Effect Of Barite On Rheology Of High Density Drilling Fluid And Control Measures

With the development of oil drilling in the direction of deep wells and ultra-deep wells,the application of high density and ultra high density drilling fluids is becoming more and more extensive.Underground high temperature and high pressure conditions and complex formation properties are more stringent on the performance of drilling fluids,especially rheological properties.In the present domestic and foreign studies,there are many factors that affect the rheological properties of high density drilling fluid.There is no clear theory or conclusion to explain the reason of the rheological property of high density drilling fluid,so the regulation of rheology is bottleneck.Because the high density drilling fluid belongs to the thick colloidal dispersion system,the solid content is high,so the interaction between the solid particles is the fundamental method to solve the rheological problem.The main reason for the high solid content in high density drilling fluid is caused by the weighting agent.According to the theory of extended DLVO(EDLVO),the ideal dispersion model of barite particles in drilling fluid is established,and the calculation of van der Waals force,electrostatic repulsion and interfacial polar interaction force between barite and water systems is deduced.The change of barite grain size,the dielectric constant of barite,the surface potential of barite and the contact angle of the particles in water were investigated.The interaction between the intergranular force and the distance between particles was investigated.The correspondence between drilling fluid density and barite particle distance is deduced.The effects of barite purity,particle size,particle size gradation,surface modification and other factors on the rheological properties of high density drilling fluid and the influence of curve jumping were studied.The influence mechanism of barite on the rheological properties of high density drilling fluid was analyzed by theoretical calculation and laboratory experiment.The rheological properties were controlled according to the calculated results.According to the theoretical calculation results,it is proved that EDLVO theory can guide and control the rheological properties of high density drilling fluid scientifically.It is found that the generation of the viscosity of the high density drilling fluid is independent of the close accumulation of the solid particles.The main reason for the poor rheological properties of the high density drilling fluid is the formation of the excipient gel.The surface properties of barite have the greatest effect on the rheological properties of the system,followed by the barite grain size,the surface potential of the barite and the dielectric constant of the water.