Four-dimensional stress induced by hydraulic fracturing and long-term extraction for shale gas well platforms: Implications for refracturing design
Zirui Yin, Fengshou Zhang, Xiaohua Wang, Lianyang Zhang, Haiyan Zhu
Abstract
Prior to refracturing, initial hydraulic fracturing and long-term production are performed, resulting in a complex temporal and spatial evolution of the stress field in the reservoir, known as four-dimensional (4D) stress evolution. However, the progression and underlying mechanisms of 4D stress evolution remain unclear. Therefore, this paper proposes an innovative simulation method that integrates the mechanical impacts related to hydraulic fracturing and the poroelastic effects associated with long-term extraction. We consider topographic variations, heterogeneous geological properties, and the irregular distribution of hydraulic fractures with different sizes. The method considers the entire process of opening, closing, and propping of hydraulic fractures. Furthermore, the actual shale gas production is precisely simulated by employing the production matching algorithm in conjunction with the bottomhole pressure history of six fractured horizontal wells. We quantitatively analyze the spatio-temporal evolution of the stress field resulting from mechanical and poroelastic effects. The results indicate that due to the mechanical effect, the horizontal stress difference within the region of fracture distribution has diminished by a range of 3.5−4.5 MPa, and the stress rotation angle is deemed negligible, as its peak value is only 4.03°. In addition, the poroelastic effect resulting from gas extraction progressively reduces the horizontal stress difference of the reservoir, most notably in regions adjacent to hydraulic fractures, while causing an increase in the rotation angle. Importantly, the maximum rotation angle generally manifests in the fracturing stages at the toe and heel ends of each well, suggesting that these stages are particularly favorable for refracturing.