The reduction in reservoir pressure may tend to draw up underlying water towards the well in a cone like shape if an oil well is produced at excessive rates. Like-wise gas can be drawn downwards from an overlying gas cap.
see water coning. 
The upward angular displacement of the rotor blades of a gyroplane or helicopter under the influence of lift. The Coning Angle is the angle between the rotor blades and the plane normal to the axis of the hub.