formation characteristics характеристики пласта
to exploit разведывать
reservoir месторождение, нефтеносный пласт
wildcat well разведочная скважина
geological trap геологический пласт, ловушка
conglomerate обломочная порода
formation water пластовая вода
rule of thumb практическое правило
sedimentary rock осадочная порода
Task 1. Read and translate the text:
Задание 1. Прочитайте и переведите текст:
If we suspect that hydrocarbons might be present in an area, we commission an exploration well to obtain further information. These are also called wildcat wells. Using various tools, we are able to analyze the formations in great detail to establish whether or not it will be worthwhile producing.
First of all, we need to establish where the hydrocarbons may have come from – the source rock – and analyze the organic content, known as kerogen. Then, we look at the reservoir formation – that is, the rock into which the oil or gas has migrated and where it accumulates in a geological trap of some kind.
The most important aspects of a reservoir formation are its porosity and permeability. Most rocks, in particular sandstones and conglomerates, have at least some porosity. If enough pores are present, the pores are large enough and the pores are interconnected so that fluids flow through them (i.e., the rock is permeable), then the rock is a potential petroleum reservoir. With sandstones, a permeability of 18% or more is usually needed for an economic oil reservoir. Gas flows easier than oil, so as little as 12% permeability may be enough for a gas reservoir. Porosity and permeability are important, but a petroleum reservoir needs to contain hydrocarbons as well. In water-bearing reservoirs, the pores are filled entirely with a salty solution called formation water, but in oil- and gas-bearing reservoirs, some oil or gas is present as well. A general rule of thumb is that 40% or more of the pore fluids must be hydrocarbons (i.e., the water saturation is less than 60%) in order for the reservoir to be economic enough to produce. If the water content is greater, then the oil tends to stay behind and the reservoir produces only water. These types of reservoirs are said to be ‘wet’. If the water saturation is less, then the reservoir may be ‘productive’. Whether or not it will be ‘economic’ to produce and make any money will depend not only on the rate of production, but also on how long the well will produce, in combination with many other factors, not least of which is market price.
Task 2. Answer the questions:
Задание 2. Ответьте на вопросы:
1. What are some of the basics of petroleum geology?
2. What two factors are mentioned in the text?
3. What is the difference between an economic and an uneconomic reservoir?
Task 3. Read this description of the three main types of sedimentary rock and complete the table below:
Задание 3. Прочитайте описание трех основных типов осадочных пород и заполните таблицу, данную ниже:
Sandstone is composed primarily of sand grains that have been naturally cemented together. It is rough to the touch and can be white to buff to dark in colour. Sandstones are commonly deposited on beaches, river channels or dunes. Sandstone is a common reservoir rock for gas and oil and is the most important reservoir rock in North America.
Shale is composed of clay-sized particles and is the most common sedimentary rock. It is relatively soft and the colour ranges from green and grey to black, depending on the organic content. Darker shales are common source rocks for oil and gas, commonly deposited on river flood plains, and on the bottom of oceans, lakes or lagoons. Some shales are now being treated as reservoirs in North America.
Limestone is composed of calcite mineral grains that range in size from very fine to large sparkling crystals. The rock is commonly white or grey in colour. Limestone is a common reservoir rock and is typical in desert areas, such as the oil and gas fields of the Middle East. An organic-rich, dark-coloured limestone can also be a source rock for oil and gas.
Many sedimentary rocks are a combination of these three types, and mixtures are described as either sandy, shaly or limey (calcerous). For example, sandy shale is a shale with a high sandstone composition. Coal is also increasingly being exploited as a gas-bearing reservoir, having originally been a source rock, as in the southern North Sea.
|| Source, reservoir rock or both?
|| Typical colour(s)
|| Typical location(s)
Task 4. Fill in the blanks in the sentences. In two of the sentences, the word is used twice – once singular and once plural. Translate the sentences into Russian:
Задание 4. Заполните пропуски словами, данными в рамочке. В двух предложениях одно из слов употребляется дважды, один раз в единственном числе, второй – во множественном. Переведите предложения на русский язык:
| maturation, migration, reservoir, seal, source, trap
1 Evaluation of the _____ uses the methods of geochemistry to quantify the nature of organic-rich rocks which contain the precursors to hydrocarbons, such that the type and quality of expelled hydrocarbon can be assessed.
