Petroleum Engineering 406

1. Petroleum Engineering 406 Lesson 13 Shallow Water Flows

2. Shallow Water Flows (SWF) What is a SWF? Where do SWF occur? Why do they occur? How common a problem is this? How serious is this problem? Standard drilling procedures Some potential solutions to the SWF problem

3. References “Shallow water flows: How they develop; what to do about them,” by William Furlow, Offshore, September 1998, p.70. “Acrylate momomer solution stops artesian water, geopressured sand flows,” by Larry Eoff and James Griffith, Oil & Gas Journal, November 2, 1998, p.89.

4. References, cont’d OTC 1997 Deepstar report, 1996. Shallow Water Flow Forum, June, 1998.

5. What are Shallow Water Flows (SWF)? Shallow water flows are flows from overpressured sands encountered at shallow depth below the mud line in deepwater regions of the world.

6. What is a Shallow Water Flow? Sometimessandflows with the water. Flow rates as high as 25,000 bbls/day have been reported (~730 gal/min). A video presentation at the “Shallow Water Flow” Forum (June, 1998) showed a SWF producing plumes of sand and debris that boiled up 60 ft from the seafloor.

7. Where do SWF Occur? SWF typically occur in water depths beyond 1,500 ft, at depths ranging from 300 to 3,500 ft below the mud line. SWF represent a recently encountered phenomenon in the Gulf of Mexico, West of the Shetlands, the Norwegian Sea, Southern Caspian Sea, and the North Sea.

8. Where in the well do SWF Occur? Seawater Hydrostatic Aquifer Pore Pressure Depth Shale Sand Pressure

9. Why do SWF occur? Basically SWF occur because the pressure in the wellbore is lower than the pressure in the aquifer. The flow rate can be very high because of thick, high- permeability sands low water viscosity, and sufficient pressure differential.

10. How common a problem is this? It has been suggested that 30 to 40% of all deepwater wells in the Gulf of Mexico encounter this problem. Once the flow begins it is very difficult to stop. This makes it difficult, and sometimes impossible, to get a good cement job around the casing.

11. How serious is this problem? Hole erosion and poor cement jobs can result in settling of the casing strings, accompanied by buckling of inner casing strings, leading to serious damage or loss of well ($10-20 million?). At Ursa a number of wells were washed out, and had to be relocated. Total cost is estimated to be around $150 million!

12. EROSION SAND

13. Typical drilling procedules - SWF 1. Jet in 30-in drive pipe to 300 ft below mud line. Do not cement. Silt forms seal. 2. Drill and under-ream hole to 600 ft. Run 26-in conductor pipe and cement to mud line. 3. The next casing string would normally be 20-in. This string might be run to 1,500 ft., etc. Where there are no SWF present the 26-in and 20-in strings may be run much deeper. Some string sizes may be eliminated.

15. Step 1a.Jet in 30-in conductor to 300 ft below mud line

16. Step 1b.30-in conductor silts in - no cementing

17. Step 2a.Drill, under-ream hole for the 26-in conductor

18. Step 2b. Cement the 26-in conductor to the mud line

19. Any solutions to the SWF problem?Soln 1. Increase the mud weight When encountering any overpressured zone, standard practice is to increase the density of the drilling fluid. This increases the pressure in the wellbore to the point where influx (SWF) should cease. Sometimes increasing the the mud weight may lead to lost circulation, and the influx continues, possibly turning into an underground blowout.

20. Soln 1. Increase the mud weight Seawater Hydrostatic Fracture Pressure Pore Pressure Depth Shale Sand Pressure

21. Soln 1a. Increase the mud weight Install riser - May lead to lost circulation Seawater Hydrostatic Drilling Riser New Mud Hydrostatic Fracture pressure Pore Pressure Depth Shale Sand Pressure

22. Soln 1b. Increase the mud weight - drill with returns to the seafloor Seawater Hydrostatic New Mud Hydrostatic Fracture pressure Depth Shale Sand Pore Pressure

23. Soln 1c. Increase the mud weight - drill with returns to the seafloor - and pump the mud to the surface… Seawater Hydrostatic New Mud Hydrostatic Fracture pressure Depth Shale Sand Pore Pressure

24. Soln 1c. Increase the mud weight (zoom) - drill with returns to the seafloor - and pump the mud to the surface… (Riserless Drilling) New Mud Hydrostatic RBOP Fracture pressure Sand Pore Pressure Pressure

25. Soln 2. Use a seafloor diverter The diverter is a pack-off device, attached to the casing, that can put back-pressure on the formation to stop the SWF. It may work, if the casing is set just above the aquifer, but may result in lost circulation, and possibly broaching to the surface.

26. Soln 2.Use a seafloor diverter New Mud Hydrostatic Fracture pressure Sand Pore Pressure Pressure

27. JIP Shallow Water Flow Diverter “Rotating Head and Drilling Choke”

28. Rotating Head and Drilling Choke

29. Soln 3a. Use a chemical grout This treatment is designed to plug off the pore space in the aquifer. It also consolidates the sand. After chemical solidifies, drilling can proceed.

30. Step 3b. Use a chemical grout cont’d AMS = acrylate monomer solution AMS is effective in downhole temperatures from 50 to 200 deg. F.

31. Soln 4. Foam Cementing Low-density foamed cements have sometimes been successful in stopping SWF. These are especially successful when used in combination with chemical grouts. Grout, drill, run casing, cement.

32. Shallow Water Flow Cementing Technology • Settable Spots • By-passed fluid and filter-cake solidify and seal formation • Foamed Cements • Variable hydrostatic gradient possible • Lightweight , high strength • Expands to fill annulus • Conforms to borehole • Fast setting at low temperature • High shear bond supports well loads WATER FLOW

33. Jet Stabilization Process Place Cement Slurry, Resin, Or Other Stabilizing Material in Enlarged Hole • Slurry is jetted against wellbore • wall at high velocity • Ensures enlarged wellbore is filled • with slurry • Displaces drilling fluid and spacer • Creates intimate contact between • slurry and wellbore • Removes filter cake

34. Jet Stabilization Process Pull out of cement and circulate to clean up drill pipe Wait for Cement to Set

35. Jet Stabilization Process Stabilized/Reconstituted Wellbore Drill through cement and continue making hole

36. Soln 5. Underbalanced drilling through the SWF zone using coiled tubing A joint industry project is underway to evaluate and develop this technique.

37. Eliminates the annulus where the water can flow. 500-1,000 ft BML is feasible. 6. Drive the conductor through the SWF zone Seawater Hydrostatic Aquifer Pore Pressure Depth Shale Sand Pressure

38. DRILL DRIVE Drilling Jar Connection Driving Tool Flow Thru Holes Conductor Adapter Connection Shear Pins Mud Motor Connection Drill Bit OTC 8731

39. Hammer Casing Anvil / Striker Plate Cushion Assembly Drive Ring Drive Point Bottom-Driven OTC 8731

40. Eliminates the annulus where the water can flow. Penetration to 500-1,000 ft BML is feasible in almost all cases. 500 ft of drive pipe provides sufficient resistance to support the weight of all the subsequent casing strings, thereby preventing settling and casing buckling, even if SWF reoccur. 6. Drive the conductor through the SWF zone

41. TheEnd