Simulation Study On Mechanical Behavior Of Completed Horizontal Well Tubular String

Thermal recovery is a heavy oil production technology with a rapid development in recent years,it has been widely used in the development of heavy oil reservoirs at home and abroad.Due to the limitation of the well structures of thermal recovery horizontal wells,the damage of the completion strings caused by steam injection is very complicated.Compared with the conventional oil mining method,the main problems of the heavy oil field are casing deformation,dislocation and leakage.Also,the failure problems caused by wellhead growth,wellhead steam and screen buckling are too many to count,which have caused great economic losses to oilfield production.It is of great significance to improve the efficiency of thermal recovery and ensure the safety of well completion with correct understanding of the stress and deformation of completion strings in the thermal recovery horizontal wells.In this paper,on the basis of previous studies,the less discussed problems about thermal recovery horizontal well completion strings are studied with theoretical and numerical simulation methods.Through the analysis of the casing strings under steam injection process,combined with mechanics of elasticity,material mechanics,and the corresponding mathematical theory,the stress analysis model of casing failure during thermal recovery in the horizontal well is established.The finite element model of thermal recovery horizontal well completion string and cement ring is built up and it is verified by the experiment.Based on the established finite element model,the mechanical behaviors and parameter sensitivity problems of vertical and horizontal completion string are studied.The main research works and conclusions are as follows.First of all,based on the theory of elastic mechanics,the triaxial stress formulas of casing under thermal stress and internal and external pressure are derived.According to the principle that the casing’s Mises stress should be under the minimal yield strength,the triaxial prestress of casing is deduced.Then,the mechanical behaviors of casing string of vertical section in thermal recovery horizontal well are studied.The cementation model and friction model between casing and cement ring are investigated,and the reliability of the finite element model is compared with the experimental results.Through the analysis of casing deformation and stress of conventional cementing and triaxial prestressed cementing,it is found that the pre tensile stress can effectively reduce the Mises stress of casing in a certain range,which can protect the casing.As long as the pre tension is selected appropriately,and ensuring the quality of cementing,the phenomenon of wellhead growth can be avoided in theory.The cementation strength,casing wall’s thickness and the base temperature are researched to discuss the effects on debonding of casing cement interface,the results show that the increase of casing wall’s thickness and the base temperature will increase the debonding rate between casing and cement ring,while the cementation strength between casing and cement ring is large enough,the phenomenon of wellhead lifting can be avoided effectively.Last but not least,the mechanical behaviors of screen of horizontal section in thermal recovery horizontal well are studied.According to the expansion performance of solid element model of screen under high temperature,the equivalent screen model based on the beam element is established.The thermal stress distribution and buckling behavior of horizontal screen under 350℃ are investigated.The number and location of thermal compensator are optimized,then,the thermal buckling characteristics and sensitivity factors of the horizontal section string under steam injection conditions are researched,and it is found that the increase of the friction coefficient and string wall’s thickness will increase the critical buckling temperature.Based on the above research,a set of relatively perfect simulation method for the mechanical behavior of the thermal recovery horizontal well completion string is established.The research of this paper is of great significance for the development of the well completion theory of special process well in China.