What are Gas Hydrates?
Gas hydrates (or clathrate hydrates) are ice-like crystalline molecular complexes formed from mixtures of water and suitably sized 'guest' gas molecules. The water (host) molecules, upon hydrogen bonding, form lattice structures with several interstitial cavities. The guest gas molecules can occupy the lattice cavities, and when a minimum number of cavities are filled, the crystalline structure will become stable and solid gas hydrates will form, even at temperatures well above the melting point of water ice. When gas hydrates dissociate (melt), the crystalline lattice breaks down into liquid water (or converts to ice if conditions are below the freezing point of water) and the gas is released. The classic image of gas hydrates is the 'burning snowball' - methane hydrate supporting its' own combustion, as shown in the picture below.
Gas hydrates may form wherever water and suitably sized 'guest' molecules (e.g. methane, carbon dioxide) exist under suitable (generally) high pressure and low temperature conditions. Suitable conditions for gas hydrate formation commonly occur during hydrocarbon production operations, where they are a major flow assurance problem. In the natural enviroment, hydrates may be found and in the sediments of the deep sea continental margins, the subsurface of Arctic permafrost regions, and in deep glacial ice.
Gas Hydrates in Hydrocarbon Production Operations
In petroleum exploration and production operations, gas hydrates are a serious economic and safety concern. Low seabed temperatures combined with high fluid pressures promote formation of clathrates in reservoir hydrocarbon-water fluid mixtures. Clathrates can block pipelines, subsea transfer lines, and, in the event of a gas kick during drilling, form in the well, in risers, BOPs (Blow-Out Preventers) and chokelines.
Drilling
In drilling, record water depths are continuously being set by oil companies in the search of hydrocarbon reserves in deep waters. Due to environmental concerns and restrictions, water based drilling fluids are often more desirable than oil based fluids, especially in offshore exploration. However, a well-recognised hazard in deep water offshore drilling, using water based fluids, is the formation of gas hydrates in the event of a gas kick.
In deep-water drilling, the hydrostatic pressure of the column of drilling fluid and the relatively low seabed temperature, could provide suitable thermodynamic conditions for the formation of hydrates in the event of a gas kick. This can cause serious well safety and control problems during the containment of the kick. The formation of gas hydrates in water based drilling fluids could cause problems in at least two ways:
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Gas hydrates could form in the drill string, blow-out preventer (BOP) stack, choke and kill line. This could result in potentially hazardous conditions, i.e., flow blockage, hindrance to drill string movement, loss of circulation, and even abandonment of the well.
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As gas hydrates consist of more than 85 % water, their formation could remove significant amounts of water from the drilling fluids, changing the properties of the fluid. This could result in salt precipitation, an increase in fluid weight, or the formation of a solid plug.
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The hydrate formation condition of a kick depends on the composition of the kick gas as well as the pressure and temperature of the system. As a rule of thumb, the inhibition effect of a saturated saline solution would not be adequate for avoiding hydrate formation in water depth greater than 1000 m. Therefore, a combination of salts and chemical inhibitors, which could provide the required inhibition, could be used to avoid hydrate formation.
Production
The ongoing development of offshore marginal oil and gas fields increases the risks of facing operational difficulties caused by the presence of gas hydrates. A typical area of concern is multiphase transfer lines from well-head to the production platform where low seabed temperatures and high operation pressures increase the risk of blockage due to gas hydrate formation. Other facilities, such as wells and process equipment, can also be prone to hydrate formation.
Different methods are currently in use for reducing hydrate problems in hydrocarbon transferlines and process facilities. The most practical methods are:
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At fixed pressure, operating at temperatures above the hydrate formation temperature. This can be achieved by insulation or heating of the equipment.
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At fixed temperature, operating at pressures below hydrate formation pressure.
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Dehydration, i.e., reducing water concentration to an extent of avoiding hydrate formation.
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Inhibition of the hydrate formation conditions by using chemicals such as methanol and salts.
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Changing the feed composition by reducing the hydrate forming compounds or adding non hydrate forming compounds.
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Preventing, or delaying hydrate formation by adding kinetic inhibitors.
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Preventing hydrate clustering by using hydrate growth modifiers or coating of working surfaces with hydrophobic substances.
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Preventing, or delaying hydrate formation by adding kinetic inhibitors.
What is my Project exactly?
I am working on a thermodynamic model to predict hydrate stability conditions to modify our inhous HWHYD model as my PhD project. HWHYD capabilities include:
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PVT (Pressure-Volume-Temperature) calculations covering systems both with and without gas hydrates. The library of the model contains a large number of components including conventional hydrate formers, heavy hydrate formers, water soluble hydrate formers, electrolytes and chemical inhibitors
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In addition to predicting hydrate stability zone for various reservoir fluids, the thermodynamic model is capable of predicting the amount and composition of various phases (including gas hydrates) at any given P & T condition.
The main topic in this part of the projet is the prediction of inhibitor loss in gas/water/liquid hydrocarbon phase. However, adequate prediction of the phase behaviour of reservoir fluids/methanol, ethanol or EG / water mixtures is essential for proper design and operation of the various processing units and transportation systems, there is limited information available on the hydrate stability zone and inhibitor loss in such systems. Therefore, high safety margins and inhibitor injection rates are used to ensure adequate protection against gas hydrate formation.
امیدوارم تونسته باشم یه توضیح مختصری در رابطه با هیدرات های گازی و اینکه من دارم روی چه پروژه ای کار میکنم داده باشم.
+ نوشته شده توسط هومن در یکشنبه 20 اسفند1385 و ساعت
2:31 بعد از ظهر |
نوروز در قلب هر كسي است . در دل و جانش . در روزي كه آن روز برايش روز ديگري باشد ، واقعا روز ديگري باشد . نوروز در خود انسانهاست . براي خود انسانها ، روزي كه چيز تازه اي بيافريني . كاري كني . چيزي كه فكر كني ، حس كني و با دل و جان ببيني كه انسان هستي . انسان . نوروز فراتر از اين جشن و سنت هاست و اينها نمادي براي آن بيش نيست . براي اينكه از ياد نبريم كه هر روز مي تواند نوروز باشد .
!!!)یه مطلب جالب دیدم که گفتم برای شما هم جالب باشه!
اعمال نفوذ منافع اقتصادی عظیم ترین امپراتوری های جهان را از این مملکت برچیده ام و پنجه در پنجه مخوف ترین سازمان های استعماری و جاسوسی بین المللی در افکنده ام و به قیمت از دست رفتن خود و خانواده ام و به قیمت جان و عرض و مالم خداوند مرا توفیق عطا فرمود تا با همت و اراده مردم آزاده این مملکت بساط این دستگاه وحشت انگیز را درنوردیدم. من طی این همه فشار و ناملایمات، این همه تهدید و تضییقات از علت اساسی و اصلی گرفتاری خودم غافل نیستم و به خوبی می دانم که سرنوشت من باید مایه عبرت مردانی بشود که ممکن است در آتیه در سراسر خاورمیانه درصدد گسیختن زنجیر بندگی و بردگی استعمار برآیند.
این روستا، آن را در شمار نمونه های كم نظیر دیدنیهای جهان درآورده است. ابیانه نقطه ای خوش منظره و خوش آب و هوا و دارای موقعیت طبیعی مساعدی است. در دورهٔ صفویه هنگامی كه شاهان صفوی برای ییلاق به نطنز میرفتند بسیاری از نزدیكان آنها و درباریان ترجیح میدادند در ابیانه اقامت كنند. شمار خانه های ابیانه در سرشماری سال 
