Patent ID: 9222311
Filing Date: 2015-12-29
Classification: E21B

Abstract:
1. A system for drilling subsea wells from a Mobile Offshore Drilling Unit (MODU), comprising; a marine drilling riser extending from the MODU to a seabed located Blow Out Preventer (BOP); a drill string extending from the MODU through the marine drilling riser and BOP and further down a wellbore, an annulus being formed between the drill string and the drilling riser, and between the drill string and the wellbore, said annulus being filled with drilling mud to a low mud level where an interface is formed between the drilling mud and either gas or liquid that extends in the annulus above the drilling mud; at least one closing devise located either in the marine drilling riser, integral with the BOP, or in a high pressure part of the system below the BOP, the closing device being adapted to close the annulus; at least one mud return outlet and mud conduit fluidly connected to the annulus either at a lower part of the marine drilling riser or below the drilling riser, said mud return outlet and mud conduit being connected to the annulus at a level below the low mud level and above said closing device, said mud return outlet and mud conduit being adapted to enable drilling mud to flow from the annulus to a subsea lift pump, said subsea lift pump being adapted to pump the drilling mud from the annulus to a location above sea level; a gas separator for separating gas from the drilling mud, said gas separator being coupled to said mud conduit; a well pressure regulator for dynamic regulation of pressure in the annulus, said well pressure regulator being coupled to said mud conduit; and a well flow outlet from the annulus below said closing device, said well flow outlet being connected to a well flow inlet into the annulus within the marine drilling riser above the at least one mud return outlet.