Method of drilling a wellbore

A method of drilling a wellbore in an earth formation, the method comprising:

• a) arranging a drill string and an expandable tubular element in the wellbore whereby a lower end portion of the wall of the tubular element extends radially outward and in an axially reverse direction so as to form an expanded tubular section extending around a remaining tubular section of the tubular element, wherein the drill string extends through the remaining tubular section;
• b) axially extending the expanded tubular section by moving the remaining tubular section downward relative to the expanded tubular section so that said lower end portion of the wall bends radially outward and in an axially reverse direction, wherein the expanded tubular section covers the wellbore wall in an upper portion of the wellbore;
• c) operating the drill string so as to drill a lower portion of the wellbore, wherein a drilling fluid is pumped into an open-hole wellbore portion via the drill string and is discharged to surface via an annular space between the drill string and the remaining tubular section;
• and
• d) transferring a compound from a layer of the earth formation surrounding the lower portion of the wellbore into the lower portion of the wellbore, wherein the method further comprises measuring a characteristic relating to said compound.