2 The _____ is a porous and permeable lithological unit or set of units that the hydrocarbon reserves. Analysis of _____ at the simplest level requires an assessment of their porosity (to calculate the volume of in situ hydrocarbons) and their permeability (to calculate how easily hydrocarbons will flow out of them).
3 The _____ , or cap rock, is a unit with low permeability that impedes the escapes of hydrocarbons from the reservoir rock. Common _____ include evaporites chalks and shales.
4 The _____ is the stratigraphic or structural feature that ensures the juxtaposition of reservoir and seal, such that hydrocarbons remain in the subsurface rather than escaping (due to their natural buoyancy) and being lost.
5 Analysis of _____ involves assessing the thermal history of the source rock in order to make predictions of the amount and timing of hydrocarbon generation and expulsion.
6Finally, careful studies of_____ reveal information on how hydrocarbons move from source to reservoir and help quantify the source (or kitchen) of hydrocarbons in a particular area.
Task 5. Complete this table using the different forms of each word:
Задание 5. Заполните таблицу недостающими формами:
Task 6. Read about geographical features where subsurface oil and gas reservoirs can often be found and decide whether operations in such environments would be onshore drilling or offshore drilling:
Задание 6. Прочитайте геологическую характеристику и решите, будет ли бурение наземнымили морским:
а A basin is a large area with thick sedimentary rocks, covered by shallow tropical water. In some cases over time, the basin has been filled by sediment and become dry land.
b Reefs are mounds of shells separated from the land by a body of water known as a lagoon. Some ancient reefs are now landlocked, created when the sea evaporated.
с A coastal plain is a strip of land adjacent to the ocean
d Shorelines or beaches are long narrow deposits of well-sorted sand.
e Sand dunes are formed by wind in both desert and coastal environments.
f A trench is a deep channel in the seabed.
g A ridge is a submarine range of mountains, including volcanoes, which sometimes appear above the surface of the ocean.
h A delta is a mass of sediments deposited by a river flowing into a large body of water, such as a lake or ocean.
i A continental shelf is a shallow platform extending into the ocean from the beach.
j A continental slope is steeper than a shelf and lies between the shelf and the ocean bed.
k A submarine canyon is a narrow eroded channel through a shelf or slope.
Task 7. Retell the text «Viability assessment».
Задание 7. Перескажите текст «Viability assessment».
Практическое занятие 18
structural trap структурная ловушка
stratigraphic trap стратиграфическая ловушка
reservoir rock порода-коллектор
anticline антиклиналь, антиклинальная складка
impenetrable rock непроницаемая порода
angular unconformity угловое несогласие в напластовании
truncation перерыв, усечение
pinch-out выклиниваться, сжимать
salt dome соляной купол
Task 1. Read and translate the text:
Задание 1. Прочитайте и переведите текст:
The geology of petroleum traps
There are two basic types of petroleum traps – structural and stratigraphic.
Structural traps occur when reservoir rock layers are deformed, such as in a fault or a fold. In a fault trap, a rift occurs in the rock, causing the layers to slip and tilt in one direction or another at the point of deformation, meaning that the migration of oil through a particular layer is halted. There are two types of folds – synclines and anticlines. Of these, normally only anticlines become petroleum traps. An anticline occurs when rock layers form an arch-like structure and the petroleum migrates to the highest point and is prevented from moving further by an overlying bed of impenetrable rock.
Stratigraphic traps can be formed by the deposition of reservoir rock, by an angular unconformity, or by a change in the porosity of the sedimentary layer. Examples of depositions include a river channel sandstone or a limestone reef encased in shale. One example of an angular unconformity is when an angular sedimentary layer is truncated, or cut off, by a horizontal layer. This is known as a truncation. Another, which is called a pinch-out, is where the sedimentary layer is trapped between two other layers when they meet at a point.
Petroleum reservoirs can also be created by traps which are both structural and stratigraphic. These are called combination traps. An example of this is a salt dome, where a layer of salt pushes upwards and deforms the surrounding layers.
