Hydrofracturing and Episodic Fluid Flow in Shale-Rich Basins-A Numerical Study

Abstract

Low-permeability sedimentary rocks commonly are fractured. Direct examination of exposed rock faces and drill cores shows evidence of hydrofracturing. The mechanism for hydrofracturing, its effects on fluid migration, and its dependence on sediment permeability, sedimentation rate, and sedimentary sequences have not been explored. In this study we carry out systematic numerical experiments to study the compaction-induced hydrofracturing. We show that the compaction-induced hydrofracturing commonly may occur in shale-rich basins and in sand-shale sequences; the frequency of such hydrofracturing depends on sediment permeability, sedimentation rate, and sedimentary sequence. An important result is that compaction-induced hydrofracturing may occur at relatively shallow depths in shale-rich basins, but it may mobilize enhanced fluid flow throughout the sedimentary basin. Over 60% of the total compaction-induced fluid flow in the basin may be expelled during hydrofracturing. We test the model against field data from the Yinggehai basin of the south China margin, where abundant hydrofractures in the uppermost Quaternary marine mud have been recently detected by seismic imaging. We suggest that the compaction-induced hydrofracturing may mobilize fluid flow at great depths and affect hydrocarbon migration in shale-rich basins.