High skin damage? when high is just too high?

[guga23]

Good day people.

I made a well testing analysis and got that the skin damage S on a gas well was around 100. Is this even possible, I mean a skin so high?. This well was tested after an stimulation job (acid), prior to that the damage was 341!!!.

When the well was drilled, it tested 50.000 sm3/d (gas) but after that, it was never put in production. Several years later (~20 years) the well was re-opened and tested around 3.000 sm3/d and after the stimulation job it produced 13.500 sm3/d.

Thanks for yours replys.

[zaheer.jamali]

this looks an intresting topic for discussion.
before 20 year>>> flow was stable ?
and 100 skin is possible
that mean ur stimulation job was perfomed well.
or mud has demages the reservoir so badly.

[guga23]

The 50.000 sm3/d gas rate was during production test phase (tested during a DST). After that the well stayed closed for 20-25 years (at that time we didnt need gas). I forgot to add that after the stimulation job the well started to produce 6.000 sm3/d and slowly rising his production around 500 sm3 per day ( I guess, cleaning himself, taking the acid/water out, etc) for around 2 weeks, then we closed it for the Well test.

Also, the 341 skin damage is posible?

Note: the reservoir permeability is ~ 23md, kh=771 md-ft.

Thanks

[zaheer.jamali]

i have seen a well, which was producing with very low drawdown having skin 500, this can only be happen when K value is high.
23 md is good permeability, we have produce a well with 320 skin and 2 md permeability.

The 50.000 sm3/d gas rate was during production test phase (tested during a DST). After that the well stayed closed for 20-25 years (at that time we didnt need gas). I forgot to add that after the stimulation job the well started to produce 6.000 sm3/d and slowly rising his production around 500 sm3 per day ( I guess, cleaning himself, taking the acid/water out, etc) for around 2 weeks, then we closed it for the Well test.

Also, the 341 skin damage is posible?

Note: the reservoir permeability is ~ 23md, kh=771 md-ft.

Thanks

[Shakespear]

Guga , where are these numbers coming from. Well test analysis ? I would use some NODEL package to test what I should expect the well to produce with no damage. Then do sensitivity analysis to understand what might be happening. To me the numbers sound unrealistic and might be the result of some bad input.

Take any well test/ NODEL book and try to understand what you are working with here. First issue is do you have the right units? Is the BHP correctly calculated? Is the open interval right, does the log interpretation make sense, and on and on .... You need to check all this out as Something is not right.

- skin means the well was stimulated
+ skin means it is producing less than it should

skin factor

1. n. [Well Testing] ID: 8152

A numerical value used to analytically model the difference from the pressure drop predicted by Darcy's law due to skin. Typical values for the skin factor range from -6 for an infinite-conductivity massive hydraulic fracture to more than 100 for a poorly executed gravel pack. This value is highly dependent on the value of kh. For example, a 20-psi [138-kPa] total pressure drop related to skin effect could produce almost any skin factor, depending on the value of kh. For any given pressure drop from skin effect, the skin factor increases proportionally as kh increases.

[i-anuar]

also some 'true' skin can be found if you plot calculated skin at different rates and extrapolate to zero rate.
if you have partial penetration that can add skin due to flow convergence

[hamra]

20 years ago, look around the well what was happen in 20 years ago, reservoir pressure, number wells drilled around it, even your skin is small but the well produce less due to reservoir pressure decline. High skin with small k doesn’t matter. Production engineer

[guga23]

20 years ago, look around the well what was happen in 20 years ago, reservoir pressure, number wells drilled around it, even your skin is small but the well produce less due to reservoir pressure decline. High skin with small k doesn’t matter. Production engineer

Nope, the reservoir didnt produce for 20 years, so the reservoir pressure was the same.

Want to add the we made a post stimulation Build-up, and we got a lower damage (100 skin with the 12.500 sm3/d gas flow).

We analized all this new info, did a nodal analysis and all the info matched perfectly, the kh, well radius etc and modifing the sking from 100 to 341 the nodal analysis gave us the same productions rates posted before (13.500 for a 100 skin dmg and 3.000 for the 341 dmg)