# Calculate heat loss of aquifer with unknown shape

I am trying to calculate the heat loss of an aquifer. An aquifer is basically a hot-cold storage $80\: \mathrm{meters}$ under the ground. It is an open system and utilizes groundwater. By pumping for example warm water ($70\: \mathrm{C}$) under the ground this can be stored for half a year and be used in the winter to heat a building.

The problem is that I'm not quite sure how to calculate the amount of heat lost during those 6 months. I was thinking of using $\frac{dQ}{dt} = \mathop{UA}(T_2-T_1)$

Where $T_2-T_1$ is the temperature difference of the ground soil and water.

However I am working with an undefined 3D shape.

So if someone could point me in the right direction as to how to find out how much heat is lost during 6 months of storage, that would be great!

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