Abstract

Multizone hydraulic fracture (HF) helps to enhance the commercial production rate of oil and gas in unconventional reservoirs. However, the efficiency of multizone HF highly depends on the cluster/perforation spacing and in situ stress field. Therefore, this paper investigates the phase field characteristic during multizone HF under different perforation spacing and in situ stress field. The total stress tensor involves the influence of initial stress while the fracture growth is characterised by the evolution equation of phase field. In addition, the numerical simulation is verified by a rectangular domain subjected to internal fluid injection. Then, the hydraulic fracture patterns from a group of pre-existing notches subjected to an identical fluid injection rate are examined. The numerical results show that the hydraulic fractures in multizone HF are the automatic product of the evolution equation of phase field without requiring any external fracture criteria. A diverted fracture scenario is shown in most cases and the fracture growth is inhibited if the stress perpendicular to the perforations increases. The fluid pressure in the fracture and the breakdown pressure increases with the increase in the notch spacing and the stress perpendicular to the perforations. The fluid pressure in the middle notch is larger than that in the upper notch. Reversion of the in situ principal stress direction greatly inhibits the growth of multizone hydraulic fractures, which causes the failure of multizone HF. The numerical investigations in this paper can provide a new perspective for multizone HF design.

摘要

多带水力压裂 (HF) 有助于提高非常规油藏中油气的商业生产速度。然而，多带 HF 的效率很大程度上取决于簇/射孔间距和地应力场。为此，本文研究了不同射孔间距和原位条件下多层高频时的相场特性。应力场。总应力张量包含初始应力的影响，而裂缝扩展则以相场演化方程为特征。此外，数值模拟通过内部流体注入的矩形域进行验证。然后，检查来自一组受到相同流体注入速率的预先存在的槽口的水力压裂模式。数值结果表明，HF多带水力裂缝是相场演化方程的自动产物，不需要任何外部裂缝判据。大多数情况下会出现转向裂缝的情况，如果垂直于射孔的应力增加，则裂缝扩展会受到抑制。裂缝中的流体压力和击穿压力随着缺口间距的增加和垂直于射孔的应力的增加而增加。中间槽口的流体压力大于上槽口的流体压力。的回归原位主应力方向极大地抑制了多带水力裂缝的生长，导致多带HF的破坏。本文的数值研究可为多区高频设计提供新的视角。