Cement Sheath Integrity Evaluation for Separated Layer Water Injection Well
Authors: Shan Yonglin , Ding JiaDi , Yang Wei , Zhao Hu , Shi Ligang , Wang Xuechun , Liu Shikang 
Published: September 2022

ABSTRACT:
Separated layer water injection is an effective method to enhance oil recovery for the low permeability reservoir. However, the frequent fluctuation of bottom hole pressure and temperature may increase the risk of losing zonal isolation which lead to the failure of separated layer water injection operation, highlighting the importance of optimizing the cement stone’s mechanical properties. This paper presented a work flow for the cement sheath integrity of water injection well. First, in order to investigate the evolution of mechanical property for cement stone during the frequent fluctuation of temperature, cement paste was cured for 7 days at 160 °C and 21MPa, then the temperature varied from 160 °C to 50 °C for several cycles. After that, a series of tri-axial compression test and tensile test were conducted to measure the mechanical property of the cement stone. Second, a coupled thermo-mechanical staged finite element model was developed to evaluate the cement sheath integrity during the injection operation. The behavior of cement was described with the extended Drucker-Prager model whose parameter came from the first part. The results indicated cyclic change of temperature leads to significant degradation of the cement, both the compressive and Young’s modulus declined with the increase of temperature cycle, the simulated result show that degradation which lower the load carrying capacity was the main reason for the failure of cement, this highlights the importance of the durability evaluation, especially for the cement sheath which served in the frequent change of temperature or corrosive environments.

1. INTRODUCTION
The main purpose of cementing operation is to keep zonal isolation of the wellbore. With the world energy consumption rising, the exploration and development of unconventional reservoirs are more and more important. Which pose a challenge not only for the design of cement slurry, but also for the evaluation of the cement sheath integrity in field. In the early days of petroleum industry, people used to focus on the conventional performance of the cement slurries, such as the rheology, the thickening time and the fluid loss. The evaluation of the zonal isolation starts with laboratory experiments, the objects can be classified into three types:
• Devices designed to study the failure modes and find the main reasons for the failure, such as temperature and pressure. And some of them are nearly full scale setups (Evans et al., 1962; Goodwin and Crook, 1992; Jackson and Murphey, 1993);
• Experiments performed to obtain the mechanical behavior or properties of the cement stones, such as uniaxial, tri-axial tests and tensile tests (Heinold et al., 2003; Simon et al., 2006), cycling tests were performed to study the plastic deformation of different cement stones (Ravi et al., 2004), isotropic loading test were also carried out to investigate the poro-mechanical behavior of cement (Ghabezloo et al., 2008);
• Test methods to quantification the failure of cement on the meta-microscale with CT visualization and 3D reconstruction (Andrade et al., 2016);