不同注液速率水力压裂多裂缝扩展规律研究

Multi-fracture expansion law of hydraulic fracturing with different injection rates

为了分析影响水力压裂效果的射孔参数,采用TCHFSM-I型大尺寸真三轴压裂渗流模拟装置,并配合声发射监测系统和高温-高压动态流量计,以均质水泥砂浆试件为研究对象,对不同注液速率下水力压裂多裂缝同步扩展规律进行研究。研究结果表明:随注液速率增大,射孔裂缝长度和宽度不同程度增加,缝间干扰程度减弱,应力阴影效应减小,射孔间距较大时裂缝扩展更加均衡,压裂效果更佳;随注液速率增大,射孔水力压裂裂缝起裂压力增大,起裂时间变短,受射孔间距影响较小;不同注液速率条件下各射孔注液流量分配差异显著,且受射孔间距影响明显,射孔间距为20 mm和60 mm时,中部射孔注液流量占比分别为7.31%、10.88%、16.12%和31.12%、32.69%、33.44%。

To analyze the perforation parameters for hydraulic fracturing,we employ an independent developed device,i.e.TCHFSM-I type large true triaxial fracturing seepage simulation device.Combined with acoustic emission monitoring system and high-temperature and high-pressure dynamic flowmeter,carry out tests on homogeneous cement mortar specimens for the study on synchronous expansion law of hydraulic fractures with different injection rates.The results show that:with the increase of injection rate,the length and width of perforated fractures will increase to some extent.The inter-fracture interference will reduce,and the stress shadow effect decreases.The fracture expansion is more balanced,and the fracturing effect is better as the perforation spacing is larger.With the increase of injection rate,the fracture initiation pressure of perforation hydraulic fracture will increase,and the initiation time becomes shorter resulting in small effect of perforation spacing.Under different injection rates,the flow distribution of perforations is significantly different,and obviously affected by the perforation spacing.When the perforation spacings are 20 mm and 60 mm,the flow ratios of the middle perforation are 7.31%,10.88%,16.12%,31.12%,32.69%,33.44%,respectively.