Patent ID: 9328574
Filing Date: 2016-05-03
CPC Classification: E21B

Claim Text:
1. A method comprising: characterizing a subsurface formation using a fluid pressure response during wellbore drilling operations, wherein characterizing the subsurface formation comprises: determining a change in volumetric flow rate out of the wellbore and determining a downhole fluid pressure in the wellbore while inducing a change in wellbore pressure proximate a surface of the Earth by lowering an annulus pressure during drilling; determining a productivity index value as a function of the determined change in volumetric flow rate, the determined downhole fluid pressure, and a reservoir pressure; and calculating, after determining the productivity index value, a subsequent change in volumetric flow rate out of the wellbore as a function of the productivity index value, the reservoir pressure, and another downhole fluid pressure determined during drilling.