Research Slurry System High Temperature Expansion

With the rapid development of China’s economy, we have a tremendous dependence and demand of oil, gas resources. The oil and gas exploration is increasing gradually in order to ensure the needs of national economy and energy security.73%of the proven oil and gas resources are stored in the deep and ultra-deep strata in China, so the numbers of deep and ultra-deep wells are increasing, and underground conditions are more complex. With the increase of the depth of wells, the bottom hole temperature rises, and it generally is above120℃. Therefore the demand on the performance of cement slurry is higher and higher.The main problems that deep and ultra-deep wells cementing faces are large water loss, the difficulty to adjust the thickening time and that the stability of the cement slurry is poor. When the temperature is higher than110℃, the compressive strength of cement stone begins to decline, this will affect the effect of cementing. The volume shrinkage of cement stone will bring about the bad cementation between the cement sheaths and interface, if the cementation is worse, it will form micro-gap, lead to gas channeling and security risks.Current test methods can’t be fully applicable to the cement performance of ultra-deep well water slurry. Especially some test methods cannot simulate the environment of underground, where the pressure and the temperature change. This paper designed a set of evaluation methods of water slurry performance under high-temperature conditions according to deep and ultra-deep well cementing working conditions. Slurry performances include sedimentation stability of cement, the loss of the water, the compressive strength of cement stone and the expansion rate in high temperature. The results show that, these evaluation methods can simulate the dynamic heating process of cementing, and the results are consistent with the site conditions. This can avoid problems that slurry’s performance is good in laboratory while is bad in the actual construction applications.We optimize the slurry additives and admixtures which use in high temperature conditions. Micro silicon and silica fume which have been optimized can improve the slurry’s performance. The slurry system is close-packed through different size of solid particle distribution. Under the premise that the slurry’s good rheological property is guaranteed, this can reduce filled-water and adsorbed-water. and improve the content of solid gelling, so as to improve the compressive strength of cement and reduce the porosity and permeability of cement stone. At the same time it can also reduce cement volume shrinkage and the decline of the compressive strength. Fluid loss agent, retarder and suspension stabilizer can be used at high temperature with the excellent compatibility. Expansion agent can reduce the volume shrinkage of the cement effectively to prevent gas channeling and improve the quality of cementing. We design a set of high-temperature expansion slurry system which can be used in deep and ultra-deep cementing. Then we Evaluate the comprehensive performance by designed evaluation methods. The results show that:slurry’s density is1.9g/cm3, applicable temperature is120～160℃, the fluidity is greater than18cm, and sedimentation stability is good, the density difference is less than0.02g/cm, water loss is less than30mL in30min, the compressive strength is greater than14MPa, thickening time is adjustable. Cement expansion ratio can be adjusted according to the amount of expansion agent, this can ensure the cementation between the cement ring and casing is good, meanwhile improve the quality of cementing.