There is a good chance that you use natural gas for cooking and heating your home. Natural gas is a very important source of energy. We usually call natural gas ‘gas’. But in fact, natural gas is just one form of gas. Unlike solid materials such as wood or metal, gases can move around freely and most cannot be seen. The most important gas is the air we breathe, which is actually a mixture of gases. Air is mostly made up of gases called oxygen and nitrogen.
Natural gas is a by-product of oil drilling and coal mining, but it can also be harvested independently from natural gas fields.
Natural gas is a mixture of hydrocarbons and varying quantities of non-hydrocarbons that exists either in the gaseous phase or in solution with crude oil in natural underground reservoirs. The main hydrocarbon in natural gas is methane, but there are also small amounts of ethane, propane and butane.
There are various descriptive terms for natural gas, which includes dry gas, wet gas, dissolved gas, associated gas, non-associated gas, natural gas liquids, sweet gas, sour gas, condensate, liquid hydrocarbons and gas hydrates. Each term describes a specific hydrocarbon gas form and characteristics.
Natural gas is a ‘fossil fuel’. This means that was formed millions of years ago, in the age of the dinosaurs, from the remains of the animals and plants. They were covered by layers of mud and sand and pushed down to makes rocks. As the pressure and the heat increased from the rocks above, they were gradually changed into oil and gas. This change takes millions of years and today we often find oil and natural gas together.
People have known about natural gas for hundreds of years. For about 150 years from the early 19th century, the gas used for heating, cooking and lighting was called town gas. Unlike natural gas, town gas was made from coal, which is why it was also called coal gas. After the gas had been taken out of the coal, what was left was a fuel called coke. People use to burn coke in their fireplaces and boilers for warmth and hot water. The gas mantle was invented in the 1880s. When lit, the gas made the mantle glow to give a brighter light than a naked gas flame, and it was safer too.
After natural gas is formed, the gas tries to force its way up through the layers of rock made from mud and sand. Some of the gas actually comes to the surface and escape. But much of it is trapped in folds of rocks which could not move through. Scientists, called geologists, have to locate the rocks which hold the gas. But in the North Sea these rocks are hundreds of meters below the sea bed and geologists cannot see them directly. Instead, they have to find other ways of discover these rocks to find gas.
If you shake a bottle of fizzy drink and open the cap, the drink squirt out of the bottle. This is because the pressure of the gas, which makes the drink fizz, has gone up. It shoots up because the pressure in the bottle is much more than the air outside. If you blow up balloon, you increase the pressure of the air in the balloon and balloon gets bigger. If you keep on blowing, making the pressure go up and up, the skin of the balloon may not be strong enough and the balloon will burst. When you pump up the tyres on your bike, you are raising the air pressure in the tyre.
When all fossil fuels are burnt, they give off gases which can damage the environment. Some of these are called greenhouse gases, which are making the world’s climate warmer and changing our weather.
More and more people and companies are using gas. When gas is burnt, it provides energy to heat homes and water, cook, meals and even keep things cold. If there is a swimming pool it can be kept warm by gas. Factories also use natural gas to provide energy, make cars, clothing, bricks, bread and things we use every day.
The natural hydrocarbon gas supply chain is a set of stages through which natural gas passes, from being found in the field until it reaches the final consumer. The gas supply chain consists of different production and processing stages depending on the developed gas business intent, nature of the produced gas fields and whether the natural gas is transported in gaseous or liquid form.
OGC as a midstream firm is engaged in the natural gas transportation and distribution activities through the developed gas transportation facilities (GTF) and gas supply stations supplying specification gas to the consumers. In addition, the GTF includes Gas Boosting Stations, Gas Limiting Stations, Fiscal Metering Stations and Block Valve Stations.
With the on-going country developments and in line with the company’s Vision and Mission, we have the potential to be an integrated company due to the availability of diversified technical expertise in the upstream, midstream and downstream business related activities.
Once natural gas is produced from wells, producers then seek to deliver the natural gas and its components, including natural gas liquids (NGLs) to the end users.
The following diagram illustrates the natural gas and NGL gathering, processing, fractionation, storage and transportation process, which ultimately results in natural gas and NGLs being delivered to the end-users.
Once extracted from the field, the natural gas must be processed and treated for transportation and later marketing (safety and quality standards must be met at the facilities and delivery points).
In order to transport natural gas in its liquid state (LNG), components must be eliminated that may interfere with the gas cooling process, while for pipeline transport, corrosive compounds must be removed that could damage the pipeline. To achieve these goals the water content is reduced and the acid gases (hydrogen sulphide and carbon dioxide), as well as nitrogen and mercury, are removed.
Once the gas is treated it can be transported in the gaseous phase through pipelines, or in the liquid phase in LNG carriers.
In the gaseous phase, the gas chain is simplified as liquefaction, shipping and regasification are unnecessary.
From the high pressure pipelines, natural gas reaches the point of consumption through gas transportation facilities and distribution networks.
The pressure at which the gas is supplied depends on the type of customer, ranging from pressures of less than 5 barg for domestic consumers up to pressures above 37 barg in deliveries to the power generating plants and large industrial consumers.
Custody transfer is the process whereby Natural Gas is measured for sale from one party to another, a process which involves measuring parameters such as gas pressure & temperature, gas quality and gas flow. The gas measurement process and adopted system is becoming ever more important as it represents a scrutinized cash register between the gas supplier and the consumer.
Fiscal flow measurement is a critical part of custody transfer, any small deviation in measurement accuracy of the meter can have a major impact on profitability. Many applications such as the supply of the gas to power stations have additional inherent challenges such as a broad range of flow rates requiring the design of high volume meters systems with a high turndown ratio.
The gas Fiscal Metering Stations (FMS), are located in the delivery lines to individual consumers whereby periodical metering system calibration and proving are practiced for accuracy assurances.
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