Abstract: Ball sealers for flowing into casing perforation holes in a wellbore to selectively seal off those perforations receiving a disproportionately large amount of well treatment fluid being injected through the perforations. The ball sealers (22) are comprised of a spherical outer deformable shell (42) defining a central core portion filled with nondeformable particulate matter (46) which is sized small enough to flow with the shape of the deformable outer shell (42) and large enough so that as it consolidates under the force of fluid flow pressure, it will cause the outer shell to bridge over the perforation opening (18) when the force of fluid flowing into the casing (12) pushes the ball sealer (22) against and into the perforation opening (18).

Abstract: A perforating-gun spacer used to position a plurality of guns to perforate a multizone reservoir is formed of a plurality of telescoping sections which are held in an extended position by tapered pins. A slidable piston maintains the pins in engaged position. When the perforating guns are fired, the resultant pressure pulse in the wellbore fluid moves the piston upwardly out of engagement with the restraining pins which then disengage permitting the telescoping sections to collapse when the expended tool is dropped into the bottom of the wellbore. This avoids partial or complte blockage of the lowermost production zone by the upper portion of the perforating gun string.