Study on hydraulic fracturing in natural gas hydrate reservoir based on thermo-hydraulic-mechanical-chemistry coupled damage model and experiment

Abstract

Hydraulic fracturing technology is a promising method for reservoir stimulation. The initiation and propagation of hydraulic fractures in gas hydrate reservoirs is a complex multi-physical field coupling process. Firstly, a thermo-hydraulic-mechanical-chemistry (THMC) coupled damage model has been established, the initiation and propagation of micro cracks and fractures are described with the damage variable D and its evolution, and the maximum tensile stress criterion and Mohr-Coulomb criterion are selected as the damage criteria. Then, hydraulic fracturing process in gas hydrate reservoirs are numerically simulated using the THMC coupling damage model to explore the synergistic mechanisms of multi-physical field coupling during fracture initiation and propagation. Finally, artificial samples simulating marine hydrate sediments are prepared for large-scale hydraulic fracturing experiments, and expanded simulations are conducted to examine influence of the key factors on hydraulic fracturing. (i) Validity of the modeling method has been verified with the experiment result. (ii) Hydraulic fractures in marine hydrate sediments has been examined to propagate along the direction of maximum horizontal stress. (iii) A smaller horizontal stress difference, a higher injection rate of fracturing fluid, or a higher fracturing fluid viscosity will accelerate the fracture initiation and propagation. (iv) Increasing the fracturing fluid injection rate have no significant impact on the breakdown pressure. This research provides theoretical guidance and design recommendations for hydraulic fracturing in gas hydrate reservoirs.