Task 2. Read this dialogue and answer questions. Act out the dialogue:
Задание 2. Прочитайте диалог и ответьте на вопросы. Разыграйте диалог по ролям:
Manager: So, can you describe the geological formation of Carson Sound?
Geophysicist: Sure. As we have explained in our report, this field appears to be an extension of the Prudhoe Bay field. If I could describe the geology of Prudhoe Bay first of all, it will help me to explain the geology of Carson Sound. This diagram shows the central North Slope. As you can see, Prudhoe Bay is the result of a combination of structural and stratigraphic circumstances. They were formed by unconformities created when the rocks were uplifted during rifting and then buried again.
Manager: So, how is the accumulation trapped?
Geophysicist: Well, on the north side of the bay the field is sealed by a normal fault, and in the south by south-dipping shales, which overlie the reservoir sand. The western extent of the oil is limited by a structural saddle in the upper surface of the reservoir. Unconformities and overlaying shales seal the crest and the eastern flank of the oilfield.
Manager: So Carson Sound is part of the same formation, is it?
Geophysicist: Well, the oil is certainly from the same source, but there are one or two crucial differences.
1 Why does the geophysicist describe the geology of Prudhoe Bay?
2 How is the field sealed on each side – north, south, west and east?
Task 3. Now read the continuation of the meeting and discuss the questions in pairs:
Задание 3. Прочитайте продолжение диалога и обсудите следующие вопросы в парах:
1. What is the connection between Mukluk and Carson Sound?
2. Do you think that the manager should be worried?
Geophysicist: I have to tell you that there is always the risk that Carson Sound could turn out to be a Mukluk.
Manager: What do you mean, a Mukluk?
Geophysicist: Yes, I suppose that was before your time! Mukluk was one of the biggest financial disasters in oil and gas history – in 1983, nearly twenty years after the huge success story of Prudhoe Bay.
Manager: Go on.
Geophysicist: Well, Mukluk is just on the other side of Prudhoe Bay, and it was also an angular unconformity trap, like Carson Sound. Seismic data indicated a potential reservoir rock in the same Sadlerochit Sandstone with a shale cap rock. The lease was sold for an estimated $1.5 billion and 12 companies spent $100 million on building an artificial island in the Beaufort Sea, and then a further $150 million on exploration drilling. They were looking at anything between two billion and 10 billion barrels of oil, depending on who you believe.
Manager: Wow! So what happened?
Geophysicist: Absolutely nothing. It turned out that the oil had leaked out of the formation centuries ago. There was nothing left. It is still the most expensive dry hole ever!
Manager:Well, this isn’t nearly as big, is it?
Geophysicist: No, but you still don’t want to waste your money, do you?
Manager:And what are the chances of that happening?
Task 4. Read the descriptions of each stage of the process below which explain how a petroleum trap is formed in the two largest fields in North America, the East Texas field and the Prudhoe Bay field. Put the first five sentences in the correct chronological order. The final stage in the last sentence is in the correct place:
Задание 4. Прочитайте описание стадий формирования нефтяных ловушек в месторождениях East Texas и Prudhoe Bay. Распределите пять предложений в хронологическом порядке:
Angular unconformity traps
1. The seas again invaded the area and a layer of chalk was deposited on the angular unconformity. This would become the cap rock of the East Texas field.
2. The sandstone was buried beneath the subsurface as it became covered by a layer of sediments from the sea.
3. Later, the Sabine Uplift, a geological event along the Texas-Louisiana border, arched up and exposed the Woodbine sandstone above the surface of the sea.
4. Approximately 100 million years ago, East Texas was covered by shallow ocean. The Woodbine sandstone was deposited during this geological era. This would become the formation rock of the East Texas field.
5. The top of the arch of the Woodbine sandstone was eroded and an angular unconformity was created.
Eventually, petroleum migrated from its source in the Eagle Ford shale along the Woodbine sandstone and became trapped by the layer of Austin chalk, accumulating into a reservoir of some five billion barrels of oil.
Task 5. Speak on «The geology of petroleum traps».
Задание 5. Перескажите текст «The geology of petroleum traps».
Практическое занятие 19