The Research And Evaluation Of Flat-Rheological Synthetic-Based Drilling Fluid

There are abundant oil and gas resources in offshore in China,and oil and gas exploitation is gradually developing towards offshore deepwater drilling.However,the offshore drilling environment is complex,including deep-water and low-temperature conditions,drilling with gas hydrate and shallow gas layer,wellbore stability,etc.,which requires high performance of drilling fluid,mainly considering the rheological properties of drilling fluid.The change range of temperature in offshore drilling is large,and the change of temperature will seriously affect the viscosity and shearing force of drilling fluid.When drilling from datum level to seabed,the decrease of wellbore temperature increases the viscosity of drilling fluid continuously and also increases the density of drilling fluid,and then the flow properties of drilling fluid become poor,which can cause the occurrence of lost circulation in serious cases;however,with the increase of drilling depth from seabed,the wellbore temperature will increase,which can reduce the viscosity of drilling fluid.In some serious cases,barite will not be suspended and results in particle sag.What's more,uneven density of drilling fluid will be measured,and at last affecting the ability of borehole cleaning.What's more,synthetic based drilling fluid(SBM)has the advantages of low viscosity,high flash point,low toxicity,and strong biodegradation ability,etc.,and the application effect of synthetic-based drilling fluid is much better than that of oilbased and water-based drilling fluid systems,which is increasingly widely used in offshore deepwater drilling.In view of the above problems,a flat rheological synthetic based drilling fluid(FR-SBM)is designed and studied in this paper.A new type of SF base fluid was developed by using heavy hydrocarbon in Daqing through hydrogenation,desulfuration and dearomatization processes under the action of catalyst,and the carbon atom number distribution of the new type of synthetic based fluid was measured by gas chromatography,so the synthetic based fluid of the designed synthetic base drilling fluid was determined by comparing the performances of different synthetic base fluids;the mechanism of flat rheological property of drilling fluid is studied.The additives,including viscosifier,emulsifier and fluid loss control agent are compounded,what's more,the effects of different additives on the properties of synthetic based drilling fluid system at different temperatures are analyzed and compared,so the problem of flat rheological properties of synthetic drilling fluid is solved,and then the formula of synthetic based drilling fluid is determined;according to the curve fitting method,the viscometer readings under different shear rates are used to calculate the plastic viscosity,etc.,and then the rheological model of synthetic based drilling fluid is determined,which is convenient for quantitative characterization of the rheological properties of drilling fluid;the performance of synthetic based drilling fluid system was evaluated in laboratory by using six-speed rotary viscometer,emulsion stability tester and high and low temperature alternating test cabinet,and the evaluation results of synthetic based drilling fluid by the experiments of rheological property,filtration performance and electrical stability under the condition of high and low temperature alternation.It was found that the prepared flat rheological synthetic based drilling fluid has good rheological property,tolerance to contamination property and sag stability.