A Downhole Electronic Thermal Management Insulation System For Drilling High Temperature Directional Wells

China has abundant Oil & Gas resources,but most of them are buried in deep earth strata.Ultra-deep well drilling technology is an important development direction of Oil & Gas drilling in China.The temperature of ultra-deep wells exceeds 200℃ and at such temperatures,the efficiency of drilling electronics declines.In a bid to solve this problem,most foreign countries start by improving the temperature resistance of electronic components and studying high temperature electronic packaging technology.Not only is it difficult to meet the temperature resistance requirements of ultra-high temperature with this approach but also extremely expensive,and thereby not solving the problem of ultra-high temperature adaptability of the drilling electronics.Therefore,this thesis studies the variation of bottomhole temperature during circulation,the structural technology of high-efficiency thermal insulation flasks and provides a theoretical basis and technical support for the thermal protection of downhole electronics used for drilling ultra-high temperature wells.The thermal insulation flask is used to insulate the downhole electronic systems as the circulating drilling fluid cools the wellbore.Therefore,it is necessary to study the temperature distribution along the wellbore during circulation of drilling fluid and the influence of structural changes on the performance of the thermal insulation flask.In order to obtain the wellbore temperature distribution during circulation of drilling fluid,a valid mathematical wellbore temperature distribution model was obtained from existing literature and applied in this study.The temperature distribution model and is based on heat transfer in cylindrical coordinates and was solved by the explicit finite volume method.The flow rate,drilling fluid properties,drill pipe size,annulus size and drilling fluid inlet temperature are analyzed.Through the analysis of the influence of different structural changes on the performance of the thermal insulation flask,based on the bottomhole temperature distribution in ultra-high temperature wells,three methods to improve performance are proposed.Solidworks and ANSYS Fluent software are used to simulate and analyze the influence of the thickness of the top and bottom covers of the thermal insulation flask,length of the vacuum column,diameter of the inner and outer shell,thickness of the vacuum column,thickness of the inner and outer shell,thickness of the top insulator,diameter of the top insulator,diameter of the bottom insulator,insulation material and the emissivity on the performance of the thermal insulation flask.Finally,methods to improve the thermal insulation performance of thermal insulation flask are proposed basing on the simulation analysis of the structure.According to the research results of wellbore temperature distribution during circulation of drilling fluid in an ultra-high temperature well,it was found that:(1)the temperature distribution significantly depends on the temperature gradient;(2)equilibrium temperature at the annulus outlet is attained after approximately 0.5 hours and at bottomhole after approximately 2.8 hours;(3)Higher flow rates,higher thermal diffusivities,lower drilling fluid inlet temperatures,drill pipes with larger inner and outer diameters and smaller annulus diameters result into lower temperatures along the wellbore after circulation.The highest temperature of drilling fluid occurs in the annulus;(4)the drilling fluid flow rate,drilling fluid properties and drill pipe size have the greatest influence on wellbore temperature distribution.According to the research results of the analysis of the influence of different structural changes on the performance of the thermal insulation flask,it was found that:(5)most of the heat accumulated inside electronic compartment is transferred from the vacuum by radiation;(6)the influence of the thickness of the cover on the performance can be ignored.The shell and vacuum column thickness have the most significant effect on the performance.Greater shell thickness,greater vacuum column thickness,lower emissivity coefficients,smaller shell diameters using lower thermal diffusivity insulation materials and a 30 mm top insulator result into better the performance;(7)the shell and the vacuum column thickness have the greatest influence on the performance;(8)by application of the proposed methods to improve performance in this study,the thermal insulation flask can keep the electronic compartment below 175℃ for 2.9 hours at bottomhole temperatures of 300℃ and more than 6 hours at bottomhole temperature of 200℃.