Well Spacing

[dipak_m]

Dear Members,
What are the factors to determine the well spacing of a particular reservoir. Give me details.
Thanks

[vinomarky]

There are rules of thumb for different areas, but no one all encompassing 'equation'

It depends of factors including but not limited to;
Permeability (low perm will benefit from tighter spacing in form of acceleration and incremental tail)
Heterogeneity (highly heterogeneous reservoirs will actually give incremental reserves - not just accelerated - from infill drilling)
Sweep patterns (if injectors used) - are they homogeneous or do they exhibit highly directional/fingering tendencies
Economics.... how expensive your wells to drill, to operate, how much will you get for your hydrocarbons in the future, and what discount factor your company uses

If you have high perm, homogeneous reservoirs - quite low well spacing will be best

If you have low perm, heterogeneous reservoirs, then tighter wells spacing will be needed, but there will be a 'creaming curve' of benefits against the escalating well costs... one of the keys here is how much accelerated oil you will get (more offtake in low perm formation) vs incremental oil (heterogeneity and incremental tail).

Good luck

Note: In referencing 'incremental tail' I mean the difference in EUR between having 1 well producing to the operational economic limit vs 1+n wells all producing to the operational economic limit... Another way of thinking about this is getting the average reservoir pressure down as low as possible... with 1 well you'll be producing to some local abandon pressure while the average reservoir pressure will be something higher, while if you have 1+n wells, your average reservoir pressure will start to approach local abandonment reservoir pressure... sorry if this is a bit confusing...

[dipak_m]

Thanks Vinomarky. Are there any books or papers regarding this matter.
Thanks

[vinomarky]

Two top hits from the SPE site are;

[link Point to another website Only the registered members can access]

[link Point to another website Only the registered members can access]
I have not read either though, so cannot vouch for them

In general though, you can test your scenarios with a reservoir simulation - put more wells in there and see what happens. This approach though probably will not do a good job of characterizing the incremental oil due to heterogeneity, as most geological/simulation models are too well connected - unless of course you have a great understanding of the formation, but heterogeneity and good understanding most often do not go hand-in-hand

[dipak_m]

Once again thanks. I will go through these papers. If possible please send me the full papers. Otherwise I will manage from our library.
Thanks. Come back after going through the papers

[ahmedm]

thanks guys,

i think you already covered most of the story just to add

i think you might do DCA for your wells then you can use the EUR as OIP for the well and find the drainage area then you can infer that to account the possible number of infill wells that you can add. here you can use the same equation of voumetric OIIP but for each well you can put the properties you have there from your petrophysicist (porosity, NTG, h, if vertical well for horizontal you can use any definition lets say Joshi eqution to define the drainage area)

others for the simulation you can put the wells based on the Remaining oil column (poro*So*h) also it is petter to consider the pressure then you run them as group you can use the option of automatic drilling as in CMG then it can prioritize your well pased on UR of each well, in this you can set the oil production to a number that you already now based on RF number, if you dont you can use the correlation , API, Dykastra-Parson, analogy, etc



i hope this can help my friend

thanks alot

[dipak_m]

Dear Ahmedm,
Thanks for your valuable contribution.
Please explian "the EUR as OIP for the well and find the drainage area then you can infer that to account the possible number of infill wells that you can add" and if possible give me "Joshi eqution to define the drainage area"
Thanks

[ahmedm]

EUR method, you can sue the OIP equation OIP = A*Por*(1-SW)/Bo
here the OIP = EUR/RF and other paramers from the log of this well

___L___
(_______)W

assuming the drainage area of the horizontal well is rectangle from the well leg and half circle from each side so the area = rectangle + circle
if you have a vertical well then you can use its drainage area (circle)
for the well length you already have it and for the width

w = 2(-L-/+ sqrt(L2+PI()A)/pi()
pi = 3.14
A vertical well area
L well length

then from the area you can get the r for the vertical well from the EUR method then roughly you can divide the total field volume OIIP*RF by the area (EUR average based on average drainage area you got) you have to see how many well you can add but make sure you are account for heterogeniety of you reservoir i mean you can produce economically at least cover the well cost

what i mean by average bacause you have different well performance so different EUR so you need to take the average. maybe if you can make the bubble map of the cum you can see where you still have oil actually it is same higher Cum oil higher Drainage area. put in you consediration the pressure distribution too

thanks i hope it is clear now

[ahmedm]

EUR method, you can sue the OIP equation OIP = A*Por*(1-SW)/Bo
here the OIP = EUR/RF and other paramers from the log of this well

___L___
(_______)W

assuming the drainage area of the horizontal well is rectangle from the well leg and half circle from each side so the area = rectangle + circle
if you have a vertical well then you can use its drainage area (circle)
for the well length you already have it and for the width

w = 2(-L-/+ sqrt(L2+PI()A)/pi()
pi = 3.14
A vertical well area
L well length

then from the area you can get the r for the vertical well from the EUR method then roughly you can divide the total field volume OIIP*RF by the area (EUR average based on average drainage area you got) you have to see how much well you can add but make sure you are account for heterogeniety of you reservoir i mean you can produce economically at least cover the well cost

waht i mean by average bacause you have different well performance so different EUR so you need to take the average. maybe if you can make the bubble map of the cum you can see where you still have oil actually it is same higher Cum oil higher Drainage area. but in you consediration the pressure distribution too

thanks i hope it is clear now

[dipak_m]

Dear Ahmedm,
Thanks for your great contribution.
This is Jhosi's equation or not?

[ahmedm]

yes

actually the main equation is for SPI of Horizontal Wells
and he defines the area using this definition it is simple you can express it
yourself,

to know more about the hor wells you can search on 4sahred.com just write
horizontal well technology joshi


thanks

[dipak_m]

Thanks Ahmedm