All About GAS

Introduction

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.

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    • When air is heated, it rises up through the cooler air around it. Hot air balloons rise up into the sky because the air inside the balloons is heated. The gas use to heat the air is called propane.
    • Airships can lift off the ground because they are filled with a gas lighter than air. Airship used to be filled with a gas called hydrogen, but because this could catch fire easily it made them dangerous to travel in. Today, airships are filled with helium gas, which is lighter than air but cannot catch fire.
    • Before reliable batteries, cars used a gas called acetylene for their lights. The acetylene was made inside the light by adding water to chemical called carbide.
    • Divers need to be able to breathe underwater- they carry tanks on their backs, filled with compressed air.
    • In cold weather, water, which is a liquid, turns into a solid called ice. When it is boiled, it turns into a gas called steam. If we make them cold enough, all gases will turn into liquids and if they are further cooled they will become solid. Natural gas is sometimes cooled to very low temperatures so that it can be stored as a liquid.
    • To cut through metals like iron and steel, welders use a mixture of two gases – oxygen and acetylene. When these are burnt together, they make a flame hot enough to melt the metal.
    • Hospitals use gases to put people to sleep so that they don’t feel any pain during operations. Nitrous oxide is one of the gases used. It sometimes called ‘laughing gas’ because small amounts can make people laugh.

Natural Gas

Natural gas is a by-product of oil drilling and coal mining, but it can also be harvested independently from natural gas fields.

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    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 - The Making

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.

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    • Almost 200 years ago, the famous scientist John Dalton discovered methane by poking into the rotting plants at the bottom of ponds. Methane is sometimes known as ‘marsh gas’ because rotting plants in marshes make methane. If this catches fire, it gives off a strange light called ‘will o’ the wisp’ which people used to think was an evil spirit.
    • You can still sometimes see in rocks the fossilized remains of plants and animals. Natural gas is mostly made up of a gas called methane. We get most of our natural gas from beneath the North Sea, but when plants, food and vegetables rot, like in this rubbish tip, they make methane. Sometimes this methane is collected and used to provide heat.
    • In India, where villages have no gas, people actually make methane from animal waste for warmth and cooking.

The History of Gas

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.

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    • In 1792, William Murdock, a Scotsman, used coal gas for lighting in a house in Cornwall where he was working as a mining engineer. In 1798 he invented the equipment to store coal gas. By 1813 coal gas was being used to light some streets in London.
    • When the town gas was made it was stored in very large gasholders. The gasholders could move up and down as the pressure and amount of gas inside rose and fell. Gasholders are still used today to store natural gas.
    • To get the town gas to people’s houses, hundreds of kilometres of pipes had to be laid.
    • The flame in a miner’s safety lamp changed colour when methane gas was present in coal mines. This was to warn them of danger of explosions. Before the safety lamp, canaries were used to detect gas. If there was gas, the canary died before the gas could harm the miners.
    • Women making gas fires in the early 20th century.
    • In 1895, natural gas was discovered under Heathfield railway station in Sussex. It was the first station to be lit by its own natural gas supply. Gas-filled balloons were released to celebrate the opening. One of them travelled as far as Germany.
    • More than a hundred years ago. Most homes in the cities and towns were lit by gas. Gas lamps were much better than oil lamps or candles and were often very decorative.
    • Gas made life much easier in the home, especially for women who used to do most of the cooking and washing. You may think the cooker and gas fire look old-fashioned, but think how much better they were than cooking and heating with coal.
    • Before electricity and even after it was available, town gas was used for street lighting. The lamp lighter had to light each gas lamp every night before dark and then turn them off again after dawn the next day.
    • Coal gas could even be used instead of petrol to drive vans and cars. In the first and second World Wars, when petrol was hard to obtain, many vehicles ran on coal gas. Today, cars can run on compressed natural gas.
    • Baths too were fitted with gas heaters to provide hot water.

Finding Gas

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.

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    • To find out the places where the gas might be, geologists sets off small explosions on the surface of the sea. The sound-waves from the explosion go deep down below the sea bed and bounce back from the layers of rocks, rather like an echo. These echoes give the geologists the information to make a map of the rock layers, indicating where to find gas.
    • Production platforms have to be firmly fixed to the sea bed so that they are safe even in very stormy weather.

Learning about pressure

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.

Taking care of our environment

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.

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    • Burning natural gas is much less damaging to the environment than burning oil and coal. That is one reason why natural gas is used more and more to generate electricity in power stations.
    • Pollution: Gas v/s Oil and Coal. When we use natural gas to make electricity, the amount of carbon dioxide (greenhouse gas) produced is much less than when we use oil or coal to make electricity.
    • Remember how town gas was used instated of petrol in cars. Today, some vehicles are designed to run on compressed natural gas (CNG). Natural gas is cleaner and produces much less pollution than petrol or diesel engines.
    • Before pipelines can be planned, surveys are carried out to make sure that route of the pipeline will not pass through or damage places that are beautiful or have important types of plants, animals or trees. Pipeline routes are also planned to avoid sites of historical or archaeological importance.

Uses of Gas

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.

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    • Power stations which generate electricity use gas instead of coal or oil.
    • Even when houses have central heating, people still have gas fires to provide more warmth and a nice glow to the living room.
    • OGC has emergency call centre, which people can ring to report escapes or if they smell gas while walking nearby OGC gas facilities. The call centre sends out engineers to mend the escapes.
    • In homes, cafes and restaurants all over Oman. People use gas for cooking.

Natural Gas Supply Chain

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.

Oman Gas as a Midstream Company

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.

Midstream Natural Gas Industry Overview

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.

Gas transportation and distribution systems

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).

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    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.

Gas measurements and accountings

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.

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    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.