Experimental study of the effect of stress anisotropy on fracture propagation in Eagle Ford shale under water imbibition

摘要

Hydration swelling due to the rock-water reaction may create induced fractures to enhance hydrocarbon recovery in shale reservoirs. This paper investigates the effects of anisotropic stress and hydration swelling on fracture generation and propagation in Eagle Ford shale. To explore whether fractures can be induced by hydration under anisotropic stress conditions, sequential imbibition tests and water imbibition tests were conducted. CT scanning was used to obtain cross-sectional images of shale cores with different axial and confining pressures. The sequential imbibition tests indicated that hydration swelling might induce fractures, and more fractures were generated under water imbibition than oil imbibition. This finding shows that hydration swelling is beneficial to fracture generation under anisotropic compressive stress, which challenges the believe that hydration swelling may cause formation damage. Experiments also show that more induced fractures were generated in the samples under anisotropic stress conditions than under isotropic conditions. The greater the stress anisotropy, the larger the induced fracture geometry is. Beddings and natural fractures can facilitate fracture initiation and propagation.