Parameter Optimization Of Replacing Abandoned Oil Well With Geothermal Well

Geothermal energy is known as a strategic energy source for the future.If the abandoned oil wells in the oilfield can be converted into geothermal wells for use,they can turn waste into treasure and contribute to the global low-carbon goal.Starting from this idea,this paper simulates the downhole part of concentric tube heat transfer technology,single U-tube heat transfer technology,double U-tube heat transfer technology and U-shaped butted well is simulated by using the heat-fluid-solid coupling module of OpenGeoSys(OGS)software,and the heat recovery mode of formation water and heat extraction is simulated by using the thermal recovery model of CMG software.The circulating flow rate,heat transfer power,operation period,heat transfer fluid,inlet temperature and other parameters of geothermal well are optimized.The simulation results show that:The downhole part of concentric tube heat transfer technology,single U-tube heat transfer technology and double U-tube heat transfer technology is simulated by using the heat-fluid-solid coupling module of OGS software,and the heat recovery mode of formation water and heat extraction is simulated by using the thermal recovery model of CMG software.The circulating flow rate,heat transfer power,operation period,heat transfer fluid,inlet temperature and other parameters of geothermal well are optimized.For concentric tube heat exchangers,the heat transfer effect of the fluid circulation method of external inlet and internal output is better than that of internal inlet and outlet;The maximum linear meter heat exchange should not exceed 100 W/m;The recommended circulating flow rate is 20 m~3/h;The specifications of the central tube have little effect on the heat transfer performance;After the abandoned well is transformed into a concentric tube heat exchanger,it can achieve 12 h intermittent mining of stable 100 W/m linear meter heat exchange power.In the long-term heat extraction simulation,the longest heating period is 5months,which can maintain the stable operation of the system for 30 years.For single-U and double-U models,the total inlet flow is recommended to not exceed 10m~3/h;The heat exchange power of water is higher than that of organic fluids such as R601A and R601;In the shallow range of 800 m,the heat collection efficiency of the double U-shaped tube is higher,the concentric tube is centered,and the single U-shaped tube is the lowest.For the U-shaped butted well model,after the circulating flow reaches 40 m~3/h,the influence of circulating flow on the heat exchange power is weakened.The lower the inlet temperature,the higher the heat transfer power,but it is not recommended to lower than 5℃;When the inlet temperature was 15℃ and the flow rate was 40m~3/h,the water temperature increased by 1.8℃/km,4.2℃/km and 1.2℃/km in the downbound,horizontal and upbound wells,respectively,and the heat transfer efficiency of the horizontal well section was 2.27 and3.46 times that of the downward and upward sections,respectively.For water layers with a thickness greater than or equal to 30 m,single well water intake and heat production can be considered,and the daily water output can be maintained at 200m~3/d within 10 years;When the production conditions of injection wells and produced wells are the same,among the three injection production modes,the heat recovery of one injection and four production mode is the largest,followed by four injection and one extraction,and the least is one injection and one extraction.