Research on a novel long-distance crude oil pipeline heating system based on medium-depth geothermal and heat pump coupling

To address the problems of high energy consumption, high operating costs, and environmental pollution associated with conventional heating furnaces used for crude oil heating at a specific station, this study proposes an innovative Mid-Depth Geothermal–Oil Heating Pipeline System (MDG-OHP). The system utilizes abundant local geothermal resources to replace traditional furnaces, aiming to improve energy efficiency and reduce emissions. To verify the technical feasibility of the proposed system, a comprehensive investigation of its long-term heat transfer performance was conducted from three perspectives: (1) typical operating condition analysis, (2) sensitivity analysis of key parameters—including the number, spacing, and depth of deep borehole heat exchangers (DBHEs), circulation flow rate, geothermal gradient, and groundwater seepage velocity—and (3) economic and reliability assessment. The results indicate that under typical operating conditions, the system exhibits an average outlet temperature attenuation rate of 26.65% over 25 years, while maintaining a coefficient of performance (COP) of 5.46, which is sufficient to meet the heating demand of the station. Increasing the DBHE number, spacing, depth, circulation flow rate, geothermal gradient, and groundwater seepage velocity enhances the overall system performance. Considering both technical and economic factors, the levelized cost of heating (LCH)—which integrates heat transfer performance, the power consumption of the heat pump and circulation pump, and initial investment—was introduced for evaluation. The analysis shows that the configuration with nine DBHEs, 30 m spacing, 2000 m depth, and a circulation flow rate of 30 m3/h yields the best economic performance, achieving a payback period of approximately 10 years. Over 40 years of operation, the average COP decreases by only 8.21%, and the system remains stable under crude oil flow fluctuations up to 120% of the nominal value, demonstrating excellent adaptability and reliability.