Horizontal well with multi-stage fracturing is one of the most effective stimulation methods for unconventional reservoirs, e.g. tight oil/gas or shale. To maximize reservoir stimulation volume (SRV), tighter fracture spacing and fewer perforations are distributed in one stage during extreme limited-entry fracturing (XLEF) in recent years. However, the fracture geometries and injection pressure curve are not clear when multiple fractures with close spacing were created simultaneously in the perforated wellbore during XLEF. This study investigated the multiple fracture simultaneous propagation in the XLEF perforated wellbore based on the true tri-axial fracturing experiments. Critical factors of horizontal stress difference (HSD), the number of perforation clusters, helical/in-plane perforated method, number of perforations per cluster and fracturing fluid flowrate were investigated in detail. The results showed that, firstly, compared to one fracture produced by the helical perforated method, XLEF with the in-plane perforated method has a higher breakdown pressure and could simultaneously create multiple transverse fractures. Secondly, longitudinal fractures and a small number of curved transverse fractures occurred simultaneously under lower HSD conditions, while multiple parallel transverse fractures could be created under high HSD conditions. Thirdly, increasing the number of perforations per cluster will reduce perforation cluster effectiveness, and increasing the number of clusters will lead to the merging of multiple fractures. Finally, three relationships between pressure response and fracture geometries during XLEF, e.g. single transverse fracture, multiple transverse fractures, co-existence of longitudinal and transverse fractures, have been revealed. This study provides a meaningful perspective for the multiple fracture propagation in the perforated wellbore, which could help the field fracturing design during XLEF.

水平井多级压裂是致密油/气或页岩等非常规油藏最有效的增产方法之一。近年来，为了最大限度地提高储层增产量（SRV），在极限进入压裂（XLEF）的一个阶段中分布更紧密的裂缝间距和更少的射孔。然而，当XLEF期间在穿孔井筒中同时形成多条间距较近的裂缝时，裂缝几何形状和注入压力曲线并不清晰。本研究基于真三轴压裂实验研究了 XLEF 射孔井筒中的多条裂缝同时扩展。水平应力差（HSD）的关键因素、射孔簇数、螺旋/平面射孔方法、详细研究了每簇射孔数和压裂液流量。结果表明：首先，与螺旋射孔法产生的一条裂缝相比，面内射孔法的XLEF具有更高的击穿压力，可以同时产生多条横向裂缝。其次，在较低的HSD条件下，纵向裂缝和少量弯曲的横向裂缝同时发生，而在高HSD条件下可以产生多个平行的横向裂缝。第三，增加每簇射孔数会降低射孔簇有效性，增加簇数会导致多条裂缝并合。最后，XLEF 期间压力响应和裂缝几何形状之间的三种关系，例如 已发现单个横断、多发横断、纵横骨折并存。该研究为射孔井筒中的多条裂缝扩展提供了有意义的视角，有助于XLEF期间的现场压裂设计。