A New Test for Determination of Individual Layer Properties in a Multilayered Reservoir

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Abstract
Summary: Many wells penetrate several layers, and flow from each layer is often commingled during production or injection. The behavior of pressure transients for layered systems has been studied in detail for two types of systems: (1) layers that are separated by impermeable barriers (no formation crossflow) and (2) layers that communicate in the reservoir. In this work, the general problem of n homogeneous layers, in which any two adjacent flowing layers may or may not be crossflowing in the formation, is solved analytically. Properties, including permeability, porosity, layer thickness, the wellbore skin factor, and the vertical permeability between crossflowing layers, are distinct for each flowing layer. Wellbore storage effects are also included, and solutions are provided for both infinite-acting and bounded systems. The key to finding the individual layer properties in a given reservoir lies in the interpretation of the transient flow rates from each layer following a change of the total flow rate for the well. Pressure transients are also used in the analysis. The limiting forms of the analytic solution are used to identify certain characteristic patterns in the flow-rate transients that provide the means for determining the individual layer properties. The methods used in this analysis are entirely new. An example of the interpretation method is provided.