Low Temperature Rheology/solidification Characteristics And Hydration Process Of Nano-composite Cement Slurry Materials

Natural gas hydrate exploration and development research is a major frontier research topic in the contemporary earth science and energy industry,and is of great significance for solving the increasingly severe energy shortage problem.Due to the physicochemical properties of natural gas hydrates and the low temperature and high pressure characteristics of the existing environment,the problem of well wall collapse and slurry leakage is more prominent and complicated than conventional oil and gas layers when drilling in frozen soil gas hydrate formations.According to the data,the geological conditions of the frozen ground layer in China are harsh,and there are often accidents such as collapse or slurry leakage during drilling.The problem of plugging and sealing the drilling wall is very serious,which seriously affects the smooth progress of the drilling of natural gas hydrate in the frozen soil.In view of the technical problems of wall plugging in the process of drilling natural gas hydrates in permafrost,based on previous research,a systematic study on the low temperature rheological/solidification characteristics and hydration process of nanocomposite cement slurry is carried out.The nanocomposite cement slurry suitable for the plugging of the natural gas hydrate in the frozen soil was developed,and its low temperature rheological/solidification characteristics were studied.Based on hydration heat measurement,scanning electron microscopy?SEM?and X-ray diffraction?XRD?analysis.The low temperature hydration process of the slurry was analyzed to explore the influence of nanomaterials on the hydration process of the composite slurry under low temperature environment,and the low temperature hydration process model of the nanocomposite cement slurry was constructed.The specific research results are:?1?Using the hydration synergistic effect of silicate-sulfate aluminate cement,the base fluid of nanocomposite cement slurry was experimentally studied.Nano-Al₂O₃ is determined as a nanomaterial type in experimental research by using a preferred nanomaterial,and the base fluid is further modified by an early strength agent and a water reducing agent.On this basis,the optimized formula of nano-composite cement slurry was developed by orthogonal test method.The formula is as follows:40%PO42.5+60%R.SAC42.5+20%EG+0.3%Al₂O₃+0.07%YJ+0.6%JSS?W/C=0.6,T=-9??.?2?Test and test the related properties of nano-composite cement slurry in different low temperature environments such as fluidity,pumping period,setting time,compressive strength and viscosity.The test results show that the properties of the nano-composite cement slurry studied meet the requirements of the frozen soil environment for the performance of the wall-blocking cement slurry,and the slurry performance is superior.The incorporation of nano-Al₂O₃ can significantly affect the performance of the composite cement slurry,which is mainly reflected in the improvement of the rheological properties of the slurry and the improvement of the compressive strength of the slurry.By testing the shear stress of nanocomposite cement slurry at different shear rates under low temperature conditions and fitting the test results,it is found that the flow pattern of nanocomposite cement slurry is more suitable by Bingham model.The nano-composite cement slurry studied showed a relatively obvious"right angle thickening"effect.?3?In order to explore the hydration behavior of the slurry in low temperature environment,the hydration heat release process of the nano-composite cement slurry was analyzed by testing the hydration heat,and the microscopic morphology of the hydration product was observed by scanning electron microscopy?SEM?.The main hydration products were analyzed by X-ray diffraction analysis?XRD?.According to the experimental analysis,the low-temperature hydration process of the nano-composite cement slurry is divided into five stages:initial stage,induction period,acceleration period,decay period and stable period.The low temperature hydration process model of nanocomposite cement slurry was constructed.The research results have scientific significance for promoting the development of composite cement hydration theory and the cross-fusion of disciplines.At the same time,it provides a systematic theoretical basis and new solutions for the study of frozen soil gas hydrate drilling and wall sealing.