Finite Element Analysis Of Multi-field Coupling In Thermal Recovery Wells

Thick oil resources are widely distributed in China. During thermal recovery processes, a large number of casing damages occur, and as a result, massive funds have to be invested in drilling new wells or repairing the damaged ones. Prevention technology for thermal recovery wells is always one of the problems that get in the way of thick oil development onshore in China. In the environment of thermal recovery, influencing factors for casing damage are more and more complex, the study on mechanism of casing damage is very important for improving economic benefit of thick oil recovery.At present, study on casing damage mechanisms under the action of single field is already more mature. Study on multi field coupling in the field of petroleum development has also made new progresses. But, proper method for studying casing damages according to multi-field coupling effects has been put forward.In this thesis, using the finite element analysis software of ANSYS and under the guidance of pipe-string mechanics, rock mechanics, heat transfer, numerical analysis and theory of finite element analysis, and by models building and solving, multi-field coupling finite element analysis method is put forward to analyze the mechanical behaviors of the system near the well bore underground. Useful exploration for the cooperative effects law of multi-field coupling is also made in this thesis. Several results of the thesis are summarized as follows:1. Some complex influencing factors of casing damages are simplified in the models building, and cooperative effects are studied mainly. Ground stress interaction model near the well bore under ground, heat insulation and transfer model for well bore and cooperative multi-field coupling model for system made up of casing, cement sheath and formation near the well bore are built.2. In order to study the cooperative effects, sequential multi-field coupling analysis is made in this thesis. The solution methods of the model are also studied. Through the second order programming using APDL (ANSYS Parametric Design Language), the calculation efficiency is greatly improved.3. Mediums in the annulus are not definite, and its diathermancy is only considered in the thermal insulation and transfer model. There is no necessary considering it in solving the complex mechanical problems in the total model. By this practice, the calculating is simplified and the effect of boundary temperature on the thermal stress is not influenced.4. Specific examples were calculated through the methods above, the influence of all sorts of factors on casing damages is analyzed. And valuable suggestions for casing design and protection are also put forward.