Unstable propagation of hydraulic fractures under varying well spacing and initiation sequence of multiple horizontal wells considering shear stress shadows

Abstract

PurposeMulti-well hydrofracturing is an important technology to create new fractures and expand existing fractures to increase reservoir permeability. The propagation morphology of the fracture network is affected by the disturbance between the fractures initiation sequences and spacings between adjacent wells. However, it remains unclear how well spacing and initiation sequences lead to fracture propagation, deflection and connection.Design/methodology/approachIn this study, the thermal-hydro-mechanical coupling effect in the hydrofracturing process was considered, to establish a finite element-discrete element model of multistage hydrofracturing in a horizontal well. Using typical cases, the unstable propagation of hydraulic fractures in multiple horizontal wells was investigated under varying well spacing and initiation sequences. Combined with the shear stress shadow caused by in situ stress disturbed by fracture tip propagation, the quantitative indexes of fracture propagation such as length, volume, displacement vector, deflection and unstable propagation behavior of the hydrofracturing fracture network were analyzed.FindingsThe results show that the shear stress disturbance caused by multiple hydraulic fractures is a significant factor in multi-well hydrofracturing. Reducing the spacing between multiple wells increases the stress shadow area and aggravates the mutual disturbance and deflection between the fractures. The quantitative analysis results show that a decrease of well spacing reduces the total length of hydraulic fractures but increases the total volume of the fracture; compared with sequential and simultaneous fracturing, alternate fracturing can effectively reduce stress shadow area, alleviate fracture disturbance and generate larger fracture propagation length and volume.Originality/valueThe numerical models and results of the unstable propagation and stress evolution of the hydraulic fracture network under thermal-hydro-mechanical coupling obtained in this study can provide useful guidance for the evaluation and design of rock mass fracture networks in deep unconventional oil and gas reservoirs.

Frac-hits and connections of multi-well hydrofracturing fracture network involving the variable factors: well spacing, perforation cluster spacing and injection rate

“…Further details of this technique can be found in the references (Wang et al. , 2018; Wang and Liu, 2022, 2023; Wang et al. , 2023a, b, c).…”

“…Actually, some previous investigations have indicated that the above method and models can provide the effective ways to handle with the propagation of hydraulic fractures in gas reservoirs (Wang et al. , 2018; Wang and Liu, 2022, 2023; Wang et al. , 2023a, b, c).…”

“…The disturbance of in situ stress is caused by fracture propagation, and the stress shadow between fractures is formed. Reducing the well spacing will aggravate the stress shadow effect, thus aggravating the deflection of the fracture and affecting the fracture propagation length and the total volume of the fractures (Wang and Liu, 2022, 2023). In addition, the well spacing also affects the formation deformation in fracture propagation.…”