Backup heave compensation system and lifting arrangement for a floating drilling vessel

A backup heave compensation system on a floating drilling vessel, the vessel comprising a rig structure for carrying out well operations in a subsea well, the rig structure comprising a primary heave compensation system operatively connected to a load-bearing structure capable of supporting a tubular structure connected between the floating drilling vessel and the subsea well, the backup heave compensation system comprising:

• a vertically extendable and retractable lifting arrangement structured for connection between the load-bearing structure and the tubular structure;
• a hydraulic system operatively connected to the lifting arrangement;
• and
• a control system operatively connected to the lifting arrangement and hydraulic system for selective control and operation thereof;
• the lifting arrangement comprising:
• a rigid frame structure comprised of:
• at least two vertically extending legs in the form of cylinders separated at a distance from each other;
• a first transverse element connecting first end portions of the cylinders;
• and a second transverse element connecting second end portions of the cylinders;
• and
• a portal structure comprised of:
• at least two vertically extending legs in the form of piston rods having first end portions provided each with a piston;
• and a transverse portal element rigidly connecting second end portions of the piston rods;
• wherein each piston of the portal structure is inserted into, and is movable within, a corresponding cylinder of the frame structure such that the transverse portal element moves in unison with the piston rods towards and away from the cylinders, thereby allowing the portal structure and the frame structure to be vertically movable with respect to one another, each cylinder and each piston defining a cylinder-piston arrangement;
• wherein the hydraulic system is connected to a high-pressure volume of each cylinder for selective hydraulic communication with the high-pressure volume and the piston;
• wherein the cylinders are connected to the control system;
• and
• wherein the control system is structured in a manner allowing it to selectively control and operate the cylinder-piston arrangement so as to compensate for heave movements of the floating drilling vessel should the primary heave compensation system become inoperative.