Chapter 3- Gas Reservoir

Question 1

How can we identify a gas reservoir ?

Answer 1

If the reservoir temperature is above the critical temperature, it is a gas reservoir

Question 2

Natural gases can be classified into how many categories?

Answer 2

4

Question 3

List the various gas reservoirs we have

Answer 3

Retrograde gas condensate

Wet gas

Dry gas

Near critical gas condensate

Question 4

How do we identify gas condensate reservoir?

Answer 4

If reservoir temperature is greater than the critical temperature of the reservoir fluid but less than the cricondentherm

Tc

Question 5

How do we identify wet gas reservoir?

Answer 5

If the cricondentherm is greater than the critical temperature but less than the reservoir temperature

Tc

Question 6

How do we identify dry gas reservoir?

Answer 6

Tc

Question 7

How do we identify near critical gas condensate reservoir ?

Answer 7

If the reservoir temperature is near the critical temperature

Question 8

What is meant by isothermal depletion

Answer 8

This means reservoir temperature doesn’t change when producing it .

Question 9

Properties of retrograde condensate reservoir

Answer 9

GOR between 8000-70000 scf/STB

Condensate gravity above 50 degree API

Stock tank liquid is usually water white or slightly colored

Question 10

In a wet gas reservoir, what happens to the reservoir fluid ?

Answer 10

It is gaseous in the reservoir during isothermal depletion , but at surface conditions , it exists as 2 phase ( liquid and gas )

Question 11

What happens to the hydrocarbon mixture in a dry gas reservoir?

Answer 11

The hydrocarbon mixture exists as a gas both in the reservoir and in the surface facilities.

Question 12

If the hydrocarbon mixture in the dry gas reservoir is entirely gas both in the reservoir and surface facilities , which other liquid is associated with the gas from a dry gas reservoir?

Answer 12

Water

Question 13

Characteristic properties of dry gas reservoir ?

Answer 13

GOR greater than 100,000 scf/STB

Question 14

What did McCain (1994) suggest about heavier components in the hydrocarbon mixtures ?

Answer 14

He suggested that heavy components in the hydrocarbon mixture have the strongest effect on fluid characteristics.

Question 15

If a wet gas reservoir and a dry gas reservoir have the same relation, what could be the difference between them ?

Answer 15

The difference is in their separator conditions .

Question 16

What happens to an undersaturated oil reservoir during production?

Answer 16

since Tres >Pb ,
At the bottom of the reservoir, we have single phase , but at the top of the reservoir I.e when we get to the well head , we begin to have two phases , or three , provided the reservoir has water

Question 17

What happens to a saturated oil reservoir during production?

Answer 17

Since Tres=Pb of the reservoir fluid ,
The moment you begin producing the well , you begin to experience 2phases.
Liquid and gas I.e if water is out of the equation.

Question 18

What happens to a gas cap oil reservoir during production?

Answer 18

Since Tres

Question 19

What happens when there’s no pressure gradient between the well head and manifold ?

Answer 19

No flow will occur

Question 20

If the pressure at the bottom is too close to the separator, What is expected to happen ?

Answer 20

There’s expected to be no flow of fluid as a result of little gradient

Question 21

What happens when we produce a dry gas reservoir ?

Answer 21

Since Tres&raquo_space; Tct
The reservoir and surface conditions is usually 1 phase . ( gaseous ) because the separator conditions doesn’t intersect with the two phase region .

Question 22

What happens to a wet gas reservoir during production?

Answer 22

Since Tres < Tct, but not far greater as compared to a dry gas reservoir, the separator conditions intersect with the two phase envelop , thereby at surface , we experience 2phase (liquid and gas )

Question 23

Why is the retrograde condensate reservoir called such ?

Answer 23

It is called such because it condenses initially on getting to dew point pressure , before it begins to vaporize once the percentage increase in liquid comes to a halt .

Question 24

When do we lose resources while producing a retrograde condensate reservoir?

Answer 24

We lose resources when vaporization occurs , and the liquid begins to go back to gas , because we begin to have pockets of liquid which are not connected scattered all over the place , and because of this lack of connection , the liquid cannot flow , thereby leading to loss of resources.

Question 25

How do we manage a reservoir such as retrograde condensate ?

Answer 25

You find a way to keep the pressure above dew point pressure . Because if you allow the pressure to drop , liquid comes out , so you have to find a way to keep it completely Gaseous.

Question 26

How do we keep the pressure above dew point pressure for a retrograde condensate reservoir?

Answer 26

We inject a fluid into the reservoir to manage the reservoir pressure , so that it doesn’t fall deep into the 2 phase region forming liquid

Question 27

What are the types of oil recovery we have ?

Answer 27

1) primary

2) improved

Question 28

What does improved recovery consist of ?

Answer 28

1) secondary

2) enhanced

Question 29

How does primary oil recovery work ?

Answer 29

You use the energy of the reservoir to produce the reservoir fluid .

Question 30

What does secondary oil recovery entail?

Answer 30

You inject something into the reservoir in order to maintain the pressure , so that oil keeps coming out at the rate you want

Question 31

What are the types of secondary recovery we have ?

Answer 31

1) water flooding - injecting water

2) immiscible gas injection - injection of gas into the reservoir

Question 32

What’s the difference between secondary and enhanced oil recovery?

Answer 32

In secondary oil recovery, what you’re injection is most likely immiscible with water , but in enhanced oil recovery, what you’re injecting is going to mix with reservoir fluid hence is going to modify the reservoir .

Question 33

When do we talk about enhanced oil recovery?

Answer 33

We talk about enhanced oil recovery when the oil is too thick to flow