Numerical Analysis of the Effect of Cement Sheath Defects on Casing Damage in Heavy Oil Thermal Recovery Wells

Abstract

ABSTRACT: In the process of thermal recovery of heavy oil, casing damage caused by local defects of cement sheath is serious and caused huge economic losses to the oilfield. Nowadays, there is a relative lack of research on the mechanism of casing damage caused by cement sheath defects in heavy oil recovery wells. In this thesis, the radial and circumferential loss of cement sheath models and the loss of gas intrusion channel models are established. Using the thermal-solid coupling finite element analysis method of transient heat transfer, the effect of cement sheath failure on the temperature field and stress field of thermal recovery wells are analyzed. The study finds that when the cement sheath missing thickness ratio increases to 1/5 to 3/5 or the missing angle exceeds 30°, the casing is prone to yield failure. When the missing angle is 60°or 120°, the cement sheath is prone to secondary collapse. As the higher proportion of gas intrusion channel area and the more gas intrusion channels, the higher the maximum Mises stress of the casing and the worse the wellbore integrity. Through systematic analysis of the impact of the lack of cement sheath on the temperature field and stress field of the wellbore, it provides an important reference for the study of casing damage caused by the failure of the cement sheath. 1. INTRODUCTION At present, the world’s heavy oil resources are quite abundant. With the declining thin oil resources and the increasing demand for energy in countries around the world, heavy oil will become the main energy source for world economic development. There are m any exploitation methods for heavy oil reservoirs, mainly steam flooding and steam huff and puff (Shi 2015). The main function of the cement sheath is to isolate the casing and the formation, prevent gas invasion and channeling, and protect the safety of casing strength and wellbore integrity (Yu 2016, Chen et al. 2016, Chen et al. 2018). In the process of thermal recovery of heavy oil, the casing and cement sheath are easily dam aged by the interaction of complex downhole conditions and various loads, failing the integrity of the wellbore and complex accidents, and in severe cases, the well will be scrapped.