Modern changes of tidal troughs among the radial sand ridges in northern Jiangsu coastal zone

Using satellite images taken on different dates, GIS analysis of aerial photos, bathymetric maps and other field survey data, tidal troughs and major sand ridges in the northern Jiangsu coastal area were contrasted. The results show that there have been three types of movement or migration of tidal trough in this area: (1) Periodic and restricted, this type of trough usually developed along the beaches with immobile gully head as a result of the artificial dams and the swing range increased from gully head to the low reaches, so they have been obviously impacted by human activity and have longer swing periods; (2) Periodic and actively, this kind of trough, which swung with a fast rate and moved periodically on sand ridges, were mainly controlled by the swings of the host tidal troughs and hydrodynamic forces upon tidal sand ridge and influenced slightly by human constructions; (3) Steadily and slowly, they are the main tidal troughs with large scale and a steady orientation in this area and have slow lateral movement. The differences in migration mode of tidal trough shift result in different rates of migration and impact upon tidal sand ridges. Lateral accumulation on current tidal trough and deposition on abandoned tidal troughs are the two types of sedimentation of the tidal sand ridges formation. The whole radial sand ridge was generally prone to division and retreat although sand ridges fluctuated by the analysis of changes in talwegs of tidal troughs and shorelines of sand ridges.

Short-term morphological changes after sand-digging during a sand sculpture activity

The morphology of the beach backshore and foreshore at Huiquan Bay, Qingdao, China, is characterized by a single intertidal sandbar system with a spring tide range of 4.59 m. The beach was measured with a laser total station of Leica TPS402. Contours of the beach were generated using data collected in March and November 2005. The survey method provided 2 mm measuring accuracy and 4-10 m horizontal spacing. The net accretion volume of the foreshore was about 11, 215 m(3) from March to November. After sand sculpture activity, the axis of the sand trough migrated onshore from about 3.5 m to 17.5 m on the foreshore beach in November. At the same time, the axis of the sandbar crest migrated onshore no more than 42.25 m on the northwest foreshore; and it migrated offshore no more than 23.75 m on the southeast foreshore. On the northwest and southeast foreshore beach, two strips of erosion areas with a thickness of 0-0.2 m appeared on the sandbar crest. Accretion occurred at the bottom of the sand trough with a thickness of similar to 0.2-0.6 m. The sandbar height decreased after sand sculpture activity, and it was no more than 0.7 m in March and 0.6 m in November. Human activities, such as sand digging on the sandbar crest during sand sculpture activity, also can disturb the beach morphology of intertidal bar systems. This phenomenon also was validated by comparison of beach morphology, the results of a color artificial tracer experiment and a sediment transportation trend prediction.

On the relationships between the radial tidal current field and the radial sand ridges in the southern Yellow Sea: a numerical simulation

The ori-in of the radial sand ridges (RSRs) in the southern Yellow Sea has been a controversial problem since they were discovered in the early 1960s. To resolve the problem, two key questions need to be answered: (1) was the radial tidal current field in the RSR area generated by the submarine topography, or (2) did it exist before the RSRs occurred? In this study, the M-2 tide and tidal currents in the RSR area were simulated with a two-dimensional tidal model using a flat bottom and a shelving slope topography, the results being then compared with the field data. It is demonstrated that the radial tidal current field in the southern Yellow Sea is independent of bottom topography, and may thus be the controlling factor generating the RSRs. The radial tidal current field probably existed before the RSRs were formed.

Observation and theoretical analysis for the sand-waves migration in the North Gulf of South China Sea

According to the environmental characteristic of the north gulf of South China Sea, a quasi-3D mechanics model has been built for simulating the small scale sand-waves migration in the seas of southwest of Hainan Island. Based on the submarine micro-geomorphic data induced by multi-beam system and hydrographic survey record, the migrations of the sand-waves in the study area are predicted. The results show that calculation is consistent with the observation data in the groove of sand ridge, but not well in the crest of sand ridge. It is indicated that the mechanics model should be used to predict the migration of the small scale sand-waves which are dominated by bed load in the seas. This paper is very meaningful to project the route of submarine pipeline.

