EXERCISE 23 Answer questions about the text.

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1. When do vast quantities of salt water exist in surrounding parts of the formation?

2. What cases is the energy of salt water considered to be more important?

3. What does the displacement of oil and gas in an upward direction depend on?

4. What fields allow getting 50% of oil?

5. What types of drive do you know?

EXERCISE 24 Give the Russian equivalents to the following word combinations

1. Oilfields where “Water-Drive” is effective

2. Producing the wells

3. Gas- Cap-Drive

4. The uniformly porous formation

5. The petroleum reservoir

6. The expansive energy in the oil

EXERCISE 25 Insert the omitted word from the text

1. Tremendous quantities of __________ occur under pressure and provide a great additional store of energy to aid in producing oil and gas.

2. The energy supplied by the salt water comes from expansion of the water as pressure in __________ is reduced by production of oil and gas.

3. The expanding water moves and displaces __________ in an upward direction out of lower parts of the reservoir.

4. By this natural “Water-Drive” process __________ spaces vacated by oil and gas produced are filled with water, and oil and gas are moved toward __________.

5. Rate of production seems to exert only minor effect on oil recoveries obtainable from __________ type fields except where conditions are favorable for gas caps to form.

6. The kind of operation and total rate of production will determine which __________ will actually be effective, and accordingly will greatly affect the oil recovery.

“Dissolved-Gas-Drive”, oil and gas, salt water, the wells, the petroleum reservoir, type of drive, the pore

EXERCISE 26 Open brackets and use active or passive form of the verb. Consult the texts 1, 2 if necessary.

1. When the well (to drill) __________ into a hydrocarbon reservoir and open at the surface, the area in the vicinity of the well bore becomes an area of low pressure.

2. The pressure (to relate) __________ to the depth and the density of the fluid, and is called hydrostatic pressure.

3. The flow rate of oil or gas into the well bore (to depend) __________ on the permeability of the reservoir rock, the area of flow into the well bore and the viscosity of the fluid.

4. The energy supplied by the salt water (to come) __________ from expansion of the water as pressure in the petroleum reservoir (to reduce) __________ by production of oil and gas.

5. The expansive energy in the oil and gas (to conserve) __________.

EXERCISE 27 Translate into Russian in written form.

1. Organic residue carried by waters eventually settled to the bottom of the ancient seas.

2. The movement of oil and gas from its place of origin was both vertical and lateral.

3. The porosity of the rock, the pore size and the size of connecting channels between pores are all related to permeability.

4. One of conditions required for generation of major oil gas accumulations is availability of impermeable rocks (caps) restricting vertical oil and gas migration.

5. The shortest distance between oil and gas bearing formation top and bottom is called formation thickness.

EXERCISE 28 Translate into English in written form.

Коллекторы с газонапорным режимом

Нефть в подземных коллекторах содержит растворенные в ней различные количества газа, который появляется и расширяется по мере понижения давления в коллекторе. Когда газ выходит из нефти и расширяется, он движет нефть через коллектор к скважинам и способствует ее подъему к поверхности. Коллекторы, из которых добыча производится при помощи выхода и расширения растворенного в нефти газа, называются коллекторами с «напорным режимом растворенного газа». Такой процесс добычи нефти обычно считается наименее эффективным режимом, позволяющим максимально получить от 15 до 25 % содержащейся в коллекторе нефти.

EXERCISE 28 Add the missing words to this puzzle.

A crossword puzzle

Across

1. It is piece of equipment that exists atop (the exposed area above ground) of a well.

2. Easiness with which oil can be poured. It means thick oil.

3. Easiness with which fluid can move through porous rock. It means numerous channels for oil and gas migration.

4. It is the geological process by which sediments, soil, and rocks are added to a landform or land mass.

Down

1. It is a naturally occurring flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface.

2. This reservoir is geological structure or trap which this has migrated and within which it has been trapped and has accumulated.

3. Availability of pore spaces between rock particles. It is a ratio of open space to total volume of rock and is calculated in percentage.

4. Underground reservoir that prevents the escape of oil contained in it.

CHAPTER III

GEOPHYSICAL METHODS OF OIL AND GAS EXPLORATION

EXERCISE 1 Read and translate the text " Exploration methods".

Be ready to answer the following questions on the content of this text.

