Origin of brine in the Kangan gasfield: isotopic and hydrogeochemical approaches

The Kangan Permo-Triassic brine aquifer and the overlying gas reservoir in the southern Iran are located in Kangan and Dalan Formations, consisting dominantly of limestone, dolomite, and to a lesser extent, shale and anhydrite. The gasfield, 2,900 m in depth and is exploited by 36 wells, some of which produce high salinity water. The produced water gradually changed from fresh to saline, causing severe corrosion in the pipelines and well head facilities. The present research aims to identify the origin of this saline water (brine), as a vital step to manage saline water issues. The major and minor ions, as well as δ²H, δ¹⁸O and δ³⁷Cl isotopes were measured in the Kangan aquifer water and/or the saline produced waters. The potential processes causing salinity can be halite dissolution, membrane filtration, and evaporation of water. The potential sources of water may be meteoric, present or paleo-seawater. The Na/Cl and I/Cl ratios versus Cl^? concentration preclude halite dissolution. Concentrations of Cl, Na, and total dissolved solid were compared with Br concentration, indicating that the evaporated ancient seawater trapped in the structure is the cause of salinization. δ¹⁸O isotope enrichment in the Kangan aquifer water is due to both seawater evaporation and interaction with carbonate rocks. The δ³⁷Cl isotope content also supports the idea of evaporated ancient seawater as the origin of salinity. Membrane filtration is rejected as a possible source of salinity based on the hydrochemistry data, the δ¹⁸O value, and incapability of this process to dramatically enhance salinity up to the observed value of 330,000 mg/L. The overlaying impermeable formations, high pressure in the gas reservoir, and the presence of a cap rock above the Kangan gasfield, all prevent the downward flow of meteoric and Persian Gulf waters into the Kangan aquifer. The evaporated ancient seawater is autochthonous, because the Kangan brine aquifer was formed by entrapment of brine seawater during the deposition of carbonates, gypsum, and minor clastic rocks in a lagoon and sabkha environment. The reliability of determining the source of salinity in a deep complicated inaccessible high-pressure aquifer can be improved by combining various methods of hydrochemistry, isotope, hydrodynamics, hydrogeology and geological settings.     

Time-domain two-dimensional site response analysis of non-homogeneous topographic structures by a hybrid BE/FE method

In this paper, an advanced formulation of the time-domain, two-dimensional hybrid finite element–boundary element method (FEM/BEM) is presented, and applied to carry out site response analysis of homogeneous and non-homogeneous topographic structures subjected to incident in-plane motions. Seismic responses of half-plane, horizontally layered site, alluvial valley and ridge sections subjected to incident P and SV waves are analyzed in order to demonstrate the applicability and efficiency of the presented method. The numerical results show that hybrid BE/FE methods require smaller time steps than those needed by BEM schemes. They also show that in case of surface irregularities with height to half-width ratio of up to one, the topography effect could be noticeable, if incident waves have wavelengths of less than approximately eight times the width.     

Application of a continuum numerical model for pile driving analysis and comparison with a real case

This paper presents the results of a so-called continuum numerical model for wave propagation analysis and soil-pile dynamic response during pile driving. An axisymmetric finite difference numerical model is developed having solid elements for both pile structure and the soil media surrounding and below the pile. Interface elements are used between the pile shaft and the soil to facilitate the sliding between the two media. The performance of the developed model is verified in two stages. First, a simple rod is subjected to a half sine-wave force function at the rod head and the corresponding reflections of force and velocity (multiplied by impedance) are presented for different boundary conditions at the rod tip. The model is then used for signal matching analysis of a real driven pile for which complete information of soil layering, dynamic test signals, and static load test results are available. The signal matching analysis was performed successfully and comparison between several other predicted and measured parameters proved the reasonably good performance of the developed continuum model.     

Numerical modelling of multistage caving processes: insights from multi‐seam longwall mining‐induced subsidence

Evaluating the induced subsidence is a critical step in multi‐seam longwall mining. Numerical modelling can be a cost‐effective approach to this problem. Numerical evaluation of longwall mining‐induced subsidence is much more complicated when more than one seam is to be extracted. Only a few research works have dealt with this problem. This paper discusses the essential requirements of a robust numerical modelling approach to simulation of multi‐seam longwall mining‐induced subsidence. In light of these requirements, the previous works on this topic are critically reviewed. A simple yet robust FEM‐based modelling approach is also proposed that is capable of simulating caving process, rock mass deterioration and subsidence around multi‐seam excavations. The effectiveness of this approach in comparison with two other conventional FEM approaches is demonstrated through numerical examples of two different multi‐seam mining configurations. Results show that the proposed numerical modelling approach is the only robust method, which is capable of simulating multi‐seam subsidence in both demonstrated cases. Copyright © 2016 John Wiley & Sons, Ltd.     

