State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University
School of Resources and SafetyEngineering, Chongqing University

In the coalbed methane extraction of surface wells in the mining area, the mining of coal seam in working facewill cause a significant disturbance to overlying rock layer, which in turn will lead to the deformation and damage of surfacewells. The coalbed methane extraction of surface wells in the mining-disturbed areas cannot be effectively performed.Cementing technology can effectively elongate the life span of mining-disturbed coalbed methane surface wells. As a criticalfactor of the cementing quality of surface wells, the early strength of the cement needs to meet the high cementing requirements.Cement stone is formed after cement consolidation. The mechanical properties of cement stone are of greatimportance to maintain the stability of mining-disturbed coalbed methane surface wells. It is an effective way to improvethe cementing effect by adding dispersants to enhance the mechanical properties of cement stone. There are few researcheson the deformation and failure characteristics of calcium lignosulfonate modified cement under the influence ofmining disturbance. Uniaxial compression tests of calcium lignosulfonate modified cement with different mass fractionsunder cyclic loading were carried out to investigate the effect of calcium lignosulfonate on the deformation and failurecharacteristics of cement stone in mining-disturbed coalbed methane surface wells and its modification mechanism. Theresults show that the P-wave velocity and peak stress of cement stone increase first and then decrease with the increase ofcalcium lignosulfonate mass fraction, while the total acoustic emission ringing counts of cement decreases first and thenincreases with the increase of calcium lignosulfonate mass fraction. With the increase of the uniaxial cycle steps, the deformationmodulus of cement stone shows a strengthening phenomenon, and the initial loading and unloading cycle hasthe most significant strengthening effect on the deformation modulus. With the addition of calcium lignosulfonate, themodified cement stone shows a tensile-dominated → shear-dominated → tensile-dominated combined damage modes. Besides,the fractal dimension of modified cement stone shows a trend of decrease before increase, indicating that the additionof the appropriate amount of calcium lignosulfonate can effectively improve the damage resistance of cement stoneunder uniaxial cyclic loading. With the increase of the mass fraction of calcium lignosulfonate, the pores between cementhydration products show a trend of decrease first and then increase. The addition of an appropriate amount of calciumlignosulfonate can promote the formation of abundant C−S−H gel and ettringite in cement, and the precipitates interweaveon the surface of cement particles, which can significantly improve the peak stress of cement stone, and play a positiverole in improving the mechanical properties of cement stone. Additionally, the porosity of cement stone decreases, whichleads to the increase in the longitudinal wave velocity of cement stone and the decrease of cumulative acoustic emissionringing counts of the cement stone during cyclic loading. However, when the calcium lignosulfonate is excessively added,the air entraining and electrical repulsion of calcium lignosulfonate play a dominant role in the hydration process, whichwill introduce more bubbles, resulting in the occurrence of the gap between the cement particles, and the inhibition of theearly formation of C−S−H gel and ettringite, which has a negative impact on the mechanical properties of cement stone.Furthermore, the porosity of cement stone increases, which leads to the decrease of the longitudinal wave velocity of cementstone and the increase of the cumulative acoustic emission ringing count of cement stone in the process of cyclicloading. Therefore, the influence of calcium lignosulfonate on the mechanical properties of cement stone has a double effect.

重庆英才计划“包干制”资助项目(cstc2022ycjh-bgzxm0077)；重庆市研究生科研创新资助项目(CYS22039)

邹全乐，王鑫，李左媛，等. 木质素磺酸钙对固井水泥石变形破坏特性的影响及其改性机制[J]. 煤炭学报，2023，48(4)：1606−1621

ZOU Quanle，WANG Xin，LI Zuoyuan，et al. Effect of calcium lignosulfonate on the deformation and failure characteristics of cementing stone and its modification mechanism[J]. Journal of China Coal Society，2023，48(4)：1606−1621