracy (r = 0.93–0.94, RMSE = 1.18–1.28 mm/day, MBE = 0.73–0.84 mm/day). The highest ET₀ differences between an urban green space and a non-urban area were 1.1 and 0.87 mm/day, which were estimated by ground measurements and MODIS PET, respectively. The sensitivity of ET₀ to wind speed and sunshine hours indicated a significant effect on cumulative ET₀ at urban sites compared to the non-urban site, which has a considerable impact on the amount of irrigation required in those areas. Although MODIS PET requires improvement to accurately reflect field level microclimate conditions affecting ET₀, it is beneficial to hydrological applications and water resource managers especially in areas where data is limited. In addition, our results indicated that using limited data methods or meteorological data from regional weather stations, leads to incorrect estimation of ET₀ in urban areas. Therefore, decision-makers and urban planners should consider the importance of precisely estimating ET₀ to optimize management of urban green space irrigation, especially in arid and semi-arid climates such as the city of Isfahan.     

Integration of Sequence Stratigraphic Analysis and 3D Geostatistical Modeling of Pliocene–Pleistocene Delta,F3 Block,Netherlands

This research is focused on the analysis of the sequence stratigraphic units of F3 Block, within a wave-dominated delta of Plio–Pleistocene age. Three wells of F3 block and a 3D seismic data, are utilized in this research. The conventional techniques of 3D seismic interpretation were utilized to mark the 11 surfaces on the seismic section. Integration of seismic sequence stratigraphic interpretation, using well logs, and subsequent 3D geostatistical modeling, using seismic data, aided to evaluat...     

Multidimensional six-stage model for flood emergency response in schools: a case study of Pakistan

Natural Hazards - Children spend more than two-thirds of their total daytime in schools and becoming more persuasive in shielding them from potential hazards. Schools have a responsibility to...     

Re‐examining green revolution diffusion and factor/input markets in Bangladesh after market liberalization

This paper re‐examines the effect of green revolution (GR) diffusion on factor/inputs demand in Bangladesh using an empirical model that allows for simultaneous determination of factors influencing adoption of GR technology at the current mature stage, as well as access to irrigation. Results reveal some alignments with conventional wisdom as well as few surprises. For example, while an increased demand for major inputs is expected, an increased demand for organic manure is an unexpected positive outcome. The GR adoption rate is significantly higher in villages with access to irrigation and fertile soils and, surprisingly, in infrastructurally underdeveloped villages. Together with other expected findings of GR technology uptake with higher cereal prices and irrigation use encouraged by access to credit, tenurial status and fertile soils, our findings suggest that investment in irrigation and soil conservation, as well as implementing measures to improve cereal prices and provide agricultural credit, could boost GR technology adoption.     

Water and sediment quality, partial mass budget and effluent N loading in coastal brackishwater shrimp farms in Bangladesh

The present study aimed to quantify the water and sediment quality and growth and production parameters and to establish nutrient budgets for an average of five selected semi-intensive shrimp ponds in Bangladesh over a growing cycle. Physico-chemical parameters of water and sediments were measured and analyzed by standard methods. Gross yield (kg ha-1) of shrimp was calculated from the stocking and harvesting data. Finally, a partial nutrient mass budget for N and P was calculated. Most of the parameters of water and sediments correlated significantly with each other suggesting a high degree of interactions between different parameters in the system. Significantly higher concentrations of all species of nitrogenous nutrients were recorded in the effluent waters than that entering into the ponds. Therefore, a high loading and net output of nitrogenous nutrients in effluent waters was documented. The study also indicated a net discharge of solids and minerals through effluent loading. However, significantly lower concentrations of phosphorus in the effluent water indicated a net retention and trapping of phosphatic nutrients in the environment. Total production ranged between 532.0 and 697.0 kg ha-1 cycle-1 and P. monodon production between 484.0 and 562.0 kg ha-1 cycle-1. Ponds gained nitrogen primarily from intake water (55%) and fertilizers (29%), and nitrogen was lost primarily from water exchange (78%) and harvested shrimp (12%). Phosphorus gain occurred mostly from intake water (52%) and fertilizers (25%), and phosphorus was lost primarily from water exchange (52%) and harvested shrimp (3.3%). About 10% of input nitrogen and 44% of phosphorus were not accounted for in measured losses, and presumably were fixed or metabolized in the system. On average, 78 g N was discharged to and 25 g P was removed from the surrounding water by the system for each kilogram of shrimp produced. Mean conversion of feed nitrogen and phosphorus to shrimp flesh averaged 74% and 40%, respectively. It was concluded that semi-intensive systems serve as net supplier of N to and net remover of P from the surrounding water.