Predicting the Healthy Operation of Heavy Oil Well Casings in Permafrost Regions

Tiecheng Sun,Yiming Liao,Zurun Yue,Cancan Liu,Tianfei Hu,Yu-Sheng Shen

doi:10.1155/2021/8893159

Abstract

This study explores the distribution of stress and deformation on casings in heavy oil recovery wells and the distribution of stress in the thaw bulb in permafrost areas. Considering the expansion of the thaw bulb, the simulation analysis method is used to explore the internal mechanisms of vertical settlement displacement development and stress redistribution within thawed soil and casing. Calculation results show the following: (a) The maximum settlement of the thawed soil and the casing was positively correlated with the expansion of the thaw bulb. Although the settlement of the thawed soil was greater than that of the casing, the initial increase in maximum settlement difference between the thawed soil and the casing eventually tended to be constant due to stabilization of the thaw bulb’s expansion. (b) The size of the thaw bulb directly affects the redistribution of internal stress in thawed soil, leading to different distribution rules for the vertical displacement of thawed soil and casing with depth. (c) Beyond a certain formation depth, the vertical stress of thawed soil gradually transits from a tensile stress state to a compressive stress state. The depth of a soil layer whose horizontal stress value is initially greater than its vertical stress value will gradually deepen with an increase in thaw bulb radius. (d) There is no significant negative friction on the lateral wall of casing in yield state, but significant negative friction exists on the lateral wall of casing in elastic state. The vertical stress of casing in elastic state increased gradually with the increase of casing depth, due to the existence of continuous negative friction and dead weight.

Highlights

With the gradual increase of the global temperature, largescale development of Arctic oil and gas resources has become possible
Based on the technology employed in constructing heavy oil wells, a certain thickness was presumed for the cement grouting layer on the lateral casing wall
As the thaw bulb gradually expands, the vertical displacement of the thawed soil increases linearly with depth. e inflection point appears in the vertical displacement curve of the casing with depth, and the location of the inflection point gradually approaches the ground surface with the expansion of the thaw bulb

Summary

Introduction

With the gradual increase of the global temperature, largescale development of Arctic oil and gas resources has become possible. E thaw bulb radius RTB was 1.0 m, 3.0 m, 5.0 m, and 7.5 m, which corresponded to the thaw bulb radius over the course of the oil well operation period at 1 year, 5 years, 10 years, and more than 20 years, respectively According to these data, a cylindrical model with a radius of 22.5 m and a vertical depth of 171 m was determined for calculation and analysis. E physical and mechanical parameters of the soil layers are shown in Tables 2 and 3. E change in casing stress state occurring during the thawing of frozen soil is closely related to the friction force generated by thawed soil on its contact surface. E friction properties of the contact surface between the casing and the thawed soil were taken to be a key parameter for calculation and analysis.

Analysis of Calculation Results

Limitations of the Model

Conclusion