Study On Alkali-activated Slag/Fly Ash Degradable Cement And Its Properties For 150-200 ? Geothermal Well

Geothermal energy as a clean energy source,one of its key technologies is the use of EGS technology to develop a structural thermal reservoir with a 3-10 km underground impermeable stratum.The existing fractures in the formation are particularly important for the hydraulic excitation,but in the drilling process,these cracks can cause a lot of mud loss.Therefore,it is utmost importance to continue drilling after blockage measures have been taken.After the completion of these wells,these fractures were hydro-reactivated and re-formed to provide access to geothermal fluid production.Therefore,this plugging is temporary.All cracks need to be deblocked before they can be put into production.On the basis of thorough investigation of the literature on porous materials,we found that domestic and foreign scholars have very little research on medium-high temperature temporary plugging cements,so a high-viscosity sodium carboxymethyl cellulose(CMC)and sodium bicarbonate(NaHCO₃)were selected out.The decomposition temperature is 275-300°C and 100-150°C,respectively.With slag/fly ash as base material,an experimental study of self-degradable cement in geothermal wells(150-200°C)was conducted.The main work and results achieved are as follows:1.Study the effect of CMC and NaHCO₃ as degradable materials on the self-degradation performance of alkali-activated cement material(AACM)at different temperatures.The experimental results show that:1)at 200°C-cured,the viscosity of AACM increases with the molecular weight of CMC.However,the strength of cement decreases with the increase of the molecular weight of CMC.Therefore,the maximum molecular weight of CMC has the best self-degradation effect on AACM,and the optimal addition of CMC is 1.2%;2)at150°C-cured and 180°C-cured,different additions of NaHCO₃ had different accelerating effects on the self-degradation of cement,and the optimal addition amount of NaHCO₃ was3%.2.Study the effect of CMC and NaHCO₃ compounding system on the self-degradation performance of AACM.Through the study,the conclusion is that under the conservation of150°C-cured and 180°C-cured,the addition of NaHCO₃ is 3%and the addition of CMC is0.8%.The compounding system has the greatest impact on the compressive strength of AACM.The compressive strength after 180°C-heated at immersed in water is as low as 1.45 MPa.The cement structure is loose and the exothermic temperature is maximal.Therefore,the self-degradation effect of AACM is promoted most significantly.3.Observe the microstructure and product of cement by using scanning electron microscope(SEM)and XRD.Combined with the macroscopic experimental results,the final analysis and evaluation of the impact of CMC and NaHCO₃ on the self-degradation performance of AACM.The study found that the self-degradation mechanism of CMC and NaHCO₃ on the one hand is generates volatile gases for pyrolysis,prompting the cement to produce a large number of connected pores,leading to the loose cement structure,On the other hand,the CMC and NaHCO₃ specimens exothermed when immersed in water.As a result,cracks occur in the cement,resulting in reduced compressive strength.Ultimately,it achieved the purpose of degradation.