Examining the rainfall–topography relationship using non-stationary modelling technique in semi-arid Aseer region,Saudi Arabia     

Javed Mallick  Ram Karan Singh  Roohul Abad Khan  Chander Kumar Singh  Nabil Ben Kahla  Essam Ibrahim Warrag  Saiful Islam  Atiqur Rahman 《Arabian Journal of Geosciences》2018,11(9):215

The mountainous region of Aseer, corresponding to the Afromontane phytogeographic region, is an eco-sensitive zone and has complex relationship between topography and rainfall. The region is located inland of the red sea escarpment edge in the west. Therefore, rainfall can occur during any month of the year in the mountain of the high Aseer region when moist air forces up the escarpment from the red sea. Monitoring the rainfall data and its topographical elevation variable in Aseer region is an essential requirement for feasible and accurate rainfall-based data for different applications, such as hydrological and ecological resource management in rugged terrain and remote areas. The relationship of elevation and rainfall are spatially non-stationary, non-linear, scale dependent, and often modelled by conventional regression models. Therefore, a local modelling technique, geographically weighted regression (GWR), was applied to deal with non-stationary, non-linear, scale-dependent problems. The GWR using topoclimatic data (elevation and rainfall) to analyse the cumulative rainfall data for rainy months (March to June) of the 4 years estimated from CHIRPS (Climate Hazards Group InfraRed Precipitation with Stations) product for Aseer region. The bandwidth (scale-size) of the Aseer region rainfall–elevation relationship has stabilised at round off 12 km. By selecting the suitable bandwidth, the spatial pattern of the rainfall–elevation relationship was significantly enhanced by using the GWR than the traditional ordinary least squares (OLS) regression model. GWR local modelling techniques estimated well in terms of accuracy, predictive power and decreased residual autocorrelation. Additionally, GWR assesses the significance of local statistic at each location and identified the location of spatial clusters with local regression coefficients significantly improved as compared with global OLS model, thereby highlighting local variations. Therefore, the GWR, local modelling approach managed to produce more accurate estimates by taking into account local characteristics.  相似文献   

Extent of diagenetic transformations in severely altered biogenic silica deposits from Tunisia: new insights from mineralogy and geochemistry     

Mohsen Henchiri  Nabil Fattah 《Arabian Journal of Geosciences》2014,7(3):1179-1186

Sedimentary biogenic silica from Redeyef in Gafsa basin (southern Tunisia) was analysed for its ²⁹Si and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra and complemented by X-ray diffraction and SEM observations. The ²⁹Si MAS NMR spectrum is characterized by the abundance of hydroxylated silicon, displayed in resonance intensities and reflects a clear tendency towards dissolution of diatomaceous amorphous silica and the occurrence of the hydrated silica, which is the main component that ensures the diagenetic transition via the mechanism of dissolution–precipitation to other more crystalline silica phases, after the lost of its hydroxyls groups (water) by heating (burial). ²⁷Al MAS NMR reveals two coordinations of Al; the octahedrally coordinated Al suggests the presence of clay relics trapped during crystal growth or a microcrystalline zeolite (clinoptilolite detected by SEM observations), while the tetrahedrally coordinated Al suggests the presence of minor quantities of minerals with tetrahedral Al, such as an Al-rich fluid and/or minerals such as feldspars.  相似文献   

Well log analysis and hydrocarbon potential of the Sa'ar–Nayfa reservoir,Hiswah Oilfield,eastern Yemen     

Nabil M. Al-Areeq  Abdulwahab S. Alaug 《Arabian Journal of Geosciences》2014,7(7):2941-2956

