Zhuang Deng-Deng, Yin Tu-Bing, Zhang Zong-Xian, Aladejare Adeyemi, Wu You, Qiao Yang
School of Resources and Safety Engineering, Central South University, Changsha 410083, China.
Oulu Mining School, University of Oulu, 90015 Oulu, Finland.
Materials (Basel). 2023 Jan 28;16(3):1118. doi: 10.3390/ma16031118.
This paper focuses on a new test method and theoretical model for measuring and evaluating the reopening pressure during hot dry rock hydraulic fracturing. Firstly, rock blocks of four lithologies were collected from the hot dry rock strata. Hydraulic fracturing tests at high temperatures in real-time were conducted using drilled cubic specimens and drilled cubic specimens with a pre-crack. Breakdown pressure, reopening pressure, and fracture toughness were measured, respectively. In addition, Brazilian splitting tests at high temperatures in real-time were performed using Brazilian disc specimens to measure tensile strength. Secondly, an empirical equation for evaluating the reopening pressure during hot dry rock secondary fracturing was developed based on fracture mechanics and hydraulic fracturing theory. Third, the values calculated by the new equation, considering breakdown pressure, fracture toughness, and tensile strength, were compared to the values determined by the classical equation and to measurement results. It was found that the new equation predicted closer reopening pressure to the measurement results, regardless of the lithology of the hot dry rock. Moreover, with increasing temperature in the specimens, the error between the value calculated by the new equation and the measurement value remained low. In contrast, the difference between the classical equation predictions and the measurement results was widened. In addition, the reopening pressure was positively correlated with tensile strength and fracture toughness. Variations in lithology and temperature affected tensile strength and fracture toughness, which then changed the hot dry rock reopening pressure.
本文重点研究了一种用于测量和评估热干岩水力压裂过程中重张压力的新测试方法和理论模型。首先，从热干岩地层采集了四种岩性的岩块。使用钻孔立方体试件和带有预制裂缝的钻孔立方体试件进行了高温实时水力压裂试验，分别测量了破裂压力、重张压力和断裂韧性。此外，使用巴西圆盘试件进行了高温实时巴西劈裂试验以测量抗拉强度。其次，基于断裂力学和水力压裂理论，建立了一个评估热干岩二次压裂过程中重张压力的经验方程。第三，将考虑破裂压力、断裂韧性和抗拉强度的新方程计算值与经典方程确定的值以及测量结果进行了比较。结果发现，无论热干岩的岩性如何，新方程预测的重张压力与测量结果更接近。此外，随着试件温度升高，新方程计算值与测量值之间的误差保持在较低水平。相比之下，经典方程预测值与测量结果之间的差异则增大。另外，重张压力与抗拉强度和断裂韧性呈正相关。岩性和温度的变化影响了抗拉强度和断裂韧性，进而改变了热干岩的重张压力。
