# US 2014/0190751 A1 · Method and System for Drilling with Reduced Surface Pressure > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0190751 A1 - Document ID: US20140190751A1 - Status: Published application - Kind: A1 - Application number: 14/240,736 - Filed: 2012-08-22 - Published: 2014-07-10 - Earliest claimed: 2011-08-31 - Assignees: Reelwell AS - Inventors: Ola M. Vestavik - Web page: https://patentgrep.com/patent/US20140190751A1 ## CPC - E21B 7/00: Special methods or apparatus for drilling - E21B 17/18: Pipes provided with plural fluid passages {(E21B17/203 takes precedence)} - E21B 17/203: {with plural fluid passages} - E21B 21/082: {Dual gradient systems, i.e. using two hydrostatic gradients or drilling fluid densities} - E21B 21/12: using drilling pipes with plural fluid passages, e.g. closed circulation systems - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS ## Abstract 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). ## Claims ### Claim 1 A drilling method, comprising: arranging a dual drill string having one inlet fluid conduit and one return fluid conduit in a well drilled in a formation such that a well annulus is formed between the dual drill string and a wall of the well; disposing a divider element in the well annulus to divide the well annulus into an upper annular region , extending above the divider element, to a surface of the well annulus and a lower annular region extending below the divider element towards the bottom of the well annulus, the lower annular region containing a first fluid having a first density; and feeding a second fluid having a second density into the upper annular region, the feeding comprising configuring the second fluid such that the second density is greater than the first density. ### Claim 2 (depends on 1) A method according to claim 1, wherein at least a portion of the first fluid is fluid from the formation. ### Claim 3 (depends on 1) A method according to claim 1, further comprising providing the second fluid as an unpressurized fluid. ### Claim 4 (depends on 1) A method according to claim 1, further comprising measuring pressure at or near at least one of an upper surface of the divider element exposed to the upper annular region and a lower surface of the divider element exposed to the lower annular region. ### Claim 5 (depends on 1) A method according to claim 1, further comprising using the measured pressure to selectively adjust the second density such that the second density remains greater than the first density during drilling of the well. ### Claim 6 (depends on 1) A method according to claim 1, further comprising arranging a rotating control unit near the surface of the well annulus, wherein pressure acting on the rotating control unit is determined by pressure in the well and density of fluid in the well annulus. ### Claim 7 A drilling system comprising: a dual drill string arranged in a well formed in a formation such that a well annulus, is formed between the dual drill string and a wall of the well, the dual drill string having one inlet fluid conduit and one return fluid conduit; a divider element arranged in the well annulus, to divide the well annulus into an upper annular region extending above the divider element to a surface of the well annulus and a lower annular region below the divider element towards a bottom of the well annulus, the lower annular region containing a first fluid having a first density; and a second fluid having a second density disposed in the upper annular region, the second fluid being configured such that the second density is greater than the first density. ### Claim 8 (depends on 7) A drilling system according to claim 7, further comprising a fluid inlet through which the second fluid is fed into the upper annular region. ### Claim 9 (depends on 8) A drilling system according to claim 8, further comprising a rotating control unit arranged near the surface of the well annulus the rotating control unit being in communication with the fluid inlet. ### Claim 10 (depends on 9) A drilling system according to claim 9, further comprising a blowout preventer arranged near the surface of the well annulus in connection with the rotating control unit, the blowout preventer forming an upper boundary of the upper annular region. ### Claim 11 (depends on 7) A drilling system according to claim 7, further comprising means for measuring pressure at or near a lower surface of the divider element exposed to the lower annular region. ### Claim 12 (depends on 7) A drilling system according to claim 7, further comprising means for measuring pressure at or near an upper surface of the divider element exposed to the upper annular region. ### Claim 13 (depends on 7) A drilling system according to claim 7, wherein the divider element is a piston. ### Claim 14 (depends on 7) A drilling system according to claim 7, wherein the divider element is fixed to the dual drill string. ### Claim 15 (depends on 7) A drilling system according to claim 7, wherein the divider element is movable relative to the dual drill string ### Claim 16 (depends on 7) A drilling system according to claim 7, wherein the two fluid conduits of the dual drill string are concentric. ### Claim 17 (depends on 7) A drilling system according to claim 7, wherein at least a portion of the first fluid is fluid from the formation. ### Claim 18 (depends on 7) A drilling system according to claim 7, wherein the second fluid is unpressurized.