Patent ID: 8322460
Filing Date: 2012-12-04
Classification: E21B

Abstract:
1. A system for lifting drilling fluid from a well bore in a formation, comprising: a drilling riser extending from a drilling structure; a drill string suspended within the drilling riser and adapted to form at least a portion of the well bore; a drilling fluid source for supplying drilling fluid through the drill string, the drilling fluid exiting from the drill string during drilling and returning up an annulus between the drilling riser and the drill string; a return line; a diverter spool positioned between the well bore and the return line, the diverter spool configured to selectably divert drilling fluid from the annulus into the return line; a power riser coupled to the return line at an interface positioned along the return line, wherein the interface is configured to prevent the drilling fluid inside the return line from flowing into the power riser; wherein the return line has a first section extending from the diverter spool to the interface and a second section extending from the interface; wherein the interface comprises a valve with a lift fluid inlet in fluid communication with the power riser, a drilling fluid inlet in fluid communication with the first section of the return line, and an outlet in fluid communication with the second section of the return line; wherein the valve has a first position with the outlet in fluid communication with the drilling fluid inlet and a second position with the outlet in fluid communication with the lift fluid inlet; wherein the valve is configured to continuously and repeatedly alternate between the first position and the second position; and a lift fluid source for supplying lift fluid through the power riser into the return line, wherein the lift fluid is injected from the power riser through the interface into the return line; wherein a combined density of lift fluid and drilling fluid in the return line is less than the density of the drilling fluid alone.