Basic Research On The Downhole Radio Frequency Heating Technology

Unconventional oil and gas resources are the strategic alternative energy and have a broad prospect of exploitation and utilization.Traditional thermal recovery technologies are difficult to meet the demand for the efficient and green development of unconventional oil and gas resources,and new technologies for the efficient extraction of unconventional oil and gas resources are urgently needed.Downhole radio frequency heating technology has the advantages of fast heating rate,obvious effect for increasing production,clean and environmental protection,and being suitable for various reservoirs.It has attracted much attention at home and abroad.At present,this technology is still in the preliminary exploration stage in China,and there are lack of relevant experimental and theoretical studies.Accordingly,upon a comprehensive review of relevant researches,this dissertation starts from the theoretical research and simulation experiments,focusing on the performance of radio frequency heating and influencing factors of single antenna,antenna array and multi-antenna distribution,and the performance of resistance heating is compared to that of radio frequency heating,which are summarized as follows:(1)The mathematical model of radio frequency heating considering dynamic changes of reservoir properties and coupling of electromagnetic and temperature fields is developed on the basis of mechanism of radio frequency heating.The relationship between specific heat capacity,thermal conductivity of specific heavy oil reservoirs and temperature,and the change of oil sands conductivity and relative permittivity with frequency are determined.The design for the processes of RF heating in the vertical and horizontal wells is done,the performance of RF heating with single antenna is evaluated,and the factors affecting heavy oil reservoir temperature distribution are analyzed.(2)Due to the fact that the RF heating with single antenna has limited heating range and low heating power,an antenna array type of RF heater structure with multiple antennas distributed along the radial and axial directions is proposed,and its feasibility is evaluated by numerical simulation.In addition,the influences of antenna voltage,frequency,and the spacing between antenna array heaters on temperature distribution are also investigated,and the heating efficiency of uniformly spaced and non-equally spaced antenna array heaters is compared and analyzed.(3)In view of the resistance heating and radio frequency heating technologies that have attracted much attention,their working performance is comparatively studied from the aspects of temperature distribution,heating rate,intermittent heating mode,effect for increasing production,and energy efficiency,which provide an important reference for selecting the best underground electric heating methods.(4)A set of downhole radio frequency heating simulation experiment system is designed,and the experimental schemes of radio frequency heating oil sand samples under constant power and different power conditions are established,and the factors affecting the oil sand temperature distribution are analyzed.The temperature data obtained from the simulation experiments have preliminarily verified the corresponding temperature calculation model.This dissertation lays the foundation for the development of the underground RF heating technology equipment,field testing,and the follow-up work.