Simultaneous hydrofracturing of multiple perforation clusters in vertical wells has been applied in the stimulation of hydrocarbon resources reservoirs. This technology is significantly impeded due to the challenges in its application to the multilayered reservoirs that comprise multiple interlayers. One of the challenges is the accurate understanding and characterization of propagation and deflection of the multiple hydraulic fractures between reservoirs and embedded interlayers.
Numerical models of the tight multilayered reservoirs containing multiple interlayers were established to study hydrofracturing of multiple perforation clusters and its influencing factors on unstable propagation and deflection of hydraulic fractures. Brittle and plastic multilayered reservoirs fully considering the influences of different in situ stress ratio and physical attributes for reservoir and interlayer strata on propagations of hydraulic fractures were investigated. The combined finite element–discrete element method and mesh refinement strategy were adopted to guarantee the accuracy of stress solutions and reliability of fracture path in computation.
Results show that the shear stress fields between adjacent multiple hydraulic fractures are superposed to cause fractures deflection. Stress shadows induce the shielding effects of hydraulic fractures and inhibit fractures growth to emerge unstable propagation behaviors, and a main single fracture and several minor fractures develop. As the in situ stress ratio increases, hydraulic fractures more easily deflect toward the direction of maximum in situ stress, and stress shadow and mutual interaction effects between them are intensified. Compared to brittle reservoir, plastic-enhanced reservoir may limit fracture growth and cannot form long fracture length; nevertheless, plastic properties of reservoir are prone to induce more microseismic events with larger magnitude.
The obtained fracturing behaviors and mechanisms based on engineering-scale multilayered reservoir may provide effective schemes for controlling and estimating the unstable propagation of multiple hydraulic fractures.
The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (grants 41877275 and 51608301), Yue Qi Young Scholar Project Foundation of China University of Mining and Technology, Beijing (grant 2019QN14), Fundamental Research Funds for the Central Universities, Ministry of Education of China (grant 2019QL02), Teaching Reform and Research Projects of Undergraduate Education of China University of Mining and Technology, Beijing (grants J210613, J200709 and J190701), and the Open Fund of Tianjin Key Lab of Soft Soil Characteristics and Engineering Environment (grant 2017SCEEKL003).
Wang, Y., Liu, N., Zhang, X., Liu, X. and Wang, J. (2022), "Influences on unstable hydraulic fractures: propagation of adjacent multiple perforations and bedded interfaces in multilayered reservoir via FE-DE model", Engineering Computations, Vol. 39 No. 4, pp. 1407-1431. https://doi.org/10.1108/EC-03-2021-0185
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