Phase field characteristic of multizone hydraulic fracturing in porous media: the effect of stress boundary

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.

Keywords:

• Phase field
• numerical simulation
• multizone hydraulic fracturing
• porous media
• fracture propagation
• staggered scheme

Disclosure statement

No potential conflict of interest was reported by the authors. 

Additional information

Funding

The authors gratefully acknowledge the financial support provided by the China Scholarship Council (201806680062) and the CSC-DAAD postdoc program (2016).