Drainage radius

[TBone]

Does anybody know how to calculate the drainage radius of a horizontal well?
When calculating production rates, a smaller drainage radius will give a higher rate, and by that logic the drainage radius should not decrease if another well is placed nearby. Thoughts?

[reservoirengineer]

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Does anybody know how to calculate the drainage radius of a horizontal well?
When calculating production rates, a smaller drainage radius will give a higher rate, and by that logic the drainage radius should not decrease if another well is placed nearby. Thoughts?

[vinomarky]

I've always had a bit of an issue with the concept of 'drainage radius'.... it seems to conjure images of constant radius cylinders of reservoir, out of which a given well will effectively drain the hydrocarbons.

I instead would prefer to picture the scenario as a large trampoline covered in honey, which you then sit in the middle of - right next to you, the trampoline goes down quite a lot, and the honey runs rapidly into your lap, as you go further and further out, the depression gets less and less so the honey moves slower and slower, until eventually their is not enough inflexion in the trampoline to overcome plastic viscosity of the honey and there is no movement. What is the 'drainage radius' in this scenario? The answer of course is that there is no hard fast number, instead the answer is simply a reduction in the rate of recovery as you step out further and further from the drawdown, the overall recovery more limited by time (and therefore economics) than anything else.

So, to get back to your question - a well can drain far more radius than is optimal (ie you'd be better off spending money to infill drill and accelerate) - the optimal drainage radius (or drill spacing) is one determined as much by economics as it is by reservoir properties

Food for thought

[i-anuar]

Check Dake's book, Material Balance section. there he is trying to get around this issue (not knowing drainage radius) to get average pressures for the reservoir. He suggests to weight dp by dN. You could perhaps try same approach?