Modelling wind-erosion risk in the Laghouat region (Algeria) using geomatics approach

Wind-erosion risk is a challenge that threatens land development in dry-land regions. Soil analysis, remote sensing, climatic, vegetal cover and topographic data were used in a geographic information system (GIS), using multi-criteria analysis (MCA) to map wind-erosion risk (R_we) in Laghouat, Algeria. The approach was based on modelling the risk and incorporating topographic and climatic effects. The maps were coded according to their sensitivity to wind erosion and to their socio-economic potential, from low to very high. By overlapping the effects of these layers, qualitative maps were drawn to reflect the potential sensitivity to wind erosion per unit area. The results indicated that severe wind erosion affects mainly all the southern parts and some parts in the north of Laghouat, where wind-erosion hazard (H_we) is very high in 43% of the total area, and which was affected mainly by natural parameters such as soil, topography and wind. The results also identified features vulnerable to R_we. The product of the hazard and the stake maps indicated the potential risk areas that need preventive measures; this was more than half of the study area, making it essential to undertake environmental management and land-use planning.     

3D geomechanical modeling and estimating the compaction and subsidence of Fahlian reservoir formation (X-field in SW of Iran)

A geomechanical model can reveal the mechanical behavior of rocks and be used to manage the reservoir programs in a better mode. Fluid pressure will be reduced during hydrocarbon production from a reservoir. This reduction of pressure will increase the effective stress due to overburden sediments and will cause porous media compaction and surface subsidence. In some oil fields, the compacting reservoir can support oil and gas production. However, the phenomena can also cause the loss of wells and reduced production and also cause irreparable damage to the surface structures and affect the surrounding environment. For a detailed study of the geomechanical behavior of a hydrocarbon field, a 3D numerical model to describe the reservoir geomechanical characteristics is essential. During this study, using available data and information, a coupled fluid flow-geomechanic model of Fahlian reservoir formation in X-field in SW of Iran was constructed to estimate the amount of land subsidence. According to the prepared model, in this field, the maximum amount of the vertical stress is 110 MPa and the maximum amount of the horizontal stress is 94 MPa. At last, this model is used for the prediction of reservoir compaction and subsidence of the surface. The maximum value of estimated ground subsidence in the study equals to 29 mm. It is considered that according to the obtained values of horizontal and vertical movement in the wall of different wells, those movements are not problematic for casing and well production and also the surrounding environment.     

Fracture analysis in Tabnak hydrocarbon field of Iran by using fractal geometry and multi-fractal analysis

High gas production from the Dashtak formation of Tabnak hydrocarbon field in Fars province, Iran, indicates the presence of natural fractured reservoir whose production potential is dominated by the structural fracture. The connectivity of fractured media depends upon the power?Claw exponent and the fracture density. Fracture pattern traces obtained from the outcrops of producing formations of six different stations in Tabnak hydrocarbon field. 2D fracture network maps of Tabnak hydrocarbon field have been analyzed from their scaling properties. The fractal analysis of fracture intensity showed heterogeneous multi-fractal structure characterized by generalized dimensions. Distribution of fracture lengths exhibits power?Claw behavior with specific exponent. Scaling laws serve to make extrapolations and to study the fracture connectivity related to scale. Fracture distribution model and reservoir productivity can be estimated, which are of great interest in decision making to optimize gas production.     

2-D electrical imaging in some geotechnical investigation of Madhupur clays,Bangladesh

Electrical imaging or electrical tomography is a survey technique suitable for the investigation of areas of shallow complex geology, where the use of other electrical and electromagnetic techniques is less effective. An electrical image has been delineated at a site located in front of the Department of Geological Sciences, Jahangirnagar University, Dhaka, Bangladesh. 16 soil samples were collected from two boreholes located on the image line and geotechnical parameters such as unit weight, water content, grain size, plastic limit, liquid limit and plasticity index were measured in the laboratory. These geotechnical parameters were compared with the measured electrical resistivity.     

