METHOD FOR DETECTING A LEAK IN A DRILL STRING VALVE

A method for detecting a leak in a drill string valve used when drilling a subsea well. The method comprises measuring a first inlet pressure at a subsea mudlift pump while a subsea mudlift pump and a surface pump are operating and before a well is fully shut-in and measuring a second inlet pressure at the subsea mudlift pump after the mudlift pump and the surface pump are shut down and after the well is fully shut-in. The first and second subsea mudlift pump inlet pressure measurements are then compared, and a check is performed to determine if the subsea mudlift pump inlet pressure has increased by an amount greater than an estimated annular friction pressure.