Liquid nitrogen (LN) fracturing is an efficient technology for the development of unconventional gas resources. Due to continuous injection of cryogenic LN, the reservoir temperature decreases and then cooled rock regions are gradually generated during fracturing process. To investigate the breakdown behaviours of sandstone induced by LN fracturing, laboratory simulation experiments were performed with a self-designed setup. The experimental results showed that rising initial rock temperature greatly reduced the breakdown pressure of sandstone, whereas hardly affected the fracture complexity. Under cryogenic conditions, both the compaction and cracking effects exerted influence on the pore structure of sandstone. Thus, the change in breakdown pressure depended on which effect played a domain role. Although the cryogenic conditions probably made the breakdown pressure of sandstone increase, the fracture complexity was expected to be significantly improved. In addition, the initial rock temperature increasing played a positive role in improving the fracture complexity under cryogenic conditions. For initial or heating sandstone samples, the fracture pattern mainly presented in the form of bi-wing fractures. However, for cryogenic samples, the fracture patterns contained both local fractures and complex fractures. The former was generated with lower breakdown pressure while the latter was generated with higher breakdown pressure. Additionally, the gas leak regions were observed in cryogenic samples during LN fracturing. Under cryogenic conditions, the sandstone used was favourable to generate more complex fractures and the permeability of rock matrix in unbroken region was proved to be improved due to LN fracturing. Collectively, fracturing with LN could improve the fracture complexity and the permeability of rock, which was very beneficial for well production.

液氮（LN）压裂是开发非常规天然气资源的有效技术。由于连续注入低温LN，储层温度降低，然后在压裂过程中逐渐生成冷却的岩石区域。为了研究LN压裂引起的砂岩破坏行为，采用自行设计的装置进行了实验室模拟实验。实验结果表明，初始岩石温度的升高大大降低了砂岩的破裂压力，而对裂缝的复杂性几乎没有影响。在低温条件下，压实和开裂作用都对砂岩的孔隙结构产生影响。因此，击穿压力的变化取决于哪个作用发挥了作用。尽管低温条件可能使砂岩的击穿压力增加，但断裂复杂度有望得到显着改善。此外，岩石初始温度的升高在改善低温条件下的裂缝复杂性方面也发挥了积极作用。对于初始或加热的砂岩样品，裂缝模式主要表现为双翼裂缝。但是，对于低温样品，裂缝模式既包含局部裂缝又包含复杂裂缝。前者以较低的击穿压力产生，而后者以较高的击穿压力产生。此外，在LN压裂过程中，在低温样品中观察到了气体泄漏区域。在低温条件下 LN压裂技术使砂岩有利于产生更复杂的裂缝，并且证明了未破裂区域岩石基质的渗透性。总的来说，LN压裂可以提高裂缝的复杂性和岩石的渗透性，这对井的生产非常有利。