Chapter 3- Gas Reservoir Flashcards
How can we identify a gas reservoir ?
If the reservoir temperature is above the critical temperature, it is a gas reservoir
Natural gases can be classified into how many categories?
4
List the various gas reservoirs we have
Retrograde gas condensate
Wet gas
Dry gas
Near critical gas condensate
How do we identify gas condensate reservoir?
If reservoir temperature is greater than the critical temperature of the reservoir fluid but less than the cricondentherm
Tc
How do we identify wet gas reservoir?
If the cricondentherm is greater than the critical temperature but less than the reservoir temperature
Tc
How do we identify dry gas reservoir?
Tc
How do we identify near critical gas condensate reservoir ?
If the reservoir temperature is near the critical temperature
What is meant by isothermal depletion
This means reservoir temperature doesn’t change when producing it .
Properties of retrograde condensate reservoir
GOR between 8000-70000 scf/STB
Condensate gravity above 50 degree API
Stock tank liquid is usually water white or slightly colored
In a wet gas reservoir, what happens to the reservoir fluid ?
It is gaseous in the reservoir during isothermal depletion , but at surface conditions , it exists as 2 phase ( liquid and gas )
What happens to the hydrocarbon mixture in a dry gas reservoir?
The hydrocarbon mixture exists as a gas both in the reservoir and in the surface facilities.
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?
Water
Characteristic properties of dry gas reservoir ?
GOR greater than 100,000 scf/STB
What did McCain (1994) suggest about heavier components in the hydrocarbon mixtures ?
He suggested that heavy components in the hydrocarbon mixture have the strongest effect on fluid characteristics.
If a wet gas reservoir and a dry gas reservoir have the same relation, what could be the difference between them ?
The difference is in their separator conditions .
What happens to an undersaturated oil reservoir during production?
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
What happens to a saturated oil reservoir during production?
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.
What happens to a gas cap oil reservoir during production?
Since Tres
What happens when there’s no pressure gradient between the well head and manifold ?
No flow will occur
If the pressure at the bottom is too close to the separator, What is expected to happen ?
There’s expected to be no flow of fluid as a result of little gradient
What happens when we produce a dry gas reservoir ?
Since Tres»_space; Tct
The reservoir and surface conditions is usually 1 phase . ( gaseous ) because the separator conditions doesn’t intersect with the two phase region .
What happens to a wet gas reservoir during production?
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 )
Why is the retrograde condensate reservoir called such ?
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 .
When do we lose resources while producing a retrograde condensate reservoir?
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.
How do we manage a reservoir such as retrograde condensate ?
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.
How do we keep the pressure above dew point pressure for a retrograde condensate reservoir?
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
What are the types of oil recovery we have ?
1) primary
2) improved
What does improved recovery consist of ?
1) secondary
2) enhanced
How does primary oil recovery work ?
You use the energy of the reservoir to produce the reservoir fluid .
What does secondary oil recovery entail?
You inject something into the reservoir in order to maintain the pressure , so that oil keeps coming out at the rate you want
What are the types of secondary recovery we have ?
1) water flooding - injecting water
2) immiscible gas injection - injection of gas into the reservoir
What’s the difference between secondary and enhanced oil recovery?
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 .
When do we talk about enhanced oil recovery?
We talk about enhanced oil recovery when the oil is too thick to flow
