Table 1: Greenhouse Gases

Greenhouse Gas	Description
Carbon dioxide (CO2)	CO2 is the dominant greenhouse gas and effectively accounts for about 75% of all greenhouse gas emissions.
Methane (CH4)	CH4 is a very effective greenhouse gas with a high global warming potential (GWP), and although present at much lower levels than CO2 may have significant impact because of this higher GWP. The main source of CH4 is from agriculture (mainly livestock).
Nitrogen oxides (NOx)	Nitrogen oxides consist of nitrogen oxide (NO) and nitrogen dioxide (NO2). NOx is a small component of greenhouse emissions (<1%).
Nitrous oxides (N2O)	N2O is a gas produced both naturally and by combustion of fuels. The majority of N2O (80%) is produced from agriculture. They mostly come from burning fuel (cars and power stations).
Volatile organic compounds (VOC's)	Volatile organic compounds are hydrocarbons (excluding methane) which are capable of forming oxidants (particularly ozone) by reactions with nitrogen oxides in the presence of sunlight. Major sources of VOC's are vehicles, solvents and process industry emissions.
Carbon monoxide (CO)	CO is generated as a result of incomplete combustion (e.g. poorly maintained wood heaters and cars), and reacts preferentially with naturally occurring hydroxyl radicals in the lower atmosphere. This has the effect of increasing the lifetime of VOC's and so enhances the formation of photochemical smog.
Hydrogen sulphide (H2S)	H2S is a toxic gas occurring naturally during decomposition. Natural gas is normally treated to remove this H2S to form sulphur or it can be burned. H2S forms SO2 during the combustion process or photochemically when released to the atmosphere.
Sulphur dioxide (SO2)	SO2 results in dry acid deposition and in the formation of acid rain thereby increasing the acidity of soils.

An inventory of greenhouse gas emissions from flaring, venting and fuel consumption in exploration and production industry reveals that approximately 50% of emissions are sourced from fuel consumed in the machinery and equipment used to produce petroleum.

Oil and gas explorers and producers are actively identifying where, and how much, greenhouse gas emissions are produced in their operations. Efforts are being made across the industry to reduce these emissions through measures that are technically and economically possible.

Natural gas is one of the cleanest fuels to use to produce heat and electricity. This growth in gas use means that emission from gas explorers and producers are likely to increase. The net effect is positive, as switching to natural gas means less emissions overall.

Text 3

Waste Discharges during the Offshore Oil and Gas Activity

I. Five sentences have been removed from the text. Choose from sentences A-F the one which you think best fits each gap. There is one extra sentence you don’t need to use. Here is a procedure for doing this type of task.

· Read the text once again to make sure that you have a good general idea what it is about.

· Look at the sentences that have been removed and try to get an idea of the subject of each one.

· Look at each gap in the text in turn, at the sentence before it and the sentence after it, try putting in the most likely missing sentences. Look for clues to help you e.g. words like that, it or he that refer to something or someone in the sentence before.

· Decide on one sentence for each gap. If later you want to use a particular sentence again, go back and check where you have used it before. There may be a different sentence that would fit in this gap.

A.Produced waters include formation water, brine, injection water, and other technological waters. B.The lubricants are added into the drilling fluids either from the very beginning as a part of the original formulations or in the process of drilling when the operational need emerges. C.For example, the amount of solid drilling cuttings usually decreases as the well gets deeper and the hole diameter becomes correspondingly smaller. D. Sometimes, it is baked or calcified and transported to the shore. E.Landfill is a common way of disposing of solid waste, while liquid waste is often injected underground. F. The first variant is the most usual and is practiced almost everywhere, while the second one still remains an unrealized ecological requirement.

Practically all stages and operations of offshore hydrocarbon production are accompanied by undesirable discharges of liquid, solid, and gaseous wastes. The proportions and amounts of discharged wastes can change considerably during production. (1) The volumes of produced waters increase as the hydrocarbon resources are being depleted and production moves from the first stages toward its completion.

The discharges of produced waters considerably dominate over other wastes. (2) Formation water and brine are extracted along with oil and gas. Injection water is pumped into the injection wells in hundreds of thousands of tons for maintaining the pressure in the system and pushing the hydrocarbons toward the producing wells. All of these waters are usually polluted by oil, natural low-molecular-weight hydrocarbons, inorganic salts, and technological chemicals. These waters need to be cleaned before they are discharged into the sea. Such cleaning under marine conditions is a complicated technical task. Special separation units on the platforms are used for oil separation. Depending on its quality, the produced water is either discharged into the sea or injected into the disposal well. Sometimes the oil-water mixtures are transported along the pipelines to onshore separation units.

Inevitably, all kinds of drilling are associated with drilling wastes, including drilling muds and cuttings. Drilling cuttings are removed from drilling muds and cleaned in special separators. The amount of oil left on cuttings after cleaning is much higher when using oil-based fluids. Separated drilling muds and cleaning fluids used to treat cuttings are partially returned to the circulating system. Drilling cuttings and the rest of the drilling muds are either dumped overboard or transported to the shore for further treatment and disposal, depending on the situation and ecological requirements. (3)Recently, a technology was developed to remove the drilling wastes, especially cuttings, by reinjecting their slurry into a geological formation. This gives some hope to achieving zero discharge of oil-containing wastes during offshore oil and gas production.

The environmental hazard of drilling muds is connected, in particular, with the presence of lubricating materials in their composition. (4) In both cases, the discharges of spent drilling muds and cuttings coated by these muds contain considerable amounts of relatively stable and toxic hydrocarbon compounds and a wide spectrum of many other substances.

One of the potential sources of oil pollution is produced sand extracted with oil. The amount of produced sand coated by oil can vary a lot in different areas and even during production in the same area. In some cases, it constitutes a considerable part of the extracted product. Most often, this sand is cleaned of the oil and dumped overboard at the well site. (5) The other discharges into the marine environment (deck drainage, sanitary and domestic wastes, and so on), do not play essential roles in the environmental situation in the areas of oil and gas developments. They are treated and disposed in accordance with the norms regulating discharges from the ships.