skin components

[aeacfm]

another expression i cant understand

skin components in general ( i need just approximation because i read too much and cant understand any thing ) like geometrical and others , pls any one explain to me ?

noticification !!! i am not petroleum engineer (i am a chemist)

[vinomarky]

From SLB website;

1. n. [Well Completions] ID: 2821

A dimensionless factor calculated to determine the production efficiency of a well by comparing actual conditions with theoretical or ideal conditions. A positive skin value indicates some damage or influences that are impairing well productivity. A negative skin value indicates enhanced productivity, typically resulting from stimulation.
2. n. [Well Testing] ID: 8150

The zone of reduced or enhanced permeability around a wellbore, often explained by formation damage and mud-filtrate invasion during drilling or perforating, or by well stimulation.

In laymans terms it is a fudge factor introduced to represent an infinitesimal thickness zone of additional pressure drop to account for what is observed. Skin can be broadly broken into introduced (such as drill fluid and cement ingress) and native such as fines migration or clay swelling. It can also be used to account for mechanical restrictions such as low perf density or partial penetrations to name a few, as well as flowrate dependant 'skin' (which in actuality is just turbulent effects). You can also have negative skin (example - hydraulic fractures) which is essentially saying that the near wellbore region is more productive (less pressure drop for given distance) than the deeper reservoir perm.

As an example, say we did a welltest on a newly drilled well in which there were significant drill fluid losses over the reservoir zone - if we knew the radius of penetration of the drill fluids, and the amount of permeability impairment of the damaged zone we could take this damage into account with a lower perm zone of a certain radius - in reality we know neither with much accuracy, so when we do the welltest, from the pressure response infer both what the average deep reservoir kh (perm x height) is as well as a 'skin' used to account for how the early time pressure behavior differs from how it should theoretically behave if it had the same kh in the near wellbore region.

When calculating skin it is important to know what the components of this skin are (can be a combination of any/all of the above), especially when planning on trying to address this skin - there is obviously little point in acidizing a high 'skin' well when this skin is due to gravel pack or partial penetration for example. The process of identifying the various components of skin is complex and should be done in conjunction with other wells in the area and take into account drill & workover history, completions, nodal analysis etc....