CO_2无水压裂工艺及核心设备综述

Review of CO_2 Non-aqueous Fracturing Process and Key Equipment

CO_2无水压裂以液态CO_2作为压裂基液,压裂过程中基本不需要水,投产前CO_2以气态返排,不会对井场造成污染。但其缺点也很明显,如CO_2管道摩阻高、黏度低造成滤失较大、形成的裂缝尺寸较小、携砂能力低、液态CO_2的低温高压环境难以实现混砂。针对上述问题,提出了应对措施:尽量采用套管压裂、采用增稠剂提高黏度、开发专用的增压设备和带压混砂设备实现混砂功能。通过这些措施,有效避免了上述问题对CO_2干法压裂效果造成的不利影响,目前该套工艺和设备已经成熟,完全满足CO_2干法压裂的施工要求。另外为保证施工过程的设备和人员安全,阐述了实施过程中的无人化井场设计思路。最后指出,以CO_2无水压裂为代表的无水压裂技术由于其对储层无伤害和较高的增产效果、对水资源的节省和保护等常规压裂无可比拟的技术优势,在可预见的未来会逐渐成为非常规油气开采的核心技术。

The CO_2 fracturing,taking the liquid CO_2 as the base fluid,do not has the need of water during the whole fracturing process. The liquid CO_2 would be flowed back as gas CO_2 before production,resulting to zero pollution to the well site. But the disadvantages of the liquid CO_2 are also obvious, including high filtrate loss caused by high pipe friction resistance and low viscosity of CO_2,the smaller fracture size compared to those formed by water-based fracturing fluid,and poor sand carrying capacity and hard sand blending in liquid CO_2 under lowtemperature and high-pressure conditions. Regarding to the disadvantages above,the corresponding countermeasures are presented： application of casing fracturing,applying thickener to increase viscosity,and developing special boosting equipment and sand blender to achieve sand blending,through which the disadvantages effect on the fracturing performance have effectively been avoided. The process and equipment becomes mature now, which could meet the operation requirements of CO_2 non-aqueous fracturing. Furthermore, the design concept of unmanned wellsite for both equipment and personal safety during operation has been introduced. The non-aqueous fracturing technology with CO_2 as the representative has unparalleled advantages over the conventional fracturing because of its zero formation damage,higher stimulation performance,water saving and protection,and may become the core technology of unconventional oil and gas exploration in the foreseeable future.