PETE 689 - UBD

1. PETE 689 - UBD Lesson 15 Special Considerations Read: UDM - Chapter 6

2. Special Considerations Safety in UBD Regulatory Requirements Environmental Issues Directional Drilling

3. Percussion Drilling High Pressure Drilling Cementing Formation Evaluation Special Considerations

4. Safety in UBD Since significantly greater volumes of oil and gas are produced in underbalanced drilling (compared to overbalanced drilling), and because these products are highly combustible, considerable attention must be paid to safety procedures. Produced fluids must be handled safely.

5. Hydrogen Sulfide Provide necessary notice of the proposed operations and hazards. Provide adequate training. Special Safety equipment, such as sensors, warning alarms, wind socks, concentration measuring devices, portable and fixed air breathing respirators.

6. An H2S emergency contingency plan with the site specific information and detailed procedures. Hydrogen sulfide resistant materials and training. Pressure surface separation vessels and auxiliary vacuum degassing equipment to isolate all personnel from possible exposure to this poisonous gas. Hydrogen Sulfide

7. Flaring Gas Adequate sized flare lines, leading to properly positioned flare stacks, equipped with automatic flame igniters, are essential. Take wind direction into consideration. Height may need adjustment. Flare lines must be properly anchored.

8. Separation and Storage Liquid hydrocarbon separation and storage facilities must be: positioned remotely provide adequate storage volume proper manifolding for transfer to sales.

9. Training Personnel training must be provided. Written procedures must be provided. Redundancy in critical man power must be provided. Redundancy in choke manifold. Emergency ingress and egress must be provided.

10. Downhole Fires Air drilling can lead to downhole fires and corrosion.

11. Drilling with Natural Gas Surface fires can be a problem. Prepare for proper handling of hydrocarbon gasses at the surface. Guidelines can be found in: API RP 500B National Fire Protection Association (NFPA) 70 NFPAA 496

12. Backflow Drillstrings need floats to prevent flow back up the drillstring. Placement of drillstring floats is important for operational and safety reasons.

13. Well Control No standards for testing of RH and RBOP has been developed.

14. Equipment Operational and equipment testing procedures must be established. Operations should not continue if pressures exceed the maximum limits established. In flowdrilling, emphasis is placed on monitoring pressure while drilling, tripping, and stripping, in addition to early kick detection.

15. To develop testing procedures, prepare a detailed BOP and manifolding flow diagrams that show step-by-step testing for system parts. Test BOPs when installed, each time they are reinstalled, once each week, and following repairs. Equipment

16. Regularly inspect and monitor surface equipment. Stop flowdrilling when H2S is detected. Inspect mud/gas separators at least daily. Inspect diverter rubber elements several times a day. Check diverter alignment with the rotary. Develop contingency plans. Equipment

17. Regulatory Requirements In planning an UB well, always check with local, state, or federal agency governing the well�s location for the latest regulations.

18. Canada Interim Directive ID 94-3, from the Energy Resources Conservation Board provides the most detailed regulations in North America. Mandates strict enforcement of: BOP system configuration. Tripping procedures. Well control certification of key personnel.

19. United Kingdom The Department of Trade and Industry sets specific requirements and regulations pertinent to the drilling and completion of underbalanced wells. Authority has be delegated to the Health and Safety Executive to review operators plans, and to grant or deny permits for proposed work.

20. United States In the United States, a survey of the primary oil and gas producing states indicated that there were no special regulations written specifically for UBD. In most cases, the existing regulations could be broadly interpreted to cover UBD.

21. Issues to Consider

22. Issues to Consider

23. Issues to Consider

24. Issues to Consider

25. Environmental Issues Regulations vary significantly from state-to-state, and country-to-country. Check applicable regulations carefully.

26. Land and Water Pollution UBD provides some environmental benefits (closed loop systems, less drilling mud, etc), but produces more formation fluids than conventional. Oil coated cuttings must be disposed of properly.

27. Air Pollution Considerations Burning hydrocarbons during drilling can become an environmental concern. Know regulations on air pollution. Dust during air drilling can be a problem.

28. Produced Water Disposal Produced water must be disposed of. Disposal operations can include: Disposal into surface water drainage systems. Reinjection. Approved land disposal Overboard offshore disposal Reserve pits

29. Directional Drilling There is no reason why directional wells cannot be undertaken with UBD. However, compressible fluids can complicate directional drilling.

30. Directional Drilling (Complications) Conventional downhole motor life is shorter, and conventional motors are not as efficient. Conventional MWD systems do not work with compressible fluids. Hole cleaning can be a problem with angles >50 deg

31. The horizontal section length is reduced due to increased drag. Not all formations and lithologies are suitable for drilling with dry gas, moist or foam. Directional Drilling (Complications)

32. Bottomhole Assemblies Main issues for directional drilling underbalanced are similar to those for conventional directional drilling: Directional control. Surveying. Hole cleaning. Drillstring friction.

33. BHA is designed to control direction and angle. The deviation tendency is a function of the stiffness of the assembly. Bottomhole Assemblies

34. Three Types of BHAs Building assemblies Dropping assemblies Holding assemblies

35. Building Assemblies

36. Dropping Assemblies

37. Holding Assemblies

38. Downhole Motors Conventional mud motors can be run with compressible fluids, but there are disadvantages.

39. Conventional Mud Motors Disadvantages Designed to run with low volumetric flow rates and high pressure drops. Leads to high inlet pressures and low efficiency with compressible fluids. Compressible fluids can lead to motor stall. High inlet pressure results in high energy stored in the drillstring above the motor.

