An Introduction to Dilution-Based Dual Gradient (DBDG) Drilling

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1 An Introduction to Dilution-Based Dual Gradient (DBDG) Drilling Presented at the 2011 IADC Dual Gradient Workshop, 5 May 2011 by Paul Boudreau, Dual Gradient Systems LLC

2 How is a Dual Gradient Achieved with the DBDG Process? Heavier downhole mud weight is pumped down drillstring, through bit, and into annulus. At injection point (i.e., usually bottom of riser), a lighter density dilution mud is injected into annulus at a fixed dilution ratio. Downhole and dilution muds combine at injection point, resulting in column of diluted mud weight above injection point. Diluted mud is returned to rig and, in a continuous process, separated by specialized centrifuges back into downhole and dilution mud weight components. 2

3 Simplified DBDG Circulating Process Surface Diluted Mud Riser SHAKERS CENTRIFUGE SEPARATION Heavy Weight Discharge Injection Point Dilution Mud Boost Line Light Weight Discharge Annulus below Wellhead Downhole, Dilution, and Diluted muds are all the same fluid, only with varying concentrations of barite. Downhole Mud Drillstring 3

4 How Do Dilution-based and Pumpbased Dual Gradient Systems Differ? Dilution-based Dual Gradient (DBDG) Pump-based Dual Gradient (PBDG) Well Design Fewer casing strings compared to single gradient design. Casing points may vary between DBDG and PBDG based on respective pressure profiles. Wellhead Hydrostatic Pressure Diluted Riser Mud Hydrostatic Usually Seawater Hydrostatic Location of Inflection (Injection) Point At seafloor, or potentially sub-mudline At seafloor Location of Complex Componentry At surface At seafloor 4

5 Basic Dual Gradient Concept Pressures and Gradients PBDG: Inflection point at seafloor To achieve 12.5ppg equivalent mud weight at 20,000ft, the PBDG system would require a 16.5ppg mud below the seabed (at 10,000ft), with seawater hydrostatic at the wellhead. 5

5ppg equivalent mud weight at 20,000ft, the DBDG system could use a 14.

6 Basic Dual Gradient Concept Pressures and Gradients DBDG: Inflection (injection) point at seafloor To achieve 12.5ppg equivalent mud weight at 20,000ft, the DBDG system could use a 14.5ppg mud below the wellhead (at 10,000ft), with a diluted 10.5ppg mud weight in the riser above the wellhead. 6

Dual Gradient Concept with Sub-Mudline Injection Pressures and Gradients DBDG w/ SMLI: Inflection (injection) point moved, e.g., to surface casing shoe To achieve 12.

7 Dual Gradient Concept with Sub-Mudline Injection Pressures and Gradients DBDG w/ SMLI: Inflection (injection) point moved, e.g., to surface casing shoe To achieve 12.5ppg equivalent mud weight at 20,000ft, the DBDG system could use a 16.5ppg mud below the sub-mudline injection point (at 13,300ft), with a diluted 10.5ppg mud weight above the injection point. 7

8 DBDG vs. Single Gradient Well Design Well Design Considerations Not all casing seats determined solely by PP/FG/MW inter-relationship. Isolation of stray hydrocarbon zones. Maintaining adequate kick tolerance. Maintaining multiple barriers between reservoir and the world. Contingency planning. Completions design. 8

9 DBDG vs. PBDG Well Design 9

10 DBDG vs. PBDG Well Design Depleted Sand 10

11 DBDG w/ SMLI vs. DBDG Well Design 11

12 DBDG Circulating System Using Surface BOP Stack (Not Shown) DRILLSTRING DEGASSER SHALE SHAKERS INJECTION STRING CENTRIFUGES MUD PITS MUD PITS MUD PITS MUD PUMPS DILUTION MUD = LIGHT WEIGHT DISCHARGE FLOW STOP VALVE DOWNHOLE MUD = HEAVY WEIGHT DISCHARGE DILUTED MUD = MIX MUD = FEED MUD 12

13 DBDG Circulating System Using Subsea BOP Stack DRILLSTRING DEGASSER SHALE SHAKERS BOOST LINE MARINE RISER CENTRIFUGES CHOKE LINE KILL LINE SUBSEA BOP MUD PITS MUD PITS MUD PITS MUD PUMPS DILUTION MUD = LIGHT WEIGHT DISCHARGE FLOW STOP VALVE DOWNHOLE MUD = HEAVY WEIGHT DISCHARGE DILUTED MUD = RISER MIX MUD = FEED MUD 13

14 CAPM (Continuous Annular Pressure Management) System 14

15 CAPM Circulating System DRILLSTRING PDP PDIL CONVENTIONAL FLOWLINE PRCD ROTATING CONTROL DEVICE SHALE SHAKERS INNER RISER DRILLING CHOKE MANIFOLD CORIOLIS FLOWMETER DEGASSER MARINE RISER PCHOKE PRISER BOOSTER LINE CENTRIFUGES CHOKE LINE KILL LINE MUD PITS MUD PITS MUD PITS PBOP SUBSEA BOP MUD PUMPS FLOW STOP VALVE PPWD DILUTION MUD = LIGHT WEIGHT DISCHARGE DOWNHOLE MUD = HEAVY WEIGHT DISCHARGE DILUTED MUD = RISER MIX MUD = FEED MUD 15

16 Customized DBDG Centrifuge 16

17 Customized DBDG Centrifuge 17

18 DGS / TO Centrifuge Testing Flottweg Centrifuge Testing Results SOBM Drilling Fluid G Force, in/sec 2 Feed Rate, gpm Diluted Feed MW, ppg Downhole Heavy MW, ppg Dilution Light MW, ppg Dilution Rate, Q Light / Q Heavy Min - Ave - Max 90/10 OWR /19 OWR, no LCM 81/19 OWR, w/ LCM Downhole, Dilution, and Diluted muds are all the same fluid, only with varying concentrations of barite. 18

19 DGS Flow Stop Valve 19

20 Dual Gradient Drilling FSV U-Tube Arrested with Pumps Off Upstream - Drillstring with Downhole Mud Downstream - BHA and Drill Bit U-tube Pressure Resisted by Spring Forces 20

21 Dual Gradient Drilling FSV Bringing on Pumps Through Choke Pump Pressure + U-Tube Overcome Spring Force Flow is Restricted to Provide Main Piston Opening Pressure 21

22 Dual Gradient Drilling FSV Main Valve Opened for Normal Drilling Choke is Bypassed once Main Valve Opens 22

23 Dual Gradient Drilling FSV Valve Closes Once Pumps Off Upstream - Drillstring with Downhole Mud Downstream - BHA and Drill Bit 23

24 Thank You

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