The geology of the polar region is complicated, and shallow gas is a common geological disaster. Drilling in shallow gas formation would lead to gas influx, gas kick and even well blowout. Therefore, numerical simulation was carried out in this paper to study the risk of drilling in shallow gas with ultra-low temperature environment. The effects of temperature, pressure of shallow gas reservoirs and density of drilling liquid on shallow gas blowout were studied to provide a basis for the development of prevention and control plans for polar drilling with ultra-low temperature.
Shallow gas is the small-scale gas reservoir below the surface without exploitation value. The overlying strata which cover the shallow gas reservoir causes the gas from the deep formation to accumulate, resulting the high pressure of shallow gas reservoir. During the drilling process, drilling in shallow gas reservoirs would easily lead to serious accidents such as gas influx, gas kick and even well blowout (Yin, et al. 2021a; Yin, et al. 2021b). If the shallow gas risk was not identified and targeted control project was not formulated in the construction design stage, the safety of operators and drilling equipment would be affected. Many studies have been conducted on shallow gas by predecessors. Yang et al. (2015) carried out a simulation experiment to identify shallow gas based on the principle of acoustic wave and found the acoustic wave velocity characteristics of shallow gas (Yang, et al. 2015). Long et al. (2023) studied the blowout mechanism of actively releasing shallow gas in Shenhu Sea area by numerical simulation, and summarized the risk caused by shallow gas blowout in drilling engineering (Long, et al. 2023). Based on the influence of shallow gas on the velocity of seismic wave, Zhang et al (2016) established the variation tend of acoustic wave velocity of shallow gas with different risk levels and formed the shallow gas prevention plan (Zhang, et al. 2016). Cao et al. (2023) used neural network algorithm to establish four different qualitative identification models of shallow gas based on 3D seismic data in the deep-water area of the South China Sea (Cao, et al. 2023). Osorio-Granada et al. (2023) used high-resolution seismic analysis to study the distribution of shallow gas on the continental shelf off the Caribbean Sea coast of Colombia and identified bright spots, pockmarks and other anomalies. The identification of these phenomena is an important basis for judging Marine geological hazards (Osorio-Granada, et al. 2023). Nguyen et al. (2023) studied the seismic acoustic data of the Pomeranian Gulf and found abnormal acoustic phenomena such as bright spots and pockmarks, which explained the characteristics of shallow gas and its migration to shallow sediments (Nguyen, et al. 2023). Shirazi et al. (2023) used a new time-frequency analysis method to interpret seismic data more efficiently, which shows great potential for accurately identifying shallow gas locations (Shirazi, et al. 2023). Most of the previous studies focused on the identification and blowout of shallow gas in sea, but the studies on shallow gas in ultra-low temperature environment is not complete. Therefore, it is important to evaluate the blowout risk of shallow gas drilling in polar with ultra-low temperature environment. According to the polar drilling data, the polar drilling temperature is −25°C∼-20°C, and the shallow gas reservoirs are mostly in the range of 50m-150m underground. Numerical simulation analysis was carried out for shallow gas drilling with ultra-low temperature. The initial temperature was set at −20°C. Based on fluid mechanics theory, the Volume Of Fluid model (VOF model) combined with k-ε turbulence model was adopted to study the blowout characteristics of drilling liquid. It would provide the basis for formulating prevention and control plan of shallow gas in polar.
