Liquid Nitrogen Preconditioning Strategy for Breakdown Pressure Reduction for Hydraulic Fracturing on Ultra-Dense Marble – A Laboratory Study

In tight and low permeability reservoirs, hydraulic fracturing enhances production by creating hydraulically conductive fracture networks. We study low permeability, high tensile strength marble cubes (side length of 150 mm) that would result in high breakdown pressures at depth requiring high power pumps for stimulation to investigate how cryogenic preconditioning using liquid nitrogen (LN2) reduces breakdown pressure. Acoustic emission (AE) monitoring is integrated for hydraulic fracture detection and characterization. The experimental results yield some key findings: (1) Cryogenic LN2 generates a steep temperature gradient around the near-wellbore region, inducing additional thermal stress fields within the marble. This leads to localized tensile stress concentrations, promoting the initiation and propagation of microfractures, thereby significantly reducing the fracture initiation pressure of marble. Meanwhile, the presence of natural weak planes facilitates the development of more complex and highly connected fracture networks. (2) Under cryogenic conditions, the formation of microfractures produces AE signals with an average amplitude of 1.76 × 10-3 V and a dominant frequency band between 20–48 kHz, while in hydraulic fracturing experiments produce signals with a higher average amplitude of 2.09 × 10-1 V, distributed mainly within 2–48 kHz, are generated by larger-scale fractures, reflecting the development of both micro- and macro-scale fractures.