in accordance with the present invention , a plurality of methods and devices are provided for solving important and serious problems posed by lateral completion in a wellbore including methods and devices for isolating a lateral well from other lateral branches in a multilateral well so as to prevent migration of fluids and to comply with regulations regarding the separate production of different production zones . various methods and devices are provided for fluid isolation of a lateral well from other lateral wells and for separate production from a lateral well without commingling the production fluids . these methods include the use of a side pocket mandrel , whipstocks with sealable bores and valving techniques wherein valves are located at the surface or downhole at the junction of a particular lateral .