Patent ID: 6843331

Claim:
A method employed at the surface in a well drilling system for varying the density of fluid in a tubular member located below the seabed, said method comprising the steps of: (a) introducing at the surface a first fluid having a first predetermined density into a drill tube, said first fluid being released from the drill tube and into the tubular member; (b) introducing a second fluid having a second predetermined density into the tubular member at a location below the seabed for producing a combination fluid having a predetermined density that is defined by a selected ratio of the first fluid and the second fluid, the fluid introduced through an insertion apparatus attached to the top of the tubular member, there being included a charging line running from the surface to the insertion apparatus, wherein the second fluid is released into the charging line and pumped downward through the charging line and into the tubular member via the insertion apparatus, said combination fluid rising to the surface; and (c) separating the combination fluid after it has risen to the surface into the first fluid and the second fluid and storing the first fluid and second fluid in separate storage units at the surface.