Patent ID: 8201634

Claim:
A subsea cementing system, the system comprising: a launching mandrel positioned within a casing string; a top plug having at least one wiper and a central bore, the top plug being releasably connected to the launching mandrel; a bottom plug having at least one wiper and a central bore, the bottom plug being releasably connected to the top plug; a lower dart including a central bore that is selectively closed by a rupture member, wherein the lower dart is adapted to engage and seal the central bore of the bottom plug, wherein a first increase in pressure releases the bottom plug and dart from the top plug, the bottom plug and lower dart collectively forming a moveable fluid barrier in the casing string, wherein the bottom plug is adapted to land on a landing device in the casing string and a second increase in pressure breaks the rupture disc; an upper dart including a central bore and an inner sealing member selectively retained within the central bore of the upper dart, wherein the upper dart is adapted to engage and seal the central bore of the top plug, wherein a third increase in pressure releases the top plug and upper dart from the launching mandrel, the top plug and upper dart collectively forming a moveable fluid barrier in the casing string, wherein the top plug is adapted to land on the bottom plug and a fourth increase in pressure releases the inner sealing member from the central bore of the upper dart; and wherein the released inner sealing member is adapted to seal the central bore of the bottom plug.