Development of fragility curves by incorporating new spectral shape indicators and a weighted damage index: case study of steel braced frames in the city of Mashhad,Iran

In this study, strong ground motion record(SGMR) selection based on Eta(η) as a spectral shape indicator has been investigated as applied to steel braced frame structures. A probabilistic seismic hazard disaggregation analysis for the definition of the target Epsilon(ε) and the target Eta(η) values at different hazard levels is presented, taking into account appropriately selected SGMR's. Fragility curves are developed for different limit states corresponding to three representative models of typical steel braced frames having significant irregularities in plan, by means of a weighted damage index. The results show that spectral shape indicators have an important effect on the predicted median structural capacities, and also that the parameter η is a more robust predictor of damage than searching for records with appropriate ε values.     

Quantifying changes in groundwater level and chemistry in Shahrood,northeastern Iran

Temporal changes in the quantity and chemical status of groundwater resources must be accurately quantified to aid sustainable management of aquifers. Monitoring data show that the groundwater level in Shahrood alluvial aquifer, northeastern Iran, continuously declined from 1993 to 2009, falling 11.4 m in 16 years. This constitutes a loss of 216 million m³ from the aquifer’s stored groundwater reserve. Overexploitation and reduction in rainfall intensified the declining trend. In contrast, the reduced abstraction rate, the result of reduced borehole productivity (related to the reduction in saturated-zone thickness over time), slowed down the declining trend. Groundwater salinity varied substantially showing a minor rising trend. For the same 16-year period, increases were recorded in the order of 24% for electrical conductivity, 12.4% for major ions, and 9.9% for pH. This research shows that the groundwater-level declining trend was not interrupted by fluctuation in rainfall and it does not necessarily lead to water-quality deterioration. Water-level drop is greater near the aquifer’s recharging boundary, while greater rates of salinity rise occur around the end of groundwater flow lines. Also, fresher groundwater experiences a greater rate of salinity increase. These findings are of significance for predicting the groundwater level and salinity of exhausted aquifers.     

Biostratigraphy of the Surgah formation in Kuh-e-Surgah and correlation with Tang-e-Gerab (West of Iran)

In biostratigraphic studies of the Surgah formation in the Kuh-e-Surgah section, 145 samples were collected. The thickness of the Surgah formation is about 175 m, and it consists mainly of limestone and shale. The lower and upper boundaries of the Surgah formation are Sarvak and Ilam formations, respectively, and they are conformable with sharp lithology. Seventeen species which belong to six genera of planktonic foraminifera and four biozones have been identified in this study. Based on foraminifera assemblages and biozone determinations, the age of the Surgah formation is Late Turonian to Early Late Santonian. This section is correlated with the Tang-e-Gerab section.     

Autonomous optical navigation using nanosatellite-class instruments: a Mars approach case study

This paper examines the effectiveness of small star trackers for orbital estimation. Autonomous optical navigation has been used for some time to provide local estimates of orbital parameters during close approach to celestial bodies. These techniques have been used extensively on spacecraft dating back to the Voyager missions, but often rely on long exposures and large instrument apertures. Using a hyperbolic Mars approach as a reference mission, we present an EKF-based navigation filter suitable for nanosatellite missions. Observations of Mars and its moons allow the estimator to correct initial errors in both position and velocity. Our results show that nanosatellite-class star trackers can produce good quality navigation solutions with low position (\(<300\,\text {m}\)) and velocity (\(<0.15\,\text {m/s}\)) errors as the spacecraft approaches periapse.     

Pushover analysis of asymmetric-plan buildings based on distribution of the combined modal story shear and torsional moment

A pushover procedure with a load pattern based on the height-wise distribution of the combined modal story shear and torsional moment is proposed to estimate the seismic response of 3D asymmetric-plan building frames. Contribution of the higher modes and torsional response of asymmetric-plan buildings are incorporated into the proposed load pattern. The proposed pushover method is a single-run procedure, which enables tracing the nonlinear response of the structure during the analysis and averts the elusiveness of conducting multiple pushover analyses. The proposed method has been used to estimate the response of two moment-resisting building frames with 9 and 20 stories. The obtained results indicate the appropriate accuracy and efficiency of the proposed procedure in estimating the trend of the drift profiles of the structures resulted from nonlinear time history analyses.