Journal Article

The Effect of Operating Pressure Variations on Water Inflow and Groundwater Drawdown in Underground Coal Gasification (UCG)

Widodo, Lilik Eko, Jasanagara, Faradilla Putri, Madiutomo, R M Nendaryono

2025

Overview

Underground coal gasification (UCG) is an in-situ and non-conventional method for extracting coal by injecting steam, air, and oxygen into the target coal seam. The resultant gas from this process is transported via production pipes to a gas processing facility, where it can be used for electricity generation and the production of synthetic gas (syngas). The UCG process creates cavities within the coal seam, which requires groundwater as a natural barrier to prevent gas loss. However, groundwater entering the cavities can lead to a drawdown of groundwater head, and if this drawdown is excessive, subsidence may occur. This study aims to predict groundwater intrusion in the gasification zone and its effects on the aquifers above and below the gasification zone. UCG modeling was performed with a coal hydraulic conductivity value of 4.5 x 10−8 m/s and operational pressure variations of 10 bar and 20 bar. The hydrostatic pressure on the target coal is 32 bar. Simulations were conducted over 144 days or for the gasification of 100 meters (10 grid models) of coal. Simulation results with coal conductivity of 4.5 x 10-8 m/s and an operating pressure of 10 bar, the model predicts a groundwater intrusion of 61.96 m3/day into the gasification zone, 0.0998 m3/day from the upper aquifer, and 0.1088 m3/day from the lower aquifer, causing a drawdown of 1.42 meters in the upper aquifer and 2.47 meters in the lower aquifer. At operating pressure 20 bar, predictions are 27.34 m3/day intrusion into the gasification zone, 0.0803 m3/day from the upper aquifer, and 0.1052 m3/day from the lower aquifer, resulting in a drawdown of 1.28 meters in the upper aquifer and 2.16 meters in the lower aquifer.

• Publisher: IOP Publishing
• Subject: Aquifers / Cavities / Coal / Coal gasification / Drawdown / Groundwater / Groundwater barriers / groundwater drawdown / groundwater modeling / Hydraulic conductivity / hydrogeology / Hydrostatic pressure / Intrusion / operation pressure of UCG / Pressure / Pressure effects / Synthesis gas / underground coal gasification / Water inflow / water inflow in UCG