Sa'ar–Nayfa reservoir is mainly made up of carbonate sediments with bands of shale that contain a substantial amount of proven oil in the Hiswah Oilfield, Sayun–Masila Basin, eastern Yemen. Several vertical wells have been drilled and penetrated these sequences. This study is concerned on the petrophysical evaluation and well log analysis of the Lower Cretaceous of 11 wells at the Hiswah Oilfield, Hadramawt Governorate, eastern Yemen. Computer-assisted log analyses were used to evaluate the petrophysical parameters such as shale volume, total porosity, effective porosity, water saturation, hydrocarbon saturation, flushed zone saturation and reservoir and pay flags. Cross-plots of the petrophysical parameters versus depth were illustrated. The Lower Cretaceous Sa'ar–Nayfa reservoir reflects that the matrix components are mainly carbonates and shales. Moreover, the lithological-geologic model reflected that these shales are strongly affecting the porosity and, consequently, the fluid saturation in the Sa'ar–Nayfa reservoir. In this study, the thickness of the Sa'ar–Nayfa reservoir increases from central toward north-eastern and north-western parts within the Hiswah Oilfield. The porosities analyses of the investigation of the Sa'ar–Nayfa reservoir for the 11 studied wells concluded that the average total porosity ranges from 5.4 % to 16.8 % while the effective porosity ranges from 5.2 % to 14.8 %. Water saturation of the Sa'ar–Nayfa reservoir ranges from 6.9 % to 75.8 %. On the other hand, hydrocarbon saturation matches with water saturation in a reverse relationship. Sa'ar–Nayfa reservoir is interpreted as good quality reservoir rocks with high average effective porosity reaching to 20 % and high hydrocarbon saturation exceeding 93 %. The Sa'ar–Nayfa reservoir reveals promising reservoir characteristics especially the upper reservoir unit, which should be taken into consideration during future development of the oilfields area. The hydrocarbon saturation map of the Sa'ar–Nayfa reservoir shows a regular pattern of distribution with a general increasing to the northeast, northwest and east directions while decreasing southwest wards, recording the maximum value of 93.1 % at the Hiswah-21 well.  相似文献   

Log-derived petrophysical characteristics and oil potentiality of the Upper Qishn Clastic Member,Masila Basin,Yemen     

Awad A. Omran  Nabil M. Alareeq 《Arabian Journal of Geosciences》2014,7(5):1733-1748

The Lower Cretaceous Qishn Formation at Masila Basin, Yemen, contains substantial amounts of proven crude oil. It is divided into a lower shaly silisiclastic member and an upper carbonate member. In the present work, detailed formation evaluation of the Upper Qishn Clastic Member was carried out using the digitized well logging data from 12 wells, via computer-assisted analysis, to accomplish its reservoir characteristics and oil potentiality. Accordingly, the true resistivity (R _t), porosity (total φ _t and effective φ _e), shale content (V _sh), permeability (K), water saturation (S _w), hydrocarbon saturation (S _h) (movable “S _hm” and residual “S _hr”) and lithologic composition in each well were estimated, analyzed, and illustrated versus depth on litho-saturation cross-plots. Likewise, the areal distribution of such parameters alongside the member in the investigated area and their relations to geological setting were defined from the constructed isoparametric contour maps. Based on the obtained results, the components of Upper Qishn Clastic Member of Masila Basin are mainly shaly sandstone and minor calcareous sandstone with considerable amount of shale. Regionally, the Member was deposited on an inner neritic to shallow-marine platform setting. It is interpreted as a good-quality reservoir rock which has been established from high total porosity (15–22 %), good effective porosity (8–13 %), and variable shale volume (24–31 %). A number of high hydrocarbon saturation zones (exceeding 55 %) are detected through intervals having S _w?<?60 % and S _hm?>?20 % which have been considered as economic oil producers. The storage and pay capacities of the reservoir intervals have been resolved. The obtained results were confirmed from the available data of core analyses and production tests. The Upper Qishn Clastic Member reveals promising reservoir characteristics which should be taken into consideration during future development of the oilfields in the area.  相似文献   

Evaluation of the Risk of Marine Slope Instability: A Pseudo-3D Approach for Application to Large Areas     

Nabil Sultan  Pierre Cochonat  Jean François Bourillet  Florence Cayocca 《Marine Georesources & Geotechnology》2013,31(2):107-133

Abstract

This article presents a methodology developed to evaluate the instability of submarine slopes that extend over a large area. Special attention was paid to (1) the complex geometry (bathymetry) and the expanse of the slope, (2) the heterogeneity of the sediment, and (3) the distribution of the pore pressure. The safety factor was considered as a spatially varying quantity. The General Formulation (GLE, Fredlund and Krahn 1977), which fully satisfies equilibrium conditions, was used for evaluating the stability of the marine slope. The submarine slope failure, which occurred on 16 October 1979 during the construction of the new Nice airport, was studied in order to test the developed model. Geotechnical parameters were taken from experimental tests carried out by IFREMER on 19 cores extracted at different depths (from 27 m to 1300 m) (Cochonat, Bourillet, and Savoye, 1993; Mulder et al., 1994). Many scenarios were proposed in order to explain the cause of the Nice slope failure (Habib, 1994). In this article, two of those scenarios were tested. Simulation results are presented and discussed.  相似文献