Transient Thermoelectric Generation in Oil Wells Under Transient Production

Abstract

Thermoelectric technology can directly transfer heat into electricity by Seebeck effect with advantages of reliability, compactness and environmental friendliness. Thermoelectric technology is applicable in a large temperature range, and it could be a solution to unlock the potential of low-temperature geothermal resources from oil wells. Methods of downhole geothermal power generation using thermoelectric technology in high water-cut wells have been recently proposed to capture the geothermal energy of produced fluids and directly transfer to electricity in the wellbore. Such method could eliminate the dependence on power plant and increase the number of oil wells qualified for geothermal production. Previous studies demonstrated the thermoelectric performance in oil wells under constant production rate, which is not always true in real-world setting. To fully illustrate the technical feasibility of downhole power generation methods, we studied the transient thermoelectric power generations under varying production rates. A mathematical model is developed to account for the unsteady state heat transfer in the wellbore and surrounding formations, and it is numerically solved using implicit finite-difference method. The temperature profile along the wellbore at any specific time during production could be computed by such model. To accurately characterize the temperature profile and subsequent power generation during oil production, the effective thermal conductivity of thermoelectric generator is included into the numerical model to account for the joule heating generated from thermal-electricity conversion. The model is validated with other models in the literature and showed good agreement. A case study in North Dakota was conducted to highlight the effect of transient heat transfer on thermoelectric power generations. This study could improve the accuracy of temperature profile and power generation calculations. It could help the operators properly evaluate a hydrocarbon-geothermal coproduction project under field operational conditions and provide accurate estimation of geothermal production for decision makings.