Staged Field Development Planning for Enhanced Geothermal Systems Under Thermal and Economic Constraints

Abstract

A field development framework is crucial to determine the optimal initial well count and subsequent development schedule under thermal and economic constraints for Enhanced Geothermal Systems (EGS). Most existing EGS studies focus on fixed upfront development design and optimization in which the project starts with the full number of wells. There is, however, a lack of studies on staged, dynamic field development planning under coupled thermal and economic constraints. This study compares these two development plans and aims to maximize commercial thermal power production and improve the economic performance of EGS projects. The proposed workflow couples heat and mass transfer simulations using the semi-analytical Gringarten model with economic constraints and performance metrics to optimize EGS development decisions through time. A target net production power of 500 MWe and an EGS lifetime of 30 years are used as development constraints linked to commercial thermal production. Drilling cost constrains well lateral length, while completion design parameters such as fracture half-length, fracture height, and fracture spacing constrain well placement and circulation geometry. These constraints are integrated with economic metrics, including levelized cost of electricity (LCOE), discounted cash flow, payback time, net present value (NPV), and profitability index (PI), to evaluate development plans that sustain thermal power output. The staged development plan, in which the EGS project starts with a limited number of horizontal wells and expands over time, is compared with an upfront development plan. Comparisons are also provided among staged plans with varying initial well count, well placement, well spacing, fracture spacing, lateral length, and deployment schedule. Results show that staged development can sustain the target power output while deferring capital expenditure, reducing levelized cost of electricity, and increasing net present value relative to upfront development. Under flexible power production, staging improves plant utilization and net present value by adding capacity as thermal performance declines, while the self-funded plan enables modular growth from a substantially smaller initial investment and achieves the highest profitability index and completion utilization. Beginning with a smaller initial development also allows the project to generate revenue earlier while providing time to improve reservoir characterization through surveillance and monitoring. The optimal initial well count depends on well spacing, lateral length, and completion design, while the subsequent development schedule depends on the forecast thermal performance of existing wells and the applicable financing constraints. This study extends EGS analysis to dynamic field development planning under coupled thermal and economic constraints. The approach provides a more realistic basis for staged EGS deployment and demonstrates that staging can defer capital expenditure, sustain productive use of installed plant capacity, and enable commercial-scale development from limited initial investment.