Chapter 7: Properties Of Wet Gases

Question 0

What are the conversion factors for:

a) lb-mol -> scf
b) bbl -> cu ft

Answer 0

a) 1 lb-mol / 380.7 scf

b) bbl / 5.615 cu ft

Question 1

How many states does a wet gas usually go through when separated?

What are the 3 fluids produced after separation at the surface.

Answer 1

A wet gas typically goes through 2 stages of separation

Fluids produced after separation:

1. Stock-tank liquid (condensate)
2. Separator gas (SP g)
3. Stock-tank gas (ST g)

Question 2

What is the first step in the conversion of GOR?

Answer 2

Calculate the density and apparent molecular weight of the stock-tank LIQUID

Ma = sum(y * M) API = (141.5 / STO specific gravity) - 131.5

STO specific gravity = STO density / 62.37

Question 3

How can you estimate the molecular weight of the stock-tank liquid if it is not known?

Answer 3

M(STO) = 5954
_________
(API - 8.8)

Or

M(STO) = (42.43 * STO specific gravity)
___________________________
(1.008 - STO specific gravity)

Question 4

What is gaseous equivalent and how is it represented in the specific gravity of a reservoir gas equation?

Answer 4

Gaseous equivalent is the volume in scf of a gas that the stock-tank liquid would occupy if it were vaporized

(133,300 * STO specific gravity) / M(STO)

Question 5

How do you find the specific gravity of the reservoir gas, if the SP gas & the ST gas properties are known?

Answer 5

Specific gravity (res g)

= [R(SP) * SP gas specific gravity + R(ST) * ST gas specific gravity]
__________________________________
R(SP) + R(ST)

R = R(SP) + R(ST)

Question 6

How do you find the MW of the reservoir gas, if SP & ST gas properties are known?

Answer 6

M(res g) = m(res) / n(res)

= [0.0762R(gas specific gravity) + 350.2(STO specific gravity)] ___________________________________________
0.00263R + [(350.2*STO specific gravity) / M(STO)]

Units = lb of gas / lb-mol of gas

Question 7

How do you estimate the PRODUCING GOR, if the properties & quantities of all surface gas streams are known?

Answer 7

2-stage: R = R(SP) + R(ST)

3-stage: R = R(SP1) + R(SP2) + R(ST)

Question 8

What are the 4 steps to calculate the composition of a gas with known surface composition of a wet gas?

Answer 8

1. calculate M(STO) & density of stock-tank LIQUID
2. convert GORs from
   (scf SP gas/STB) => (lb mol SP gas/lb mol STO)

    (scf ST gas/STB) => (lb mol ST gas/lb mol STO)

3. create a table
4. calculate mol fraction of the recombined reservoir gas

Question 9

If given the SP GOR and/or ST GOR, what additional steps do you have to take to find the composition of the recombined res gas?

Answer 9

Convert (scf gas/STB) => (scf gas/STO)

(scf gas/STB) * (1/380.7) * (1/5.615) * [M(STO)/density(STO)]

Question 10

How do you estimate the specific gravity of the res gas from production data, if the properties & quantities of all surface streams are known?

Answer 10

Find the weighted avg of the specific gravities of the SP gas & ST gas

=[R(SP) * SP spec gravity] +
[R(ST) * ST spec gravity] / [R(SP) + R(ST)]

Question 11

How do you find the specific gravity of a ST gas that has gone through a 3-stage SP system, if the quantity of the second SP gas is unknown?

Answer 11

= [R(SP1)specific gravity(SP1) + 4600 specific gravity oil + AGP] / R(SP1) + VEQ

Question 12

What is equivalent volume (VEQ)?

How do you calculate it if GORs, specific gravity(STO), & M(STO) are known?

Where else can you get the VEQ?

Answer 12

The vol of second SP gas & ST gas in scf/STB + the vol (in scf) that would be occupied by a bbl of ST liquid if it were a gas

VEQ = R(SP1) + R(ST) + 133,300*(STO specific gravity) / M(STO)

Can get VEQ value from VEQ Correlation charts

Question 13

What does addition gas produced (AGP) relate to?

How do you determine the AGP value?

Answer 13

The mass of gas produced from the second SP & ST in a 3-stage separator system

AGP = R(SP2)(SP2 specific gravity) + R(ST)(ST specific gravity)

Can get AGP value from AGP Correlation charts

Question 14

How do you define the formation volume factor of a wet gas in:

a) words
b) an equation, with units

Answer 14

a) the volume if res gas required to produce 1 STB of liquid at the surface

b) Bwg = V res gas @ res P and T
________________________ ,
V ST liquid @ Std P and T

Scf at res conditions / STB

Question 15

What are the 4 steps required to calculate Bwg, if surface composition & res conditions are known?

Answer 15

1. calculate pseudo critical properties of res gas
2. determine z factor & calculate Vm of res gas
3. calculate vol of ST liquid condensate from 1 lb mol of res gas
4. calculate Bwg

Question 16

How can you determine the vol of res wet gas required to produce 1 STB of liquid?

What are the units?

Answer 16

vol of res wet gas = R(SP1) + VEQ, (scf/STB)

Question 17

How do you calculate the molar vol (Vm) of ST liquid?

Answer 17

Vm of ST liquid = M(STO) / STO density

Question 18

How do you calculate the vol of wet gas in scf?

Answer 18

Bwg = z * [R(SP1) + VEQ] * R T
______________________
380.7 * P

Ideal gas equation of state

Question 19

What are the 2 simplified equations used to find Bwg in:

a) res cft gas/STB
b) res bbl gas/ STB

Answer 19

a) 0.0282 * z * [R(SP1) + VEQ] * T res scf gas
____________________________ , ___________
P STB

b) a) 0.00502 * z * [R(SP1) + VEQ] * T res bbl gas
_____________________________ , ____________
P STB

Question 20

What are plant products?

Answer 20

Liquified intermediate hydrocarbons removed from surface gas

Question 21

How do you find the quantities of liquid product that can be removed from a surface gas (GPM)?

What do you need to know in order to determine these quantities .

Answer 21

Calculations are for individual components

GPM = 19.65 * [ (y * M) / density] , (gal/Mscf)

Or

GPM = 0.3151* [ (y * M) / specific gravity as a liquid], (gal/Mscf)

Must know the composition of the gas

Question 22

How do you find the density of the ST liquid if given API?

Answer 22

STO density = 141.5 * 62.37
_____________
API + 131.5