Underground coal gasification (UCG) is a promising clean coal technology to convert unmineable and deep coal reserves into syngas, which can be used in many industrial applications. In UCG field, real time monitoring of hydrological and geological conditions such as water influx rate, cavity growth and its interaction with overburden is a formidable task. UCG project Thar (UPT) lacks real time data acquisition system to monitor these parameters. In this work, a 3D axisymmetric cavity simulation model (CAVSIM) is parameterized with operating conditions of UPT and properties of Lignite B coal of Thar coal fields. For model validation, a comparison has been made between simulated and the UPT field data for the composition and heating value of syngas. The results of CAVSIM are also compared with our previous ID packed bed model, which show the superiority of CAVSIM model. Moreover, a comprehensive simulation study has been carried out to predict the cavity growth and its interaction with overburden. The effect of operating parameters of UPT on volumetric cavity growth and heating value of syngas are also investigated. (C) 2019 Elsevier Ltd. All rights reserved.