超临界CO2压裂液增黏剂的长管实验评价及增黏机制探讨

针对超临界CO₂压裂中CO₂黏度低、携砂困难等问题，开展6种超临界CO₂压裂液增黏剂的性能研究。分析增黏剂聚乙酸乙烯酯、聚苯乙烯、氟化丙烯酸酯、聚甲基倍半硅氧烷、聚甲基倍半硅氧烷-乙酸乙烯酯以及氟化丙烯酸酯-苯乙烯的分子结构，测试其增黏效果及热稳定性，评价温度、压力、增黏剂注入量对超临界CO₂压裂液黏度的影响，测试不同管径中压裂液的阻力系数，并探讨超临界CO₂增黏的机制。实验结果表明，在温度为50℃、压力为12MPa、注入增黏剂质量分数为3%时，氟化丙烯酸酯-苯乙烯对超临界CO₂的增黏效果最好，增黏倍数为316.7倍，黏度值为15.202mPa·s；改善增黏剂在CO₂中的溶解性可以有效提高超临界CO₂压裂液的黏度；具备两亲特性、具有无定形、无规则结构特征以及分子上既存在路易斯酸又有路易斯碱的共聚物能有效提高其在CO₂中的溶解性，并形成大分子相互缠绕的空间网络结构，达到增黏的效果。该研究对超临界CO₂增黏剂的研制以及超临界CO₂压裂施工具有重要的现实意义。

Experimental evaluation and thickening mechanism of long tube in supercritical CO2 fracturing fluid tackifier

Aiming at the problems of low CO₂ viscosity and difficulty in carrying sand in supercritical CO₂ fracturing, the performance of six supercritical CO₂ fracturing fluid tackifiers was studied. The molecular structure of tackifiers polyvinyl acetate, polystyrene, fluorinated acrylate, polymethylsilsesquioxane, polymethylsilsesquioxane-vinyl acetate, and fluorinated acrylate-styrene is analyzed. The thickening effects and the thermal stability of those tackifiers are tested, the effect of temperature, pressure, and the amount of tackifier injection on the viscosity of the supercritical CO₂ fracturing fluid is evaluate, and the drag coefficient of the fracturing fluid in different pipe diameters is tested, at the same time we explore the mechanism of supercritical CO₂ viscosity increase. The results of experimental show that fluoroacrylate-styrene has the best thickening effect on supercritical CO₂, at a temperature of 50℃, a pressure of 12MPa, and an injection mass percentage of 3%. And its adhesion increase rate is 316.7 times, viscosity value is 15.202mPa·s. To improve the solubility of the tackifier in CO₂ can effectively increase the viscosity of the supercritical CO₂ fracturing fluid. The supercritical CO₂ fracturing fluid possesses amphiphilic characteristics and is characterized by amorphous and irregular structures, which has both Lewis acid and Lewis base copolymers on molecules, that can effectively increase their solubility in CO₂ and forms a spatial network structure with large molecules intertwined to achieve the effect of increasing viscosity. This research has important practical significance for the development of supercritical CO₂ tackifiers and the application of supercritical CO₂ fracturing.