Fracturing and Porosity Channeling in Fluid Overpressure Zones in the Shallow Earth’s Crust

Figure 9

Illustration of the different geometries that produce variable fracture patterns. Fluid overpressure in blue color, cracks in black, and arrows showing the movement of the solid. (a) Hydrofracture symmetry depending on the geological scenario. (i) High fluid pressure in a horizontal layer or a sedimentary basin and symmetry breaking in one orientation because the pressure gradients are aligned horizontally. The resulting patterns are horizontal hydrofractures. (ii) High fluid pressure in a confined zone or an offset horizontally aligned layer. Symmetry breaking in two orientations because both cases lead to variably aligned gradients and dilation in two directions. Hydrofractures develop as a function of pressure gradients and dilation, first in the direction of the lowest effective stress followed by brecciation of the layers. (b) Two processes produce hydrofractures: (i) pressure gradients at the rims of high-pressure zones and (ii) dilation of high-pressure zones.

(a)

(b)