Question

A producing formation consists of two horizontal layers A and B: a) The thickness of Layer A is three times of the thickness of Layer B. However, the permeability of Layer B is 25% of the average permeability of the formation. What will be the ratio of permeabilities of these layers?? (15 pts) b) In Layer A, the grain volume is three times of the pore volume, and in Layer B the grain volume is five times of the pore volume. What will be the average porosity of the formation?

Answer 1

Ans:- permeability depends upon 3 factors:-

a-diffusion coefficient (D)

b-thickness (h)

c-slippery constant (K)according to question ha=3hb, let permeability of A and B= Ka and Kb respectively.

average permeability =Kaha+Kbhb/ha+hb

3/4Ka+1/4Kb=average permeability

so Ka/Kb= 3:1

ans-2) porosity= Vb-Vg/Vb

now Vb=Vg+Vp

where Vg=grain volume

Vp=pore volume

Vb=bulk volume

layer A=Vg=3Vp

layer B=Vg=5Vp

Vb=Vg+Vp=4Vg/3 (for layer A)

layer B, 6Vg/5

pororsity (A)= 1/4 (from formula given above)

porosity (B)=1/6

average porosity=0.208