淹没环境下超临界二氧化碳喷砂射孔流体动力学特征及成孔特性研究

Using supercritical carbon dioxide jet perforation to fracture shale and enhance the development of shale gas has lots of advantages like water saving, high recovery efficiency and environmental protection. However, this technology is now in its infancy with many basis theoretical problems waiting to be solved. As there exist great differences between lab experiments and field trials on the depth of hole made by hydraulic jet perforation and inadequate theoretical studies, the differences of physical characteristics between supercritical carbon dioxide and traditional working fluid for well drilling were taken into consideration. By method of combining theoretical analysis, numerical simulation and experimental, quantitative analysis of the main factors during the process of jet perforation will be carried out. Meanwhile, the flow field in the hole made by supercritical carbon dioxide jet perforation and abrasive motion and distribution characteristics will be studied, as well as the dynamic and erosion characters. To reveal the interaction mechanism of supercritical carbon dioxide abrasive jets and eroded target and interaction laws of the various operating parameters, models for predicting the depth caused by supercritical carbon dioxide jet perforation will be established and visualization experiment and numerical simulation will be used as validations for improvement. The present research will provide technical basis for effective fracturing and rock breakup and also be meaningful for shale gas development using supercritical carbon dioxide.

超临界二氧化碳喷砂射孔、压裂强化页岩气开采技术具有节水、高效、环保等优势。目前国内对该技术的研究仍处于起步阶段，尚有大量基础理论问题亟待解决。本课题针对水力喷砂射孔深度室内预测与工程实际差别较大、理论研究不足的特点，考虑超临界二氧化碳与传统钻井液的物性差异及孔眼影响，拟采用理论分析、数值模拟和实验研究相结合的方法，量化分析射孔过程中的主要影响因素，研究淹没条件下超临界二氧化碳喷砂射孔孔内流场特征、磨料的分布和运移规律、分析超临界二氧化碳磨料射流的动力学特征及冲蚀破岩成孔特性，揭示超临界二氧化碳磨料射流与冲击靶物相互作用机理以及各影响因素之间的交互作用规律,建立淹没条件下超临界二氧化碳喷砂射孔深度预测模型，并设计可视化实验，结合计算机模拟结果进行对比验证，进一步修正完善理论模型。研究成果为高效射孔破岩、压裂提供技术支撑，对推进超临界二氧化碳强化页岩气开采有重要意义。

页岩气高效开发的关键技术是对页岩储层的压裂改造，增大储层的渗透率，超临界二氧化碳喷砂射孔、压裂强化页岩气开采技术具有节水、高效、环保等优势，是未来页岩气开采技术的主要发展方向。现有水力喷砂射孔模型已经不足以预测实际超临界二氧化碳喷砂射孔工程，新技术的理论研究进展缓慢。本项目针对以上问题，采用室内实验、理论分析和数值模拟等多种手段，研究了超临界二氧化碳 射流流场特征和影响超临界二氧化碳喷砂射孔过程中的主要因素孔。主要研究成果如下：（1）研究淹没环境下超临界二氧化碳喷砂射孔流场特性，主要包括超临界二氧化碳射流动力学特性和不同的环境下环境下超临界二氧化碳射流的流场形态。（2）分析了超临界二氧化碳携带颗粒的加速特征，研究了超临界二氧化碳射流的颗粒携带能力，总结了射流压差、流体温度及磨料粒径对颗粒加速的影响，总结了超临界二氧化碳淹没射流中磨料的加速特性和运移规律。（3）进行了淹没环境下超临界二氧化碳射流冲击水泥试样和页岩岩样的室内实验，分析了两种样本的冲蚀形貌，总结了射流参数和岩心材质等对射孔效果的影响规律。以上研究剖析了超临界二氧化碳喷砂射孔的整个流程，建立了超临界二氧化碳喷砂射孔、冲蚀的基本规律，研究成果为高效射孔破岩、压裂提供技术支撑，对推进超临界二氧化碳强化页岩气开采有重要意义。