Finite Element Analysis of Induced Stresses on Injection Wells using Plane Stress and Strain Elements

摘要

Casing failure has become a common occurrence especially in injection wells, which often affect development objectives of intended reservoirs. Stresses induced by injection of fluids (e.g. water, CO2, steam) in a well may affect the integrity of the casing, cement and surrounding formations. Thus, a simplified and reliable assessment of the thermal stresses induced in casings are necessary in predicting the integrity of well in complex and unconventional production activities. The injected fluid cause fracturing of the formations and this induces local compression and tensile stresses in the various casing strings landed and cemented in the well. This work presents a quick and cost effective procedure for obtaining appropriate grades of casing using finite element (FE) method. The model is developed for quick assessment of well integrity using a well-known commercial FE package- ABAQUS 6.12-1. The ABAQUS’ plane stress and plane strain elements with associated material properties were used to model the thermal stresses in casing, cement and near well bore. The effect of varying the thickness of casing was investigated and an optimum thickness corresponding to various fluid conditions was obtained. The developed model was compared to existing models in other to assess the accuracy of the model. A parametric study was conducted on the effect of casing dimensions on the stresses and strains developed in the steel casing. The results of the study showed that strains and stresses on the casing vary directly with increasing temperature and pressure of transported fluid in the wellbore casing. A strain based failure criteria was developed to aid the well design engineer in selecting appropriate casing thickness and diameter. The model presented shows a quick and reliable procedure for obtaining dimensions of casing subjected to unconventional environments.