Chapter 8: Properties of Black Oils - Definitions

Question 0

What is the conversion factor used to convert cc to bbl?

Answer 0

6.2898 x 10 ^-6 bbl/cc

Question 1

What type of chemical species are present in black oils?

Answer 1

Heavy - 27.9 mol % C7+

Non-volatile molecules

Question 2

What is the definition of liquid specific gravity in:

a) words
b) equation w/ units

Answer 2

a) the ratio of the density of the liquid to the density of water (at same T & P)
b) density oil / 62.37 (unit less)

Question 3

What are the 3 changes that cause the ST volume to be less than res volume?

Answer 3

1) evolution of dissolved gas as pressure is decreased from reservoir to surface
2) oil expansion because of reduction in pressure
3) oil contraction because of temperature reduction

Question 4

What is the definition of the formation volume factor of oil in:

a) words
b) equation, with units

Answer 4

a) the vol of reservoir oil required to produce one bbl of oil in the ST

b)
Bo = vol of oil + dissolved gas leaving res @ res condition
________________________________________________
vol of oil entering ST @ STP

Question 5

As the reservoir pressure increases, what happens to the oil formation factor (Bo) at the bubble point (Pb)?

Why?

Answer 5

Bo increases to a max value

Because of the expansion of the liquid in the reservoir

Question 6

What is the shrinkage factor?

Answer 6

The reciprocal of the vol formation factor

bo = 1
____
Bo

Question 7

What does the solution gas-oil ratio (Rs) represent and what equation do you use to find it?

Answer 7

It represents the solubility of gas in oil

Rs = vol of gas produced at std. conditions
____________________________________
vol of oil in ST at std conditions

Question 8

What happens to the solution gas-oil ratio (Rs) above the bubble point (Pb)?

What happens to it at the bubble point (Pb)?

Answer 8

Above the Pb, Rs remains constant and at max value as pressure is decreased

At the Pb, Rs begins to decrease as pressure is decreased

Question 9

When is black oil considered:

a) saturated
b) under saturated

Answer 9

a) at the Pb, where release of some gas is allowed (2 phases, liquid & gas)
b) above Pb, the oil could dissolve more gas (light molecules) if the gas were present

Question 10

What is the total volume factor, Bt in:

a) words
b) an equation, with units

Answer 10

a) the total vol that would be occupied by oil & gas if all of the free gas remained in the reservoir
b) Bt = Bo + Bg (Rsb - Rs) res bbl/STB
* where Rsb is the solution gas-oil ratio at bubble point)

Question 11

What is the total formation volume factor (Bt) above the bubble point?

Answer 11

Bt = Bo

because above the bubble point, the Rsb & Rs are the same, therefore =0

Question 12

What is the coefficient of isothermal compressibility of oil (Co) in:

a) words
b) an equation, with units

When is this applicable?

Answer 12

a) the fractional change of vol as pressure is changed at constant temperature
b) Co = - 1/v (partial V / partial P), psi-1
* only applicable at pressure above the bubble point pressure

Question 13

What is the equation for the coefficient of isothermal compressibility of oil (Co), if Co is assumed to be constant with pressure change?

Answer 13

Co (P2 - P1) = - ln (V2 / V1)

V2 = V1 EXT [Co (P1 - P2)]

Question 14

What is Co in terms of density?

If Co is assumed constant with pressure change AND pressure is above Pb, what is the equation?

Answer 14

Co = (1/ density oil) (partial density oil / partial pressure)

Co is constant when pressure changes above the bubble point

density oil = density oil at bubble point * EXT [ Co (P - Pb)]

Question 15

What happens to the vol of reservoir liquid as pressure is reduced below Pb?

What happens to the reservoir vol occupied by the mass that was originally liquid? Why?

Answer 15

The vol of reservoir liquid decreases as pressure is reduced below Pb

The reservoir volume increases, due to the evolution of gas

Question 16

What is the coefficient do isobaric thermal expansion in:

a) words
b) an equation

Answer 16

a) the fractional change in vol of a liquid as temperature changes under constant pressure

b) oil vol @ high temp
___________________
oil vol @ low temp

Question 17

What happens to the viscosity of oil, when:

a) temperature goes up
b) the amount of dissolved gas goes down
c) the size of HC molecules increases

Answer 17

a) temp goes up => oil viscosity goes down
b) amount of dissolved gas goes down => oil viscosity goes up
c) oil viscosity increases with the increase in size of HC molecules

Question 18

What are the 5 physical properties required for the reservoir engineering material balance calculations?

Answer 18

1) formation vol factor of oil (Bo)
2) solution gas-oil ratio (Rs)
3) total formation vol factor (Bt)
4) coefficient of isothermal compressibility (Co)
5) coefficient of viscosity of oil

Question 19

How can you find the volume of reservoir oil required to produce the volume of stock-tank oil, if Bo and ST vol (Vst) is known?

Answer 19

Vol of reservoir oil = formation vol factor x vol of stock-tank

Vol of reservoir oil = Bo * Vst