Thermal and Flow Modeling of Gas Lift Applications in Liquid-Dominated Geothermal Wells
Authors: Khankishiyev O. , Hasanov G. , Karami H. , Nygaard R. , Vivas C. , Salehi S. 
Published: September 2024

The global consumption of electrical energy is constantly increasing, and the demand for sustainable and net-zero energy is more critical now than ever. In the context of the energy transition, Enhanced Geothermal Systems (EGS) are emerging as a promising solution for renewable and sustainable energy production. The economic efficiency of geothermal wells depends on production performance, which can be enhanced through various artificial lifting systems such as gas lift and submersible pumps. This paper investigates the application of gas lift in liquid-dominated geothermal wells to increase the production rate of hot liquid/steam, ultimately improving the enthalpy recovery per well.

A steady-state multiphase flow model is employed to simulate the impact of gas lift on the flow rate within the geothermal well. The model considers various parameters such as fluid properties, wellbore geometry, and operational conditions. Sensitivity analysis is conducted to assess the influence of different gases on gas lift performance under varying reservoir conditions. The thermal performance of the geothermal well during gas lift operations is analyzed. The model accounts for heat transfer mechanisms, including conduction, convection, and radiation, within the wellbore and the surrounding formation. Factors such as fluid temperature, flow rate, gas injection temperature, and thermal properties of the materials are incorporated into the model to accurately simulate thermal dynamics. Different gas compositions, including compressed air, methane, nitrogen, and carbon dioxide are analyzed for their suitability as gas lift agents.

Application of the gas lift results in up to a 30% increase in liquid production rates. Methane exhibits superior performance due to its lower density, with an increase in production from 1350 STB/day to 4050 STB/day at a 1 mmscf/day gas injection rate. CO2 shows potential for Carbon Capture, Utilization, and Storage (CCUS) projects, though it accelerates the corrosion risks by up to eight times. The study also finds that deeper gas injection points enhance mass production rates by 13%, albeit with higher surface gas injection pressures required. Overall, methane showed the best performance in terms of increasing production rates, producing the highest temperatures and therefore, the highest produced heat. However, the flammability and environmental damage risks must be considered.

Thermal modeling indicates that while higher gas-to-liquid ratios lead to increased temperature drop, the overall enthalpy production rises due to the elevated production rate. The combination of multiphase flow and thermal modeling, along with comprehensive sensitivity analyses, provides a robust framework for evaluating gas lift applications in liquid-dominated geothermal wells. These findings contribute to optimizing geothermal well performance, highlighting the potential of gas lift systems to play a significant role in the transition towards sustainable and renewable energy sources.