Patent ID: 7650950

Claim:
In a drilling arrangement for drilling a well into a subterranean formation which includes, a tubular drill string ( 1 ) having an upper and lower end and with a drill bit ( 2 ) at its lower end, a drive mechanism arranged and designed to turn said drill bit ( 2 ) in a borehole where a borehole annulus ( 3 ) is defined between an outer diameter of said tubular drill string ( 1 ) and an inner diameter of said borehole, a drilling fluid pump ( 6 ) in fluid communication with a drilling fluid reservoir ( 5 ), a drilling fluid injection line ( 14 ) extending between said pump ( 6 ) and said upper end of said drill string ( 1 ) and providing fluid communication between said pump ( 6 ) and said drill string ( 1 ), a fluid return line ( 27 ) extending between an outlet of said borehole annulus ( 3 ) and said drilling fluid reservoir ( 5 ), a pressure containment device ( 26 ) arranged and designed to keep said borehole closed from the atmosphere at all times while said well is being drilled with said drill string ( 1 ) having drilling fluid circulating therethrough, said injection line ( 14 ), drill string ( 1 ), borehole annulus ( 3 ) and return line ( 27 ) defining a flow path, an output flow measurement device ( 10 , 11 ) in said fluid return line ( 27 ) arranged and designed to generate an actual drilling signal F outactual (t) representative of actual flow rate of fluid in said fluid return line ( 27 ) as a function of time (t), a pressure measurement device ( 9 , 17 , 24 ) disposed at a position in said flow path and arranged and designed for determining a downhole pressure signal P actual (t) as a function of time (t), a central data acquisition and control system ( 18 ) arranged and designed to receive at least one of said actual drilling signals, a method for determining the fracture pressure of said well at said depth, said method comprising the steps of, employing said central data acquisition and control system ( 18 ), having software responsive to said F outactual (t) signal and other drilling signals, to identify a loss event at a drilling time and depth of the well, and recording said P actual (t) signal at said drilling time as the fracture pressure of said formation at said depth.