be substantially vertical additionally it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations such as inclined inverted horizontal vertical etc and in various configurations without departing from the principles of the present invention referring now to fig1 the method 10 is described herein as being performed at a wellbore junction 16 formed by an intersection between a main wellbore 12 and a branch wellbore 14 the wellbores 12 14 are depicted in fig1 as being cased or lined but it is to be clearly understood that the principles of the invention may be incorporated into other methods performed in uncased or unlined wellbores furthermore the principles of the invention are not limited to wellbore junctions formed between main and branch wellbores as illustrated in fig1 the main wellbore 12 extends below the wellbore junction 16 to intersect a formation or zone 18 it is desired to perform a stimulation operation such as fracturing on the formation 18 to thereby increase production of hydrocarbons therefrom however it is also desired not to apply excessive internal pressure to the wellbore junction 16 of course the principles of the invention may be incorporated into other methods in which it is not desired to produce hydrocarbons from a formation or in which it is not desired to perform stimulation operations referring additionally now to fig2 a somewhat enlarged view of the wellbores 12 14 and the junction 16 therebetween is representatively illustrated further steps of the method 10 have been performed in which a wellbore isolation assembly 20 is installed in the main wellbore 12 in a single.