Method for uniquely estimating permeability and skin factor for at least two layers of a reservoir

Claim 1

A well test method for uniquely estimating permeability and skin factor for each of at least two layers of respective thicknesses, h 1 and h 2 , of a reservoir comprising the steps of, positioning a logging tool of a logging system in a wellbore traversing the two layers at the top of the upper layer, said logging system having means for measuring downhole fluid flow rate and pressure as a function of time, changing the surface flow rate from an initial flow rate at an initial time, t l , during a first time interval, measuring and recording the downhole fluid flow rate, q l (t), and downhole pressure, p l (t), during the first interval, t l to t 2 , at the top of the upper layer, positioning said logging tool to the top of the lower layer, measuring and recording the downhole flow rate, q 1 (t 3 ), at time, t 3 , from the top of the lower layer, changing the surface flow rate at time, t 3 , to another flow rate, measuring and recording the downhole fluid flow rate, q 22 (t), and downhole pressure, p 2 (t), during a second interval, t 3 to t 4 , at the top of the lower layer, determining functions and , where where k 1 = permeability of upper layer k 2 = permeability of lower layer by matching the measured change in downhole pressure, Δp 1 (t) = p 1 (t 1 ) - p 1 (t) , with the convolution of the measured fluid flow rate, q 1 (t), and an influence function, Δp sf (t), which is a function of combined-layered permeability, , and skin effect, , determining the permeability,k 2 , of the lower layer and the skin factor, s 2 , of the lower layer by matching the measured fluid flow rate, q 22 (t), with the convolution of the measured change in downhole pressure Δp 2 (t) = p 1 (t 3 ) - p 2 (t) and an influence function f (t) which is a function of the lower layer permeability, k 2 , and skin factor, s 2 , and determining k 1 and s 1 from estimates of k 2 , s2 and and .