Constitutive Model And Particle Flow Code Analysis Of Combustible Ice Sediments

Combustible ice is a new clean energy source with abundant reserves and no pollution.The development of combustible ice resources has become a new direction of energy strategy in the future.The physical and mechanical properties of combustible ice reservoir are the primary factors affecting the wellbore structure stability in the process of drilling and production.In order to realize the controllability of combustible ice mining and ensure the wellbore structure stability in the process of drilling and production,it is necessary to fully understand the mechanical characteristics of combustible ice reservoir.In this paper,a constitutive model of combustible ice sediments is established based on linear elasticity theory and considered non-linear mechanical behavior of combustible ice sediments.Compression simulation tests of conventional triaxial and compression simulation tests of true triaxial based on numerical algorithm of granular flow for combustible ice sediments are carried out to study mechanical properties of combustible ice sediments.This paper mainly focuses on the following work:1.The constitutive model for combustible ice sediments is developed based on the generalized Hooke's law.The weakening equation of elastic modulus is established considering the strain softening characteristics.Considering the cementation of combustible ice,the particle flow algorithm for material parameters is developed by linking the saturation and confining pressure with the modulus of elasticity.The softening coefficients and softening exponents of elastic modulus are determined by using the available laboratory triaxial compression test data.The comparison between numerical results and experimental results shows that the constitutive model can accurately calculate the mechanical behaviors of combustible ice sediments.2.The cylindrical numerical samples of combustible ice sediments were prepared based on the particle flow algorithm.A series of conventional triaxial compression simulation tests were carried out on samples to analyze effects of saturation and confining pressure on mechanical properties of combustible ice sediments.Results shows that the higher saturation of combustible ice,the greater strength and stiffness of sediments.Volumetric deformation tends to shrink first and then dilate during compression,and dilatancy phenomenon becomes more obvious with the increase of saturation.The increase of confining pressure helps to improve the compressive deformation capacity of combustible ice sediments.The analysis of cohesion and friction angle of combustible ice sediments that strength of sediments is mainly dominated by friction between particles,not by cohesion of combustible ice.3.The cube numerical samples of combustible ice sediments with specific saturation were prepared,and the true triaxial compression numerical simulation tests were carried out.Considering influence of mean stress and intermediate principal stress,strength and deformation of combustible ice sediments are analyzed.The criteria for determining strength of combustible ice sediments was studied in three-dimensional unequal stress state,and relationship between changes of micro-structure and evolution of macro-mechanical behavior of combustible ice sediments was discussed.The analysis results show that increase of intermediate principal stress has effect of first restraining and then promoting lateral deformation resistance of combustible ice sediments.In three-dimensional unequal stress state,Lade-Duncan criterion is more suitable for strength failure criterion of combustible ice sediments.The mechanical properties of combustible ice sediments are mainly affected by the strong contact between particles in the samples.