1. What kind of the activity deals with the search for hydrocarbon deposits?

2. What does the term " petroleum geology" mean?

3. Can you tell about the visible features that provide evidence of hydrocarbon generation?

4. What for do we need highly sophisticated technology in oil and gas exploration?

5. What kind of exploration methods do you know?

6. Is the seismic survey different from the other two ones?

7. When and what for is oil exploration well drilled?

8. What reasons can you suggest to prove that oil exploration is a high-risk operation?

9. What do smaller companies search for?

10. Why are hydrocarbons expelled from the source rock?

11. What 3 density related mechanisms could you name?

12. Why do hydrocarbons migrate upwards?

13. Where do hydrocarbons get trapped?

14. Why do you think hydrocarbons staying in traps?

15. Can you characterize a reservoir rock?

16. What happens when oil and gas are brought to the surface?

Exploration Methods

Visible surface features such as oil seeps, natural gas seeps, pockmarks (underwater craters caused by escaping gas) provide basic evidence of hydrocarbon generation (be it shallow or deep in the Earth). However, most exploration depends on highly sophisticated technology to detect and determine the extent of these deposits.

Areas thought to contain hydrocarbons are initially subjected to a gravity survey or magnetic survey to detect large scale features of the subsurface geology. Features of interest (known as leads) are subjected to more detailed seismic surveys which work on the principle of the time it takes for reflected sound waves to travel through matter (rock) of varying densities and using the process of depth conversion to create a profile of the substructure. Finally, when a prospect has been identified and evaluated and passes the oil company's selection criteria, an exploration well is drilled in an attempt to conclusively determine the presence or absence of oil or gas.

Oil exploration is an expensive, high-risk operation. Offshore and remote area exploration is generally only undertaken by very large corporations or national governments. Typical Shallow shelf oil wells (e.g. North sea) cost $10 - 30 Million, while deep water wells can cost up to $100 Million plus. Hundreds of smaller companies search for onshore hydrocarbon deposits worldwide, with some wells costing as little as $500, 000 USD.

Elements of a petroleum prospect

A prospect is a potential trap which geologists believe may contain hydrocarbons. Five elements have to be present for a prospect to work and if any of them fail, neither oil nor gas will be present.

• A source rock. When organic-rich rock such as oil shale or coal is subjected to high pressure and temperature over an extended period of time, hydrocarbons form.

• Migration. The Hydrocarbons are expelled from source rock by three density-related mechanisms: the newly-matured hydrocarbons are less dense than their precursors, which cause overpressure; the hydrocarbons are lighter medium, and so migrate upwards due to buoyancy, and the fluids expand as further burial causes increased heating. Most hydrocarbons migrate to the surface as oil seeps, but some will get trapped.

• Trap. The hydrocarbons are buoyant and have to be trapped within a structural (e.g. anticline, fault block) or stratigraphic trap.

• Seal or cap Rock. The hydrocarbon trap has to be covered by an impermeable rock known as a seal or cap-rock in order to prevent hydrocarbons escaping to the surface.

• Reservoir. The hydrocarbons are contained in a reservoir rock. This is a porous sandstone or limestone. The oil collects in the pores within the rock. The reservoir must also be permeable so that the hydrocarbons will flow to surface during production.

Terms used in petroleum evaluation

• Lead - a structure which may contain hydrocarbons.

• Prospect- a lead which has been fully evaluated and is ready to drill.

• Chance of Success - an estimate of the chance of all the elements (see above) within a prospect working, described as a probability. High risk prospects have a less than 10% chance of working, medium risk prospects 10-20%, low risk prospects over 20%. Typically about 40% of wells recently drilled find commercial hydrocarbons.

• Hydrocarbons in Place – amount of hydrocarbons likely to be contained in the prospect. This is calculated using the volumetric equation - GRV x N/G x Porosity x Sh x FVF:

• GRV - gross rock volume - amount of rock in the trap above the hydrocarbon water contact;

• N/G - net/gross ratio - percentage of the GRV formed by the reservoir rock (range is 0 to 1);

• Porosity- percentage of the net reservoir rock occupied by pores (typically 5 - 35%);

• Sh - hydrocarbon saturation - some of the pore space is filled with water - this must be discounted;

• FVF - formation volume factor - oil shrinks and gas expands when brought to the surface. The FVF converts volumes at reservoir conditions (high pressure and high temperature) to storage and sale conditions.

• Recoverable hydrocarbons – amount of hydrocarbons likely to be recovered during production. This is typically 10-50%) in an oil field and 50-80%) in a gas field.

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