Measuring behind casing hydraulic conductivity between reservoir layers

A measure of the hydraulic conductivity, FC, is obtained to characterize the leaky medium behind well casing between adjacent hydrocarbon producing layers is a subsurface reservoir. The value of FC can be utilized in estimating the rate of flow from a secondary reservoir layer contributing to the total production through the wellbore based on the respective well pressures at a given time. The well pressures are calculated from a model based on the individual properties of and the amounts of fluid produced from these layers. Once there is a reasonable match between the calculated pressures and the measured pressures during a transient test, the parameters that have been used in calculating the model pressures are stored as characteristic parameters of the reservoir system. Such characteristic parameters are utilized in assessing the commercial producibility of the reservoirs.