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Case Study: Stratified Gas Hydrate Reservoir with Associated Free Gas

Case Study: Stratified Gas Hydrate Reservoir with Associated Free Gas. Group Project PETE 680: Horizontal well Technology Presented By, Namit Jaiswal, Adejoke M Ibironke. Objective. Gas Hydrates Overview of horizontal well and designer well Case description Results Conclusion

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Case Study: Stratified Gas Hydrate Reservoir with Associated Free Gas

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  1. Case Study: Stratified Gas Hydrate Reservoir with Associated Free Gas Group Project PETE 680: Horizontal well Technology Presented By, Namit Jaiswal, Adejoke M Ibironke

  2. Objective • Gas Hydrates • Overview of horizontal well and designer well • Case description • Results • Conclusion • Recommendation

  3. Alaska Methane Hydrate Estimated Resource EILEEN TREND MPU 100% FREE GAS? 44 TCF KRU 39% DIU PBU 26% GAS HYDRATE & FREE GAS 60 TCF? GAS HYDRATE TARN TREND (After Collett, 1993)

  4. GAS HYDRATES – AN OVERVIEW • Crystalline structures of ice that form cages around guest molecules • Guests are gas molecules (methane, ethane, CO2, N2…) • No chemical bond between guest and host lattice • Physically stable with only partial occupancy • Different structures sI, sII, sH, sT, …? • Large amounts of gas molecules are entrapped within these cages • Up to 180 volumes of gas (scf) per volume of hydrate • Gas molecules can penetrate through the hydrate zone to form new gas hydrates at boundary • Formation and growth occurs only under certain pressure and temperature conditions • Hydrate formation conditions are high pressure and low temperature

  5. Reserves Estimation

  6. Gas Hydrate Production Methods Depressurization Thermal Injection Inhibitor Injection Methanol Hot Brine or Gas Gas Out Gas Out Gas Out Imperm. Rock Imperm. Rock Imperm. Rock Gas Hydrate Gas Hydrate Gas Hydrate Hydrate Dissociated Free-Gas Reservoir Dissociated Hydrate Dissociated Hydrate Impermeable Rock Impermeable Rock After Collett, 2000

  7. Boundary Condition Gas zone Hydrate zone Pin t Peq Po Pwf Radial distance

  8. Algorithm for Performance of a Hydrate Reservoir Evaluation • Assume an average pressure pavg, and calculate gas compressibility cg using • Using the value of cg , calculate total compressibility and hydraulic diffusivity constant  from the known reservoir parameters. • For a desired gas withdrawal rate, solve eqn Above equation has on both sides; it requires a numerical scheme to solve. As a special case, when there is no gas flow from the undissociated hydrate zone, so above equation is simplified to

  9. Above equation has on both sides; it requires a numerical scheme to solve. As a special case, when there is no gas flow from the undissociated hydrate zone, so above equation is simplified to • Using the value of , solve below equation (1) and (2 • Using the value R*, Po and solve eq 3. and 4.

  10. and for the un-dissociated region is to obtained pressure profiles as a function of radial distance from the wellbore. • From the pressure values obtained in step 5. find pwf and calculate a new average pressure using • Using the new value of pavg, calculate new values of cg, ct and  . Compare the new value of  with that calculated in step 2. If the new value is within 10% of the old value, use the pressure profile generated in step 5. If not, go to step 3 and repeat Steps 4-8 till the consecutive values of  agree.

  11. Overview of horizontal well technology

  12. What is horizontal well ?

  13. Parameter Effects • Skin Factor • Payzone thickness • Anisotropy

  14. Productivity by Well Testing • To obtain reservoir properties • To find total producing length • To estimate mechanical skin factor

  15. Gas Reservoir • Low Permeability

  16. High Permeability hydrate

  17. Water and Gas Coning Vertical well Horizontal well

  18. 6 x 50’ 2’ Kh=15 md Case Description Highly Stratified Gas Hydrate Reservoir 0.35’

  19. VERTICAL WELL

  20. Temperature for free gas zone is constant. Average viscosity is used for calculation. Individual well bore pressure are assumed taken from literature. Pressure drop across tubing is negligible. ASSUMPTIONS FOR VERTICAL WELL RESERVOIR

  21. Productivity for vertical gas well is calculated by using following equation: Where, q = gas flow rate, Mscfd k= permeability, md h = Thickness, ft Pe =Pressure at external radius, re, Psia Pwf = well bore flowing pressure, Psia Z= average compressibility factor T = Reservoir temperature, R re = drainage radius, ft

  22. Graph of Pressure Vs production from vertical well

  23. Variation of productivity with payzone thickness.

  24. Vertical Fractured Wells • Any technique that helps to create fissures and openings in the reservoir rock of an oil and (or) gas formation, and help increase the flow of oil and (or) gas.