40. Volume to clean the hole with air drilling is three times greater than the recommended flow rate for the conventional mud motor. Mud motors are hydrostatic, they can use only the displacement work, and not the expansion work of the compressed air. Conventional Mud Motors Disadvantages

41. Mud Motors Mud motors have been developed for use with compressible fluids. Advantages: Boosters are not needed. Efficiency is improved. Motors do not stall as easily. Overspeed is less likely. Can be used with compressible and slightly compressible fluids.

42. Surveying Conventional MWD signals cannot be sent up compressible fluids. Electromagnetic MWD (EMWD) tools are being developed. Steering tools are still available.

43. Hole Cleaning Hole cleaning is more difficult in highly deviated wells. A rule-of-thumb is that for adequate hole cleaning in horizontal wells, a volumetric rate of 2.5 times greater than a vertical well is necessary.

44. Torque and Drag Friction coefficient in an air-drilled hole can be three to four times than expected in mud-filled hole.

45. Horizontal Section Length Additional torque and drag can lessen the achievable horizontal displacement of high angle and horizontal wells.

46. Lithology and Target Constraints Lithologies that can be drilled with air are limited. Younger less consolidated rocks are usually not good candidates for air. Directional wells sometimes must be drilled overbalanced to prevent wellbore collapse.

47. Percussion Drilling In percussion drilling, rock is broken by causing the bit to repeatedly strike the workfront, without imparting any significant shearing component to its action. A hammer tool is used in the BHA. Normally only used with dry gas, mist, and foam drilling.

48. Background

49. Approximation of ROP Assume that the MSE = Co Determine the hammer manufacturer�s power output value. The penetration rate is related to the rock�s unconfined compressive strength, the hammer power output and the hole area by:

50. Approximation of ROP

52. Equipment

55. Hole Cleaning Pratt modified Angel�s minimum velocity by: Using a revised air prediction module inside the drillstring where the friction factor was calibrated from actual measurements. Exit boundary conditions were modified as an input parameter and exit chip velocity was fixed at zero. The influence of the BHA and changing hole size were incorporated. Chip size change was built into the model.

56. Gauge Wear

57. Smooth Hole?

58. Smooth Hole?

59. Summary Maintain proper WOB. Rotate as slowly. Provide an air bypass. Deep the threads clean and use recommended lubricants. Dope the pins only. Never run on junk.

60. When changing out bits, make sure that the new bit is no more than 0.25 in larger than the old. Stabilize as required. Monitor compressors. Blow the hole clean. Summary

61. High Pressure Drilling Special attention should be given to high surface pressures because of the additional force required to trip pipe. Stringent safety considerations are required.

62. Flowdrilling in High Pressured Formations The use of CT drilling is increasing with high pressure flowdrilling. Surface well control equipment must be rated based on maximum anticipated conditions. RBOPs should replace rotating heads.

63. Coiled Tubing Drilling Design Criteria Select the CT size, hole size, drilling fluid, and BHA. Calculate the reel weight and size. Calculate the tubing forces and stresses. Do not let them exceed 80% of the yield strength, and the minimum WOB can be provided at TD.

64. Coiled Tubing Drilling Design Criteria 4. In vertical wells. Dmax = (sy) / ( 4.245 - 0.06493Wdf ) Dmax maximum depth (feet) Wdf drilling fluid weight (ppg) sy yield stress (psi) 5. In Deviated wells. Ensure that the injector can supply the necessary push/pull.

65. Coiled Tubing Drilling Design Criteria 5. In Deviated wells. Ensure that the injector can supply the necessary push/pull. Calculate the drilling fluid pressure drop in the CT, BHA and annulus at 100 % motor flow capacity and determine the absolute pressure in the CT during drilling. Asses torsional limitations. The downhole motor-stall torque should not be longer than the maximum working torque for the CT.

66. Coiled Tubing Drilling Design Criteria 5. In Deviated wells. Calculate the fatigue life of the pipe. Asses any hydraulic limits . Consider hole cleaning in vertical, inclined , and horizontal wellbores. Be sure that directional control is possible.

67. Cementing Extremely light cement can be used to: Provide primary cementing in formations with low fracture pressures. Cure lost circulation in cavernous vugs. Squeeze depleted zones. Zonal isolation. Heat Insulation.

68. Properties of Foamed Cement Will the strength be adequate and will the sheath be destroyed by perforating? Compressive strength of foamed cement is generally higher than a comparable non-foamed cement of the same density. Will there be gas migration through the cement itself? Will the bond be different than for conventional cements?

69. Systems with Low Density Particulate Matter Cement companies have additive in which the HSP of the cement can be reduced. Example is hollow glass micro spheres.

70. Design Considerations Foam quality. PVT behavior. Cement system. Free water. Backpressure. Permeability. Compressive strength. Fluid Loss.

71. Formation Evaluation

72. Evaluation of Formation Fluids While Drilling Evaluation of formation fluids during UBD is more accurate than conventional. Qualitative and Quantitative information can be obtained or inferred.

73. Evaluation with Logging Tools

74. Evaluation with Logging Tools

75. MWD If a compressible fluid is used, conventional mud pulse telemetry tools cannot be used. Electromagnetic devices can.

76. Coring Underbalanced Reducing coring fluid invasion allows for careful determinations of formation properties where wettability alteration has been minimized.

77. Permeability and Deliverability Assessments Effective monitoring of production rates permits real-time decisions regarding changes in drilling depth, wellbore orientation, and overall section length.