Interactions of Hydraulic Fractures With Grain Boundary Discontinuities in the Near Wellbore Region. Issue 3 (11th March 2023)

• Record Type: Journal Article
• Authors: Yoshioka, Keita; Katou, Masafumi; Tamura, Kohei; Arima, Yutaro; Ito, Yoshiharu; Chen, Youqing; Ishida, Tsuyoshi
• Is Part Of: Journal of geophysical research. Volume 128:Issue 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-11
• Subjects: fracture interaction -- fracture energy -- hydraulic fracture; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2022JB024509
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Hydraulic fractures often turn or branch, interacting with preexisting discontinuities in the rock mass (e.g., natural fractures or defects). The criteria for fracture penetration or deflection are typically based on the in situ stress, and the angle and strength of discontinuities. However, in hydraulic fracture experiments on carbonate rocks (Naoi et al., 2020, https://doi.org/10.1093/gji/ggaa183 ), small scale analyses show that the fractures deflected more frequently at discontinuities (grain boundaries) as they propagated farther from the wellbore, a finding not explained by the conventional criteria. Here, we demonstrate that the energy dissipation of a deflecting fracture increases with the distance from the wellbore, such that a propagating hydraulic fracture more easily deflects at a discontinuity from an energetic standpoint. This tendency was confirmed by hydraulic fracture simulations based on a successive energy minimization approach. Our findings, which show that wellbores appreciably affect the behavior of hydraulic fractures, highlight the importance of energetic stability analysis for determining fracture paths. Plain Language Summary: Hydraulic fractures may form complex patterns as they grow outward from a wellbore by turning or deflecting when they interact with preexisting discontinuities in rocks. Because complex fractures enhance the permeability of rock formations more effectively than planar fractures, many studies have investigated how a fracture interacts with a preexisting discontinuity such as a natural fracture. The fate of a growing fracture at a discontinuity—whether it penetrates or deflects—is typically judged based on the in situ subsurface stress, and the characteristics of the discontinuity. However, we observed in experiments that fractures deflected more often at discontinuities (grain boundaries) as they propagated farther away from the wellbore, which cannot be explained by the conventional criteria. To explain these observations, we analyzed the energy expenditure of a deflecting fracture and showed that it becomes energetically more favorable for a fracture to deflect at a discontinuity as it grows farther away from the wellbore. We confirmed this insight by using numerical simulations. We thus caution that the conventional criteria may not be applicable in the near wellbore region, and we suggest that energetic stability, rather than the local stress at the fracture tip, should be analyzed to determine fracture paths. Key Points: Experimental results show that hydraulic fractures deflect more frequently at grain boundaries with increasing distance from the wellbore Numerical analyses demonstrate that energy dissipation increases with the distance from the wellbore, consistent with our experimental findings Criteria for fracture deflection/penetration based on the in situ stress and fracture geometry may not apply to near wellbore regions