纳米微球缔合成胶的新型低伤害压裂液研制

For unconventional oil and gas reservoirs, in contrast to marine shale in U.S.A., continental shale is abundant in china, and characterizes in less brittle minerals, more clay minerals, and strong water sensitivity. Thus, the applicable fracturing fluid, featured in high sand carrying, low filtration, fast flowing back and low residue is urgently needed..In our project, the new fracturing fluid gelled with associating nano-microspheres (NMS) is proposed on the principle that self-assembly of nanoparticles into mesoscopic clusters and networks is driven by non-bonding forces. It overcomes the tricky gel-broken problem of common polymer fracturing fluid and the high leakage of viscoelastic surfactant fracturing fluid. The major contents and innovative are list below: ① The NMS are prepared by microemulsion polymerization and, by developing multi-addition process, the gel breaker is uniformly placed in NMS; ② According to rheology theory of hard sphere colloids, the gelation mechanisms and rules of water suspension of NMS are revealed by property analysis and rheology measurement, and then the high sand-carrying, low-filtration and easy flow-back properties of this new fluid are constructed；③ After the degradation monomers and gel breaker are incorporated in NMS, the gel-breaking process and inner cause are elaborated on the basis of the thermal stability analysis, and eventually the efficient degradation of NMS is achieved and dramatically reduces the residual gel damage..The objective is to supply theory foundation and experiment support for the application of this new fracturing fluid in development of unconventional oil and gas reservoirs of china continental shale.

我国有丰富的陆相页岩非常规油气藏，与美国的海相页岩相比，其脆性矿物含量低、黏土矿物含量高、水敏性强，因此亟需开发具有高携砂、低滤失、易返排和高效降解性能的低伤害压裂液体系。本项目根据纳米颗粒在非共价键作用下自组装为团簇或网络的原理，提出了纳米微球缔合成胶的新型压裂液体系，克服了常规聚合物体系地下破胶不彻底和黏弹性表面活性剂体系易滤失的缺点。主要研究内容和创新点：①通过微乳液聚合制备纳米微球，发展多步聚合方法在体系中均匀预置破胶剂；②通过微球基本性质和悬浮液流变性研究，结合硬球胶体流变理论，揭示微球悬浮液的成胶机理和规律，构建缔合成胶微球体系，实现高携砂、低滤失和易返排能力；③通过引入不稳定单体和预置破胶剂后微球的热稳定性分析，阐明体系的破胶过程和机理，实现微球的高效降解，大幅降低残余凝胶伤害。旨在为新型压裂液体系在陆相页岩非常规油气藏开发中的应用提供理论基础和实验支撑。

本项目针对我国陆相页岩非常规油气藏脆性矿物含量低、黏土矿物含量高、水敏性强的特征，结合纳米颗粒在非共价键作用下自组装为团簇或网络的原理，探索了纳米微球缔合成胶的新型压裂液体系。项目应用微乳液聚合方法制备了一系列阴离子和阳离子微球，通过多步聚合工艺在微球中预置了破坏剂，并应用通过交联密度控制和引入疏水壳材的方法尝试控制破胶时间，在此基础上进一步探索了纳米微球溶液流变规律和复合微球体系的可能应用，对比分析了其做为压裂液的性能。具体工作有如下五个方面。.(1)应用反相微乳液聚合合成了阳/阴离子度0~40%，粒径小于100 nm的纳米级微球。以合成产物分子量筛选了最佳反应条件，发现一次合成的微球乳液中，仍能增溶20%以上的离子单体溶液。不同离子度的微球溶液的粘性指数与浓度的关系曲线存在一凹形区域，该区域能反映微球之间电粘效应的强弱。.(2)通过两步聚合分别加入阴阳离子单体的方法，成功制备了固含量在32%以上的阴阳离子复合微球乳液。该体系经过乳化分散后对0.1~4μm2的中高渗透率地层的封堵率可达90%，具有较好的调剖应用前景。.(3)微球包覆过硫酸铵做为破胶剂，基液初始粘度下降速率较低且破胶数小时后能下降至5mPa∙s。通过改变交联剂浓度或引入疏水壳材的方法能一定程度上控制基液的破胶速率。.(4)P(AM-AMPS)微球溶液在降解反应的0~4h内，自由基氧化降解作用使溶液粘度迅速降低，pH维持在3以下。降解规律分析表明，微球外层的阴离子聚合物链段首先降解，而4h后微球内核逐渐破碎，导致粒径快速下降。包覆微球疏水聚合物壳层能有效抑制了聚丙烯酰胺的自由基氧化降解。.(5)纳米微球、疏水缔合物、CTAB-NaSal三种物质做为压裂液增稠剂的对比评价表明，微球体系具有较好的增粘携砂性能，其破胶液粘度低，残渣含量、滤液及破胶液的岩心基质伤害基本能达到水基压裂液的要求，但是短时破胶后颗粒物质稍多。建议对其破胶后形成的聚合物凝胶颗粒物质对地层的伤害进行进一步研究。