Overpressure-driven hydrofracture growth in the northern South China Sea

Abstract

Overpressure-driven hydrofracturing pervasively occurs in sedimentary basins worldwide. Hydrofracture zones can vertically penetrate several kilometres of rocks and are dominant pathways for basin-scale fluid migration and energy circulations. Although hydrofracture zones have been extensively described and analysed in the literature, the mechanisms on how hydrofracture zones form and evolve are still poorly understood. In this study, we explore the formation and evolution of a hydrofracture zone in the northern South China Sea, using numerical models constrained by borehole and seismic data. We show that the radius of hydrofracture zone decreases with the strata permeability. The growth of hydrofracture zone is mainly controlled by rock density ($\rho$), pressure at the origin of hydrofracture zone (p_b), Poisson's ratio (v), and the radius of the hydrofracture zone at its origin (r). Moreover, as the hydrofracture zone grows, a transition layer forms between the overpressured hydrofracture zone and the overlying hydrostatic pressure zone. The thickness of this transition layer is controlled by strata permeability, strata thickness, overpressure, and pressure gradient within the hydrofracture zone. This study quantitatively explores the development and evolution of overpressure-driven hydrofractures for the first time, and has wide applications in geohazard assessment, hydrocarbon exploration, carbon circulation, and climatic change.