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Lesson 12

Lesson 12. Well Engineering. Well Engineering. Circulation Programs Circulation Calculations (air, gas, mist) Circulation Calculations (gasified liquids). Well Engineering. Wellhead Design Casing Design Completion Design. Well Engineering. Bit selection Underbalanced perforating

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Lesson 12

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  1. Lesson 12 Well Engineering

  2. Well Engineering • Circulation Programs • Circulation Calculations (air, gas, mist) • Circulation Calculations (gasified liquids) Harold Vance Department of Petroleum Engineering

  3. Well Engineering • Wellhead Design • Casing Design • Completion Design Harold Vance Department of Petroleum Engineering

  4. Well Engineering • Bit selection • Underbalanced perforating • Drillstring design • Separator design Harold Vance Department of Petroleum Engineering

  5. Hole Cleaning • Optimizing hydraulics with gasses is primarily concerned with hole cleaning - getting the cuttings that are generated by the bit out of the hole. • With gas, rheological properties have very little to do with hole cleaning • Hole cleaning with gasses is almost entirely dependent on the annular velocity Harold Vance Department of Petroleum Engineering

  6. Drag and Gravitational Forces • Flowing air exerts a drag force on cuttings • Gravitational force on the cuttings • Therefore there is a threshold velocity in which the cuttings will be lifted from the wellbore. • Threshold velocity increases with size of cuttings. Harold Vance Department of Petroleum Engineering

  7. Hole cleaning • Compressibility of air (or gas) complicates matters. • Frictional pressure increases downhole pressure - decreases velocity downhole • Suspended cuttings increase the density of the air, increasing downhole pressure. • Temperature has an effect on volumetric flow rate. Harold Vance Department of Petroleum Engineering

  8. Hole Cleaning • We must pump at a velocity high enough to remove the cuttings, but not too high where we waste energy. Harold Vance Department of Petroleum Engineering

  9. Hole Cleaning Criteria • Terminal Velocity Criteria • Minimum Energy Criteria • Minimum BHP Criteria Harold Vance Department of Petroleum Engineering

  10. Terminal Velocity Criteria • Gray determined that the minimum velocity of the gas must be at least as high as the terminal velocity of the cutting in order to lift the cutting from the wellbore. • Vc = Vf - Vt Harold Vance Department of Petroleum Engineering

  11. Terminal velocity Harold Vance Department of Petroleum Engineering

  12. Terminal Velocity Harold Vance Department of Petroleum Engineering

  13. Terminal Velocity • Terminal velocity in air drilling is determined mainly by: • cutting diameter, shape, and density • bottom hole temperature and pressure Harold Vance Department of Petroleum Engineering

  14. Terminal Velocity • As pressure increases Vt decreases. • As pressure increases Air velocity decreases • If the mass flow rate of gas remains constant the local air velocity decreases with increasing pressure. • The air flow rate required to lift the cuttings increases with increasing BHP Harold Vance Department of Petroleum Engineering

  15. Friction Pressure Eq. 2.5 Harold Vance Department of Petroleum Engineering

  16. Friction Pressure Harold Vance Department of Petroleum Engineering

  17. Friction Pressure • Mixture density is a function of air density, cuttings density, and mass of the cuttings. • Air density is a function of the pressure • Mass of the cuttings is a function of: • ROP • Hole cleaning efficiency Harold Vance Department of Petroleum Engineering

  18. Friction Pressure • Pressure drops down the drillstring and through the bit play a part in BHP due to temperature effects. • Temperature is also effected by: • formation temperature • influx of formation fluid (expansion of gas into the wellbore) • Mechanical friction • Pressure Harold Vance Department of Petroleum Engineering

  19. Required injection rates??? • Relating downhole air velocities to surface injection rates is quite complex. • We need cuttings shape and size to determine terminal velocity Harold Vance Department of Petroleum Engineering

  20. Minimum Energy Criteria • Probably the most widely used criteria was developed by Angel in 1957. • Angel assumed that, for efficient cuttings transport downhole, the kinetic energy of the air striking each cutting should be the same as that of air giving efficient cuttings transport at standard pressure and temperature. Harold Vance Department of Petroleum Engineering

  21. Minimum Energy Criteria Harold Vance Department of Petroleum Engineering

  22. Minimum Energy Criteria Harold Vance Department of Petroleum Engineering

  23. Minimum Energy Criteria • Experience from shallow blast holes, drilled in limestone quarrying operations, indicated that cuttings were transported efficiently if the air velocity equaled or exceeded 3,000 feet per minute. • This is equivalent to Gray’s terminal velocity for flat cuttings with a diameter of 0.46 in. or sub-rounded particles of 0.26 in. Harold Vance Department of Petroleum Engineering

  24. Minimum Energy Criteria Angel computed the downhole air pressure with eq. 2.5 Harold Vance Department of Petroleum Engineering

  25. Minimum Energy Criteria Harold Vance Department of Petroleum Engineering

  26. Minimum Energy Criteria Harold Vance Department of Petroleum Engineering

  27. Minimum Energy Criteria This was combined with the cuttings transport criterion defined in Eq 2.10 to deduce the minimum air flow rate as a function of hole depth, annular geometry, and penetration rate. Eq. 2.10 Harold Vance Department of Petroleum Engineering

