are effectively circular however this is not required the more advanced formation testers have pad and snorkel assemblies that will pivot and tilt so that the tester will provide a better seal to the formation conventional prior art snorkel designs have a flat surface so that the edges of the snorkel rest on the curved surface of the wellbore this leaves a gap between the snorkel and the wellbore that is at a maximum in a plane orthogonal to the initial contact between the snorkel and the wellbore in various embodiments described below the interface surface of the snorkel is formed with a cylindrical geometry to minimize the extrusion gap between the snorkel and the wellbore the snorkel may be configured to prevent rotation of the snorkel to ensure that the cylindrical geometry is correctly oriented with the wellbore surface fig1 and 5 are orthogonal cross section views of a snorkel 110 according to one embodiment fig1 is a cross section view along line b b of fig5 while fig5 is a cross sectional view along line a a of fig1 for purposes of clarity only the snorkel 110 of the formation tester tool is illustrated in fig1 and 5 as illustrated in fig1 the snorkel 110 has been extended from piston cylinder 120 through the pad 116 shown in phantom to make contact with surface 102 of the borehole formed in formation 100 a screen 114 is preferably threaded into the body 118 of the snorkel to screen cuttings or other solid matter from entering the snorkel 110 other common elements of a snorkel such as a mud plug.