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Doesn't quite work like that Ravi... plus I think you made an error in your volume calculation. :) I get 3000 x 5000 x 28 = 420M cu. m which is 2.64B bbls.

I think you might have multiplied by 15 twice.

Anyway, if the structure is fairly flat (like Surprise is) that's probably a pretty good approximation of the gross reservoir volume.

Then you need to apply the oil volumetric equation which is:

OIP = GRV x NTG x Phi x Sh / Bo

where NTG is net-to-gross ratio, Phi is porosity, Sh is saturation and Bo is the formation volume factor which basically accounts for how much volume you lose from dissolved gas (high for light oil, low for heavy oil).

Obviously we don't know these values but we can guess Phi is 10%, Sh is 90%, and Bo is 1.1 for heavy oil.

NTG is tricky because we have no idea but this is a tight sand so let's use 50% and keep in mind it could be lower. The 28m of continuous oil shows does not mean 28m net pay (though in some circumstances it can do).

We also don't know for sure that Sh is 90% but if it's much less than that this well is not going to flow so we might as well aim high.

So 2.64B x 0.5 x 0.1 x 0.9 / 1.1 = about 100MMbbls OIP.

But if NTG is only 25% then we get 50MMbbls which is the original high-end estimate so we're probably in the ballpark.

It might be as low as 10% which is 20MMbbls.

That's before you even think about applying the recovery factor which might be 10 to 30%. Probably towards the lower end in this sort of reservoir.

Disclaimer: not an oil geologist, stand to be corrected by anyone who is. :)

Disclaimer Mk II: may have suffered fat finger syndrome on my calculator so if anyone wants to check my figures please do.