Development And Properties Evaluation Of Flat Rheological Water-based Drilling Fluids In Deepwater Drilling

There were big diffrenece between in offshore deepwater drilling engineering and ashore or shallow sea drilling engineering for water-based drilling fluids,because it would undergo the high temperature at downhole and the low temperature at seabed alternately which would cause a big change of rheological properties for water-based drilling fluids.With the decreasing of the temperature,the equivalent circulating density?ECD?would increase in the results of the safe weigh window of deepwater drilling was low,and the increase of ECD would cause a series of complex accidents downhole such as lost circulation.Therefore,the flat rheology control of offshore deepwater water-based drilling fluids?WBDF?was an very important challenge in the wide range of temperature which would restrict the exploration of deepwater oil and gas resources.In this paper,in order to study the influence of drilling fluids compositions on the flat rheology?FR?respectively in offshore deepwater for WBDF in 4?⁶5?,We adopted the single factor optimization trials.The research results indicated the rheological properties contral of Ca-bentonite based drilling fluids,sepiolite based drilling fluids,attapulgite based drilling fluids,kaolinite based drilling fluids were insensitive to the change of temperature,and the viscosity changed a little;and the pulpification rate of Na-bentonite based drilling fluids were efficient,and the viscosity was moderate.Different kinds of weighting materials?such as barite,micronized barite and manganese oxide?would largely change the rheological properties while increasing the weight.The research results indicated that through adjusting pH,adding the mineral salt?such as NaCl,KCl,CaCl₂ and AlCl₃?would worsen the flat rheology of WBDF in 4?⁶5?.Tackifier,thinner,filtrate reducer,shale inhibitor and lost circulation additive would change the flat rheology of deep-water WBDF.Through the optimization formula of the flat rheology of WBDF,which apparent viscosity rate was lessen than 2,plastic viscosity rate was lessen than 2.5,10s-Gel rate was lessen than 1.7,10min-Gel rate was about 1.3.The long-term stability was well,the lubricating property was well,and the drill solids evaluation capacity was strong,and the property of inhibit shale formation collapse prevention was strong,the reservoir protection was well.