Articles techniques et présentations

Overpressure-driven hydrofracture zones are pipe-like structures and widespreadly develop in sedimentary basins worldwide. They have the ability to penetrate vertically for multiple kilometers, acting as pathways for fluid on the basin scale. When the hydrofracture zone penetrates the near-seafloor, it can infuse the upper strata (transition layer) with a substantial quantity of overpressured fluid, leading to seabed liquefaction potentially. Similarly, if the hydrofracture zone breaches the seabed, it has the potential to destabilize the sediment, triggering the shallow gas eruptions. All these geological processes could cause submarine landslides potentially. Despite extensive research on hydrofracture zones, the mechanisms of their formation and evolution are still poorly understood. In this study, the hydrofracture zones are explored by numerical models constrained by well log data and seismic data in the South China Sea. Drawing upon the stress condition and the fracture pattern within the study area, we've deduced the critical pore fluid pressure and developed the coupled fluid-geomechanical fracture model. Then the multiple linear regression is used to analyse the factors influencing hydrofracture zone growth. We find that the formation of hydrofracture zone is mainly controlled by rock density, bottom overpressure, Poisson's ratio, and radius of hydrofracture zone at its origin. Moreover, there is always a pressure transition layer between the hydrofracture zone and the overlying hydrostatic pressure zone. The thickness of this layer depends on strata permeability, strata thickness, and pressure within the hydrofracture zone. What's more, hydrofracture zones can continuously act as fluid pathways for a long time after their formation. Our study quantitatively explores the development and evolution of overpressure-driven hydrofracture zone for the first time. This research has broad implications for marine engineering and geohazard assessment.