A Study On The Low Density Cement Slurry In Shallow-layer Leakage Well

The low density cement slurry system generally refers to a slurry system with a density of less than 1.75g/cm3,and it is a mixture of oil well cement,oil well cement weight lighting agent,cement additive and a certain amount of water.It is widely used in the cementing operations of shallow-layer leakage well,coal-bed gas well and long sealing well.For the cementing of shallow-layer leakage well and coal-bed gas well,because of massive weak gelling substance in low downhole temperature and low density slurry,it results in slow cement hydration speed and low strength.Meanwhile,admixture with low density cement slurry is relatively less,which seriously affects the application effect of the low density cement slurry.This thesis focuses on three core technologies of particle gradation and optimization of low density cement slurry,early strength technology at low temperature and stability control and the compatibility of admixture.The high-strength microbeads with with good pressure capacity and performance should meet the requirements of low-density design.Micro-silicon with good performance ensures that the low-density cement slurry has good stability,and it can prevent the low-density cement slurry from deteriorating.Ultra-fine cementitious material with good performance replaces part of the oil well cement and the comprehensive performance of the low density cement slurry system is improved.The theoretical ratio of each component of cement slurry is determined by using particle gradation technique.Through the experimental study,the actual ratio of each component of different density cement slurry system is determined.Considering the characteristics of low temperature and low density cement slurry system with more additive and slow cement hydration speed,early strength agent with low temperature is selected.The suspension stabilizer is selected by using the polymer coating and coupling principle.From the view of filtration loss and no retardation at low temperature,the influence of different types of fluid loss agent on the performance of cement slurry with low temperature and low density is determined.Though the researches on rheological properties,sedimentation stability,water loss,compressive strength and etc,the comprehensive performance of low density cement slurry is evaluated,and the low density cement slurry is practically tested in cementing engineering.Cementing is one of the key links for shallow-layer leakage well and coal-bed gas well and cementing quality is largely dependent on cement slurry with the performance of low density.This thesis focuses on the cement slurry system with low temperature,early strength and low density of 1.30~1.50g/cm3,which has the advantages of low temperature,early strength,short bonding time and good stability.And it improves the operation safety and cementing quality of shallow-layer leakage well,and provides strong technical support for the development of shallow-layer leakage well.