CFD Modelling and Simulation of Drilled Cuttings Transport Efficiency
205
μ g,in = μ i + μ A sin(2π ft)
(28)
where μ g,in is the nitrogen injection velocity, μ A is the pulse amplitude, and f is the
pulse repetition frequency; μ i = 20 m/s, μ A = 2.5, 5, 10 m/s, and f = 1.0, 2.0, 4.0 Hz.
At the walls of the wellbore and drill pipe, the no-slip boundary conditions are applied
for the gas and solid phases. The restitution coefficient for the collisions between the
cuttings particles is specified as 0.9.
2.7 Solution Procedure
In order to simulate the drill pipe rotation, the sliding mesh model is enabled for the
drill pipe cell zone. The Phase Coupled SIMPLE (Semi-Implicit Method for Pressure
Linked Equations), which is an extension of the SIMPLE algorithm [16], is adopted as
the pressure-velocity coupling scheme. The QUICK (Quadratic Upstream Interpolation
for Convective Kinematics) spatial discretization scheme is selected to solve all the
convection-diffusion equations. A fixed time step of 5 × 10 −4 s is used for the transient
flow calculations which are performed for a time period of 50 s. The simulations are run
on a high-performance computer with the 28-core Intel® Xeon® W-3175X processor
(38.5 M Cache, 3.1 GHz) and 64 GB RAM.
3 Results and Discussion
3.1 Nitrogen Injection Velocity and Pressure Drop
Figure 2 shows the effect of gas injection method on the nitrogen inlet velocity and pressure drop. The constant-rate gas injection method has a gas inlet velocity of 20 m/s. The
parameters of the gas inlet velocity of the pulsed gas injection method are composed of
different pulse amplitudes ranged from 2.5 to 10 m/s and different pulse repetition frequencies ranged from 1.0 to 4.0 Hz. It is evident that the nitrogen inlet velocity and pressure drop oscillate in different sinusoidal waves based on various pulse amplitudes and
pulse repetition frequencies. Moreover, the pressure drop across the annulus increases
with the gas inlet velocity and decreases with the decrease of the gas inlet velocity. The
cumulative gas injection volume is the integral of the flow rate (the product of the gas
velocity and cross-sectional area) with respect to time. Consequently, the cumulative
gas injection volumes are identical within the time of the integer multiple of one second
during the multiphase flow processes of different gas injection methods. Compared with
the constant-rate gas injection method, the pressure drop under the pulsed gas injection
method can be divided into two portions. One is the high pressure drop section and the
other is the low pressure drop section. This can be attributed to the fluctuation of the
frictional resistance which caused by the gas velocity variation and its induced changes
in the cuttings volume fraction. Hence, the pulsed gas injection method certainly will
contribute the improvement of the cuttings transport efficiency under the same condition
of gas injection volume.
205
μ g,in = μ i + μ A sin(2π ft)
(28)
where μ g,in is the nitrogen injection velocity, μ A is the pulse amplitude, and f is the
pulse repetition frequency; μ i = 20 m/s, μ A = 2.5, 5, 10 m/s, and f = 1.0, 2.0, 4.0 Hz.
At the walls of the wellbore and drill pipe, the no-slip boundary conditions are applied
for the gas and solid phases. The restitution coefficient for the collisions between the
cuttings particles is specified as 0.9.
2.7 Solution Procedure
In order to simulate the drill pipe rotation, the sliding mesh model is enabled for the
drill pipe cell zone. The Phase Coupled SIMPLE (Semi-Implicit Method for Pressure
Linked Equations), which is an extension of the SIMPLE algorithm [16], is adopted as
the pressure-velocity coupling scheme. The QUICK (Quadratic Upstream Interpolation
for Convective Kinematics) spatial discretization scheme is selected to solve all the
convection-diffusion equations. A fixed time step of 5 × 10 −4 s is used for the transient
flow calculations which are performed for a time period of 50 s. The simulations are run
on a high-performance computer with the 28-core Intel® Xeon® W-3175X processor
(38.5 M Cache, 3.1 GHz) and 64 GB RAM.
3 Results and Discussion
3.1 Nitrogen Injection Velocity and Pressure Drop
Figure 2 shows the effect of gas injection method on the nitrogen inlet velocity and pressure drop. The constant-rate gas injection method has a gas inlet velocity of 20 m/s. The
parameters of the gas inlet velocity of the pulsed gas injection method are composed of
different pulse amplitudes ranged from 2.5 to 10 m/s and different pulse repetition frequencies ranged from 1.0 to 4.0 Hz. It is evident that the nitrogen inlet velocity and pressure drop oscillate in different sinusoidal waves based on various pulse amplitudes and
pulse repetition frequencies. Moreover, the pressure drop across the annulus increases
with the gas inlet velocity and decreases with the decrease of the gas inlet velocity. The
cumulative gas injection volume is the integral of the flow rate (the product of the gas
velocity and cross-sectional area) with respect to time. Consequently, the cumulative
gas injection volumes are identical within the time of the integer multiple of one second
during the multiphase flow processes of different gas injection methods. Compared with
the constant-rate gas injection method, the pressure drop under the pulsed gas injection
method can be divided into two portions. One is the high pressure drop section and the
other is the low pressure drop section. This can be attributed to the fluctuation of the
frictional resistance which caused by the gas velocity variation and its induced changes
in the cuttings volume fraction. Hence, the pulsed gas injection method certainly will
contribute the improvement of the cuttings transport efficiency under the same condition
of gas injection volume.