Research On Damage Mechanism And Design Of Casing In Composite Salt-Gypsum Layer

The salt rock of sedimentary basin is the best caprock,under which 80%-90% of the world's oil and gas resources are buried.It is not only the focus of the world's oil industry,but also the focus of C hina's oil and gas resources development.China is rich in deep sub salt oil and gas re sources,and the composite salt gypsum layer is widely distributed,mainly in the tertiary,Carboniferous and Cambrian,mainly salt rock,gypsum and mudstone.According to statistics,in Xinjiang area of China,nearly 50% of casing damage occurs at the interface of composite salt paste layer,which is quite different from the traditional design and protection theory of composite salt paste layer casing.Therefore,it is very important to study the damage mechanism of composite salt gypsum layer casing in view of the engineering requirements and technical problems of composite salt gypsum layer interface casing damage.In this paper,the creep mechanism of composite salt-gypsum layer and the mechanism of casing damage are studied,and the corresponding casing structure optimization design is carried out,which can effectively reduce the casing damage in the process of drilling salt-gypsum layer and increase the service life of casing.Firstly,the physical properties of the salt-gypsum layer are studied to facilitate the subsequent numerical simulation;secondly,the indoor experiment of salt rock creep is carried out to explore the general law of salt rock creep;on this basis,the mechanism of casing damage caused by the composite salt-gypsum layer is studied,which is mainly caused by the non coordinated deformation caused by the fault movement of the ground layer,resulting in the shear stress of the casing and the casing production Based on the ABAQUS finite element analysis software,the corresponding mechanical model is established according to the actual situation of the composite salt-gypsum layer.The influence of the composite salt-gypsum layer's elastic modulus,Poisson's ratio,formation dip angle and the rheological characteristics of the composite salt-gypsum layer on the casing damage is comprehensively considered.At the same time,the formation casing cement ring triple medium model is established,which proves that in the composite salt layer there is stress concentration at the interface of salt-gypsum layer.Finally,the prevention measures of casing deformation are put forward,and the corresponding casing structure optimization design is carried out.