超临界CO_(2)压裂液对页岩储层支撑剂悬浮性能的影响因素分析

Influence Factors of Supercritical CO_(2) Fracturing Fluid on Suspended Sand Performance of Shale Reservoirs

超临界CO_(2)压裂液的极低表观黏度导致了低携砂悬砂、漏失严重和压裂效果弱等诸多缺陷。针对超临界CO_(2)的上述缺陷,设计并合成了一种能显著提高CO_(2)压裂液黏度的增稠剂,并探索了不同地质条件(储层温度和储层压力)和化学剂等因素对CO_(2)悬砂性能的影响,同时揭示了超临界CO_(2)压裂液的悬砂机理。研究结果表明:较高含量的增稠剂不仅能够增加压裂液黏度,同时也能改善CO_(2)压裂液对颗粒的悬砂能力,0.5%(质量分数)的增稠剂可使CO_(2)压裂液黏度增大至3.2mPa·s,静置20 s的砂砾沉降量为0.5 g,沉降量低于纯CO_(2)压裂液(其表观黏度为0.04 mPa·s)时的1.7 g。此外,储层压力的升高也有助于提升超临界CO_(2)对颗粒的悬砂性能,而升高储层温度会降低超临界CO_(2)压裂液黏度和悬砂能力,此现象主要归因于超临界CO_(2)压裂液体系中微观网格密度的变化。通过以上研究,可为页岩储层的高效开采和超临界CO_(2)的应用提供切实有效的途径和方案。

The extremely low apparent viscosity of supercritical CO_(2) fracturing fluid is associated with such defects as low sand carrying capacity and suspended sand,severe leakage,and weak fracturing effects.The paper designs and synthesizes a thickener significantly enhancing the viscosity of CO_(2) fracturing fluid,analyzes the effects of different geological conditions and chemical agents on the suspended sand performance of CO_(2) fracturing fluid,and reveals reasons on the sand suspension of supercritical CO_(2) fracturing fluid.The results indicated that an increased concentration of CO_(2) thickener not only could enhance the viscosity of the fracturing fluid but also enables the CO_(2) fracturing fluid to suspend sand particles.The viscosity of the CO_(2) fracturing fluid can increase to 3.2 mPa·s with the a 0.5%thic kener and the gravel settlement would be 0.5 g with a gravel settlement time of 20 s,lower than the 1.2 g observed in pure CO_(2) fracturing fluid(0.04 mPa·s).Furthermore,an increase in reservoir pressure would help enhance sand suspension performance of supercritical CO_(2) on particles,whereas elevated reservoir temperature would impair supercritical CO_(2) fracturing fluid and sand suspension capabilities,which is predominantly attributed to the changes in microgrid density in supercritical CO_(2) fracturing system.The study would provide practical and effective approaches and projects for the high effective development of shale reservoirs and applications of supercritical CO_(2).