A Design of Downhole Thermoelectric Generation for Horizontal Oil Wells

摘要

Harnessing geothermal energy for power generation from oil wells features significant advantages over traditional geothermal wells, especially in reducing capital expenditure and operational risks. Downhole geothermal power generation using thermoelectric technology in a vertical well was recently proposed to develop the geothermal energy from oilfields. This paper proposes a new design of downhole power generation to extend the application of thermoelectric generation to horizontal wells which have enlarged contact area with high temperature formation and better heat transfer and conversion efficiency. In the design, we retrofit the horizontal wellbore to circulate cold water inside the tubing so that the cold temperature interface can be created. The formation fluids (oil and water) flow through the annulus of the tubing and casing so that we can keep hot temperature on the side of tubing. By attaching thermoelectric generators (TEG) on the outer surface of tubing, this retrofit will make it possible to capture subsurface in-situ geothermal energy and directly transfer to electricity in hydraulically fractured unconventional wells. Furthermore, we also built the mathematical model to account for the heat conduction and convention in the horizontal wellbore and formation, which could accurately simulate the temperature distribution and power generation under variable operational conditions. Based on the model, we identified the key parameters with significant impact on power generation and established the well section criteria for best power generation performance. To discover the potential of power generation in horizontal wells, we conducted a case study using the data of YS-1 horizontal well in Daqing Oilfield in northeast China and compared the power generation performance in YS-16 vertical well with same TVD and same power generation device installation. The results of case study indicated that Daqing Oilfield is of great potential for geothermal power generation using its horizontal wells, and the horizontal well displayed exceeding power generation performance over vertical wells. In practice, this paper enriches geothermal development methods and provides the foundation for oil and gas producer to identify the opportunity and capitalize on geothermal power generation from horizontal wells.