Formation of nano-crystalline corrosion products on Zn-Al alloy coating exposed to seawater

Hot dip Zn-Al alloy coating performs better than hot dip galvanized coating and 55% Al-Zn-Si coating as well with regard to general seawater corrosion protection. A characterization of the corrosion products on Zn-Al alloy coating immersed in dynamic aerated seawater has been performed mainly based on transmission electron microscopy (TEM) for morphological analysis and X-ray diffraction (XRD) technique for crystalline phase identification. The XRD and TEM analyses showed that the corrosion products mainly were typical nanometer Zn4CO3(OH)(6).H2O, Zn-5(OH)(8)Cl-2 and Zn6Al2CO3(OH)(16). 4H(2)O microcrystals. This probably is connected to the co-precipitation of Zn2+ and Al3+ ions caused by adsorption. Zn-Al alloy coating being suffered seawater attacks, AI(OH)(3) gel was first produced on the coating surface. Zn and Al hydroxides would co-precipitate and form double-hydroxide when the concentration of adsorbed Zn2+ ions by the newly produced gel exceeded the critical degree of supersaturation of the interphase nucleation. However, because the growth of the crystals was too low to keep in step with the nucleation, a layer of nano-crystalline corrosion products were produced on the surface of the coating finally. (C) 2001 Elsevier Science Ltd. All rights reserved.

Characteristics of sulfide corrosion products on 316L stainless steel surfaces in the presence of sulfate-reducing bacteria

It has been found that microbial communities play a significant role in the corrosion process of steels exposed in aquatic and soil environments. Biomineralization influenced by microorganisms is believed to be responsible for the formation of corrosion products via complicated pathways of electron transfer between microbial cells and the metal. In this study, sulfide corrosion products were investigated for 316L stainless steel exposed to media with sulfate-reducing bacteria media for 7 weeks. The species of inorganic and organic sulfides in the passive film on the stainless steel were observed by epifluorescence microscope, environmental scanning electron microscope combined with energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The transformation from metal oxides to metal sulfides influenced by sulfate-reducing bacteria is emphasized in this paper. (c) 2005 Elsevier B.V. All rights reserved.

水热条件下钾长石碱性分解反应机理的实验研究

It is well known that our country is short of water-soluble potassium, but rich in insoluble potassium ores. Based on the work of the formers, using the orthogonal and monofactor experiments, the author optimized the production technology of micro-porous potassium silicon calcium mineral fertilizer by non-stirring hydrothermal chemical reaction when the alkaline earth booster CaO was available. The influences of temperature、time、reactant ratio and water-solid ratio on the dissolution rate of production’s elements were studied by orthogonal experiments, and the production technology was further optimized by monofactor experiments. By XRD、SEM、EDS and dissolving experiments, it was systematically studied that the effects of the reactant ratio、reaction time and reaction temperature on the properties of the production obtained by the hydrothermal reaction between KAlSi3O8 and CaO. The results showed that：when changing of the reaction condition, the reaction productions included tobermorite、 hibschite、α-C2SH and K2Ca(CO3)2; among which, K2Ca(CO3)2 was not the first production containing potassium, but K2Ca(CO3)2 was synthesized by the reaction among KOH、Ca(OH)2 and CO2. Whether the phase was synthesized was related to not only the reaction condition, but also their physicochemical properties; when the reaction condition was changed, the changes of different phases were different. The results of XRD and dissolution rate experiments explained the dissolution characteristic of every element of hydrothermal productions very well, and the relation between the dissolution rate of element and the phase of productions poured a good illumination on the production technology. The results of SEM and EDS showed that: hydrogarnet looked like spherical, and its surface was covered by some productions including K phase and Ca、Si phase; but the morphology of tobermorite was platy or lamellar or needlelike, and parts of Si in the structure of tobermorite were substituted by Al，and some K+ cations were inserted into the Ca interlayer of tobermorite at the same time. It was the first time that the interface between KAlSi3O8 and Ca(OH)2 was observed directly by SEM and EDS after the hydrothermal reaction, and the mechanism of hydrothermal reaction of KAlSi3O8 and Ca(OH)2 was further discussed. These results indicated that: the Ca-KAlSi3O8 intermediate compound was formed at first, and some K was released into the solution and KOH was produced at the same time; the C-S-H phase appeared before hydrogarnet, and then hydrogarnet was synthesized when the chemical reaction was carried on; if the reaction was carried on furthermore, α-C2SH、tobermorite and other C-S-H phases of different atom ratio appeared. The author found that the structure of KAlSi3O8 would be more drastically destroyed if there were some reactants, such as Ca(OH)2 which reacted with KAlSi3O8 and new phases were formed after the hydrothermal reaction between KAlSi3O8 and alkaline solution of equal ionic strength was finished. With the combination of calcination and hydrothermal reaction methods, the dissolution rate of products were greatly improved when the hydrothermal reaction was carried out after KAlSi3O8 and CaCO3 were calcined. Furthermore, the author has tentatively explored how to evaluate the effects of the differences of the activity of lime on the dissolution properties of hydrothermal products.

