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Petroleum Engineering 411 Well Drilling

Petroleum Engineering 411 Well Drilling. Lesson 27 Dual Gradient Drilling. DESIGN PROJECT. Your PETE 411 Design Project will be assigned on Friday, November 15 The Project Report is Due in Dr. J-W’s Office by 5 p.m. on Monday, Dec. 9. What is Dual Gradient Drilling? (DGD)?.

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Petroleum Engineering 411 Well Drilling

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  1. Petroleum Engineering 411Well Drilling Lesson 27 Dual Gradient Drilling

  2. DESIGN PROJECT Your PETE 411 Design Project will be assigned on Friday, November 15The Project Report is Due in Dr. J-W’s Office by 5 p.m. on Monday, Dec. 9

  3. What is Dual Gradient Drilling? (DGD)? • In dual-gradient drilling the pressure profile in the annulus appears to have two distinct pressure gradients • An example would be a heavy mud below the mudline and a seawater gradient above the mud line

  4. Conventional Riser Drilling - Wellbore Pressures FLOATER SEA WATER HYDROSTATIC DRILLING RISER CHOKE LINE MUD HYDROSTATIC BOP SEAFLOOR DEPTH PRESSURE ATM

  5. Static Wellbore Pressures FLOATER MUD HYDROSTATIC PRESSURE DGD MUD HYDROSTATIC PRESSURE Conventional RISER CHOKE LINE BOP DEPTH SEA WATER HYDROSTATIC PRESSURE PRESSURE DGD

  6. Dual Gradient Drilling Projects • Subsea Mudlift Drilling (SMD) • Hollow Glass Spheres • Deep Vision • Shell • Gas Lift • H.P. Riser

  7. Subsea Mudlift Drilling ( SMD )Note Pump and Return Line

  8. Subsea Mudlift Drilling What is Subsea Mudlift Drilling? How does it work? Why do we need it? Pore pressures and fracture pressures Mud weights and casing programs What about connections and trips? What about kicks?

  9. References 1.“Riserless Drilling: Circumventing the Size/cost Cycle in Deepwater,” by Allen D. Gault. May 1996, Offshore, p.492.“Subsea Mudlift Drilling JIP: Achieving dual-gradient technology,” by K.L. Smith et al., World Oil - Deepwater Technology, August 1999, pp 21-28. HW #15 (due 11-15-01)

  10. Current SMD Concepts • A water-filled drilling riser • One or more separate small-diameter mud return line(s) from seafloor to surface (e.g., two 4.5-in ID lines) • A “dual mud density” system (DGD) • Seawater gradient from surface to seafloor • Heavier drilling mud inside the wellbore

  11. Current SMD Concepts - cont’d • A seafloor mud pump to lift mud to surface • Pressure inside wellbore at seafloor is ~ the same as the pressure in the ocean at seafloor • Theoretically the well is always dead • Important in case of drive-off • Retains a Riser Margin

  12. Current Problems Deeper water results in longer, larger diameter and heavier drilling risers High pore pressures and low fracture pressures lead to more casing strings This leads to larger wellheads, even larger and heavier risers, and finally to bigger and more expensive rigs Well control is more difficult - because of the pore pressure / fracture pressure proximity, and long choke lines with high friction pressure drops

  13. Effect of Increasing Water Depth Weight of drilling riser increases with depth. In 10,000 ft of water: 21-inch riser has an internal capacity of ~ 4,000 bbls! (value ~ $1 million) Weight of riser ~ 2 million lbs. Weight of 16 lb/gal mud inside riser ~ 2.7 million lbs

  14. What About Subsea Mudlift Drilling? Two 4.5” ID return lines with ~ 400 bbls capacity can do the job Requires much less weight and volume for storage! A smaller vessel can do the job A smaller vessel can easier be upgraded to do the job

  15. What is Subsea Mudlift Drilling? • SMD refers to drilling where mud returns DO NOT go through a conventional, large-diameter, drilling riser • Instead the returns move from the seafloor to the surface through two small - diameter pipes separate from the drillpipe (outside the main riser pipe) • A Mudlift system is used in the Return Line ATM

  16. Equivalent Mud Density, ppg Fig. 7.21 ADE Pore pressure gradient and fracture gradient data for Jefferson Parish, LA. Fracture Gradient 0.5 ppg 0.5 ppg Pore Pressure Gradient

  17. Conventional Casing Seat Selection SEAFLOOR Frac Pressure Max Mud Wt Min Mud Wt Pore Pressure Equivalent Mud Wt, lb/gal

  18. Typical Overburden Pressure grad.vs. Depth Ref: “Fracture gradient prediction for the new generation,” by B.A. Eaton and T.L. Eaton. World Oil, October 1997. 17.3 ppg 11.5 ppg

  19. Conventional Riser Drilling - Wellbore Pressures FLOATER STATIC PRESSURE CIRCULATING PRESSURE BOP DEPTH SEAFLOOR Drill String SEA WATER HYDROSTATIC PRESSURE PBIT PRESSURE ATM

  20. Static Wellbore Pressures MUD HYDROSTATIC PRESSURE SMD MUD HYDROSTATIC PRESSURE Conventional SEAFLOOR DEPTH SEA WATER HYDROSTATIC PRESSURE PRESSURE ATM

  21. Example: Static Wellbore Pressures At 30,000 ft, in 10,000 ft of water, the pore pressure is 21,000 psig. For conventional drilling, what is the minimum mud weight that can control this pressure? For SMD, what is the minimum mud weight that can control this pressure? ATM

