Water-Drive Reservoirs

Where the formation containing an oil reservoir is fairly uniformly porous and continuous over a large area compared to the size of the oil reservoir itself, vast quantities of salt water exist in surrounding parts of the same formation often directly in contact with the oil and gas reservoir. These tremendous quantities of salt water occur under pressure and provide a great additional store of energy to aid in producing oil and gas.

The energy supplied by the salt water comes from expansion of the water as pressure in the petroleum reservoir is reduced by production of oil and gas. This effect is slight for any small quantity, but becomes of great importance when changes in reservoir pressure affect enormous volumes of salt water that are often contained in the same porous formation adjoining or surrounding a petroleum reservoir.

The expanding water moves into the regions of lowered pressure in the oil and gas saturated portions of the reservoir caused by production of oil and gas and retards the decline in pressure. In this way, the expansive energy in the oil and gas is conserved. The expanding water also moves and displaces oil and gas in an upward direction out of lower parts of the reservoir.

By this natural “Water-Drive” process the pore spaces vacated by oil and gas produced are filled with water, and oil and gas are moved towards the well.

The “Water-Drive” is generally the most efficient oil-production process. Oilfields where “Water-Drive” is effective are capable of yielding recoveries ranging up to 50 percent of the oil originally in place, depending on:

1. The physical nature of the reservoir rock and of the oil.

2. The care exercised in producing the wells.

3. The rate of oil and gas production from the field or reservoir.

These factors also greatly affect the oil-recovery efficiency in the case of “Gas- Cap-Drive” reservoirs. However, rate of production seems to exert only minor effect on oil recoveries obtainable from “Dissolved-Gas-Drive” type fields except where conditions are favorable for gas caps to form.

In many cases reservoirs may possess the possibilities for either “Water Drive” or “Gas Drive”. In such event, the kind of operation and total rate of production will determine which type of drive will actually be effective, and accordingly will greatly affect the oil recovery.

EXERCISE 23 Answer questions about the text.

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.