travel from formation 20 to the surface and for injection fluids to travel from the surface to formation 20 at its lower end tubing string 22 is coupled to a completions string that has been installed in wellbore 12 and divides the completion interval into various production intervals adjacent to formation 20 the completion string includes a plurality of sand control screens 24 each of which is positioned between a pair of annular barriers depicted as packers 26 that provides a fluid seal between the completion string and wellbore 12 thereby defining the production intervals tubing string 22 may include a variety of tools such as packer 28 that provides a seal between tubing string 22 and casing string 16 an annulus 30 is defined between tubing string 22 and casing string 16 above packer 28 as discussed above during drilling and completions operations a weighted column of fluid is usually present in the wellbore 12 to exert hydrostatic pressure on formation 20 sufficient to prevent uncontrolled flow of fluid from formation 20 into wellbore 12 to enable production however the weighted column of fluid must be removed from wellbore 12 in the illustrated embodiment a circulating valve 32 is positioned within tubing string 22 above packer 28 and may be operated via a slickline or wireline deployed rotating tool depicted as downhole power unit 34 circulating valve 32 serves the primary purpose of selectively permitting fluid flow between the interior of tubing string 22 and annulus 30 for example when it is desired to remove the weighted.