Greater Kick Tolerance and Fewer Casing Strings Make Dual Gradient Drilling a Winner

1. Greater Kick Tolerance and Fewer Casing Strings Make Dual Gradient Drilling a Winner Schubert, J. J., Seland, S., Johansen, T. J., Juvkam-Wold, H. C. Well Control Conference of the Americas

2. Introduction • Problems Associated With Deepwater Drilling • Single Gradient vs. Dual Gradient Concept • Methodology • Results • Conclusions Well Control Conference of the Americas

3. Problems Associated With Deepwater Drilling • Longer, heavier marine risers requires • Larger drilling vessels w/ greater storage requirements • Large volume of mud just to fill the riser • Large forces imposed on the riser by currents • Large tension forces on the riser Well Control Conference of the Americas

4. Problems Associated With Deepwater Drilling • Narrowing of the Window between the Pore Pressure and Fracture Pressure • Increase in number of casing strings • Near elimination of kick tolerance Well Control Conference of the Americas

5. Single vs. Dual Gradient Concept Pressure, psi • Single Gradient Wells • Wellbore contains a single density fluid • Single pressure gradient • Dual Gradient Well • Wellbore feels seawater gradient to the seafloor, and mud gradient to bottom Seawater HSP Depth ft Seafloor @ 10,000’ 12.4 ppg mud 13.5 ppg mud 23,880 psi @ 37,500’ Well Control Conference of the Americas

6. Dual Gradient Achieved by: • Taking returns at the seafloor • Gas lift at the seafloor • Inject hollow gas spheres • Seafloor mud pumps Well Control Conference of the Americas

7. Assumptions • Water depth of 10,000’ • Total depth of 37,500’ • For dual gradient drilling: • annulus pressure at the seafloor is kept equal to seawater HSP during normal drilling operations • during kicks seafloor pressure adjusted to control BHP equal to formation pressure Well Control Conference of the Americas

8. Pore and Fracture Gradients Well Control Conference of the Americas

9. Methodology • Conventional Riser Drilling • Picked casing points graphically with with a 0.5 ppg stand off • Looked at the effect of 750 psi SIP • Looked at the effects of circulating pressures for both: • 0 bbls influx • 50 bbls influx Well Control Conference of the Americas

10. Methodology • Compared results to a dual gradient system: • Statically • Dynamically Well Control Conference of the Americas

11. Methodology • Dual Gradient System, we picked casing points: • Graphically (static wellbore pressures) • Dynamically: • 0 bbl influx • 50 bbl influx Well Control Conference of the Americas

12. Graphical Casing Seat Selection Well Control Conference of the Americas

13. Kick w/ 750 psi SIP Mud HSP (13.1 ppg) Mud HSP + 750 psi Formation has fractured Pore Pressure Fracture Pressure Well Control Conference of the Americas

14. Casing Seat Pressures Well Control Conference of the Americas

15. Static Pressure - Dual Gradients Mud HSP (15.5 ppg) Mud HSP = 750 psi Pore Pressure Fracture Pressure Well Control Conference of the Americas

16. Choke Pressures Well Control Conference of the Americas

17. Well Control Conference of the Americas

18. Well Control Conference of the Americas

19. Graphical Casing Seat Selection - Dual Density Well Control Conference of the Americas

20. Dynamic Casing Seat Selection Pressure, psi D e p t h ft. 1.0 ppg kick 0 bbl influx volume Well Control Conference of the Americas

21. Dynamic Casing Seat Selection 1.0 ppg kick 50 bbl influx volume Well Control Conference of the Americas

22. Conclusions • The narrow gap between pore pressure and fracture pressure results in excess number of casing strings for conventional riser drilling. • The large number of casing strings may result in such a small production string that high flow rates may not be possible. Well Control Conference of the Americas

23. Conclusions • The narrow gap between pore pressure and fracture pressure results in virtually no kick tolerance for conventionally drilled wells. • The dual gradient system drastically reduces the number of casing strings required to reach total depth. Well Control Conference of the Americas

24. Conclusions • The dual gradient system widens the gap between pore pressure and fracture pressure resulting in a much higher kick tolerance. • The higher kick tolerance increases the probability of a kick being killed successfully. Well Control Conference of the Americas

25. Conclusions • The dual gradient system will increase the probability of reaching the geologic objective in ultra-deep water. • Dual gradient drilling will allow large enough production casing to be able to install production tubing as large a 7” in diameter. Well Control Conference of the Americas

26. The End Well Control Conference of the Americas

27. 6000’ WD Well Control Conference of the Americas

28. 6000’ WD Well Control Conference of the Americas

29. 6000’ WD Well Control Conference of the Americas

30. 6000’ WD CONVENTIONAL SMD Kick Tolerance is Back 520 psi Underbalance from Kick Formation Intact 15.5 PPG MUD 15.5 ppg mud + 520 psi 18.4 ppg mud 18.4 ppg mud + 520 psi Formation has Fractured Well Control Conference of the Americas

31. Kick Tolerance Conventional SMD 30” @ 6300’ 20” @ 7000’ 0.5 ppg kick - 90 bbl gain 0.5 ppg kick - 35 bbl gain 16” @ 10,000’ 13 3/8” @ 16,500’ 11 3/4” @ 17,500’ 9 5/8” @ 20,000’ 0.5 ppg kick - 50 bbl gain 0.5 ppg kick - 80 bbl gain Well Control Conference of the Americas