Methods for forming a barrier around at least a portion of a treatment
area in a subsurface formation are described herein. Sulfur may be
introduced into one or more wellbores located inside a perimeter of a
treatment area in the formation having a permeability of at least 0.1
darcy. At least some of the sulfur is allowed to move towards portions of
the formation cooler than the melting point of sulfur to solidify the
sulfur in the formation to form the barrier.