Research Of Low Temperature And Early Strength Cement System

With the exploration and development of deepwater oil and gas resources,deepwater cementing has currently become one of the most popular research domains.Deepwater cementing has a low ambient temperature.The seabed temperature in deepwater is about 4?.This low temperature seriously slow down the cement strength development.In addition,seabed and near-seabed formations in deepwater are usually loose and unconsolidated,so the cement slurry prone to leakage during cementing.Therefore,the requirements of cement in deepwater surface cementing are low density,rapid early strength development and low fluid loss.However the existing cement systems have low hydration rate in low temperature,hence this paper put forward the research of the low density and early strength cement system.Through the optimization of common cements and admixtures,the materials of low temperature and early strength cement system were identified based on the theory of compact packing.The main materials were P.O 52.5R cement?mass fraction,31-41%?,ultra fine cementitious material?40-41%?,microsilica?10-17%?,and glass microsphere?8-12%?.Then the composition of low temperature and early strength cement system was determined through experiments as follows:mixed cement?P.O 52.5R cement and ultra fine cementitious material with the mass ratio of 1:1?+12%microsilica+10%-20%glass microsphere?Y6000?.The density of the cement system was between 1.37-1.54 g/cm³.The compressive strength for 1 day curing at 15?was greater than 6.5MPa?1.9 times of pure G cement stone?.The cryogenic early strength behavior of nano-SiO₂ was investigated.By means of progressive superposition optimization,a nano-SiO₂ complex accelerator was obtained.The nano-SiO₂ complex accelerator composed of nano-SiO₂+sodium sulfate+triethanolamine+sodium aluminate is adopted,with its volume added being 3.05%of the cement volume.The enhancement rate of compressive strength of cement stone for 1 day curing at 4?and 15?,30?are 150%and 157%,respectively.The hydration products were determined by XRD and SEM.The accelerator could accelerate the hydration of mineral clinkers and had no influence on the hydration product types.Due to the pozzolanic effect and nucleating effect,nano-SiO₂could act as center of early hydration of oil well cement,a fact would accelerate the hydration process.The additives of the cement system were optimized and the performance of the cement slurry were tested.The properties of the cement slurry are listed below:cured at the temperature of 4?for 1 day the compressive strength are 3.8-6.2 MPa,density is 1.38-1.55 g/cm³,API loss of water is 37-41 mL,free water is 0mL,permeability is less than 0.0067×10^-3?m²(less than the National standard 0.01×10^-3?m²),gelling transition time is less than 30min,cementing strength is stronge?greater than 2 times of pure G grade cement stone?.The excellent cryogenic early strength,low density and gas blocking performance of the cement slurry contribute to solving such problems as low temperature leakage and superfcial water/gas flow confronted in deepwater cementing.