  28. Minimum Energy Criteria To simplify, the average downhole temperature can be used to calculate BHP. This was solved numerically for the gas injection rate required to give an annular velocity equivalent in cuttings lifting power to air with a velocity of 3000 ft/min. A series of charts was generated for different geometries and penetration rates Harold Vance Department of Petroleum Engineering

  29. Minimum Energy Criteria • Qmin can be approximated by: • Qmin = Qo + NH • Qo = injection rate (scfm) at zero depth that corresponds to an annular velocity of 3000 ft/min • N = factor dependent on the penetration rate (Appendix C) • H = hole depth, 1000 ft. Harold Vance Department of Petroleum Engineering

  30. Harold Vance Department of Petroleum Engineering

  31. Harold Vance Department of Petroleum Engineering

  32. Harold Vance Department of Petroleum Engineering

  33. 7-7/8” hole 3-1/2” drillpipe 6” drill collars 3800’ hole depth Harold Vance Department of Petroleum Engineering

  34. Minimum BHP Criteria Angel’ analysis does not predict a minimum BHP, but gives a pressure that decreases monotonically with decreasing air flow rate. Harold Vance Department of Petroleum Engineering

  35. Natural Gas Drilling Harold Vance Department of Petroleum Engineering

  36. Terminal velocity of natural gas • Vtg = Vtair(1/S)0.5 Harold Vance Department of Petroleum Engineering

  37. Natural gas drilling • Lower density of natural gas than air results in: • lower BHP • lower drag forces • Higher required circulation rates • Non-ideal behavior of natural gas is not usually a problem since operating pressures are low and ideal behavior can be assumed. Harold Vance Department of Petroleum Engineering

  38. Natural gas injection rate • A first order estimate can be derived by taking Angel’s figures for air drilling at the appropriate depth and penetration rate and dividing these by the square root of the gas’s specific gravity. • Usually acceptable in practice Harold Vance Department of Petroleum Engineering

  39. Mist Drilling • Liquid volumes are only 1 to 2 percent at the prevailing temperature and pressure. Harold Vance Department of Petroleum Engineering

  40. Hole cleaning, mist • Water droplets act similarly to cuttings with slip velocity of near zero - mists do not clean the wellbore more efficiently than dry gas. Therefore annular velocities are high. • Circulating fluid density is increased however and may add to the frictional pressure losses. Harold Vance Department of Petroleum Engineering

  41. Hole cleaning, mist • The increased density will lower the terminal velocity of the cuttings, but will increase the BHP reducing the volumetric flow rate at the bottom of the hole. • Higher air injection rates are usually required when misting than with dry air. Harold Vance Department of Petroleum Engineering

  42. Application of Angel’s method to mist drilling • Determine the penetration rate that would generate the same mass of cuttings as the mass of liquid entering the well over a time period. This includes any base liquid, foamer, and water influx. Harold Vance Department of Petroleum Engineering

  43. Apparent equivalent ROP Harold Vance Department of Petroleum Engineering

  44. Angel’s method for mist • The minimum air injection rate, required for good hole cleaning during mist drilling, is determined; either from Angel’s charts or from the approximation in equation 2.17 Harold Vance Department of Petroleum Engineering

  45. Example • Hole size = 7 7/8” • depth = 5000’ • Drillpipe size = 4 1/2” • Anticipated ROP = 30 feet/hr • Qo = 671, N = 65, H = 5000/1000 = 5 • Minimum air rate for dry air = • Qa = Qa +NH = 670 + 65x5 = 995 scfm Harold Vance Department of Petroleum Engineering

  46. Example • Liquid injection rate is 6 BPH • Water influx is 3.8 BPH • Total liquid rate is 9.8 BPH • Penetration rate that would give this mass cuttings per hour is 60 ft/hr. Harold Vance Department of Petroleum Engineering

  47. Example • The minimum air rate required for dry air drilling at a penetration rate of 90 ft/hr using the value of N for 90 ft/hr, N = 98.3 would be 1162 scfm Harold Vance Department of Petroleum Engineering

  48. Wellhead Design - Low pressure • Gas, mist, and foam drilling are normally utilized on low pressure wells • Low pressure wells require simple wellhead designs • Some operators opt for a simple annular preventer alone Harold Vance Department of Petroleum Engineering

  49. Wellhead Design - Low pressure • However, a principal manufacturer of such equipment strongly cautions that such use exceeds the design criteria of this equipment. • The minimum setup should consist of a rotating head mounted above a two ram set of manually-operated blowout preventers, consisting of a pipe ram and a blind ram Harold Vance Department of Petroleum Engineering

  50. Wellhead Design - Low pressure • Slightly higher pressure systems should also have an annular preventer between the rams and the rotating head. • For added safety the BOP system should be hydraulically operated • Working pressure of these rotating heads is ~400-500 psi Harold Vance Department of Petroleum Engineering

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