| Natural gas hydrate is abundant in reserves,high calorific value,clean and pollution-free,and is the most potential replacement energy in the 21st century.The hydration exothermic of cementing cement will decompose hydrate and lead to the decrease of cementing quality.Phase change material refers to the material that conducts heat absorption and release through phase change near the phase change temperature point.The process of heat absorption and release is not affected by temperature difference and has latent heat of phase change far beyond sensible heat.Using phase-change material to absorb the heat of cement hydration is an ideal control method of cement hydration heat release.At present,the commonly used phase change materials are solid-liquid phase change materials,but the solid-liquid phase change materials will produce liquid phase in the phase change process,which will seriously affect the cement structure and strength and other properties.Therefore,a new solid-solid phase change heat absorber was developed in this paper,and its control law of hydration heat release on cement slurry was analyzed.Based on this material,a set of cement slurry system with low temperature and low hydration heat and early strength was formed.Solid-solid phase change heat absorber SSP was prepared by melt adsorption-deposition plugging method.Firstly,a single factor experiment was designed to optimize the phase change core material,skeleton material and blocking material for the preparation of SSP,and the best preparation process was determined.Then,SSP was characterized by infrared analysis,differential thermal analysis and particle size analysis.The results show that the expected design of SSP composite has a phase transition temperature of 15.7℃,a latent heat of 168 J·g-1,a structure still intact after 50 thermal cycles,and no change in phase transition properties.The thermal control material SSP was used to effectively control the hydration heat of cement slurry,and the addition of 15%SSP solid-solid phase change heat absorber could effectively reduce the adiabatic temperature rise of cement slurry by 50%.The control ability of SSP,fly ash and phase change microcapsule MP on hydration heat of cement slurry and the properties of cement slurry were compared through comparative experiments.The results show that SSP reduces the adiabatic temperature rise peak value of cement more than twice that of fly ash and MP,and the 24 h compressive strength of cement with SSP is 45%and 28%higher than that of cement with fly ash and MP,respectively,indicating that SSP is an ideal cement hydration heat control material.Through optimizing the superfine cement with low temperature early strength agent,the class G oil well cement+30%superfine cement+1%KCl+2%A-Ⅰrealized the purpose cement early strength at low temperature.The 24 h strength of cement stone is increased by300%.Eventually build A low temperature and low hydration heat early strong cement slurry system LTLH:class G oil well cement+30%superfine cement+15%solid-solid phase change heat absorbent SSP+1%KCl+2%A-Ⅰearly strength agent+1%MT-L lost agent+0.8%USZ drag reduction agent+0.5%defoaming agent+44%water.Compared with cement-based slurry,the compressive strength of the system after curing at 15℃for 24 h is 13.5 MPa,the density is1.78 g·cm-3,the API standard water loss is 41m L,and the free liquid amount is 0.And the system has a good suspension stability,the density difference between the upper and lower sections is 0.015 g·cm-3 less than 0.03 g·cm-3,has a good anti-channelling ability. |
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