High Temperature And Large Temperature Difference And Low Density Cement Slurry System Research And Application

According to the exploration and development needs, tarim oil field gradually simplified the casing program. So that it leads to serious problems of cementing in a long-term zonal isolation (about6000m) and low fracture gradient section. To solve the problems that the drilling fluid is easy to leak and the strength development of the top cement column is slow during the progress of cementing, a lightweight cement slurry system which could bearing the large temperature difference is developed and it is significant to improve the cementing quality and ensure the safety of the well.Facing the problems of bad sedimentation stability and the strength development of the top cementing column is slow. From the view of material physical and chemical, the lightweight cement slurry was developed by optimizing lightweight additive and filler which was based on the particle size distribution.The L/S of the slurry was also decreased to coordinate the materials. So that not only the density of the slurry was decreased but also the gelling composition of the slurry increased, which could improve the strength and compactness of the cementing paste. The suspension stabilizer agent was used to solve the problem of the lightweight cement slurry system with bad sedimentation stability under high temperature. Though selecting cement retarders, accelerating agent and fluid loss additive, the early strength of cement paste was kept at a high degree which could also satisfy the enough thickening time. The combination properties, engineering adaptability, strength developing, permeability and microstructure of the lightweight cement slurry system or cementing paste was analyzed and discussed in this paper. Finally, the large temperature difference lightweight cement slurry system was successfully applied in practical cementing.The lightweight cement slurry with a1.20-1.40g/cm3slurry density which could satisfy the BHST of100-140℃and large range of temperature difference of70-120℃was developed in this paper. With the advantages of good sedimentation stability, rheology, low fluid loss, easily controlled thickening time and good combination properties, this kind of slurry could fit the design requests by simulating the process of slurry returning to ground from the annulus. The strength of the cementing column developed very well and the inner structure of this cementing paste was very compact with a low permeability and shrink rate which could isolate different layers and protect the casing well.This lightweight cement slurry of large temperature was successfully applied in ZG52of which cementing quality acceptability is nearly96%and ZG514, it effectively prevented the cementing leakage and oil-gas channeling. So the application of this slurry system would develop the quality and save the drilling cost of low pressure gradient and easily leaking wells and support the benefits of exploration and development.