Study on the Separation Technology of HGS and Its Effect
153
4.5 Conclusions
(1) The separation efficiency increased with the increase of diameter before the diameter
of HGS reached critical value range and then decreases with the continuous increase
of diameter. When the frequency of pump and the diameter of HGS were fixed, the
separation efficiency increased with the augment of the opening degree of the inlet
valve. However, the uptrend slows down when the valve reaches critical opening
degree 40°. As the opening degree of the inlet valve 2 increased from 15° to 40°, if
the diameter of HGS remained unchanged, the separation efficiency difference in
the downtrend section was gradually narrowed under different pump frequencies.
(2) When the opening degree of the inlet valve and the diameter of HGS remain
unchanged, the separation efficiency first increased and then decreased with the
frequency of the pump greater than critical frequency. When the frequency reached
critical frequency 40 Hz, the separation efficiency showed an obvious downtrend.
(3) With the increase of the separation efficiency of the HGS, the annulus temperature
decreases gradually and the most affected region was in the adjacent annulus area
above the separator.
(4) The higher the injection rate of the HGS was, the lower the annulus temperature
was. In addition, the deeper the separator was located along the direction of well
depth from the wellhead, the broader area along the direction of well depth was
affected.
(5) The higher the separation efficiency was, the lower the density or viscosity of
drilling fluid was in annulus, and the most affected area was in the adjacent annulus
area along direction of the well depth above the separator.
Acknowledgements. This research was supported by the National natural science foundation
of China, “basic research on wellbore pressure control in deep water oil and gas drilling and
production” (51734010).
Appendix A. Discretization and Solution of the Model
The transient wellbore temperature calculation model coupled heat and mass transfer
as well the coupled temperature and wellbore pressure established in this paper is discretized by finite difference method. In the grid division, i represents the direction of
borehole axis and j represents the radial direction.
1. Heat Transfer Model in Drill String
Depending on the separation efficiency of the separator, the HGS were injected from the
wellhead and then passes through the upper part inside drill string. As it passes through
the separator, most of the HGS will be separated into the upper annulus. Because there
are HGS with different contents in the upper and lower part of the drill string as well as
the upper and lower part of the annulus, the thermal-physical parameters of the mixed
fluid in each part will be different.
153
4.5 Conclusions
(1) The separation efficiency increased with the increase of diameter before the diameter
of HGS reached critical value range and then decreases with the continuous increase
of diameter. When the frequency of pump and the diameter of HGS were fixed, the
separation efficiency increased with the augment of the opening degree of the inlet
valve. However, the uptrend slows down when the valve reaches critical opening
degree 40°. As the opening degree of the inlet valve 2 increased from 15° to 40°, if
the diameter of HGS remained unchanged, the separation efficiency difference in
the downtrend section was gradually narrowed under different pump frequencies.
(2) When the opening degree of the inlet valve and the diameter of HGS remain
unchanged, the separation efficiency first increased and then decreased with the
frequency of the pump greater than critical frequency. When the frequency reached
critical frequency 40 Hz, the separation efficiency showed an obvious downtrend.
(3) With the increase of the separation efficiency of the HGS, the annulus temperature
decreases gradually and the most affected region was in the adjacent annulus area
above the separator.
(4) The higher the injection rate of the HGS was, the lower the annulus temperature
was. In addition, the deeper the separator was located along the direction of well
depth from the wellhead, the broader area along the direction of well depth was
affected.
(5) The higher the separation efficiency was, the lower the density or viscosity of
drilling fluid was in annulus, and the most affected area was in the adjacent annulus
area along direction of the well depth above the separator.
Acknowledgements. This research was supported by the National natural science foundation
of China, “basic research on wellbore pressure control in deep water oil and gas drilling and
production” (51734010).
Appendix A. Discretization and Solution of the Model
The transient wellbore temperature calculation model coupled heat and mass transfer
as well the coupled temperature and wellbore pressure established in this paper is discretized by finite difference method. In the grid division, i represents the direction of
borehole axis and j represents the radial direction.
1. Heat Transfer Model in Drill String
Depending on the separation efficiency of the separator, the HGS were injected from the
wellhead and then passes through the upper part inside drill string. As it passes through
the separator, most of the HGS will be separated into the upper annulus. Because there
are HGS with different contents in the upper and lower part of the drill string as well as
the upper and lower part of the annulus, the thermal-physical parameters of the mixed
fluid in each part will be different.