against the casing as weight is set on the tubing string the elastomeric packer 56 deforms into sealing engagement with the casing as shown in fig3 accordingly fluid communication between the casing annulus above and below the packer is prevented after sealing the casing the seal may be tested by injecting fluid under pressure at the surface into the annulus between tubing 12 and casing 14 check valve 126 prevents passage of the fluid in the annulus through bores 50 52 fig1 a into bore 46 and through conduit 32 thus if packer 56 has formed an effective seal there is no pressure drop in the annulus when pressure is applied thereto by way of fluid injection after testing the seal gravel packing of the screen may proceed a gravel slurry is injected into tubing 12 at the surface the slurry is a fluid which contains gravel suspended therein the slurry descends downwardly in tubing 12 through crossover 40 into the annulus between the outer surface of conduit 32 and the inner surface of conduit 30 mandrel 78 extends downwardly from conduit 30 and lower mandrel 88 extends downwardly from mandrel 78 each mandrel forming a continuous annulus about conduit 32 through which the slurry passes the slurry continues through a somewhat larger annulus formed between the outer surface of conduit 32 and the inner surface of casing 104 through the annulus between the outer surface of conduit 32 and the inner surface of bore 110 and out gravel packing ports 33 34 such flow is indicated by arrows in fig4 a and 4b the flow continues downwardly into hole 17 and through holes 124 in screen 22 as will be recalled the gravel is sized slightly larger than holes 124 as the flow continues gravel in the slurry is.