射孔对致密砂岩气藏水力压裂裂缝起裂与扩展的影响

Impact of perforation on hydraulic fracture initiation and propagation in tight gas reservoir

为降低致密砂岩气藏偏高的地层破裂压力及增加储层改造体积,设计小型水力压裂实验装置,通过鄂尔多斯致密砂岩气藏钻井取心,研究不同射孔数量﹑射孔间距﹑射孔深度及水平应力差条件下水力压裂裂缝起裂与扩展规律.结果表明,射孔可以有效地降低致密砂岩气藏的破裂压力;增加射孔数量可以增加裂缝条数,并且裂缝沿射孔的方向扩展,有利于均匀布缝,提高储层的改造体积;低水平应力差和较小的射孔间距产生的缝间干扰导致裂缝在扩展的过程中发生偏转,缝间干扰随着射孔间距的增加及水平应力差的增大而减弱;射孔深度对于裂缝起裂也有一定的影响,裂缝更容易从射孔较深的区域起裂,为致密砂岩气藏压裂井射孔参数优化提供依据.

In the exploitation of tight gas reservoirs,reducing the high breakdown pressure and increasing the number of fractures to enlarge the stimulated reservoir volume are key points of the treatment.We designed a piece of equipment called mini-sized true tri-axial hydraulic fracturing simulation system for the experiments.Combining the downhole drilling cores which are gotten from the Erdos basin tight gas reservoir,we mainly examined the impact of number,spacing,depth of perforation and horizontal stress difference on fracture initiation and propagation.Experimental results show that the existence of perforation could effectively reduce the breakdown pressure.The number of fractures could increase as the perforation increase,and fractures initiate at the perforation points,which is conductive to forming fractures uniformly and enhancing the stimulated reservoir volume.The interaction among fractures mitigates as the perforation spacing or the horizontal stress difference increases.The depth of perforation affects fracture initiation.Factures are easier to initiate in deeper perforations.This study could provide theoretical principles for the perforation parameter optimization of fracturing wells in tight gas reservoirs.