Evaluation of production performance in open-loop systems for repurposed abandoned oil wells into geothermal wells: A comparative study of various single-well types

The decommissioning of abandoned oil wells incurs high sealing costs and significant maintenance challenges. However, many oilfields have abundant geothermal resources, and repurposing these wells for geothermal energy extraction can lower drilling and sealing expenses while reducing environmental pollution. Given the challenges of wellbore damage and the low-grade geothermal resources typically found in oilfield regions, converting these wells into single-well open geothermal systems simplifies retrofitting and enhances production efficiency. This study introduces a coupled oil-water two-phase thermal-hydrological model for horizontal and vertical single-well open systems to examine the impact of perforation intervals on system performance. The model analyzes operational characteristics of different well types and key influencing factors. Research shows that due to anisotropic permeability and gravitational effects, horizontal well systems experience greater temperature drops and differential pressure (30 °C and 4.4 MPa) compared to vertical systems (2.4 °C and 0.5 MPa). While vertical well systems yield more daily oil production, horizontal systems are more sensitive to variations in operating parameters. Injection temperature significantly impacts production temperature, while injection mass rate affects pressure differences. Additionally, cycle periods play a crucial role in overall system performance. Choosing appropriate perforation locations in abandoned oil wells can enhance system performance. This study serves as a reference for selecting optimal well types and retrofitting strategies when converting abandoned wells into geothermal wells, providing valuable guidance for process design.