Method and system for wireline intervention in a subsea well from a floating vessel

A method for wireline intervention in an subsea well from a floating vessel(4) comprises: a) arranging a tubular tool riser(1) in a substantially horizontal position at a deck(4A) of the vessel(4); b) connecting a wireline assembly(7A) to a wireline(7) that is connected to a winch(7B)at the deck (4A); c) inserting the wireline assembly(7A) into the tool riser (1) such that the wireline (7) passes along a riser sheave(8) connected to a first end(1A) of the tool riser(1); d) connecting the first end(1A) of the tool riser(1) to a crane hook(2) that lifts the tool riser(1)in an upright position above a guide sleeve(5)that is connected to a side wall(4B) of the vessel(4) adjacent to the deck(4A); f) inducing the crane to lower the tool riser (1) through the guide sleeve(5) such that the second end(1B) of the tool riser(1) is located subsea and the first end(1A) of the tool riser(1) and the riser sheave(8) are located above the deck(4A); and g) inducing a crane heave compensation mechanism to control the motion of the tool riser(1) and riser sheave(8) relative to the seafloor while unreeling the wireline(7) from the winch(7B) such that the wireline assembly(7A) is lowered from the tool riser(1) through the water 11 into an subsea well.