The present invention provides a method of isolating a selected reservoir zone in a subterranean reservoir comprising at least the step of squeezing a treatment fluid into the selected reservoir zone, the treatment fluid comprising: a viscosifying agent; a fluid loss control agent; and a particulate material. The invention further provides a treatment fluid comprising a base fluid; a viscosifying agent; at least 20 kg/m3 of a fluid loss control agent; and a particulate material.