干热岩工况下水泥高温劣化性能的调控措施

Control Measures of Cement High-temperature Deterioration Performance under Dry-hot Rock Conditions

干热岩地热井固井中,井底温度常常高达200℃以上。针对干热岩工况下井底高温导致的水泥石强度衰退的问题,从水泥的化学组分入手,通过调控C_(3)S和C_(2)S的比例,并在硅粉的协同作用下复配具有更低钙硅比的低热硅酸盐水泥来改善这一问题。首先对复相C_(3)S-C_(2)S矿物体系的比例调控可知,当C_(3)S∶C_(2)S=1.0时其力学性能最好,结合XRD、TGA、SEM测试可知,钙硅比的降低对有利相硬硅钙石的生成有积极作用。引入具有更低钙硅比的低热水泥增强G级水泥,结果表明:“30%G级水泥+70%低热水泥”复配水泥体系(C_(3)S与C_(2)S的比例为1.07)在40%硅粉的作用下,其抗压强度达27.34 MPa。在实际生产中适当调整水泥中的矿物组分,使C_(3)S与C_(2)S的比例为1.0左右,可从水泥本身大幅度提高水泥石耐高温性能。

When cementing geothermal wells in dry hot rocks,the bottom temperature is often as high as above 200℃.Aiming at the problem of strength decline of cement paste caused by high temperature at the bottom of the well under dry-hot rock conditions,this paper directly starts from the chemical composition of cement,and improves this problem by adjusting the ratio of C_(3)S and C_(2)S,and compounding low-heat portland cement with lower calcium-silicon ratio under the synergistic effect of silicon powder.Firstly,the mechanical properties of multiphase C_(3)S-C_(2)S mineral system are the best when C_(3)S∶C_(2)S=1.0.Combined with XRD,TGA and SEM tests,it is known that the reduction of calcium-silicon ratio has a positive effect on the formation of favorable phase xonotlite.Low-grade cement with lower calcium-silicon ratio is introduced to strengthen G-grade cement.The results show that the compressive strength of"30%G-grade+70%low-grade cement"composite cement system(the ratio of C_(3)S to C_(2)S is 1.07)is 27.34 MPa under the action of 40%silicon powder.The high temperature resistance of cement paste can be greatly improved from the cement itself by properly adjusting the mineral composition in cement to make the ratio of C_(3)S to C_(2)S about 1.0.