| Cement slurry conductivity test is a simple and effective method to test cement paste early hydration properties.In order to establish a model for evaluating the oil-well cement slurry properties,the electrical performance of cement slurry was evaluated.And study the causes of oil-well cement slurry gas channeling leads to weight loss by electricity performance tests,so as to provide a theoretical basis and practical significance in the field of application.In this paper,the cement structure evolution at macro and micro scales was investigated,and established the model of relationship between the structure of cement paste and conductivity.Results have revealed the influence of the evolution of cement slurry sttructure on the conductivity.This paper firstly analyzes the change law of cement slurry conductivity and evaluates the effect of temperature,water cement ratio and additives on the electrical conductivity of cement slurry,respectively.Then according to the tests results of cement slurry conductivity,setting time,strength development,hydration heat,water distribution,pore solution concentration,XRD,TG and ESEM,the relationship between the structure evolution and conductivity of cement paste has been deeply studied.The results show that the variation of conductivity of cement slurry is firstly increased with duration and then shows a decrease trend,the initial increased conductivity of cement slurry is due to the increased of ion concentration,especially Ca2+ concentration,and then decreasing conductivity can be partly explained by the increase of hydration products leads to the decrease of porosity and reduce the evaporation water content.Fluid loss additive G33S and accelerator CaCl2 increased the conductivity of cement slurry and increased the availability of water in cement slurry,the effect of admixture on the conductivity of cement slurry can reflect the condensation characteristics of cement slurry.Through the test of setting time and strength development of the cement in early hydration process,the structure of cement slurry is denser from a macro point of view,the initial setting time and final setting time of cement slurry presents significant linear relationship,it proved reliability of the final setting time of cement slurry.There is a certain relationship between the initial/maximum value of cement slurry conductivity and the setting time,respectively.There exists a critical value in the initial/maximum value of conductivity,before the critical value,the setting time of cement slurry increases with conductivity increasing;while the setting time of cement slurry is shortened with conductivity increasing when setting time is after critical value.Results shown a linear positive correlation between the time of the maximum electrical conductivity and the setting time.The Ca(OH)2 and the chemically combined water content test shows that with the increase of cement hydration degree of cement paste,the conductivity decreases,the increase of hydration products leads to the decreasing conductivity.Test analysis of the impact of evaporative water and chemically combined water distribution of cement slurry,resulting in conducting medium reduced so that the electrical conductivity decreases the hydration process of the evaporative water converted into chemical water.Results show that with development of the hydration process,hole water content decreased gradually in pore solution of cement slurry,when the hole water content is completely consumed,the hole is generated in the cement slurry,the electrical conductivity of cement slurry is still decreased gradually,which indicates that in addition to the free water is conductive,capillary water and gel water are also conductive,but the ability of conductivity is very small,At the later stage of hydration,the changes of hydration products increased and morphology of the resulting decrease of porosity are the main reasons for the decrease of the electrical conductivity of cement slurry. |
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