Study On The Effect Of Foaming Agents On Self-degradation Of Alkali-activated Temporary Cementitious Sealing Materials

Alkali-activated slag fly ash cement modified by sodium carboxymethyl cellulose（CMC）as a degradable temporary plugging material plays an important role in the drilling of geothermal wells.However,due to the well-developed fissures in the geothermal wells,there are also deficiencies in the plugging materials.In this paper,the disadvantages of high density,high viscosity,and poor fluidity of alkali-activated slag fly ash cement modified by carboxymethyl cellulose sodium（CMC）occur during the drilling of geothermal wells.Three different types of foaming agents were added to the CMC-alkaline-activated temporary plugging cement.The foaming performance and high temperature degradation characteristics of the foaming agent were used to effectively reduce the density of the cement slurry and improve the flow properties of the cement slurry,and promote the self-degradation effect of alkali-activated temporary plugging cement.The main research methods and conclusions are as follows:The thermal decomposition characteristics of the three blowing agents were measured by thermogravimetric-mass spectrometry and thermogravimetry-infrared scanning.The results showed that the thermal decomposition temperature of sodium lauryl sulfate was about 200°C,the thermal decomposition products were H₂O,SO₂,CO₂ and other gases;the thermal decomposition temperature of the animal and vegetable protein foaming agents was about 300°C,and the thermal decomposition products were H₂O,NH₃,CH₄,CO,CO₂ and other gases.Three kinds of foaming agents were added to the alkali-activated temporary plugging cement,and the density,the setting time,the compressive strength at different temperatures,the internal pore structure of the cement block were measured.It was found that the three kinds of blowing agents all reduced the density and compressive strength of the cement to different extents,and the internal structure of the cement became loose and porous.The optimal amount of sodium dodecyl sulfate is 0.3%,and the optimal addition amount of animal and vegetable protein foaming agents is 8%.By measuring the loss of cement strength and the amount of heat released after the cement block cured in high-temperature and immersed in water,the effect of the foaming agent on the self-degradation effect of the alkali-activated temporary plugging cement was analyzed.The experimental results show that the thermal degradation characteristics of the three kinds of foaming agents can promote the subsequent reaction of the cement,and the strength of water loss is greater,the amount of heat released is more,and the self-degradation effect of the cement is more obvious.At the same time,sodium dodecyl sulphate has the greatest promotion effect compared with the effects of three blowing agents.The above experiments show that compared with animal and vegetable protein foaming agents,sodium lauryl sulfate as an additive with better performance of alkali-activated temporary plug cement can effectively reduce the density of cement slurry,improve the flow properties of cement slurry,and promote the self-degradation performance of alkali activated temporary plugging cement.