A method of zonal isolation of a horizontal well

A method of zonal isolation of a horizontal well including running a tubing string 2, a cable 3, upper 4 and lower 5 control devices in the form of electrical valves 6, sensors for measuring pressure and/.or temperature 7, 8, and one or more packers 9. Packers are installed in a horizontal section of the well to isolate various permeability zones A, B, and the tubing interior is isolated with a plug 17, above which are the control devices in a vertical part of the well. Zones of the same or approximately the same permeability are connected to form two streams, the streams communicate with the downhole space and inlet 23 of the upper control device or the tubing interior and inlet 19 of the lower control device. The degree to which the valves are opened is determined by data from the sensors. Zones with the same permeability may be broken in two groups which are connected using conduits 26, 27.