  22. Static Wellbore Pressures P = 0.052 * MW * Depth For conventional drilling, Minimum mud wt. MWmin = 21,000/(0.052 * 30,000) = 13.5 lb/gal Seafloor pressure = 0.052*8.6*10,000 = 4,472 psig For SMD, Minimum mud weight = (21,000 - 4,472)/(0.052 * 20,000) = 15.9 lb/gal ATM

  23. Solution: Static Wellbore Pressures SEA WATER HYDROSTATIC PRESSURE 8.6 lb/gal 15.9 lb/gal SMD 13.5 lb/gal Conventional DEPTH 4,472 psi 21,000 psi ATM

  24. Wellbore Pressures MUD HYDROSTATIC PRESSURE Conventional SEAFLOOR FRACTURE PRESSURE DEPTH SEA WATER HYDROSTATIC PRESSURE PORE PRESSURE PRESSURE ATM

  25. Wellbore Pressures MUD HYDROSTATIC PRESSURE SMD MUD HYDROSTATIC PRESSURE Conventional SEAFLOOR FRACTURE PRESSURE DEPTH SEA WATER HYDROSTATIC PRESSURE PORE PRESSURE PRESSURE ATM

  26. Casing Requirements - Conventional MUD HYDROSTATIC PRESSURE Conventional SEAFLOOR DEPTH FRACTURE PRESSURE SEA WATER HYDROSTATIC PRESSURE PORE PRESSURE PRESSURE ATM

  27. Casing Requirements - SMD MUD HYDROSTATIC PRESSURE SMD SEAFLOOR FRACTURE PRESSURE DEPTH SEA WATER HYDROSTATIC PRESSURE PORE PRESSURE PRESSURE ATM

  28. Pressure Considerations MUD HYDROSTATIC PRESSURE SMD MUD HYDROSTATIC PRESSURE Conventional SMD SEAFLOOR FRACTURE PRESSURE DEPTH SEA WATER HYDROSTATIC PRESSURE PORE PRESSURE PRESSURE ATM

  29. Wellbore Pressures - Conventional FLOATER STATIC PRESSURE CIRCULATING PRESSURE SEAFLOOR BOP DEPTH SEA WATER HYDROSTATIC PRESSURE PBIT PRESSURE ATM

  30. Static Pressures - SMD FLOATER ANNULUS AND RETURN LINE SEAFLOOR BOP DEPTH SEA WATER HYDROSTATIC PRESSURE PRESSURE ATM

  31. Drillstring Circulating Pressures CONVENTIONAL SMD SEAFLOOR DEPTH SEA WATER HYDROSTATIC PRESSURE PBIT PRESSURE ATM

  32. Annulus Circulating Pressures CONVENTIONAL (13.5 lb/gal) SMD (15.9 lb/gal) SEAFLOOR PPUMP DEPTH SEA WATER HYDROSTATIC PRESSURE PRESSURE ATM

  33. Circulating Pressures - SMD DRILLSTRING PRESSURE ANNULUS AND RETURN LINE SEAFLOOR PPUMP DEPTH SEA WATER HYDROSTATIC PRESSURE PBIT PRESSURE ATM

  34. Circulating Pressures - Summary CONVENTIONAL PBIT PRESSURE PML_PUMP SMD DISTANCE FROM STANDPIPE ATM

  35. Transients Transient Behavior when Stopping Rig Pump (U-tubing or Free-fall) • Why does the drillpipe fluid level fall? • How fast does the Fluid Level in the drillpipe drop? • How far does the Fluid Level drop? ATM

  36. U-Tubing in SMD FLOATER ~SEAWATER HYDROSTATIC PRESSURE Drillstring STATIC FLUID LEVEL Annulus BOP MUDLIFT ATM

  37. Static Pressures - SMD Static Fluid Level in DP ANNULUS AND RETURN LINE DRILLSTRING PRESSURE SEAFLOOR DEPTH SEA WATER HYDROSTATIC PRESSURE PRESSURE ATM

  38. 10,000 ft Water Depth ATM

  39. 10,000 ft Water Depth ATM

  40. Well Control Considerations How do you shut a well in after taking a kick? • With a DSV this is almost routine • Better still, it is not necessary to shut the well in. The wellbore pressures can be increased by temporarily slowing down the mudlift pump • Friction in the choke line is handled by the Mudlift Pump and is not seen by the weak formations ATM

  41. General Summary • Dual Gradient Drilling is a method that offers potential for lowering drilling costs in very deep waters: • Fewer casing strings • Smaller rigs • Less time on location • The method utilizes one or more small-diameter return lines from the seafloor to the surface. The drillpipe is separate from the return lines ATM

  42. Summary - cont’d A mudlift system (pump) is used to feed the return lines, thereby making a “dual-density” mud system possible Wellhead pressure is maintained at seawater hydrostatic, so well is “dead” at all times Well control is quite similar to that in conventional drilling with a riser, but offers a number of significant advantages ATM

  43. THE END ATM

  44. Gas Lift? Glass Beads? Pumps? Gas Lift? Glass Beads? Dual Gradient Alternatives How to Handle Connections? Trips? Rotating BOP

  45. Advanced SMD System FLOATER ~SEAWATER HYDROSTATIC PRESSURE 10,000’ SEAFLOOR BOP MUDLIFT Circulation Rate 650 gpm Drillpipe OD 6 5/8 in Return Line ID 6 in Hole Size 12 1/4 in 30,000’ ATM

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