25-26 August 1999Well Control Conference of the Americas 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.

25-26 August 1999Well Control Conference of the Americas Houston, Texas Introduction Problems Associated With Deepwater Drilling Single Gradient vs. Dual Gradient Concept Methodology Results Conclusions

25-26 August 1999Well Control Conference of the Americas Houston, Texas 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

25-26 August 1999Well Control Conference of the Americas Houston, Texas 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

25-26 August 1999Well Control Conference of the Americas Houston, Texas Single vs. Dual Gradient Concept 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 Pressure, psi DepthftDepthft 10,000’ Seawater HSP 23,880 37,500’ 12.4 ppg mud 13.5 ppg mud

25-26 August 1999Well Control Conference of the Americas Houston, Texas Dual Gradient Achieved by: Taking returns at the seafloor Gas lift at the seafloor Inject hollow gas spheres Seafloor mud pumps

25-26 August 1999Well Control Conference of the Americas Houston, Texas 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

25-26 August 1999Well Control Conference of the Americas Houston, Texas Pore and Fracture Gradients

25-26 August 1999Well Control Conference of the Americas Houston, Texas 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

25-26 August 1999Well Control Conference of the Americas Houston, Texas Methodology Compared results to a dual gradient system: –Statically –Dynamically

25-26 August 1999Well Control Conference of the Americas Houston, Texas Methodology Dual Gradient System, we picked casing points: –Graphically (static wellbore pressures) –Dynamically: 0 bbl influx 50 bbl influx

25-26 August 1999Well Control Conference of the Americas Houston, Texas Graphical Casing Seat Selection

25-26 August 1999Well Control Conference of the Americas Houston, Texas Kick w/ 750 psi SIP Pore Pressure Fracture Pressure Mud HSP (13.1 ppg) Mud HSP psi Formation has fractured

25-26 August 1999Well Control Conference of the Americas Houston, Texas Casing Seat Pressures

25-26 August 1999Well Control Conference of the Americas Houston, Texas Static Pressure - Dual Gradients Pore Pressure Fracture Pressure Mud HSP (15.5 ppg) Mud HSP = 750 psi

25-26 August 1999Well Control Conference of the Americas Houston, Texas Choke Pressures

25-26 August 1999Well Control Conference of the Americas Houston, Texas

25-26 August 1999Well Control Conference of the Americas Houston, Texas

25-26 August 1999Well Control Conference of the Americas Houston, Texas Graphical Casing Seat Selection - Dual Density

25-26 August 1999Well Control Conference of the Americas Houston, Texas Dynamic Casing Seat Selection D e p t h ft. Pressure, psi 1.0 ppg kick 0 bbl influx volume

25-26 August 1999Well Control Conference of the Americas Houston, Texas Dynamic Casing Seat Selection 1.0 ppg kick 50 bbl influx volume

25-26 August 1999Well Control Conference of the Americas Houston, Texas 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.

25-26 August 1999Well Control Conference of the Americas Houston, Texas 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.

25-26 August 1999Well Control Conference of the Americas Houston, Texas 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.

25-26 August 1999Well Control Conference of the Americas Houston, Texas 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.

25-26 August 1999Well Control Conference of the Americas Houston, Texas

25-26 August 1999Well Control Conference of the Americas Houston, Texas 6000’ WD

25-26 August 1999Well Control Conference of the Americas Houston, Texas 6000’ WD

25-26 August 1999Well Control Conference of the Americas Houston, Texas 6000’ WD

25-26 August 1999Well Control Conference of the Americas Houston, Texas 6000’ WD Kick Tolerance is Back 520 psi Underbalance from Kick Formation has Fractured Formation Intact SMDCONVENTIONAL 15.5 PPG MUD 15.5 ppg mud psi 18.4 ppg mud 18.4 ppg mud psi

25-26 August 1999Well Control Conference of the Americas Houston, Texas Kick Tolerance 6300’ 7000’ 10,000’ 13 16,500’ 11 17,500’ 9 20,000’ 0.5 ppg kick - 90 bbl gain 0.5 ppg kick - 35 bbl gain 0.5 ppg kick - 50 bbl gain 0.5 ppg kick - 80 bbl gain SMD Conventional