Abstract: A packer with a liner assembly depending from it is packed off and anchored in well casing so that a screen portion of the liner assembly straddles casing perforations within a producing formation. An outer tubing string is lowered through the well casing and engaged with the packer to isolate the formation from well fluids above the packer and to provide a passage to the surface for the formation fluids.A member having crossover fluid passages and external seals engageable with internal seal surfaces in the liner and packer is lowered through the outer tubing string into the liner and packer on an inner string. Fluid passages between the two strings, and between the two strings and the interior and exterior of the liner to control the flow of circulating, washing or acidizing fluids and for placement of gravel on the outside of the liner are selectively opened or closed by manipulation of the inner string.