Study on Stress Field of Underground Coal Gasification Shaft Based on Thermo-Mechanical Coupling

According to the characteristics of high bottom hole temperature and large difference between inner outer walls reservoir casing in process underground coal gasification (underground gasification), field stress model wellbore gas production wells is established based on thermo-mechanical coupling, distribution different steel grades under limit working conditions studied. The results show that: (1) condition daily rate 30×104m3/d gasifier 1000°C, P110 grade always meets strength requirement; N80/L80 yielded at 188°C, critical J55 was 990°C after cooling by spraying device. (2) can be selected when lower than 600C, range 600°C–900°C, exceeds 900°C.