Analysis Of Settlement Stability Of Water-in-oil Drilling Fluids With High Temperature And High Density Resistance

With the deepening of exploration and development,high-temperature and high-density water-in-oil drilling fluids have been widely used in ultra-deep wells because of the ability to reduce downhole complexity.The Kuche piedmont structure in the Tarim Oilfield faces challenges such as high temperature(200°C),high pressure(2.6g/cm~3)and long completion period,which puts higher requirements on the settlement stability of water-in-oil drilling fluid under high temperature and high pressure conditions.Temperature and pressure have a great influence on the rheology of water-in-oil drilling fluid,which affects the sedimentation stability of drilling fluid.Therefore,the sedimentation stability of drilling fluid under high temperature conditions is an important problem that needs to be solved in water-in-oil drilling fluid research.In this paper,the static and dynamic settlement stability of water-in-oil drilling fluids are evaluated by the static aging kettle method and the improved VST sedimentation test method,respectively.The effects of density,temperature,emulsifier addition,oil-water ratio,water-in-oil drilling fluid rheological parameters and weighting agent particle size on the sedimentation stability of water-in-oil drilling fluid were analyzed,and the influence law of sedimentation stability of various factors was obtained.Stability and drilling fluid rheological parameters play a decisive role in sedimentation stability.Micronized barite can significantly improve the sedimentation stability of water-in-oil drilling fluid system.The optimum ratio of API barite to micronized barite is from 30:70to 50:50.Linear regression method was used to fit the water-in-oil drilling fluid variable parameters with static/dynamic sedimentation stability.It was concluded that the dynamic-plastic ratio and final cutting determined the static settlement stability,and the dynamic-plastic ratio and dynamic shear force determined the dynamic settlement stability.The research results have certain guiding significance for the on-site construction of high-density water-in-oil drilling fluid.