Gor

[ahmedj9579]

dear all
Why do we need to calculate a GOR for an oil well???
is it obligatory that the GOR stayed constant during all the life of the well?
regards

[vinomarky]

1. it tells you when you have dropped below bubble point pressure
2. unless you track the gas rate, you cant properly do any material balance calculations
3. Generally usefull aditional piece of info you can use to help diagnose problems such as multiayered production etc

[ahmedj9579]

many thanks, but ones we have a GOR different to zero means we produce above the bubble point. right? so how can we know when we produce below bubble point pressure?
what is the relationship between them?

sorry but i didn't get your second and 3rd point!

[kader_007]

In additon to Vinomarky points, I'de add that tracking GOR in a Gas Injection pressure maintained field will help you identify the Gas breakthrough from injection as a sudden increase in GOR could be a result of intensive Gas injection around the oil producer (due to low spacing, high perm or high injection rates).

Regarding your second post, GOR is never zero man! you are measuring it at surface hence at stock tank condition Oil will release gas and here is your GOR computation i.e. GOR= [produced gas/produced oil] keep in mind that when your field was "virgin" its GOR is calles Rs and is versus the latter that you know if you are facing an increasing GOR as (GOR-Rs)xOil production = Free gas i.e. the secondary gas cap effect.

The bubble point is the point at which the first buble of gas forms in a liquid phase, the more you go bellow the more you'll have gas bubbling (building up) thus increasing GOR.

Finally Vinomarky 3rd point refers (if I'm not wrong) to the muli-layer wells (imagine a well producing from more than one layer/reservoir) running an MPLT (PLT) will help you identify the fluid type and related rates from each layer, ther is also another tool called RST that can help you identifying from where the gas is comming (RST stands for reservoir Saturation Tool).

No secret man! you have to track rpoduced fluids (how much and from where) and the pressure obviously (through static pressure surveys i.e. SBHP vs. Pb).

SBHP: static bottom hole pressure;
Pb: bubble point.

Regards,
--
Kader

[ahmedj9579]

In additon to Vinomarky points, I'de add that tracking GOR in a Gas Injection pressure maintained field will help you identify the Gas breakthrough from injection as a sudden increase in GOR could be a result of intensive Gas injection around the oil producer (due to low spacing, high perm or high injection rates).

Regarding your second post, GOR is never zero man! you are measuring it at surface hence at stock tank condition Oil will release gas and here is your GOR computation i.e. GOR= [produced gas/produced oil] keep in mind that when your field was "virgin" its GOR is calles Rs and is versus the latter that you know if you are facing an increasing GOR as (GOR-Rs)xOil production = Free gas i.e. the secondary gas cap effect.

The bubble point is the point at which the first buble of gas forms in a liquid phase, the more you go bellow the more you'll have gas bubbling (building up) thus increasing GOR.

Finally Vinomarky 3rd point refers (if I'm not wrong) to the muli-layer wells (imagine a well producing from more than one layer/reservoir) running an MPLT (PLT) will help you identify the fluid type and related rates from each layer, ther is also another tool called RST that can help you identifying from where the gas is comming (RST stands for reservoir Saturation Tool).

No secret man! you have to track rpoduced fluids (how much and from where) and the pressure obviously (through static pressure surveys i.e. SBHP vs. Pb).

SBHP: static bottom hole pressure;
Pb: bubble point.

Regards,
--
Kader

thank you for this especially for the third point! but what how can we get this second gas cap???? you mention Oil production *(GOR-RS) =free gas. i have all this informations, so how can i used it to identify or to interpret this second gas cap? can i plot this formula vs time to see something special???? i'm really confused

[kader_007]

thank you for this especially for the third point! but what how can we get this second gas cap???? you mention Oil production *(GOR-RS) =free gas. i have all this informations, so how can i used it to identify or to interpret this second gas cap? can i plot this formula vs time to see something special???? i'm really confused

well I was too much in hurry!
so here is the long story:
the GOR-Rs should be used as a tabulated form (keepins in an excel spreadsheet the Rs reference cell fixed) multiplying this by the current gas production (let's say the monthly average production for each month) will lead you to the free gas amount built monthly.

The so-called free gas is all what is down in the reservoir NOW and that wasn't before when the field was brand virgin!
we call secondary gas cap, the free gas that built up after some years of production which is the result of a Reservoir pressure decrease bellow or near Pb

In terms of plotting results, my advice would be to plot the GOR vs time and a straight line for Rs when both line intersect is the time your GOR started increasing from its original value, the slop of the GOR trend can only be used as indication of th velocity the GOR is increasing.
Keep in mind that if you have an injector near by, you have to be causcious as it is likely that the GOR your are measuring at surface is the results of a combined effect (Rs, pressure and injection breakthrough) thats' why you have to have a clear image of what's going on (reservoir characteristics i.e. mainly permeability, producing zones/layers, static pressure historical trend or MDTs and injection/production data)

Good luck!
--
Kader

[ahmedj9579]

well I was too much in hurry!
so here is the long story:
the GOR-Rs should be used as a tabulated form (keepins in an excel spreadsheet the Rs reference cell fixed) multiplying this by the current gas production (let's say the monthly average production for each month) will lead you to the free gas amount built monthly.

The so-called free gas is all what is down in the reservoir NOW and that wasn't before when the field was brand virgin!
we call secondary gas cap, the free gas that built up after some years of production which is the result of a Reservoir pressure decrease bellow or near Pb

In terms of plotting results, my advice would be to plot the GOR vs time and a straight line for Rs when both line intersect is the time your GOR started increasing from its original value, the slop of the GOR trend can only be used as indication of th velocity the GOR is increasing.
Keep in mind that if you have an injector near by, you have to be causcious as it is likely that the GOR your are measuring at surface is the results of a combined effect (Rs, pressure and injection breakthrough) thats' why you have to have a clear image of what's going on (reservoir characteristics i.e. mainly permeability, producing zones/layers, static pressure historical trend or MDTs and injection/production data)

Good luck!
--
Kader

good good good many thanks for this clarification. but normally for an oil field and what we should have is a staight line of the GOR vs time else we can't rely on production data.( especially when we are working above the bubble point?)