Research On Fractional Damage Model Of Mudstone Dynamic Creep

Accurate description of mudstone deformation characteristics is the primary problem of identifying the casing damage.Mudstone after swelling,its mechanics parameters, such as volume,compressive strength and modulus of elasticity,will obviously change.Mudstone with different water quantity inhaled generate different actions of the creep characteristics when under fixed outside load.Creep model has always been the hot spot of the rock mechanics study.In this paper, by introducing the fractional order calculus and the theory of damage mechanics to establish mudstone fractional damage creep model under different water conditions, provides a new train of thought for studying the characteristics of rock creep mechanics.Main work content is as follows:First of all,this paper introduced the basic theory of rock rheology and characteristics of rock creep deformation, analyzed the important influence factors of rock creep property, studied the rock mass creep models such as Maxwell Model, the Kelvin Model and St. Venant Body, and analyzed each component and its parameters significance of the combined model and the applicable scope of all kinds of classical models;Secondly, according to the classical theory of solid and fluid mechanics,the ideal solid stress-strain relationship meet Hooke’s Solid Law,and the ideal fluid meet Newton’s Viscosity Law. Then we can think that the mudstone between ideal solid and ideal fluid can be expressed by fractional order differential form. By introducing the theory of fractional order calculus, this paper constructed a new fractional order calculus viscous element,reflected the different mudstone creep stages by the range of order,established a new fractional order mudstone creep model by combining the fractional order calculus viscous element and the classical mechanics element.Again,in this paper,the mudstone creep is divided into decay type creep and non-decay type creep based on the different magnitude of the applied load stress on rock mass.By introducing the concept of damage threshold to distinguish the different types of mudstone creep, non-decay type mudstone creep will occur when the applied load stress is less than the damage threshold,and in the accelerating creep stage the damage variable is introduced to describe the process of mudstone produce damage.Finally,by coring in the mudstone layer of Daqing Oilfield to conduct uniaxial compression creep tests under different saturated water conditions,the results of tests show that the fractional damage creep model can better represent the characteristics of mudstone creep deformation after water suction.