Hydraulic fracturing of poorly-consolidated and weakly-cemented sandstones: from experiments to numerical modelling

ABSTRACT: Poorly-consolidated and weakly-cemented sandstones are common host rocks for hydrocarbon reservoirs, gas storage, and CO2 sequestration due to their high porosity. However, their transitional mechanical properties pose challenges in predicting their response to hydraulic fracturing. This study investigates hydraulic fracturing in artificially cemented weak sandstones through laboratory experiments and numerical simulations. Experiments were conducted on bio-cemented specimens under true triaxial stress conditions, using a novel apparatus that enables real-time visualization of fracture propagation. Results indicate that at low cementation levels, fractures exhibit irregular patterns with significant grain-scale disaggregation, while higher cementation levels produce more localized fractures perpendicular to the least compressive stress. Numerical simulations extend the analysis to nearly cohesionless sands, revealing transitions from cavity expansion to mixed-mode and tensile fracturing depending on cementation and stress state. These findings highlight the role of stress anisotropy in fracture development and emphasize the limitations of conventional hydraulic fracturing criteria for weak rocks.