Patent ID: 9506305
Filing Date: 2016-11-29
CPC Classification: E21B

Claim Text:
1. A method of drilling a subterranean wellbore using a drill string, including the steps of: estimating or determining a reduced static density of a drilling fluid based on the equivalent circulating density of the drilling fluid in a section of the wellbore; providing a drilling fluid having substantially that reduced static density; introducing the drilling fluid having said reduced static density into the wellbore; using a tubular riser to form a substantially annular space around the drill string; using a sealing device to seal the annular space so as to form a first section of the tubular riser below the sealing device having a first annular space, and a second section of the tubular riser above the sealing device having a second annular space, such that a substantially fluid tight seal is formed between the first and second annular spaces, wherein a top end of the first section of the tubular riser has a first side outlet which is connected to a first end of a return line, a second end of the return line being connected to surface control equipment comprising at least one of a managed pressure device and a riser gas handling device, and a second side outlet which is connected to a first end of a flow line and a second end of which is connected to a side outlet situated at a bottom end of the second section of the tubular riser, there being a valve provided for opening and closing the flow line; and removing the drilling fluid from the wellbore via the return line.