Modeling of gas generation from the Alam El-Bueib formation in the Shoushan Basin, northern Western Desert of Egypt

The Shoushan Basin is an important hydrocarbon province in the northern Western Desert, Egypt, but the burial/thermal histories for most of the source rocks in the basin have not been assigned yet. In this study, subsurface samples from selected wells were collected to characterize the source rocks of Alam El-Bueib Formation and to study thermal history in the Shoushan Basin. The Lower Cretaceous Alam El-Bueib Formation is widespread in the Shoushan Basin, which is composed mainly of shales and sandstones with minor carbonate rocks deposited in a marine environment. The gas generative potential of the Lower Cretaceous Alam El-Bueib Formation in the Shoushan Basin was evaluated by Rock–Eval pyrolysis. Most samples contain sufficient type III organic matter to be considered gas prone. Vitrinite reflectance was measured at eight stratigraphic levels (Jurassic–Cretaceous). Vitrinite reflectance profiles show a general increase of vitrinite reflectance with depth. Vitrinite reflectance values of Alam El-Bueib Formation range between 0.70 and 0.87 VRr %, indicating a thermal maturity level sufficient for hydrocarbon generation. Thermal maturity and burial histories models predict that the Alam El-Bueib source rock entered the mid-mature stage for hydrocarbon generation in the Tertiary. These models indicate that the onset of gas generation from the Alam El-Bueib source rock began in the Paleocene (60 Ma), and the maximum volume of gas generation occurred during the Pliocene (3–2 Ma).     

Seismic sequence stratigraphy of Miocene deposits related to eustatic,tectonic and climatic events,Cap Bon Peninsula,northeastern Tunisia

The Cap Bon Peninsula, belonging to northeastern Tunisia, is located in the Maghrebian Alpine foreland and in the North of the Pelagian block. By its paleoposition, during the Cenozoic, in the edge of the southern Tethyan margin, this peninsula constitutes a geological entity that fossilized the eustatic, tectonic and climatic interactions. Surface and subsurface study carried out in the Cap Bon onshore area and surrounding offshore of Hammamet interests the Miocene deposits from the Langhian-to-Messinian interval time. Related to the basin and the platform positions, sequence and seismic stratigraphy studies have been conducted to identify seven third-order seismic sequences in subsurface (SM1-SM7), six depositional sequences on the Zinnia-1 petroleum well (SDM1-SDM6), and five depositional sequences on the El Oudiane section of the Jebel Abderrahmane (SDM1–SDM5). Each sequence shows a succession of high-frequency systems tract and parasequences. These sequences are separated by remarkable sequence boundaries and maximum flooding surfaces (SB and MFS) that have been correlated to the eustatic cycles and supercycles of the Global Sea Level Chart of Haq et al. (1987). The sequences have been also correlated with Sequence Chronostratigraphic Chart of Hardenbol et al. (1998), related to European basins, allows us to arise some major differences in number and in size. The major discontinuities, which limit the sequences resulted from the interplay between tectonic and climatic phenomena. It thus appears very judicious to bring back these chronological surfaces to eustatic and/or local tectonic activity and global eustatic and climatic controls.     

http://www.sciencedirect.com/science/article/pii/S1674987112001545

The presence of natural voids and cavities in subsurface karstic limestones causes severe problem for civil engineering and environmental management.The presence of such features hinders the extension of urbanizations particularly in the new metropolitan.The eastern part of Saudi Arabia contains various types of karstic limestone,sinkholes,solution cavities and voids.In this context,geophysical methods particularly electrical resistivity technique is used as a cost-effective solution for investigating subsurface caves,voids,and shallow weathered zones.2-D electrical resistivity data sets have been acquired along seven profiles in the new urbanization at Al Hassa area.Data processing has been carried out taking into consideration the response of synthetic models,which simulates physical models of the most common karstic features in the area.The results are very useful to determine the extension of shallow weathered zones and to locate different cavities underneath them.The hard limestone bedrock can also be detected and traced along the surveyed profiles.     

Runoff responses at different watershed scales in semi arid region: exploration of a developed rainfall runoff model (Merguellil and Skhira watershed, Central Tunisia)

Understanding the hydrological response of small and large river basins is crucial for regional climate and hydrology studies. Also, rainfall space–time variability (Known in semi arid climate) has a major influence on hydrological dynamics. As consequent, we developed a software application (with MATLAB) in order to take into account the rainfall space-time variability, and that open a major prospects of studying hydrometeorological effects such scale effect and moving storms. In this context, in order to asses scale and dynamic rainy events effect in hydrologic modelling, this study focuses on instantaneous rainy data in central Tunisia (Merguellil and Skhira watershed): a rainfall runoff modelling was done to investigate basins responses and a developed geomorphology-based transfer function, was applied. A systematic hydro-meteorological analysis have been implemented to understand different types of variability and rainy fields dynamic, the relevance of rainfall network and scale effects. As result, two different behaviours of studied basins are detected. Responses of studied areas are much related to event dynamic (East/West and West/East) and hydrographs change according to event direction.     

