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Offshore CW 3

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  NM 957/ 518 Offshore Engineering Practice Course Work Prof Carl Schaschke Explain why oil and gas are separated offshore in preference to on-shore separation, and highlight the challenges faced in the 21 st  century offshore oil and gas development. [guide on the essay length: approximately three A4 pages]  The main reason why oil and gas are separated offshore is to separate hydrocarbon products into liquid or gaseous form as well as the removal of any impurities such as water that may be  present that could affect transportation. The separation of oil and gas are usually done offshore on platforms such as semi-submersibles, FPSOs etc. The main reasons why oil and gas are separated offshore are discussed below: Flow Assurance (Transportation Issues) Flow assurance refers to an engineering analysis process which uses the knowledge of fluid  properties to develop strategies that will prevent the formation of hydrates and wax and reduce corrosion and erosion problems during transportation of hydrocarbons. These issues to a large extent are determined by temperature and pressure differences. The hydrocarbons are usually received at the platform as a mixture which contains oil, gas, water, sand and other impurities. The mixture of hydrocarbons must be separated before transportation in order not to experience flow assurance issues. Flow assurance can be a very complex issue when dealing with multi-phase flows, these hydrocarbons must therefore be transported at controlled temperatures and pressures after separation. Water is separated from the hydrocarbon mixture during processing to avoid problems associated with corrosion. Sand is separated from the hydrocarbon mixture during processing to avoid problems associated with erosion. A slug catcher is used to remove large surges of water and sand from the gas mixture during offshore processing. Moisture in the gas can cause corrosion problems when transporting the gas, the moisture is often removed by the use of a glycol contactor during  processing. Also, impurities such as hydrogen sulphide exist in some gas fields which must  be removed before transporting the gas because hydrogen sulphide is extremely toxic as well as being very corrosive. The hydrogen sulphide is removed through a process known as sweetening. Generally, impurities present during transportation can cause pressure drops and hence the need to repressurize the gas more often than necessary to avoid flow issues. Under certain conditions of temperature and pressure, water can separate from the gas, freeze and trap methane to form a solid ice substance known as hydrate. These hydrates can block  pipelines with disastrous consequences. Methanol and monoethylene glycol (Meg) are often used to prevent the formation of hydrates during the transportation of hydrocarbons. Enhanced Oil Recovery When water is separated from the mixture of oil and gas, it is treated and pumped back into the sea or re-injected into another part of the reservoir to maintain pressure. Also, when the gas is separated, it can be compressed and piped back to shore or re-injected back into the reservoir to increase pressure. These methods of enhanced oil recovery are only economically  possible with offshore processing since it will not be cost effective to do the processing onshore and transport the water or gas back to the field for disposal or re-injection in order to enhance oil recovery.  Power Generation Electrical power on large offshore installations is usually generated by either gas turbines or alternators. The fuel used, called fuel gas is taken from the main outlet header, or produced as a by-product from the offshore process. The gas is usually separated, dried and filtered before use. The Importance of offshore processing is seen here since from an economic point of view, it will not be viable to do the processing onshore and transport the fuel gas back to the offshore installation to generate electrical power. Government Taxes (Metering) Another reason for offshore processing is metering which determines the amount of tax to be  paid to the government. Offshore processing of hydrocarbons gives a more precise measurement of the quantity of oil and gas export through metering rather than the mixture of oil and gas with water and sand. This helps to avoid a situation where excess tax will be paid on oil and gas exports. Cost  In carrying out production activities, cost is always a key factor since we always strive to achieve higher productivity at a reduced cost. All the other reasons for carrying out offshore  processing from flow assurance to transportation, enhanced oil recovery, power generation and metering for taxes are all tied in to achieving a reduced cost of production and maintenance. We can therefore conclude that offshore processing is a more viable economic option than onshore processing. Challenges of Offshore Oil and Gas Development    in the 21  st   Century The challenges faced by the offshore oil and gas industry include: Safety and Environmental Considerations Most activities carried out offshore have to conform to certain safety standards. The effects that the production activities will have on the environment in the future also have to be considered. Therefore, in carrying out production activities, high priority must be given to the safety of personnel and equipment and the methods used in producing the oil and gas must not have a negative impact on the environment.  Demand and Supply There is a very high rate of demand for energy which surpasses the supply rate. This is due to the fact that it takes a bit of time to develop oil and gas fields. Therefore oil and gas companies are constantly investing in research to develop new and more efficient drilling and production methods in order to meet the increasing demand for energy globally. Acquisition of Oil Reserves There are a lot of emerging oil companies and hence the competition for exploration licences has been on the increase over the past few years resulting in higher bids. Deep Water Exploration As a result of depleting reserves onshore and in shallow waters, oil and gas reserves which would have been impossible to explore because of their depth years ago, are now being explored. The definition of deep water is constantly changing, this is because of the modern sophisticated technologies which make it possible to produce oil and gas from these reservoirs, though at a higher cost. Improved Recovery Rate Due to depletion of oil reserves, wells which would not have been deemed economically viable to produce from are now becoming relevant as a result of sophisticated technologies that enhance the recovery rate. There is however a higher capital expenditure. Increased Cost of Offshore Equipments As a result of increase in demand, there is a lot of pressure on the companies that construct and design offshore equipments in order to meet deadlines which ultimately leads to an increase in cost. Challenges in the Arctic Region As a result of depleting oil and gas reserves, the focus is slowly shifting to the arctic regions. Due to low temperatures, 24 hours darkness and the nature of the environment, new technologies are being developed to facilitate the production of oil and gas in this region. There are however various issues which are a major concern such as oil spills, global warming and polar bears.
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