Autonomous inflow control device

A technique facilitates improved control over inflowing fluids with respect to, for example, a screen assembly or screen assemblies of a tubing string deployed in a wellbore. The improved control may be provided by at least one inflow control device comprising a housing defining a chamber having a first end and a second end through which fluid may flow. Additionally, the inflow control device comprises at least one inlet passage disposed at the first end and having a contour which provides a desired effect on the inflowing fluid according to the type of fluid, e.g. according to the viscosity of the fluid. The contour may comprise an expanding cross-sectional area, e.g. a cone or other expanding shape. In some embodiments, the entrance of the inlet passage may have a rounded edge to, for example, create an initially decreasing and then increasing cross-sectional area along the inlet passage.