Zhang Kun, Liu Yuxuan, Sheng Lianqi, Li Bojun, Chen Tianxiang, Liu Xiongfei, Yao Erdong
State Key Laboratory of Oil and Gas Resources and Prospecting, China University of Petroleum at Beijing, Beijing 102249, China.
China University of Petroleum Beijing Unconventional Natural Gas Institute, Beijing 102249, China.
ACS Omega. 2022 Apr 1;7(14):11903-11913. doi: 10.1021/acsomega.1c07386. eCollection 2022 Apr 12.
Igneous rock oil and gas reservoirs have great development potential. Hydraulic fracturing is an important means for the development of these reservoirs. In the process of fracturing and increasing production, fracturing fluid is prone to a hydration reaction with clay minerals in igneous rock, and then, the structure and mechanical properties of the igneous rock are changed, affecting increased production. Therefore, it is necessary to establish a systematic water-rock reaction experiment method to understand the influence of fracturing fluid on the structure and mechanical properties of igneous rocks and to optimize the fracturing fluid system of igneous rock reservoirs. In this experiment, four solutions were used: slickwater, guar fracturing fluid, 2% KCl aqueous solution, and 4% KCl aqueous solution. Acoustic testing, porosity and permeability testing, XRD analysis, micro-CT scanning, and displacement experiments were performed. The influence of different fracturing fluids on the structure and mechanical properties of igneous rocks was studied. Igneous rock samples with a permeability of 0.05-0.1 mD and average porosity of 7-14% were used. The results show that all four liquid systems will reduce the permeability, Young's modulus, and brittleness index and increase the porosity and Poisson's ratio of the rock after fracturing. Among them, the permeability damage rate is as high as 37.37%, which may be related to the plugging of pores with solid residues in the gel breaking liquid; CT results show that there are microcracks in the rock, which increase over time, up to 13.54%. The brittleness index decreases. Among the fluids, the influence of slickwater on the rock brittleness index is the smallest, no more than 5%. Guar gum had the greatest effect on the Gel breaking liquid, up to 58%. One of the reasons for the increase in porosity is that adding a clay stabilizer composed of inorganic salts and organic cationic polymers to the slickwater fracturing fluid can effectively reduce the damage caused by the fracturing fluid to the rock during the fracturing process and can reduce the maximum by 50%. This paper can clarify the damage law of fracturing fluid systems to igneous rock reservoirs and provide the theoretical basis for the hydraulic fracturing of igneous rock reservoirs.
火成岩油气藏具有巨大的开发潜力。水力压裂是开发这些油藏的重要手段。在压裂增产过程中，压裂液易与火成岩中的黏土矿物发生水化反应，进而改变火成岩的结构和力学性能，影响增产效果。因此，有必要建立系统的水岩反应实验方法，以了解压裂液对火成岩结构和力学性能的影响，优化火成岩油藏的压裂液体系。本实验采用了四种溶液：滑溜水、瓜尔胶压裂液、2%氯化钾水溶液和4%氯化钾水溶液。进行了声学测试、孔隙度和渗透率测试、X射线衍射分析、微观计算机断层扫描和驱替实验。研究了不同压裂液对火成岩结构和力学性能的影响。使用了渗透率为0.05 - 0.1毫达西、平均孔隙度为7 - 14%的火成岩样品。结果表明，所有四种液体体系都会降低压裂后岩石的渗透率、杨氏模量和脆性指数，并增加孔隙度和泊松比。其中，渗透率损害率高达37.37%，这可能与破胶液中固体残渣堵塞孔隙有关；CT结果表明岩石中存在微裂纹，且随时间增加，增幅达13.54%。脆性指数降低。在这些流体中，滑溜水对岩石脆性指数的影响最小，不超过5%。瓜尔胶对破胶液的影响最大，高达58%。孔隙度增加的原因之一是，在滑溜水压裂液中添加由无机盐和有机阳离子聚合物组成的黏土稳定剂，可有效降低压裂过程中压裂液对岩石的损害，最大可降低50%。本文可阐明压裂液体系对火成岩油藏的损害规律，为火成岩油藏的水力压裂提供理论依据。
