Abstract: A method and apparatus for maintaining the fluid column in an annulus are provided. The fluid column support, or fluid column seal is disposed about a second casing being lowered into a well through a first casing already cemented in the well. The fluid column support includes a seal connected to the second casing that engages the first casing as it is lowered therethrough. The seal will allow flow in an upward direction but prevents downward flow. The seal will support, or maintain a fluid column in the annulus between the first and second casing in the event that the fluid level below the seal drops for any reason, such as lost circulation or the failure of a buoyancy chamber in the second casing. The fluid seal, in conjunction with stage tools, provides hydrostatic pressure in the well to maintain proper fluid placement therein.

Abstract: Improved methods and apparatus for placing and cementing a casing string in a horizontal well bore section are provided. A float shoe is attached to the end of the casing string and a float collar is connected in the casing string for trapping air in a first portion of the casing string thereby causing it to be buoyed up during placement by drilling fluid contained in the well bore. A selectively openable and releasable closed baffle assembly is connected within the casing string for trapping air or a low density fluid in a second portion of the casing string thereby causing it to also be buoyed up by drilling fluid in the well bore. The buoying up of the casing string reduces placement drag and consequent compressive loading on the casing string. After placement, the closed baffle means is opened to allow fluid circulation and conditioning of the annulus. A bottom cementing plug is then landed on the baffle assembly and the baffle assembly is released and moved to the float collar.