Research And Evaluation Of Nano-plugging Materials For Water-based Drilling Fluids

With the gradual expansion of oil and gas resources exploitation,ultra-deep oil and gas reservoirs have become an important development resource.However,ultra-deep drilling is faced with problems such as high temperature,high pressure and complex wellbore stability.Nanomaterials have small size,large specific surface area,and high surface energy.It has been widely used in nanometer plugging and ultra-deep drilling wall stabilization.In this paper,through the comparative evaluation of the plugging performance of nanoparticles,nano-paraffin and other materials,a composite synergistic plugging mechanism of rigid bridging of nanoparticles and deformation filling of paraffin emulsion was proposed,and a new type of"internal rigid support+external flexible"was prepared.Deformation"of novel nano-core emulsions.In this study,the plugging performance of five micro-nanoparticle materials,including nano-SiO₂,nano-Al₂O₃,nano-Mg O,nano-Ti O₂ and nano-Fe₃O₄,was first evaluated.The evaluation results showed that nano-SiO₂ had better plugging and salt resistance;then,The plugging performance of paraffin microemulsion（self-made）was evaluated,and the results showed that adding 1.5%paraffin microemulsion could reduce the fluid loss of base slurry by 34%and form a denser mud cake.Finally,based on the research on the plugging performance of two different plugging materials,nano-SiO₂and paraffin microemulsion,guided by the broad-spectrum nano-plugging mechanism integrating bridging and deformation,a silane coupling agent（KH-570）and vinyltriethoxysilane（VTEO）for hydrophobic coating modification of nano-SiO₂,and then dispersed in a nanoemulsion system constructed by n-octane,water,Tween 80 and n-butanol to prepare a D₅₀ particle.The new nano-core-emulsion with a diameter of about100nm,the nano-core-emulsion can be stabilized in 5%KCl solution,and when 0.8%of the nano-core-emulsion is added to the 5%base slurry,the filtration loss can be reduced by 40%.Thickness reduced by 84%.In this study,the obtained new nano-core-emulsion was further applied to the potassium-based polysulfonic drilling fluid system to improve the sealing performance of the water-based drilling fluid and alleviate the problems of wellbore instability such as collapse and leakage during the drilling process.The laboratory evaluation test results show that the high temperature and high pressure fluid loss of the drilling fluid added with nano-core-emulsion is 3.6ml,and the mud cake thickness is 1.2mm;the permeability plugging instrument（PPT）fluid loss is 4ml;Compared with the drilling fluid without nano-core-emulsion,the plugging rate of the tight sandstone of the Kiziluoyi Formation was increased by 20.9%;The plugging rate of limestone in the Kalatal Formation was increased by 33.13%;the results of triaxial rock mechanics evaluation showed that adding the nano-core-emulsion to the drilling fluid can increase the compressive strength of the limestone of the Karatal Formation（soaked for 4 hours）by 10.32%,and the elastic modulus Compared with water soaking,the elastic modulus of the Atushi Formation sand-mudstone increased by 55.82%.The indoor evaluation and field application show that the new nano-core-emulsion has broad application prospects.