Patent ID: 7992655
Filing Date: 2011-08-09
Classification: E21B

Abstract:
1. A system in well drilling operations for controlling the density of a drilling fluid in a wellbore extending into the earth from a top end adjacent the surface, said system comprising: a first rotatable tubular member having a top end and a bottom end, the top end of said first tubular member extending adjacent to or above the top end of the wellbore, the bottom end of said first tubular member being located in the wellbore, said first tubular member having a predetermined outer diameter; a second tubular member having a top end and a bottom end, the top end of said second tubular member being located adjacent to or above the top end of the wellbore and the bottom end of said second tubular member being located in the wellbore, said second tubular member having a predetermined inner diameter which is greater than the outer diameter of the first tubular member, said second tubular member being arranged such that the first tubular member is rotatingly disposed within at least a portion of the second tubular member to define a first annular space between the outer diameter of the first tubular member and the inner diameter of the second tubular member; a third tubular member having a top end and a bottom end, the top end of said third tubular member being located adjacent to said drilling rig and the bottom end of said third tubular member extending to at least the top of said wellbore so as to be in fluid communication with said wellbore, said third tubular member having an inner diameter which is greater than the outer diameter of the second tubular member, said third tubular member being arranged such that the first tubular member passes through at least a portion of said third tubular member and such that the second tubular member is disposed within at least a portion of the third tubular member to define a second annular space between the outer diameter of the second tubular member and the inner diameter of the third tubular member; a drilling device connected to the bottom end of the first tubular member; a first blowout preventer adjacent the top end of the wellbore and through which the first and second tubular members pass; a drilling fluid having a predetermined density disposed in said first tubular member; a base fluid having a predetermined density different than the predetermined density of the drilling fluid wherein the base fluid is disposed in one of the annular spaces selected from the group consisting of the first annular space and the second annular space; and a combination fluid comprised of the base fluid and the drilling fluid wherein the combination fluid is disposed in one of the annular spaces not occupied by the base fluid, wherein said second and third tubular members are substantially fixed relative to said first rotatable tubular member.