Research On Mechanical Properties And Wellbore Stability Of Methane Hydrate-bearing Sediments

Methane hydrate is the most prospective energy in the 21 st century.The mechanical properties of hydrate sediments and wellbore stability are important factors affecting the safe and efficient development of methane hydrate resource.The research in this paper combines the discrete media model and the continuum media model,building numerical core samples of hydrate sediment through discrete media particle flow(PFC)to study the mechanical properties of hydrate sediment and the formation and evolution laws of shear failure.The mechanical parameters and variation laws obtained from numerical experiments were substituted into the continuous media finite element model(FEM)to study the effect of hydrate decomposition on the wellbore stability.This paper has carried out in the following aspects:1.Focusing on the mechanical properties of hydrate sediment,a series of triaxial compression simulations were performed based on the discrete media particle flow method.The hydrate sediment samples with different hydrate saturation were prepared through generating soil particles and hydrate particles simultaneously and giving them liner contacts.Studying the effects of confining pressure and hydrate saturation on the mechanical parameters such as elastic modulus,shear strength,volumetric response of hydrate sediment.The strength parameters of sediments such as cohesion and internal friction angle variation laws with saturation are obtained.2.The formation and evolution of the hydrate sediments shear bonds were studied by the combination of linear contact model and parallel bond model in particle flow.The biaxial numerical loading scheme of hydrate sediments under different saturations was designed to obtain the stress and strain curve of hydrate sediments.The shear deformation,the mechanism of shear band formation and evolution of hydrate sediments is analyzed from displacement field and contact effect of force chain network.The progressive destruction process of hydrate sediments is studied.3.Aiming at the influence of hydrate decomposition on the stability of the wellbore,the heat injection and pressure reduction hydrate decomposition model was established.The multi-physical process analysis method is used to simulate the decomposition process of hydrate under heat injection and pressure reduction using finite element software ABAQUS.The changes of hydrate saturation and the effects of hydrate decomposition on the stress environment,local structural plastic damage and wellbore stability of near-wellbore sedimentary layers were studied.The key environmental parameters and loading conditions which are beneficial to the stability of hydrate sediment wellbore are determined.