Effect of damage zones around fault core on failure development during fluid injection into porous reservoirs

• Published in: Geomechanics for energy and the environment Vol. 32; p. 100327
• Main Authors: Nguyen, Trung-Kien, Rohmer, Jérémy, Vo, Thanh-Trung
• Format: Journal Article
• Language: English
• Published: Elsevier 01-12-2022
• Subjects: Earth Sciences; Sciences of the Universe; Fault zone; Damage zone; Shear failure; Fluid injection; Stress regime
• ISSN: 2352-3808; 2352-3808
• DOI: 10.1016/j.gete.2022.100327

Fault zones (FZ) in porous reservoirs used for diverse underground activities are complex and heterogeneous geological systems generally constituted of one (or several) fault cores (FC) surrounded by damage zones (DZ). The latter compartment is characterized by a distribution of fractures, which can strongly affect the sustainable injection pressure, especially when the injection operation is performed in the vicinity of a FZ. This study aims at considering the effect of a realistic FZ structure on shear failure initiation and tendency during fluid injection into porous reservoirs, under extensional and compressional stress regimes. Fracture networks observed from the outcrops at the Cirques de Navacelles, were incorporated in the analysis to compute the distribution of hydro-poro-mechanical properties within the FZ. A hydromechanical simulation for geological model containing the FZ is proposed to study the reservoir behavior. Comparisons between homogeneous (HO-without DZ) and heterogeneous (HE-with DZ) cases for the most critically fracture orientation, were made in terms of the initiation and development of shear failure. We show that taking into account the DZ generally leads to higher sustainable injection pressure (more than twice in compressional and about 30% in the extensional regime). Under compressional, shear failure initiates and grows from the FC/DZ interface in HE, whereas it preferably develops in the injection zone in HO. Under extensional regime, the HE exhibits shear failure development in the DZ adjacent to the FC. Further investigations on shear failure integrating the orientations of the FC and pre-existing fractures in the DZ confirm that FC/DZ interface is the reservoir compartment where failure first occurs when DZ with realistic hydro-poro-mechanical properties are taken into account. Finally, we show through an extensive parametric study that our conclusions remain valid when considering uncertainty in the hydro-poro-mechanical properties as well as when the ratio of horizontal-to-vertical initial stress field remains small (+/-10%).