an annulus collar around a well production tube is cast in cement by a procedure that axially delineates the collar between two expandable well packers in the production tube string . between the packers are a pair of cementing valves . an ingress valve is most proximate to the lower packer whereas an egress valve is most proximate to the upper packer . additionally , the egress valve is modified to enclose the egress valve with a screen having mesh or slot openings that correspond with a screen plugging material that is mixed with the cement .