两亲性碳点在硅酸盐钻井液中的润滑性能

The Lubricity of Amphiphilic Carbon Dots in Silicate Drilling Fluids

硅酸盐钻井液具有抑制封堵能力强、环保等优点,但其润滑性能差,这制约了硅酸盐钻井液的广泛应用。利用极压润滑仪测定含有两亲性碳点和聚氧乙烯型表面活性剂的硅酸钠溶液的润滑系数,筛选出性能优异的润滑剂,并采用总有机碳分析仪、动态光散射和接触角仪等分析其润滑机理。实验结果发现,两亲性碳点具有优良的润滑性能和耐温性,在5%硅酸钠水溶液中添加0.3%两亲性碳点C_(12)-CDs,经过110℃高温热滚16 h前后体系的极压润滑系数可从0.500左右分别降低至0.065和0.063,润滑系数降低率高达87.52%,而聚氧乙烯型表面活性剂并无润滑效果。进一步探究其润滑机理,C_(12)-CDs在石英砂表面具有优异的吸附性能,100 mg/L的C_(12)-CDs溶液吸附前后的表面张力从44.81 mN/m上升为64.03 mN/m,其吸附量可达到89.23 mg/L;且粒径分析数据表明,C_(12)-CDs可将Na_(2)SiO_(3)溶液的平均粒径从514.0 nm分散为63.2 nm。碳核表面的多羟基结构和长疏水链可促进两亲性碳点在金属钻杆、井壁和硅酸聚集体表面的吸附,两亲性碳点作为润滑剂与硅酸钠钻井液体系配伍性能好,添加C_(12)-CDs的现场硅酸盐钻井液润滑系数降低率可达到86.34%,可为硅酸盐水基钻井液润滑剂的现场应用提供理论指导。

Silicate drilling fluids have strong inhibitive capacity and good environment protection property,but their poor lubricity limits their application.In screening good lubricating agents for silicate drilling fluids,extreme pressure(EP)lubrication tester is used to measure the coefficient of friction of silicate drilling fluid samples containing amphiphilic carbon dots and polyoxyethylene surfactant.The best lubricating agent selected is then tested with total organic carbon analyzer,dynamic light scattering tester and contact angle tester to analyze its mechanisms of lubrication.The test results show that the amphiphilic cardon dots have excellent lubricity and high temperature stability.A 5%sodium silicate(Na_(2)SiO_(3))water solution treated has EP coefficient of friction of around 0.500.The solution is then treated with 0.3%amphiphilic carbon dots(C_(12)-CDs),and the EP coefficient of friction is reduced to 0.065.After hot rolling the C_(12)-CDs treated Na_(2)SiO_(3)solution at 110℃for 16 h,the EP coefficient of friction of the solution is further reduced to 0.063,that is,the EP coefficient of friction of the Na_(2)SiO_(3)solution is reduced by 87.52%.On the other hand,the polyoxyethylene surfactant shows no effect on the lubricity of the Na_(2)SiO_(3)solution.Further study shows that C_(12)-CDs has excellent adsorption performance on the surface of the quartz sands,the surface tension of a C_(12)-CDs solution(c=100 mg/L)increases from 44.81 mN/m before the adsorption process to 64.03 mN/m after the adsorption process,the adsorption capacity is 89.23 mg/L.Particle size analysis shows that the C_(12)-CDs can effectively reduce the particle sizes of the Na_(2)SiO_(3)solution;the average particle size of the Na_(2)SiO_(3)solution is reduced from 514 nm to 63.2 nm.The multi-hydroxy structure and the long hydrophobic chain on the surface of the carbon nuclei can improve the adsorption of the amphiphilic carbon dots on the surfaces of the drill string,the borehole walls and the silicate aggregates.The amphiphilic carbon dots as a good lubricating agent have good compatibility with silicate drilling fluids.Field application shows that C_(12)-CDs can reduce the coefficient of friction of silicate drilling fluids by 86.34%,and are thus a good lubricating agent for silicate drilling fluids.