Research On Oil-displacing Rinsing Fluid

Oil-based drilling fluid is widely used in complex deep wells due to its many functions,such as high shale inhibition,excellent lubrication,strong anti-high temperature and anti-poluution capacity and superior reservoir damage resistance.However,these characteristics are detrimental to well completion and workover operations because they lead to difficult filter-cake cleanup,poor compatibility with slurry,and weak cementing quality.So we usually pump some flushing fluid between drilling fluid and cement slurry.Flushing fluid can serve to dilute,buffer,wash,isolate,and so on.Besides,it can prevent slurry thickening and decrease formation damage by drilling fluid.In this paper,the action mechanism of flushing fluid and additives was introduced.The domestic and international current situation of flushing fluid have been analyzed.Additives were screened preliminarily by combinating theoretical analysis with tests(cloud point,interfacial tension,tube oscillation,microscope,contact angle).Different formulas were got by mixing different additives,then their performance were evaluated.The cleaning efficiency of different formulas was evaluated for different oil-based drilling fluid.Then formula which has high efficiency was chosen to experiment.The anti-high temperature performance of formulas was tested by static curing and dynamic simulation.Next,the composition of formula was optimized by the compatibility of mixture,interface cementing strength and salt tolerance.Finally,the formula was concentrated.The results showed that flushing fluid TGD-80 has a better cleaning effect for oil emulsion and diesel oil-based drilling fluid at room temperature.The cleaning efficiency of flushing fluid KY-65 is 85.43%for Changning oil-based drilling fluid.Flushling fluid BH-OFS can completely destroy the structure of the oil-based drilling fluid,and its cleaning efficiency reached more than 97%at temperature of 25? to 180?.Meanwhile,BH-OFS can be compatable with drilling fluid and cement slurry.It can improve interface cementing strength to some extent,and be compounded with 6.5%saline.Field applications showed that flushing fluid BH-OFS achieve good cementing quality.