210
K. Zhang et al.
dissipation rate decreases from 29757 to 21641 m 2 /s 3 . The turbulence dissipation rate
is the rate at which the turbulence kinetic energy cascades down from larger to smaller
eddies until it is ultimately converted into heat due to viscous forces. In the case of gas
drilling, the higher average turbulence dissipation rate denotes that the gas-solid mixture
has a better mixing characteristic which benefits to the cuttings transport. Meanwhile,
the higher average turbulence dissipation rate also indicates a higher energy transmission
efficiency from the pulse generator to the cuttings conveyance. On the contrary, the low
average turbulence dissipation rate stands for a poor mixing of the two phases and a
low energy transmission efficiency. This can explain why the gradient of the reduction
in cuttings volume fraction descends with the increase of the pulse repetition frequency
(Fig. 4). Hence, one can infer that the pulse repetition frequency of the pulsed gas
injection method should not be too high.
4 Conclusion
In this work, a numerical model is developed for the simulation of the cuttings transport
in a 3D eccentric horizontal annulus during the gas drilling process. The effects of
different gas injection methods on the gas inlet velocity, pressure drop, cuttings volume
fraction, granular temperature, turbulence kinetic energy, and turbulence dissipation rate
are systematically investigated. These following conclusions are derived from the data
and results in the present research. (1) The cuttings volume fraction under the pulsed gas
injection method is lower than that under the constant-rate gas injection method. (2) The
higher the pulse amplitude and pulse repetition frequency, the lower the cuttings volume
fraction is. Nevertheless, the pulse repetition frequency should not be too high, which
may result in the poor mixing of the gas-solid mixture and the low energy transmission
efficiency. (3) Almost no stationary cuttings bed is found under the pulsed gas injection
condition, the cuttings particles are conveyed out within the wave-like moving cuttings
bed. (4) Compared with the constant-rate gas injection method, the pulsed gas injection
method provides a much better cuttings transport efficiency at the same condition of the
gas injection volume.
Acknowledgements. This work was supported by the National Science and Technology Major
Project of the Ministry of Science and Technology of China (2017ZX05009-004).
References
1. Okpobiri, G.A., Ikoku, C.U.: Volumetric requirements for foam and mist drilling operations.
SPE Drilling Eng. 1(1), 71–88 (1986)
2. Mitchell, R.F.: Simulation of air and mist drilling for geothermal wells. J. Petroleum Technol.
35(11), 2120–2126 (1983)
3. Ozbayoglu, M.E., Kuru, E., Miska, S., Takach, N.: A comparative study of hydraulic models
for foam drilling. J. Canadian Petroleum Technol. 41(6), 52–61 (2002)
4. Kuru, E., Okunsebor, O.M., Li, Y.: Hydraulic optimization of foam drilling for maximum
drilling rate in vertical wells. SPE Drill. Completion 20(4), 258–267 (2005)
K. Zhang et al.
dissipation rate decreases from 29757 to 21641 m 2 /s 3 . The turbulence dissipation rate
is the rate at which the turbulence kinetic energy cascades down from larger to smaller
eddies until it is ultimately converted into heat due to viscous forces. In the case of gas
drilling, the higher average turbulence dissipation rate denotes that the gas-solid mixture
has a better mixing characteristic which benefits to the cuttings transport. Meanwhile,
the higher average turbulence dissipation rate also indicates a higher energy transmission
efficiency from the pulse generator to the cuttings conveyance. On the contrary, the low
average turbulence dissipation rate stands for a poor mixing of the two phases and a
low energy transmission efficiency. This can explain why the gradient of the reduction
in cuttings volume fraction descends with the increase of the pulse repetition frequency
(Fig. 4). Hence, one can infer that the pulse repetition frequency of the pulsed gas
injection method should not be too high.
4 Conclusion
In this work, a numerical model is developed for the simulation of the cuttings transport
in a 3D eccentric horizontal annulus during the gas drilling process. The effects of
different gas injection methods on the gas inlet velocity, pressure drop, cuttings volume
fraction, granular temperature, turbulence kinetic energy, and turbulence dissipation rate
are systematically investigated. These following conclusions are derived from the data
and results in the present research. (1) The cuttings volume fraction under the pulsed gas
injection method is lower than that under the constant-rate gas injection method. (2) The
higher the pulse amplitude and pulse repetition frequency, the lower the cuttings volume
fraction is. Nevertheless, the pulse repetition frequency should not be too high, which
may result in the poor mixing of the gas-solid mixture and the low energy transmission
efficiency. (3) Almost no stationary cuttings bed is found under the pulsed gas injection
condition, the cuttings particles are conveyed out within the wave-like moving cuttings
bed. (4) Compared with the constant-rate gas injection method, the pulsed gas injection
method provides a much better cuttings transport efficiency at the same condition of the
gas injection volume.
Acknowledgements. This work was supported by the National Science and Technology Major
Project of the Ministry of Science and Technology of China (2017ZX05009-004).
References
1. Okpobiri, G.A., Ikoku, C.U.: Volumetric requirements for foam and mist drilling operations.
SPE Drilling Eng. 1(1), 71–88 (1986)
2. Mitchell, R.F.: Simulation of air and mist drilling for geothermal wells. J. Petroleum Technol.
35(11), 2120–2126 (1983)
3. Ozbayoglu, M.E., Kuru, E., Miska, S., Takach, N.: A comparative study of hydraulic models
for foam drilling. J. Canadian Petroleum Technol. 41(6), 52–61 (2002)
4. Kuru, E., Okunsebor, O.M., Li, Y.: Hydraulic optimization of foam drilling for maximum
drilling rate in vertical wells. SPE Drill. Completion 20(4), 258–267 (2005)