METHOD AND SYSTEM FOR DRILLING WITH REDUCED SURFACE PRESSURE

摘要

A drilling method includes arranging a dual drill string (20) having an inlet fluid conduit (9) and a return fluid conduit (10) in a well (14) formed in a subsurface formation such that a well annulus (22) is formed between the dual drill string (20) and a wall (21) of the well (14). A divider element (3) is disposed in the well annulus (22) to divide the well annulus (22) into an upper annular region (5) extending above the divider element (3) to a surface of the well annulus (22) and a lower annular region (12) extending below the divider element (3) towards a bottom of the well annulus (22). The lower annular region (12) contains a first fluid (25). A second fluid (27) is fed into the upper annular region (5). The method includes configuring the second fluid such that the density of the second fluid (27) is greater than the density of the first fluid (25).