Subsurface structural trends of the offshore Nile Delta area, Egypt: evidences from gravity and magnetic data

Subsurface structural trends and tectonics affecting the offshore Nile Delta area, Egypt, have been studied through the interpretations of gravity and magnetic data. Reduced to the pole, regional–residual separation, Tilt derivative and Euler deconvolution techniques are applied for the processing and interpretations of the magnetic and gravity data. The average depth of the sedimentary cover, estimated from the two-dimensional power spectrum technique ranges between 8 km and 13 km. The interpretation of the gravity and magnetic data indicates that the study area is affected by many subsurface structural trends. The NW–SE is the major trend related to El-Temsah and Misfaq-Bardwil trend. The NE–SW direction is the second dominant trend, related to the Rosetta trend. Other trends defined through the interpretation of gravity and magnetic data include: the N–S direction, related to the Baltim fault trend, the E–W direction, related to the Neogene hinge line and the NNE–SSW related to the Gulf of Aqaba. Accessory trends include the ENE–WSW, WNW–ESE and finally the NNW–SSW.     

Interaction of longitudinal surface settlements for twin tunnels in shallow and soft soils: the case of Istanbul Metro

Increasing demands on infrastructures increases the attention on shallow soft ground tunneling methods in urbanized areas. Especially, in metro tunnel excavations, it is important to control the surface settlements observed before and after excavation, which may cause damage to surface structures. To solve this problem, earth pressure balance machines (EPBMs) have widely been used throughout the world. This study focuses on surface settlement measurements, the interaction of twin tunnel surface settlement, and the relationship between shield parameters and surface settlement for parallel tunnels using EPBM shields in clay and sand soils. In this study, the tunnels were excavated using two EPBMs. The tunnels were 6.5 m in diameter, as twin tubes with a 14 m distance from center to center. The EPBM in the first tube followed about 100 m behind the other tube. Segmental lining with 1.4 m of length was employed as a final support. The results from this study showed that (1) the most important parameters for the maximum surface settlements are the face pressure and backfill; (2) in twin tunnel excavation with EPBM for longitudinal profile, the settlement rate reached its peak value when the shield came to the monitoring section and this peak value continued until the shield passed the monitoring section; (3) every shield affected the other tunnel’s longitudinal surface settlement profile by approximately 35–36.8 %; (4) S _A, S _B and S _C values were found to be 38.0, 35.8 and 26.2 %, respectively for an EPBM, and (5) ensuring good construction quality is a very effective way to control face stability and minimize surface settlement.     

Modeling of limestone aquifer in the western part of the River Nile between Beni Suef and El Minia

A robust classification scheme for partitioning groundwater chemistry into homogeneous groups was an important tool for the characterization of Eocene limestone aquifer. The aquifer locally is composed of chalky limestone with thin clay intercalated (Samalut Fm.), the fissures, the joints, and the fractures are represented the conduits of the aquifer system. The flow patterns are conditioned by karstification processes which develop a conduit network and preserve low permeability microfractured blocks. The aquifer is mainly recharged by surrounding aquifers and agricultural wastewaters. The groundwater flows in the eastern part (due the Bahr Yossef and River Nile), which is a discharge area rather than a recharge. Twenty-eight groundwater samples was collected from the Eocene limestone aquifer and analyzed for isotopes, major, and trace elements. δD and δ¹⁸O concentrations ranged widely due to geology, infiltration of different surface waters, evaporation, and hydrogeology. The concentration of δD and δ¹⁸O isotopes is depleted in the northern zone of the northern part and western zone of the central and southern part of the study area. They are enriched due the eastern area of the central and southern part of the study area. δD vs. δ¹⁸O delineate the Pleistocene aquifer and has a strong influence than other waters on aquifer hydrogeochemistry. It is confirmed by the AquaChem outputs of the mixing proportions of different water types included in the aquifer system. Cl-δD and Cl-δ¹⁸O relationships indicate the role of evaporation especially due the eastern area of the central and southern part of the study area. This research tests the performance of the many available graphical and statistical methodologies used to classify water samples. R-mode clustering, correlation analysis, and principal component analysis were investigated. All the methods were discussed and compared as to their ability to cluster, ease of use, and ease of interpretation. Nearly most low-salinity waters are in equilibrium to supersaturate with respect to both carbonate minerals, while it is shifted to undersaturate with salinity. The inverse modeling findings clarify that the calcite, gypsum, and anhydrite dissolution increased due the northeastern area, middle zone, and southern corner of the northern, central, and southern part of the study area, respectively. The latter areas also were characterized by the lowest precipitation of the dolomite. Such areas are distinguished by much more enhancement for aquifer permeability and therefore transmissivity. The latter areas can be use as injection zone by fresh water. It can be a triple function; firstly, it recharges the saline Eocene limestone aquifer through the enhancement hydraulic conductivity and dilutes it. Secondly, it enhances much more the aquifer permeability and therefore the transmissivity. The Eocene limestone aquifer can be improved in quality and quantity by using such a model and exploits it as an alternative water resource with Quaternary aquifer and Nile water. Thirdly, it irrigates more areas to increase the income/capita. The dedolomitization represents the main hydrogeochemical process in the aquifer system. The geomedia (limestone, clay, marl, shale, and sand deposits) are in contact with water, therefore, the rock/water interaction, mixing, and ion exchange were estimated by the geochemical evolution of the groundwater systems.     

