Study On The Mechanism Of Casing Failure Of Oil & Gas Well In Salt Rock Formation

Casing as a migration channel concerns oil-gas production directly, which is an important hub to assure oil and gas wells operation normaly after drilling and well completion.During oil and gas field development, casing failure causes tremendous economic loss. We must prevent and reduce casing failure in salt rock formation which is an important roof rock of oil and gas resources.This thesis focus on analysis of casing failure during oil and gas field development. In order to make a deep study on analyzing the root cause, on the basis of field observation and relative data analysis, with the solution of casing failure problem as its goal, this paper adopts combination of experiments,theoretical analysis,statistical analysis and numerical simulation. The major conclusions of present paper as follows.1. Study on the creep characteristic of salt rock under different confining pressure and different deviatoric stress conditon by triaxial compression creep tests. The result shows that confining pressure and deviatoric stress are significant effect on the steady creep rate. This paper investigates creep mechanism and constitutive relations of salt rock. The steady creep strain law is studied and the creep parameters are obtained from these test results.2. We have mechanical analysis according to borehole shrinkage problems in salt rock formation during drilling process. The numerical simulation research on the problem of stability of a borehole drilled through salt formation and provide a borehole shrinkage ratio relationship map at different depth,different mud weight, which can be as a theoretical basis drilling through salt rock formation.3. Use the borehole shrinkage rate data obtained from Well Logging Curves of Shengke one as initial parameters, according to forward and inverse methods for calculating using three dimensional numerical simulation to carried off the creep parameters under creep rate of 0.55mm/h & 0.46mm/h conditions. The creep parameters can be applied to mud weight optimal design.4. Based on synthetically analysis of all kinds of researched results about casing loads in creep stratum. On the base of it then presents casing loads in creep stratum under uniform in-situ stresses and non-uniform in-situ stresses are studied.5. In order to casing loads calculation in creep stratum,the mechanical model of merits and absence of cementing annulus are set up.Using three dimensional numerical FLAC3D to simulate under uniform in-situ stresses and non-uniform in-situ stresses conditions. With the casing equivalent stress as the research target, carried off the variation law of casing equivalent stress used for drilling optimal design and operations.6. Study is made on borehole dissolving rate simulation tests, known the borehole expand rate and size, the equation of dissolving rate is given with the relationships between different temperature and different saturation, its corresponding equation is as following.7. Based on the theory of equilibrium arch, the corrosion cavity configuration is analyzed by considering the interaction of casing and salt rock formation. It deduces the calculation formula of axial force acting on the casing the relationship between casing destabilization failure and corrosion cavity height and volume is established.8. Orthogonal experimental design method is used to analyze the parameters sensitivity of casing loads in creep stratum under uniform in-situ stresses and non-uniform in-situ stresses. Obtain the main factors of the casing equivalent stress are casing wall thickness and cement annulus elastic modulus, can be used for drilling optimal design and operations.