Reservoir fluids

Reservoir Fluids

VOCABULARY SECTION

Be sure you know the following words and their translation

#	English	Ukrainian	Russian
	reservoir fluid	пластовий флюїд	пластовый флюид
	reservoir rock	порода-колектор	порода-коллектор
	liquefied	зріджений	сжиженный
	pumping	перекачування	перекачивание
	sedimentary formations	осадові утворення	осадочные образования
	deposit	поклад, родовище	залежь; месторождение
	sedimentary bed	пласт осадових порід	пласт осадочных пород
	connate interstitial water	реліктова порова вода	реликтовая поровая вода
	interstitial	проміжний	промежуточный
	bottom water	вода в підошві	подошвенная вода (в пласте)
	edgewater	контурна вода	краевая вода
	wetting ability	змочувальна здатність	смачивающая способность
	film	плівка	плёнка
	oil saturation	нафтонасиченість (колектора)	нефтенасыщенность (коллектора)
	porosity	пористість	пористость
	solution gas	природний газ, розчинений у нафті коллектора	природный газ, растворённый в нефти коллектора
	gas cap	газова шапка (в колекторі нафти)	газовая шапка (в коллекторе нефти)
	soda water	сода	сода
	fizz	пінитись	пениться
	dissolve	розчинятись	растворяться
	accumulate	накопичувати	образовывать скопление
	saturated	насичений	насыщенный
	viscosity	в’язкість	вязкость
	wellbore	стовбур свердловини	ствол скважины
	layer	пласт	пласт
	oil-water contact line	лінія водонафтового контакту	линия водонефтяного контакта
	distribution	розподіл	распределение

Match the words in column A with their definitions in column B

A	B
1	free gas	a	liquid produced or originating at the same time as the rocks surrounding them
	sedimentary formations	b	process of compressing, driving, raising, or reducing the pressure of a fluid, esp. by means of a piston or set of rotating impellers
	connate water	c	a gaseous mixture consisting mainly of methane trapped below ground; used extensively as a fuel
	saturate	d	to soak or suck up (liquids)
	film	e	gas that is not dissolved in oil
	natural gas	f	to make a hissing or bubbling sound
	viscosity	g	rocks formed by the accumulation and consolidation of mineral and organic fragments that have been deposited by water, ice, or wind
8	pumping	h	a thin coating or layer
9	fizz	i	to fill, soak, or imbue totally
	absorb	j	the state or property of being viscous

Pre-reading tasks

A) scan the text and define the main idea of the text

B) skim the text and answer the questions

- What kind of fluids does reservoir rock contain?

- What position do oil, gas and salt water take when they are mixed in a reservoir?

- Why do petroleum companies prefer that a reservoir contain all three fluids in layers?

- What kind of reservoirs are sedimentary formations and why?

- What does the term connate interstitial water mean?

- Where do bottom and edgewater occur?

- What happens when the oil comes to the surface and pressure is relieved?

- What kind of gas is called free gas?

- Why is oil-water contact line important?

- How are oil and water distributed in reservoirs?

RESERVOIR FLUIDS

A fluid is any substance that will flow. Reservoir rock usually contains three fluids: in addition to oil and gas, it contains salt water. Oil and water are liquids as well as fluids. Natural gas is a fluid but not a liquid in its natural state, although it can be liquefied by artificial means.

In a reservoir, the three fluids can be mixed together or layered or both. When they are layered, the lightest (gas) is on top, the oil is in the middle, and the heaviest (water) is on the bottom, like the contents of a bottle of Italian salad dressing (fig. 1.33).

Petroleum companies prefer that a reservoir contain all three fluids in layers because the pressure of gas and water can often drive oil out of the rock to the surface, making pumping unnecessary.

Figure 1.33 When hydrocarbons are layered in a reservoir,

the water is on the bottom and the gas on the top

Water

Most oil reservoirs are sedimentary formations that were deposited in or near the sea. These sedimentary beds were originally saturated with salt water. The forming petroleum displaced part of this water, but some remained. The salt water that remains in the formation is called connate interstitial water – connate from the Latin meaning "born with" and interstitial because the water is found in the interstices, or pores, of the formation. By common usage this term has been shortened to connate water and always means the water that stayed in the formation when the reservoir was being formed.

Connate water is distributed throughout the reservoir. However, nearly all petroleum reservoirs have additional water that accumulated along with the petroleum. It is this "free" water that supplies the energy for a water drive. Bottom water occurs beneath the oil accumulation; edgewater is found at the edge of the oil zone (fig. 1.34).

Oil

Oil, which is lighter than water and will not readily mix with it, makes room for itself in the pores of reservoir rock by pushing the water downward. However, oil will not displace all the water. A film of water sticks to, or is adsorbed by, the solid rock material surrounding the pore spaces (fig. 1.35). This film is called wetting water. In other words, water is not only in the reservoir below the oil accumulation but also within the pores along with the oil. The rare exceptions are oil-wet reservoirs, which have no film of water lining the pores but which may have an oil saturation of 100 percent of the available porosity.

Figure 1.35 Wetting water usually coats the grains of the reservoir rock

Natural Gas

Reservoirs usually contain natural gas along with oil. The energy supplied by gas under pressure is probably the most valuable drive for forcing oil out of reservoirs. The industry has come a long way since the day it was general practice to "blow" the gas into the atmosphere. Gas occurs with oil and water in reservoirs in two principal ways – as solution gas and as free gas in gas caps.

Given proper conditions, such as high pressure and low temperature, natural gas will stay in solution in the oil while in the reservoir (fig. 1.36). When the oil comes to the surface and pressure is relieved, the gas comes out of solution, much as a bottle of soda water fizzes when you remove the cap. Gas in solution occupies space in a reservoir, and geologists allow for this space when calculating how much oil is in the reservoir.

Figure 1.36 Solution gas stays in solu­tion until a well is drilled into the reservoir.

Free gas – gas that is not dissolved in oil – tends to accumulate in the highest structural part of a reservoir, where it forms a gas cap (fig. 1.37). As long as there is free gas in a reservoir gas cap, the oil in the reservoir will remain saturated with gas in solution. Dissolved gas lowers the viscosity of the oil (its resistance to flow), making the oil easier to move to the wellbore.

Figure 1.37 Free gas forms a gas cap

Дата добавления: 2015-10-30