Prediction of Heat Energy Productivity of Geothermal Wells Converted from End-Of-Lifetime Shale Gas Wells in the Haynesville Area of Louisiana: Horizontal Well Pairs

Abstract Conversion of end-of-lifetime hydrocarbon wells to geothermal wells has received extensive attention in the oil and gas industry for cost-saving and revenue generation. Before the well conversion, it is essential to predict the thermal-energy productivity of geothermal wells. This paper presents a numerical simulation model to predict the temperature at the fracture exits in horizontal well pairs. This research employs numerical modeling to resolve the complex heat transfer processes in fracture-connected horizontal well pairs. A finite-volume method is used to discretize the governing equations for energy conversion in the system. These equations include heat conduction in the rock matrix and wellbores, as well as advective heat transport in the fractures and wellbores. This numerical method enables the simulation of transient heat flow, accurately representing the dynamic thermal interaction among the fluid, fractures, and the reservoir formation. A case analysis was performed using the model to predict temperature profiles and heat energy productivity of a well pair in the Haynesville area of Louisiana. The model analysis indicates that at a water flow rate of 1000 m3/day, the temperature of the water at the fracture exit is 174 °C after one month, which is attractive for producing water at temperatures required for electrical power generation. The thermal power of the produced water at the fracture exit is 1.35 MW, which is significant for heating commercial and residential houses. The sensitivity analysis revealed that the heat-energy productivity of converted wells declines over time at varying rates, depending on the fracture geometry, flow rates, and fracture permeability. This work provides engineers with a rigorous and easy-to-use method for predicting the heat energy productivity of geothermal wells converted from end-of-lifetime hydrocarbon wells. It also offers a tool for optimizing parameter values in geothermal well systems.