Fully Coupled Thermal-Hydraulic-Mechanical Analysis of Hydraulic Fracture in Offshore Cuttings Re-Injection

Cuttings reinjection is an effective way to treat oilfield waste. There is still a risk of slurry leakage during the field operations although cuttings re-injection technology has been widely used. The study of fracture initiation and propagation during cuttings re-injection is important for operational design. Fracturing is a complex physical process that combines fluid seepage, temperature diffusion, stress change, and rock damage. In offshore cuttings re-injection projects, the temperature difference between the injection slurry and the formation has a significant impact on the fracture behaviors, especially in high-temperature-high-pressure (HTHP) formations. In this paper, a fully coupled thermal-hydraulic-mechanical (THM) model was developed by the cohesive element method for modeling cuttings re-injection. The multi-physical field evolution in cuttings re-injection process in HTHP offshore formation was studied. The simulation results show that the cooling effect of the injection fluid causes the contraction of the formation which leads to an increase in the tensile stress of the rock and a decrease in the formation fracture pressure. The cooling effect results in a wider and shorter fracture than the case without the consideration of the cooling effect. Therefore, it allows more slurry to be injected in a limited near-wellbore zone, reducing the risk of slurry leakage during the injection process. The cooling effect is positively correlated with the temperature difference between the injection slurry and the formation.