Shen Lan, Tan Huijing, Ye You, He Wei
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China.
Key Laboratory of Deep Geodrilling Technology, Ministry of Natural Resources, China University of Geosciences (Beijing), Beijing 100083, China.
Materials (Basel). 2022 Jul 21;15(14):5087. doi: 10.3390/ma15145087.
During geothermal energy development, the bottom high-temperature fluid continuously exchanges heat with the upper low-temperature wellbore and the stratum during its rising process. Thermal insulation cement (TIC) can increase the outlet temperature, thus effectively reducing the heat loss of the geothermal fluid and improving energy efficiency. In this study, vitrified microbubbles (VMB) were screened out by conducting an orthogonal test of compressive strength (CS) and thermal conductivity (TC) on three inorganic thermal insulation materials (VMB, expanded perlite (EP), and fly-ash cenosphere (FAC)). Fumed silica (FS) was introduced into the cement with VMBs, as its significant decreasing effect on the TC. Moreover, a cement reinforcing agent (RA) and calcium hydroxide [CH] were added to further improve the CS of TIC at 90 °C. The fresh properties, CS, TC, hydration products, pore-size distribution, and the microstructure of the cement were investigated. As a result, a TIC with a TC of 0.1905 W/(m·K) and CS of 5.85 MPa was developed. The main conclusions are as follows: (1) Increasing the mass fraction of the thermal insulation material (TIM) is an effective method to reduce TC. (2) The CH content was reduced, but the C-S-H gel increased as FS content increased due to the pozzolanic reaction of the FS. (3) As the C-S-H gel is the main product of both the hydration and pozzolanic reactions, the matrix of the cement containing 60% FS and VMBs was mainly composed of gel. (4) The 10% RA improved the cement fluidity and increased the CS of TIC from 3.5 MPa to 5.85 MPa by promoting hydration.
在地热能开发过程中，底部高温流体在上升过程中不断与上部低温井筒和地层进行热交换。隔热水泥（TIC）可以提高出口温度，从而有效减少地热流体的热损失并提高能源效率。在本研究中，通过对三种无机保温材料（玻璃化微泡（VMB）、膨胀珍珠岩（EP）和粉煤灰空心微珠（FAC））进行抗压强度（CS）和导热系数（TC）的正交试验，筛选出了玻璃化微泡。由于气相二氧化硅（FS）对导热系数有显著降低作用，因此将其引入到含有玻璃化微泡的水泥中。此外，还添加了水泥增强剂（RA）和氢氧化钙[CH]，以进一步提高90℃下TIC的抗压强度。研究了水泥的新拌性能、抗压强度、导热系数、水化产物、孔径分布和微观结构。结果，开发出了一种导热系数为0.1905W/（m·K）、抗压强度为5.85MPa的TIC。主要结论如下：（1）增加保温材料（TIM）的质量分数是降低导热系数的有效方法。（2）由于FS的火山灰反应，CH含量降低，但随着FS含量的增加，C-S-H凝胶增加。（3）由于C-S-H凝胶是水化反应和火山灰反应的主要产物，含有60%FS和玻璃化微泡的水泥基体主要由凝胶组成。（4）10%的RA提高了水泥的流动性，并通过促进水化作用将TIC的抗压强度从3.5MPa提高到5.85MPa。
