The Format Criterionof Doctoral Dissertation Of CUP

The application of water-based drilling fluids in shale gas drilling is increasing,but the formulation of the drilling fluids is complex,and its rheological properties,plugging inhibition and lubricity need to be improved.In this paper,wesystematically evaluatedthe performance of shear-responsive Laponite gel material in water-based drilling fluid.It was found that Laponite had the high performance of thickening,nanoporous plugging and shale inhibition,and the corresponding mechanism was explored.We also synthesized two water-basedester lubricants with strong absortion performance on metal surface,and studied influence of molecular structure on lubrication performance.At rheological properties,wemeasured the yield stress,shear thinning and viscoelastic modulus of Laponite and bentonite in aqueous solution or polymer solutionby Harrk rheometer.Zeta potential-particle size distribution and transmission electron microscopy analysis were used to explain the rheological mechanism.The results showed that 2%Laponite has higher yield stress and viscoelasticity than 6%bentonite after high temperature aging.Laponite gel structure can respond quickly to shear stress.Moreover,Laponite can dissolve rapidly in acidic environment,and dissolved Mg²⁺mainly affected its rheological properties.At nano-cracks plugging and shale inbition properties,we used the core saturation treatment to study the nano-cracks plugging of shale.N₂ isotherm adsorption-desorptionand scanning electron microscopemethods are used to explained the plugging mechanism.The results showed that Laponite can greatly reduce the pore volume?diameter=10 nm–100 nm?of shale,and the effect was much better than that of nano-silica and bentonite.Shale inhibition performance of Laponite nanomaterials was investigated by shale rolling recovery,clay linear expansion and mud cake immersion experiments.2%Laponite had better shale inhibition performance than 7%KCl,and the inhibition mechanism of Laponite was releated to the excellent shear-thinning behaviors.At lubricity properties,we developed two kinds of ester lubricants,and analyzed the lubricity,temperature and salt resistance,foaming,filter cake adhesionand compatibility performance.In the first type of synthetic ester,we investigated the effect of the amount of phenolic hydroxyl groups on the performance of the synthetic ester.Compared with ester with no and one phenolic hydroxyl group,the synthetic ester with two or three phenolic hydroxyl groups hadmuch better lubricity performance,which had a lubrication coefficient reduce ratio by 90%in 4%bentonite.In the second type of synthetic polyol ester,we investigated the effect of the amount of residual alcoholic hydroxyl groups on the lubricating properties of polyol esters.The polyol ester with no residual alcohol hydroxyl had the best lubricity and hydrolysis resistance properties,and the temperature resistance was 150°C.n-dodecyl mercaptan and polyol The ester had a synergistic effect on the lubricating properties,and n-dodecylmer could increase the temperature resistance of the polyol ester to 180°C.The mechanisms of these lubricants were analyzed by scanning electron microscopy,three-dimensional shaper and photoelectron spectroscopy.Laponite has good rheological properties,nano cracks plugging and shale inhibition properties.The two synthetic ester lubricants have strong adsorption properties on the metal surface and excellent extreme pressure lubrication properties.These two types of materials have certain application prospects in shale gas-water based drilling fluids.