页岩纳微米储层保护压裂液降滤失作用机理研究

In recent years, the development of shale gas in the Sichuan basin of China has gained remarkable achievement. On account of fine pore throats and low permeability in shale matrix, hydraulic fracturing of long horizontal segment shall be employed in shale reservoirs to achieve high productivity. However, micro-fractures and developed clay minerals in shale result that severe aqueous trapping is prone to occur in gas shale formation caused by fracturing fluid filtration during fracturing process, and most wells with low productivity and unstability production. In order to reduce the damage caused by fracturing fluid filtration, technique of compound temporary plugging agent enhanced fracturing fluid for filtration control is developed, which can seal matrix pore throats in fracture face; and after fracture operation, high productivity can be achieved by seal removing operation. A comprehensive evaluation experimental platform was built and experiments were performed on micro-nano temporary plugging agents. The project is to character the pore structures, investigate the mechanism of plugging of force imbibition and capillary imbibition, and optimize the temporary plugging fracturing fluid system. The research further reveals the filtration damage mechanism, develops mathematical model of nano and micro scale temporary plugging, and perfects protective fracturing fluid and technological parameter for formation protection in nano and micro-scale shale gas reservoirs. This project has great guiding significance for efficient development of shale gas reservoirs.

近年来页岩气开发在中国四川盆地周缘已经取得显著成效。页岩气层先天孔喉细小、渗透率低的特性需要借助于水平井大型水力压裂才能实现高产。压裂过程中，页岩储层微裂缝及黏土矿物发育易遭受压裂液滤失带来的严重水相圈闭损害，开发过程中多数气井表现出产量低、稳产困难的特征。为降低压裂液滤失带来的损害，创新性设计了前置液中添加复合暂堵剂降低滤失的暂堵压裂液技术，通过压裂过程中对裂缝面基块孔喉的封堵、压裂后高效解堵来实现页岩气的高产及稳产。已初步搭建能实现纳微米暂堵效果室内评价综合实验平台，能够对纳微米暂堵剂暂堵效果进行室内实验评价。拟通过页岩储层纳微米孔喉结构特征研究、正压差及毛细管自吸压裂液封堵实验及机理分析、暂堵压裂液技术体系优选等工作，进一步明确页岩纳微米孔喉滤失及损害机理、建立纳微米页岩储层暂堵数学模型、完善相应的保护页岩储层纳微米暂堵压裂液体系及工艺提供基本参数，为页岩气的高效开发提供新的思路。

川东龙马溪组露头页岩基质内纳米级有机孔发育，以及颗粒内存在无机质溶蚀孔缝、粒缘缝、黄铁矿，测试页岩样品表面润湿性为水湿。采用改进Hummers法能成功合成单层或者少层的氧化石墨稀；在影响氧化石墨烯横向尺寸的众多因素中，超声波分散时间、原材料初始粒径、氧化石墨烯分散液浓度、溶液pH值均能对氧化石墨烯的横向尺寸产生较大的影响；使用十六烷基三甲基溴化铵（CTAB）、硅烷偶联剂（KH570）对氧化石墨烯进行改性后，改性产物保留氧化石墨烯片层结构，其鳞片状结构变得较为均匀，层间距远大于氧化石墨烯，片层表面较氧化石墨烯更粗糙，且存在明显的皱褶，此外，改性产物润湿角测试结果表明，KH570疏水改性效果较好。. 添加改性材料后压裂液流变性、携砂性、滤失性等压裂液基础性能均得到提高，且改性效果随改性材料浓度增加而增加。当改性材料浓度为0.05%时，为封堵页岩基质孔隙的最佳浓度。随着改性压裂液对基质型页岩岩心进行封堵的时间的延长，封堵率先迅速增加，后趋于平缓，封堵20 min后，实现了较好的封堵效果。纳米材料与压裂液中的胶束发生化学或物理吸附，增强网络状胶束结构，进入地层后形成假滤饼。通过扫描电镜分析改性材料封堵行为，当材料浓度较低时，材料呈单层连片状，当提高材料浓度时，材料以多层堆叠的形式存在。. 明确了页岩纳微米孔喉滤失及损害机理、建立纳微米页岩储层暂堵数学模型、完善相应的保护页岩储层纳微米暂堵压裂液体系及工艺提供基本参数，为页岩气的高效开发提供新的思路。