Evaluation of Zonal Isolation Material for Low Temperature Shallow Gas Zone Application

Abstract

Abstract Methane gas leaks from shallow gas zone have been reported in some areas in the North Sea. In the North Sea, shallow gas zones can have temperatures below 25°C with relatively low pore pressure. It is necessary to prevent the flow of this gas behind casings by performing proper zonal isolation with cementitious materials. A series of experiments were performed on three different types of industrially used and state-of-the-art cementitious materials and a rock-based geopolymer to evaluate their performance for shallow gas zonal isolation. Neat class G Portland cement, industrial rapid-hardening cement, gas-tight cement, and granite-based geopolymer were the selected materials. The research aims to reveal the performance of these zonal isolation materials and their potential shortcomings due to the low-temperature effect. Material characterizations were performed on three states of the materials: liquid-state, gel phase, and solid-state. Rheological properties and consistency are evaluated at the liquid state of the materials. Static gel strength tests were performed to evaluate the strength of gel structure and transition time. The compressive strength of samples was evaluated using an ultrasonic cement analyzer (UCA) and unconfined compressive strength (UCS). In addition, the scanning electron microscopy (SEM) technique was utilized to reveal microstructure of the materials. To have a similar hydration process as in the low-temperature shallow gas zone, slurries were mixed and pre-conditioned at temperatures of 4 and 25°C. The experiment shows that the hydration process of the cement is less optimum in the low-temperature condition, which affects the gel strength development of the cement during the transition from liquid to a solid phase. It also resulted in the lower final compressive strength of the cured specimens.