Groundwater flow and gas distribution in a coal-bearing sedimentary basin, East Kalimantan, Indonesia

Unconventional hydrocarbon gas development has attracted much attention in recent years. Concerns arise over the vulnerability of shallow groundwater and surface water resources to potential impacts from deep groundwater abstraction and hydraulic fracturing. This thesis explores the relationship between the distribution of unconventional gas in coalbed methane reserves and its relationship to groundwater in the Kutai Basin in East Kalimantan, Indonesia. The aim is to further the understanding of this relationship to improve predictability and manageability of water management practices in coalbed methane developments. The research uses a range of geological, hydrogeological, hydrochemical and geochemical data and interpretive techniques to characterize the basin-wide hydrogeological environment. Groundwater samples from the study area were analysed for inorganic composition and stable isotopes for groundwater characterization, and 14C for groundwater dating purposes. Using hydrogeological and hydrochemical theory to explain the distribution of unconventional gas within the basin, a new hypothesis is proposed that groundwater circulation in the Kutai Basin constrains the distribution of methane derived from secondary biogenic and thermogenic origins. The hypothesis explains the spatial variation of gas composition as a result of basin-wide groundwater circulation. Deep basin compaction-driven flow converges with shallow topographic-driven flow leading to a groundwater convergence zone and gas alteration (mixing) zone between secondary biogenic gas and deeper thermogenic gas. The convergence zone is further explored using hydrochemical theory to better understand the hydrodynamics of the flow system. Groundwater modelling is used to simulate the concept and to explore the effects of a hypothetical development involving deep groundwater pumping to gain an understanding of potential impacts on shallow groundwater and surface water resources. The research demonstrates the value of a holistic approach to basin hydrogeology to help determine more accurate prediction of potential impacts in order to improve the manageability of unconventional gas development.