A downhole oilfield tool assembly, comprising: a mandrel (110, 130, 140, 150); a valve comprising a flapper and a setting sleeve, wherein the flapper is oriented to block downwards flow through the mandrel (110,130,140,150) in a closed position; and a first piston located above the valve and positioned at least partly around an outside of the mandrel, wherein the first piston is configured to develop motive force from a pressure differential between an interior of the mandrel and an exterior of the downhole oilfield tool assembly when the flapper is in the closed position; characterised in that the valve further comprises: a collet mandrel rotatably disposed concentric with the mandrel (110,130,140,150), wherein the collet mandrel comprises first collet mandrel teeth and second collet mandrel teeth, a collet prop, wherein the collet prop comprises collet prop teeth, and a flapper prop, wherein the flapper prop comprises flapper prop teeth, wherein the first collet mandrel teeth interact with collet prop teeth to provide a first rotational position of the collet mandrel relative to the collet prop in which the second collet mandrel teeth engage with the flapper prop teeth to hold the flapper in an open position, and a second rotational position of the collet mandrel relative to the collet prop in which the second collet mandrel teeth rotate out of alignment with the flapper prop teeth to allow the flapper prop to translate axially under the force of a spring and transition the flapper to the closed position. a mandrel (110, 130, 140, 150); a valve comprising a flapper and a setting sleeve, wherein the flapper is oriented to block downwards flow through the mandrel (110,130,140,150) in a closed position; and a first piston located above the valve and positioned at least partly around an outside of the mandrel, wherein the first piston is configured to develop motive force from a pressure differential between an interior of the mandrel and an exterior of the downhole oilfield tool assembly when the flapper is in the closed position; characterised in that the valve further comprises: a collet mandrel rotatably disposed concentric with the mandrel (110,130,140,150), wherein the collet mandrel comprises first collet mandrel teeth and second collet mandrel teeth, a collet prop, wherein the collet prop comprises collet prop teeth, and a flapper prop, wherein the flapper prop comprises flapper prop teeth, wherein the first collet mandrel teeth interact with collet prop teeth to provide a first rotational position of the collet mandrel relative to the collet prop in which the second collet mandrel teeth engage with the flapper prop teeth to hold the flapper in an open position, and a second rotational position of the collet mandrel relative to the collet prop in which the second collet mandrel teeth rotate out of alignment with the flapper prop teeth to allow the flapper prop to translate axially under the force of a spring and transition the flapper to the closed position. a collet mandrel rotatably disposed concentric with the mandrel (110,130,140,150), wherein the collet mandrel comprises first collet mandrel teeth and second collet mandrel teeth, a collet prop, wherein the collet prop comprises collet prop teeth, and a flapper prop, wherein the flapper prop comprises flapper prop teeth, wherein the first collet mandrel teeth interact with collet prop teeth to provide a first rotational position of the collet mandrel relative to the collet prop in which the second collet mandrel teeth engage with the flapper prop teeth to hold the flapper in an open position, and a second rotational position of the collet mandrel relative to the collet prop in which the second collet mandrel teeth rotate out of alignment with the flapper prop teeth to allow the flapper prop to translate axially under the force of a spring and transition the flapper to the closed position.