  25. Techniques • Fracturing can either be • Natural - created by faults in the formation) • Artificial -This can be • Pneumatic - by the flow of high pressure compression of air. • Hydraulic - pumping of fluid under high pressure.

  26. Application • Increase the flow rate of gas from low permeability reservoirs. • Increase the flow rate of gas from wells that have been damaged. • Connect natural fractures or cleats in a formation to the wellbore. • Decrease pressure drop around well to minimize sand production. • Decrease pressure drop around well to minimize problems with asphaltene or paraffin deposition. • Increase the area of drainage. • Connects the full vertical extent of a reservoir to a slanted or horizontal well.

  27. Candidate Selection • Must have a need to increase the productivity index. • A thick pay zone. • Medium to high pressure. • In-situ stress barriers to minimize vertical height growth. • It will either be a low permeability zone or a zone that has been damaged (high skin factor). • Must have a substantial volume of gas in place.

  28. A fractured vertical well behaves much like a horizontal well. • Advantages of Fractured Vertical Wells • Can be used in thick formations • Not affected by low vertical permeability • Disadvantages of Fractured Vertical Wells • No control over the fracture orientation • Possibility of uncontained fracture growth resulting in excessive gas or water influx. • TYPES OF FRACTURES • INFINITE-CONDUCTIVITY FRACTURES • UNIFORM FLUX FRACTURES • FINITE-CONDUCTIVITY FRACTURES

  29. Assumptions • Drainage volume is box shaped • The well fully penetrates the formation • There is no restricted entry to flow • The production is predominantly stabilized flow for all layers • The effect of non-Darcy flow is ignored • The rock property in each layer is the same

  30. Equations

  31. RESULT

  32. Conclusion • Vertical fracture well productivity decreases with pay thickness • Fracture can only be beneficial when permeability is relatively low • For the gas hydrate reservoir, it is expedient to perforate in the free gas zone

  33. α SLANT WELL

  34. α Definition • A directionally drilled well, that is inclined at an angle α to the vertical. • α is usually between 30˚-75˚ to be effective

  35. To reduce the cost of drilling several wells from a single platform To allow extraction of oil/gas from areas unreachable conventionally In reservoir with down-dip For formation with low permeability to gas The Great Lakes, along the shores of Lake Michigan and Huron In the Coalbed Methane field of Valencia Canyon in Northern San Juan basin of Colorado. In the Greater Green River Basin of Colorado. Reason for use & Areas of Practical Application

  36. Equations

  37. Result:

  38. The slant well is highly dependent on the vertical permeability When the kv is low, then productivity will be low Gas migrates vertically upward and because the kv is very low the productivity turned out low The result shows that the slant well has a higher productivity than the vertical well Conclusion

  39. Model of the given field

  40. Staircase Horizontal Well

  41. A steady state equation for gas flow in a Horizontal section • Where, • q = gas flow rate, Mscf/day kh= permeability, md • h = Thickness, ft Pe =Pressure at external radius, re, Psia • Pwf = wellbore flowing pressure, Psia • Z= average compressibility factor • T = Reservoir temperature, R • re = drainage radius, ft r'w =effective wellbore radius, ft •  = SQRT (kh/kv) Sm = mechanical skin factor

  42. Negligible pressure drop. Permeability of each zone is same No production from vertical sections. Open hole completion to increase hydrate production in long run. Assumptions

  43. Production Plot for L=500 ft. for staircase horizontal well

  44. Productivity Plots for staircase.

  45. Multilateral Wells

  46. Initialization For stratified well the partial differential equation, Pj denoting the pressure in the jth layer, Cases : Shell Barrier Communication

  47. Multilateral well in hydrate reservoir with no communication

  48. A Steady state equation for Multilateral Well Where, F=4,2,1.86 and 1.78 for n=1,2,3,4. m =number of levels. For this case, m=6 and n=1.

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