港西地区河流相砂岩油藏剩余油分布研究

The Gangxi oil field has reached a stage of high water production. The reservoir parameters, such as reservoir physical characteristics, pore structure, fluid, have obviously changed. This thesis therefore carries out a study of these parameters that control reservoir characteristics, physical and chemical actions that have taken place within the reservoirs due to fluid injection, subsequent variations of reservoir macroscopic physical features, microscopic pore structures, seepages, and formation fluid properties. This study rebuilds a geologic model for this oil field, establishes a log-interpreting model, proposes a methodology for dealing with large pore channels and remnant oil distribution, and offers a basis for effective excavation of potential oil, recovery planning, and improvement of water-injection techniques. To resolve some concurrent key problems in the process of exploration of the Gangxi area, this thesis carries out a multidisciplinary research into reservoir geology, physical geography, reservoir engineering, and oil-water well testing. Taking sandstone and flow unit as objects, this study establishes a fine geologic model by a quantificational or semi-quantificational approach in order to understand the remnant oil distribution and the reservoir potential, and accordingly proposes a plan for further exploration. By rebuilding a geological model and applying reservoir-engineering methods, such as numerical simulation, this thesis studies the oil-water movement patterns and remnant-oil distribution, and further advances a deployment plan for the necessary adjustments and increase of recoverable reserves. Main achievements of this study are as follows: 1. The Minghazhen Formation in the Gangxi area is featured by medium-sinuosity river deposits, manifesting themselves as a transitional type between typical meandering and braided rivers. The main microfacies are products of main and branch channels, levee, inter-channel overflows and crevasse-splay floodplains. The Guantao Group is dominantly braided river deposit, and microfacies are mainly formed in channel bar, braided channel and overbank. Main lithofacies include conglomerate, sandstone, siltstone and shale, with sandstone facies being the principal type of the reservoir. 2. The reservoir flow unit of the Gangxi area can be divided into three types: Type I is a high-quality heterogeneous seepage unit, mainly distributed in main channel; Type II is a moderate-quality semi-heterogeneous seepage unit, mainly distributed in both main and branch channels, and partly seen within inter-channel overflow microfacies; Type III is a low-quality, relatively strong heterogeneous seepage unit, mainly distributed in inter-channel overflow microfacies and channel flanks. 3. Flow units and sedimentary microfacies have exerted relatively strong controls on the flowing of underground oil-water: (1) injection-production is often effective in the float units of Type I and II, whilst in the same group of injection-production wells, impellent velocity depends on flow unit types and injection-production spacing; (2) The injection-production of Type III flow unit between the injection-production wells of Type I and II flow units, however, are little effective; (3) there can form a seepage shield in composite channels between channels, leading to inefficient injection and production. 4. Mainly types of large-scale remnant-oil distribution are as follows: (1) remnant oil reservoir of Type III flow unit; (2) injection-production well group of remnant oil area of Type III flow unit; (3) remnant oil reservoirs that cannot be controlled by well network, including reservoir featured by injection without production, reservoir characterized by production without injection, and oil reservoir at which no well can arrive; (4) remnant oil area where injection-production system is not complete. 5. Utilizing different methods to deal with different sedimentary types, sub-dividing the columns of up to 900 wells into 76 chronostratigraphic units. Four transitional sandstone types are recognized, and contrast modes of different sandstone facies are summarized Analyzing in details the reservoirs of different quality by deciphering densely spaced well patterns, dividing microscopic facies and flow units, analyzing remnant oil distribution and its effect on injection-production pattern, and the heterogeneity. Theory foundation is therefore provided for further excavation of remnant oil. Re-evaluating well-log data. The understanding of water-flood layers and conductive formations in the Gangxi area have been considerably improved, and the original interpretations of 233 wells have changed by means of double checking. Variations of the reservoirs and the fluid and formation pressures after water injection are analyzed and summarized Studies are carried out of close elements of the reservoirs, fine reservoir types, oil-water distribution patterns, as well as factors controlling oil-gas enrichment. A static geological model and a prediction model of important tracts are established. Remaining recoverable reserves are calculated of all the oil wells and oil-sandstones. It is proposed that injection-production patterns of 348 oil-sandstones should be adjusted according to the analysis of adaptability of all kinds of sandstones in the injection-production wells.