Abstract：
In order to study the influence of the slip of the hollow glass spheres (referred to as HGS) on the wellbore tempera
ture and pressure field for dual gradient deep-water drilling. Firstly, the drag force model between the hollow glass spheres
was established considering the collision between the HGS particles based on collision theory. Secondly, according to the force
analysis of a single HGS in the drilling fluid, the mathematical model of slip velocity rate under different flow regimes was estab
lished, and then the calculation results of this model were compared with that of laboratory experiments to verify the rationality
of this mathematical model. Then based on the mathematical model of the slip rate, the relationship model between slip rate,
slip distance and the thermophysical parameters of the mixed fluid was derived. Not only taking the condition of the slip process
for hollow glass spheres into account, but also the mutual influence between the parameters, such as the wellbore temperature,
pressure and fluid thermophysical properties were also considered, thereby the prediction model of wellbore pressure for the
dual-gradient drilling in deep water was established. The results show that the slip rate is positively correlated with the diameter
of the HGS and the density of the drilling fluid, but negatively correlated with the density of HGS and the viscosity of the drilling
fluid. At the position of the separator, the distribution curve of the mixed fluid density in the annulus has a sudden change, while
distribution curve of the annulus pressure has an inflection point at the same position. As the slip distance increases, the length of
the liquid column of the light fluid in the upper annulus gradually decreases and the degree of sudden change and bending degree
of curve for the mixed fluid density and the distribution curve for annulus pressure gradually increase. When the slip distance
increases, the annulus pressure gradually increases, while density of the mixed fluid for the light drilling fluid in the upper
annulus and the temperature of the entire annulus gradually decrease. When the position of the separator and the volume fraction
of HGS increase, the annulus pressure and the density of the mixed fluid for the light drilling fluid in the upper annulus decrease.
This research can provide a theoretical reference for more accurate prediction of wellbore pressure for variable gradient drilling,
and it also provides theoretical guidance and technical support for safe drilling under the conditions of narrow pressure windows
in deep water.