Role of Crystal Interlocking on the Strength of Brittle Rocks

Results of an experimental programme on heterogeneous rock-like specimens of dental plaster confirm the pronounced role of tensile microcracks on brittle failure. Microbuckling of very small rock-columns formed amid closely located tensile cracks was observed as the key incident connecting stable phenomenon of tensile cracking to unstable phenomenon of shearing and subsequent macroscopic failure. Using the classical beam and buckling theories and considering geometry of the problem a new failure criterion is proposed. As a novel attempt, this new failure criterion relates the compressive strength of rock to three basic microstructural properties, i.e. degree of crystal interlocking, average Young modulus and average tensile strength of rock forming minerals.     

Factor and cluster analysis of water quality data of the groundwater wells of Kushtia, Bangladesh: Implication for arsenic enrichment and mobilization

The study area is located in the southwestern part of Bangladesh. Twenty-six groundwater samples were collected from both shallow and deep tube wells ranging in depth from 20 to 60 m. Multivariate statistical analyses including factor analysis, cluster analysis and multidimensional scaling were applied to the hydrogeochemical data. The results show that a few factors adequately represent the traits that define water chemistry. The first factor of Fe and HCO₃ is strongly influenced by bacterial Fe (III) reduction which would raise both Fe and HCO₃ concentrations in water. Na, Cl, Ca, Mg and PO₄ are grouped under the second factor representing the salinity sources of waters. The third factor, represented by As, Mn, SO₄ and K is related to As mobilization processes. Cluster analysis has been applied for the interpretation of the groundwater quality data. Initially Piper methods have been employed to obtain a first idea on the water types in the study area. Hierarchical cluster analysis was carried out for further classification of water types in the study area. Twelve components, namely, pH, Fe, Mn, As, Ca, Mg, Na, K, HCO₃, Cl, SO₄ and NO₃ have been used for this purpose. With hierarchical clustering analysis the water samples have been classified into 3 clusters. They are very high, high and moderately As-enriched groundwater as well as groundwater with elevated SO₄.     

Shallow and deep aquifer hydrochemistry and chemical variability of water quality at Shariatpur district, Bangladesh

Water quality and hydrochemistry of Shariatpur district were evaluated in terms of hydrochemical composition and some important physico-chemical parameters. The groundwater of the study area is good for drinking, domestic as well as for irrigation purposes. Among the major ions, shallow tube well waters give higher concentration of Ca²⁺ which ranges from 24 to 260 mg/L. The deep tubewell waters show higher concentration of Na⁺ which varies from 74 to 582 mg/L during dry season. Among the trace elements most of the shallow aquifer samples show higher concentration of Fe²⁺, Mn²⁺ and As. Concentration of Fe²⁺ varies from 0.655 to 18.8 mg/L, and Mn²⁺ from trace to 0.868 mg/L during dry period. Hydrochemical analyses reveal significant seasonal variation in water quality of shallow aquifer. Both the shallow aquifer and the surface water of the study area are predominantly of Ca–Mg–HCO₃ type, while the deep aquifer water is mainly of Na–K–Cl–SO₄ type with slight inclination to Ca–Mg–HCO₃ type. The study area is suitable for groundwater development if comprehensive and holistic approaches towards water resource management are taken into consideration.     

Hawking non-thermal and thermal radiations of Schwarzschild anti-de Sitter black hole by Hamilton-Jacobi method

The massive particles tunneling method has been used to investigate the Hawking non-thermal and purely thermal radiations of Schwarzschild Anti-de Sitter (SAdS) black hole. Considering the spacetime background to be dynamical, incorporate the self-gravitation effect of the emitted particles the imaginary part of the action has been derived from Hamilton-Jacobi equation. Using the conservation laws of energy and angular momentum we have showed that the non-thermal and purely thermal tunneling rates are related to the change of Bekenstein-Hawking entropy and the derived emission spectrum deviates from the pure thermal spectrum. The result obtained for SAdS black hole is also in accordance with Parikh and Wilczek’s opinion and gives a correction to the Hawking radiation of SAdS black hole.