Abstract: There are possibly three initiation modes of hydraulic fracture on wellbore because of influence of the trend and dip of natural facture. The three modes include tensional fracture along natural fractures, shear fracture along natural fractures and tensional fracture initiating from rock body. It is important for fracturing design and operation to determine hydraulic fracturing initiation pressure and mode. Based on the occurrence, geometric distribution and the stress status of naturally fractured formations, the calculation models for hydraulic fracturing initiation pressure were established. The identification methods for hydraulic fracturing initiation mode and initiation pressure were obtained. A field case verified that these models could be applied to predict the fracture pressure of naturally fractured formations.

Key words: naturally fractured formation, vertical well, hydraulic fracturing, initiation mode, initiation pressure, calculation model

摘要： 受天然裂缝走向和倾角的影响,水力裂缝在井壁处起裂可能有3种方式,即:沿天然裂缝面张性起裂,沿天然裂缝面剪切破裂,从岩石本体起裂。确定水力裂缝在井壁处起裂的压力和方式,对水力压裂设计和施工有重要的作用。根据天然裂缝产状和地层地应力状态,建立了水力裂缝3种起裂方式的起裂压力计算模型,给出了水力裂缝起裂方式和起裂压力的判别方法。现场实例证明,该模型较为成功地解释了天然裂缝性地层的破裂压力。

关键词: 天然裂缝地层, 垂直井, 水力压裂, 起裂方式, 起裂压力, 计算模型