Thermo-tectonic and reservoir controls on geothermal energy feasibility in a foreland basin: A probabilistic thermo-hydraulic assessment from the Upper Assam Basin, India

This study evaluates the feasibility of repurposing mature hydrocarbon reservoirs for geothermal energy production in the Upper Assam Basin, India, through an integrated thermo-tectonic and petrophysical framework. Bottom-hole temperature data from 34 deep wells (3000–4800 m) are corrected using multiple empirical methods to construct an uncertainty-bounded thermal envelope (P10–P90), yielding geothermal gradients of ∼2.0–3.7 °C/100 m and conductive heat-flow values of ∼41–108 mW m⁻². A statistically significant inverse correlation (r ≈ –0.6) between basement depth and heat flow reveals strong thermo-tectonic control via sedimentary thermal blanketing. Petrophysical analysis of 18 wells identifies the Lakadong–Therria Formation as the most favourable reservoir, with stable effective porosity (∼0.16–0.17) and permeability ranging from sub-millidarcy to tens of millidarcies. Probabilistic thermo-hydraulic simulations based on 50,000 Latin Hypercube realizations indicate that geothermal performance is controlled primarily by reservoir transmissivity rather than thermal availability. Peclet-number analysis reveals strongly advection-dominated heat transport within the Lakadong–Therria reservoir (median Pe ≈ 132), whereas Langpar and Nurpuh show mixed conductive–advective behaviour. Simulated median electrical power output ranges from approximately 320–1960 kW for Lakadong–Therria depending on permeability assumptions, while Langpar and Nurpuh generally remain below 200 kW owing to limited reservoir deliverability. The results show that geothermal feasibility in foreland sedimentary basins is governed by the interaction between basin-scale conductive heat accumulation and reservoir-scale permeability-controlled fluid circulation, highlighting that such systems are fundamentally flow-limited rather than heat-limited. These findings identify the Lakadong–Therria Formation as the most promising geothermal target in the Upper Assam Basin and provide a transferable workflow for geothermal screening of mature hydrocarbon basins.