地热井用复合增强导热固井水泥浆OA

To reduce the thermal resistance between the wellbore of a geothermal well and the rock formation and enhance the heat extraction capacity of the geothermal well,this paper selects graphite(SG)with excellent thermal conductivity as the heat-conducting material,and uses a surfactant to prepare a graphite dispersion.High aspect ratio carbon fibers(CF)are introduced to construct a heat-conducting network,which cooperatively improves the thermal conductivity of the cement paste.The performance of the graphite dispersion-cement slurry,as well as the mechanical and thermal conductivity properties of the cement paste,were evaluated.The phase composition,pore structure and microstructure of the cement paste were characterized by X-ray diffraction(XRD),thermogravimetric analysis(TG/DTG),mercury intrusion porosimetry(MIP)and scanning electron microscopy(SEM),and the thermal conduction mechanism was explored.The results show that when the W/S ratio is 0.51,the performance of the cement paste prepared by adding SG and CF meets the engineering requirements.The 24-hour compressive strength of the cement paste is not less than 17.0 MPa,the 7-day compressive strength is higher than 25.0 MPa,and its thermal conductivity can reach 2.86 W/(m·K).Under the combined effect of SG promoting hydration and CF inhibiting hydration,the weight loss of C—S—H and CH in the high-conductivity cement Ppaste was 10.91%,which was slightly lower than 11.04%of the pure cement paste.Appropriate SG can refine the pore size of the cement paste and reduce the porosity of the cement paste,while CF will significantly increase the porosity of the cement paste and increase the number of large pores.When the two are mixed,the porosity of the cement paste is 36.95%,which is higher than that of the pure cement paste.However,the number of pores larger than 70 nm in the high-conductivity cement paste is not much different from that of the pure cement paste.Adding SG and CF to the cement slurry can form a thermal conductivity network.