Determination of Individual Layer Properties by Layer-by-Layer Well Tests in Multilayer Reservoirs with Crossflow

An interpretation theory is given for drawdown and buildup tests, which are given to an individual layer of a multilayer reservoir with crossflow. The crossflow behavior and its influence on drawdown and buildup curves are discussed. It is found that both drawdown and buildup curves have two straight lines with a transition period between them. The first straight line corresponds to the period when the well test theory for a single-layered reservoir is effective for an individual-layer test in a multilayer reservoir with crossflow. The first straight line determines the kh product and the skin factor of the test layer. The second straight line determines the total kh product of the reservoir. The vertical permeabilities of the shales between layers can be determined by three analytical methods, using the crosspoint of the two straight lines of drawdown or buildup curves, the steady wellbore pressure differences between the test layer and the closed layers, and the wellbore pressure in the early transition period respectively. The last method can considerably decrease the test time for drawdown.