The Casing Deformation Mechanism Study For Deep Salt-gypsum Layer

The casing deformation mechanism for deep salt-gypsum layer is vital in instructing well design program and drilling operation in the deep salt-gypsum interval. In this paper, the author conducted systematic study on the main issues of casing deformation in the deep salt-gypsum interval through theoretical analysis, numerical calculations and model experiments. The main work and the conclusions are presented:1. Geomechanic characteristics of deep salt-gypsum layerConstitutive models of salt-gypsum rock under the conditions of high temperature and pressure are obtained by performing triaxial compression test. in high temperature and pressure condition, salt-gypsum rock exhibits plastic and rheological properties after reaching a small yielding strength, elastic-plastic analysis of deep salt-gypsum Rock is problematic in solving engineering problems, the time-dependent creep property has to be considered.2. Creep of deep salt-gypsum layerSalt rock creep experiments are performed to obtain creep property. Through the analysis of the mechanical properties of composite rock salt with time in different mineral composition and differential stress conditions, it is proposed that creep of deep salt-gypsum rock is not only affected by the temperature and differential stress, but also by lithology/mineral composition; based on the creep properties of different mineral compositions, the author introduces a lithology factor affecting creep, the heard creep model is used to describe creep quantitatively.3. Deformation analysis of casing complex in deep salt-gypsum layerA finite element model of casing collapse pressure change resulting from composite salt rock relaxation is established, the non-uniform loading on casing plays a major role in casing deformation, the thickness of composite salt rock interval affects casing deformation as well, casing manufacturing defects have significant effect on the collapse resistance strength of casing.4. Casing design and application of deep salt-gypsum layerThe iterative method of casing intensity design under high temperature and pressure conditions and casing intensity check are adopted to analyze the casing deformation of Yingmaili and Dabei oil wells in Tarim oilfield.