定向射孔参数对压裂裂缝扩展规律的影响

为了探究直井水力压裂过程中定向射孔参数对压裂裂缝扩展规律的影响,采用扩展有限元方法对水压致裂岩石的流固耦合模型进行求解,从射孔方位、射孔长度和射孔相位角3个方面分析了裂缝自射孔孔眼起裂的扩展和转向规律。研究结果表明:射孔方位对裂缝周围地层压力分布几乎没有影响;射孔方位角较小的孔眼具有较低的起裂压力和较高的扩展压力,压裂后容易形成长而宽的裂缝;射孔方位角较大的孔眼则具有较高的起裂压力和较低的扩展压力,压裂后容易形成短而窄的裂缝;随着射孔长度的增加,重新定向距离逐渐增长,在转向处易形成相对较宽的裂缝;射孔相位角过小容易引发裂缝干扰,射孔方位角较小的裂缝优先扩展并对后扩展的裂缝产生较强的抑制作用。在施工时,为获得较好的改造效果,应尽量选择小方位射孔;为避免缝间干扰,射孔相位角应大于45°。

Influence of directional perforation parameters on fracture propagation

In order to explore the effect of directional perforation parameters of straight well during the process of hydraulic fracturing,the laws of fracturing initiation and extension originated from perforation tunnel were analyzed in such three aspects as perforation orientation,perforation length and perforation phase angle by using extended finite element method.The results show that perforation orientation has hardly effect on the fracturing around the formation pressure distribution;long and wide fracturing is easily founded in the perforation tunnel with small orientation angle,however,it is opposite in the orientation angle with big orientation angle;with the increase of perforation length,reorientation distance increase,it is easy to form relatively wide fracture in turning point;too small perforation phase angle causes fracture interference easily,the fracture originated from perforation tunnel with smaller orientation angle extends firstly,and it has a strong inhibition on the followed fracture.In the field operation,in order to make a better stimulation,the small orientation angle should be chosen as far as possible.In order to avoid the interference of the fracture,the phase angle should be more than 45°.