why tight reservoirs has negative skin ?

[anbu_ongc]

why tight reservoirs has negative skin ? can any one pl explain.

[vinomarky]

They normally don't - perhaps yours have natural fractures in them, which could be analyzed as negative skin

[kochichiro]

Well, I’ll have a little different answer. In many cases, after drilling operations such reservoirs do not flow naturally, because they are completely plugged. Therefore, drilling team run several acid stimulations to get stable rate. From my experience I know that in Russia such operations in many cases are performed silently to cover inappropriate drilling conditions.

[vinomarky]

Interesting observation, and one I will keep in mind for the future

In tight gas though "typically" doing an acid treatment will not help - in fact typically it will hinder - due to very low perms being extremely susceptible to slight swelling of clays

[darcyoil]

Simple. I was stumped the first time I saw such a situation. Answer is, in v. tight formations, the flow thru the perfs shows up as linear flow !!!!

[gunner]

Hi yes tight gas when fractured produces linear flow in fracture.
This skin is not mechanical skin but the rate dependent skin ...that's why it turns negative

[Tejaswy]

From my experience I know that in Russia such operations in many cases are performed silently to cover inappropriate drilling conditions.

That does not make any sense, what does in appropriate drilling conditions have anything to do with Acid stimulation?

[vinomarky]

I think he was conveying that when the Drilling group fill the hole with overbalanced mud and damage the well, they may try to acid stimulate to recover some of the lost productivity, but avoid telling anyone for fear of repercussions

[kochichiro]

Well, yes. Typically mud extremely overbalanced. Moreover, during drilling in shale layers swelling occurs and mud density increasing further. Conventional reagents that employed as shale inhibitors as good as shit. Supervisor’s notifications are usually ignored by drilling team. Therefore, when time comes to DST test of such reservoirs they do not flow naturally and drilling team runs several acid flushes until they receive some, even negligible rate. I know many cases when reservoirs were considered as dry basing on results of such DST tests.

[Tejaswy]

I think what he meant was that the BOP/safety conditions are not so good and hence they use overbalanced technique to make sure there is no blow out. Then they acidize it to undo some of the formation damage.