Groundwater investigation in the southern part of Gabes using resistivity sounding, southern Tunisia

The groundwater hydrogeology of southern Tunisia emphasizes two main groundwater bodies so-called Zeuss-Koutine and south Gabes. These groundwater bodies yielding economically important storage of useful water present complex internal architecture and heterogeneity allowing exchange flows throughout permeable or/and fractured bodies. A geophysical survey using resistivity soundings was carried out along this area to describe in detail the field structure and the 3D extent of these groundwater bodies by the hydrogeological new data and detailed subsurface mapping based on resistivity sounding and seismic data. This survey discusses also the potentialities of some permeable layer in water storage and purposes potential favorable areas for optimum groundwater mining.     

Coastal progradation in response to the recent sea level rise: a case study of El Grine coast, Gulf of Gabes (Southeastern Tunisia)

Over the last 30 years El Grine coast recorded significant morphological changes leading to the shoreline progradation. Diachronic coastal evolution, through a set of satellite images data, supported by sedimentologic analysis of five sand cores have been applied to elucidate tidal flat reaction following the recent sea level rise. We found that an emerging sandy barrier and salt marsh domain were shaped by the local hydro-sedimentary processes. The marine sediments, mobilised by wave and tide currents, have been the sole sedimentary source. Recent sandy accumulations, occurred around 1987, have been able to balance a recent sea level rise. While during a mid-Holocene period, El Grine coast was governed by net erosion tendency inducing cliff recession.     

Inorganic geochemical evidence for the depositional facies associations of the Upper Jurassic Chia Gara Formation in NE Iraq

Four wells (K-109, Hr-1, Tk-3, and Bj-1) in NE Iraq (including parts of the Kurdistan Region) were selected to study the Tithonian–Berriasian Chia Gara Formation from the inorganic geochemical point of view. The intervals studied in each well occurred at present-day burial depths of Hr-1 3,075–3,310 m; K-109 2,780–3,090; Tk-1 2,770–2,890; and Bj-1 2,150–2,310 m. A total of 16 samples from the four studied wells were investigated geochemically using X-ray fluorescence in order to measure their major element oxides and their trace element contents. Among the major oxides, CaO has the highest weight percentages in all samples as expected in this limestone-dominated formation. SiO₂ and Al₂O₃ show higher concentrations only in well Bj-1 than the other sections, due to its shallower depth of deposition and its marginal location within the depositional basin. The general trace element distribution along all studied well successions showed good similarity. However, the ratios of V/Ni and V/Cr were of higher values in the lower part of the formation, which is considered as a good indicator to the deposition of this part of the formation within anoxic depositional environment. An exception was in well Bj-1, where the V/Ni ratio was lower in the this lower part of the formation than the upper part that may be due to the different lithology in this succession which is lacking distinct shale or calcareous shale beds. However, the V/Cr ratio can still indicate the prevailing of reducing condition because V/Cr ratios in all samples are >2. Also, Th/U ratio in the lower part of the studied successions was lower than the upper part, which is also coinciding with the domination of the reducing geochemical conditions in the depositional environment. It may be concluded from this study that the R-mode cluster analysis of the main oxides indicated to the main mineral constituent of the rock which is calcite. It is also confirmed that the SiO₂ and Al₂O₃ contents in the Chia Gara limestones are especially high in well Bj-1, particularly in the lower and upper parts of the succession. On the other hand, R-mode cluster analysis of the trace elements showed lower amounts of Zr and V in relation to silica and confirmed the random distribution of Sr and Ba in the studied samples. Q-mode cluster analysis indicated that the upper part of the studied formation is pure limestone in well H-1 and such purity of limestone beds also occurs in the lower part of the studied formation in well Tk-3. The elemental distribution within the sections as inferred from the studied samples indicates that the anoxic depositional conditions were prevailed during the Chia Gara Formation, especially during the accumulation of the lower part.