A riser system in the form of a pumped riser, i.e. a riser having an outlet from the riser at a depth below the surface of a body of water, where the outlet is coupled to a return pump to return fluid from the riser to the surface, and various operational methods to facilitate greater versatility when performing hydrocarbon drilling related operations. A sealing element to seal an annulus of the riser, and a by-pass around the sealing element. Various methods make it possible to switch between open mode and closed mode, and vice versa, monitoring leakage across the sealing element, as well as performing other operations exploiting the advantages of the two different modes.

A riser system in the form of a pumped riser, i.e. a riser having an outlet from the riser at a depth below the surface of a body of water, where the outlet is coupled to a return pump to return fluid from the riser to the surface, and various operational methods to facilitate greater versatility when performing hydrocarbon drilling related operations. A sealing element to seal an annulus of the riser, and a by-pass around the sealing element. Various methods make it possible to switch between open mode and closed mode, and vice versa, monitoring leakage across the sealing element, as well as performing other operations exploiting the advantages of the two different modes.

A riser system in the form of a pumped riser, i.e. a riser having an outlet from the riser at a depth below the surface of a body of water, where the outlet is coupled to a return pump to return fluid from the riser to the surface, and various operational methods to facilitate greater versatility when performing hydrocarbon drilling related operations. A sealing element to seal an annulus of the riser, and a by-pass around the sealing element. Various methods make it possible to switch between open mode and closed mode, and vice versa, monitoring leakage across the sealing element, as well as performing other operations exploiting the advantages of the two different modes.