Spray Cooling Schemes and Temperature Field Analysis of Ultra-High-Temperature Production Wells in Underground Coal Gasification

Abstract

In underground coal gasification (UCG), it is essential for UCG production to accurately control the temperature of the gas produced at the wellhead of the production well and correctly calculate the variation law of the temperature field in the whole wellbore. UCG wellbore structures use three wellbore sprayed water cooling schemes. These schemes consider the heat exchange mechanism between the wellbore and the formation, the division of the production wellbore into the spray chamber section and the non-spray section, and the established temperature field model of the whole wellbore. The research shows that, due to the large temperature gradient formed in the wellbore heat transfer route under the spray tubing water injection cooling scheme, the temperature of the produced gas drops the most. The annular water injection cooling scheme can protect the cement sheath to a certain extent and is easier to implement; therefore, it is more suitable to use this scheme to cool the production well. It is feasible to control the temperature of the production wellhead by controlling the temperature of the spray chamber. The greater the daily output of produced gas or the thermal conductivity of the tubing, the smaller the temperature change between the bottom hole and the wellhead, and the more the spray water temperature rises.