页岩气CO_2泡沫压裂技术

页岩气开发过程中不仅要注重产量的突破,还应加强对节水/无水压裂等技术的攻关,以确保水资源紧缺地区页岩气开发的有序进行。为此,比较了CO_2泡沫压裂与滑溜水压裂、其他节水/无水压裂技术的特点与优势,认为CO_2泡沫压裂技术能大幅减少用水量,通过增加施工排量和规模可弥补其在改造体积方面与滑溜水压裂所存在的差距,设备改造要求、混注工艺、施工难度较其他节水/无水压裂低,安全风险小;分析了CO_2泡沫压裂液物理特性,由于CO_2相态变化复杂,储层条件下处于超临界状态的CO_2,与水基压裂液形成CO_2泡沫;研究了CO_2泡沫压裂施工设备及工艺技术,认为在施工设备、分段工艺、施工步骤、安全保障方面,增加了液态CO_2泵注流程,需考虑CO_2的特殊性,制定相应的施工保障、安全预防措施。此外,还调研了CO_2泡沫压裂在美国Ohio和Lewis、加拿大Monteny、延长油田页岩气开发中的应用情况,发现其增产改造效果明显。所取得的研究成果为四川盆地页岩气的压裂改造提供了新的思路和方法,也为水资源紧缺地区页岩气开发提供了重要的技术储备与补充。

CO2 foam fracturing technology in shale gas development

Shale gas development in areas with deficient water resources should focus on water-conservative or water-free fracturing technologies besides production. In this paper, first, CO₂foam fracturing was compared with slickwater fracturing and other water-conservativeor water-free fracturing technologies in terms of their technical characteristics and advantages. It is indicated that CO₂ foam fracturing is advantageous in that much less water is consumed; that its stimulated reservoir volume (SRV) can be as good as that of slickwater fracturing if its displacement rate and volume are increased; and that it presents lower requirements for equipment reformation, less difficulty in mixed injection and operations, and lower safety risks compared with other water-conservative or water-free fracturing technologies. Second, the physical properties of CO₂foam fracturing fluid were analyzed. It is shown that CO₂in the reservoir conditions is at a supercritical state due to the complexity of CO₂ phase change, and it, together with water base fracturing fluid, forms CO₂foam. Third, the equipment and technologies for CO₂ foam fracturing were reviewed. In view of equipment, staged technology, operational procedureand security insurance, liquefied CO2 pumping process is added, so the special properties of CO2 should be considered and correspondingsecurity precautions should be taken. Finally, the application of CO2 foam fracturing in Ohio and Lewis of the USA, Monteny of Canada, and Yanchang of China was investigated, and remarkable stimulation results were obtained. The study results provide a new idea and method for fracturing stimulation of shale gas in the Sichuan Basin, as well as important technical reserves and supplement for shale gas development in water shortage areas.