Study on thermal conductivity of cement with thermal conductive materials in geothermal well

In the exploitation of geothermal resources, geothermal single-well heat extraction technology can realize geothermal development without extracting water, which has a wide application prospect. The single-well heat extraction relies on heat conduction between wellbore and reservoir, and heat convection between wellbore and reservoir water. Therefore, the thermal resistance between wellbore and reservoir is an important factor affecting performance of heat extraction. Employing cement with thermal conductive materials in the thermal recovery section of geothermal reservoir is an effective method to enhance heat extraction performance. The study presents a method of producing thermal conductive cement by mixing oil well cement with thermal conductive materials, including graphite, ferrum and copper. Then thermal conductivity and compressive strength tests are carried out, and the influence of thermal conductive material exerted on the thermal conductivity of cement paste is studied. Moreover, relations between porosity and thermal conductivity of cement paste, and relations between particle continuity and thermal conductivity of cement paste are studied by porosity test and SEM scanning. The study demonstrates that with graphite increases, the porosity of cement paste decreases firstly and then increases, and the thermal conductivity of cement paste increases firstly and then decreases; With ferrum increases, the porosity of cement paste decreases, and the thermal conductivity of cement paste increases; With copper increases, the porosity of cement paste decreases, and the thermal conductivity of cement paste increases; As the temperature rises, the thermal conductivity of cement paste decreases gradually; Thermal conductive materials can enhance thermal conduction in cement, and pore would provide thermal insulation; On the condition of improve thermal conductivity, cement with 0.05-0.15 graphite, cement with 0.05-0.20 ferrum and cement with 0.05-0.20 copper can meet requirements. The results of this study provide theoretical guidance for improving the thermal conductivity of cement in geothermal well.