页岩储层改造无水压裂液稠化与破胶新方法和机理研究

Shale reservoir resources need fracturing treatment to realize commercial exploitation and hydraulic fracturing with slick water as fracturing fluid is a common method. However, it has confronted with some problems such as low viscosity, consuming a large amount of water and inapplicability to water sensitive reservoir. Waterless fracturing fluid is an ideal system for shale reservoir treatment, which is suitable for strong water sensitive reservoir and avoiding waste of water. After viscosified, it also improves the performance properties. Due to micro-magnitude molecular size and gel breaking incompletely, polymer-based thickeners for waterless fracturing fluid showed serious damages to the nano-scaled shale pore and fracture face. In this project, a new thickening method was provided to resolve the contraction between viscosify and reservoir damage of waterless fracturing fluid. A series of functional surfactants with 1~2 nano-meter molecular length will be synthesized and used for constructing organized assembly to viscosify waterless fracturing fluid by regulating the surfactant molecular structure and interaction. The automatically gel breaking methods will be also build up by controlling the variation of composite and phase behavior.Combined further analysis on the effect of broken fluid to matrix permeability, wettability and gas adsorption, it was expected to obtain clean waterless fracturing fluid at low thickener concentration with superior viscoelasticity and low formation damage. The relationship between molecular structure, microscopic ordered structure and macroscopic viscoelasticity will be investigated and it is aimed to reveal the thickening and breaking mechanisms for small molecule viscosified waterless fracturing fluid. These studies will provided important technical support and scientific foundation for efficient development of shale reservoir resources.

页岩储层资源必须经过压裂改造才具有商业开发价值，以滑溜水作为压裂液进行水力压裂是常用手段，但滑溜水存在粘度低、消耗大量水资源、难适用于水敏储层等问题。无水压裂液适用于强水敏储层、且避免使用清水资源，经稠化后可提高压裂液性能，是理想的页岩储层改造用压裂液。本项目针对目前无水压裂液聚合物类稠化剂分子尺寸大、破胶不彻底，严重伤害页岩纳米级孔隙和裂缝面等问题，提出一种稠化无水压裂液的新方法。利用1~2 nm的小分子通过调节分子结构和分子间作用力构筑有序组合体结构稠化无水压裂液，建立基于体系组成和相态变化的自动破胶方法，分析破胶液对基质渗透率、岩石润湿性和页岩气吸附性质的影响，实现在低浓度下获得具有优异增粘效果和低伤害性的清洁无水压裂液体系；揭示分子结构-微观有序结构-宏观粘弹性能间的内在联系，从微观上阐明小分子化合物稠化无水压裂液体系的稠化与破胶机理，为我国页岩资源高效开发提供技术支撑和科学依据。

项目针对目前无水压裂液聚合物类稠化剂分子尺寸大、破胶不彻底，严重伤害页岩纳米级孔隙和裂缝面等问题，提出稠化无水压裂液的新方法。设计合成含双脲基、单脲基、多链-高枝化三类小分子稠化剂，构筑具有增粘效果的分子有序组合结构，将分子自组装和压裂液体系设计相结合，建立了小分子化合物稠化无水压裂液的新方法。对于烷烃类无水压裂液体系，获得了双脲基小分子稠化剂、多链-高枝化稠化剂混合体系稠化剂、复合交联剂/烷基磷酸酯交联体系三种稠化体系；对于甲醇和乙醇无水压裂液体系，获得了单脲基小分子混合体系稠化剂，且考虑到国内对醇基压裂液定义的拓展，获得了羧甲基羟丙基胍胶交联体系稠化醇水溶液；对于超临界CO2无水压裂液体系，获得了低分子量苯甲酸乙烯酯/丙烯酸1H,1H,2H,2H-全氟癸基酯嵌段共聚物稠化体系，建立了小分子稠化无水压裂液的耐温性能评价方法和自动破胶方法，通过双烷基脲型小分子稠化烷烃体系与烷基磷酸酯型交联稠化烷烃体系的性能对比分析，明确了小分子稠化无水压裂液的性能特点，除耐温性能外，耐剪切性能、携砂性能、自动破胶性能、破胶液储层伤害性方面，双烷基脲型小分子稠化烷烃体系均优于烷基磷酸酯型交联稠化烷烃体系，获得了低破胶液粘度、无残渣并对储层低伤害的清洁无水压裂液体系，并从微观上阐明小分子化合物稠化无水压裂液体系的稠化与破胶机理。这种稠化无水压裂液的新方法相比于目前页岩储层改造中常用的滑溜水型压裂液体系，在应用中解决了需要消耗大量清水资源的环境保护问题，相比于常规交联体系作为稠化剂，由于不需要加入破胶剂，因而解决了页岩储层改造过程中的储层伤害性问题。综上所述，本课题的研究成果可为无水压裂液的稠化和应用提供新的途径和科学依据，对于解决目前页岩储层改造用压裂液存在的性能问题、环境保护问题、储层适应性问题具有重要的理论和现实意义。