a method of preventing intrusion of fluid into a horizontal well bore . a quantity of liquid composition capable of gelling and containing a breaker is introduced into a horizontal well bore up to a point corresponding to the bottom of the intrusion zone . after the liquid composition gels into a temporary gel , a second liquid composition capable of gelling into a permanent gel is introduced into the zone to shut off fluid flow from the zone . the temporary gel prevents flow of the permanent gel into the horizontal well bore . thereafter the breaker in the temporary gel causes the gel to revert to a liquid , which is removed from the horizontal well bore upon production of the well .