Formation testing in managed pressure drilling

A method of testing an earth formation, the method comprising:

• drilling into the formation, with an annulus between a drill string and a wellbore being pressure isolated from atmosphere;
• ceasing circulation of drilling fluid into the wellbore;
• then incrementally opening a choke, thereby reducing pressure in the wellbore;
• then detecting an influx into the wellbore due to the reduced pressure in the wellbore while circulation is ceased;
• and
• determining approximate formation pore pressure as pressure in the wellbore when the influx is detected.

A method of testing an earth formation, the method comprising:

• drilling into the formation, with an annulus between a drill string and a wellbore being pressure isolated from atmosphere;
• circulating drilling fluid into the wellbore;
• then ceasing drilling the wellbore and ceasing circulation of drilling fluid into the wellbore;
• then incrementally opening a choke while drilling is ceased, thereby reducing pressure in the wellbore;
• detecting an influx into the wellbore due to the reducing pressure in the wellbore;
• and
• determining approximate formation pore pressure as pressure in the wellbore when the influx is detected.