Development And Application Of Polycarboxylate Superplasticizer For Oil Well Cement

The special environment of cementing engineering requires oil well cement slurry to have both good initial fluidity and a good fluidity maintaining ability.Superplasticizer has become one of the basic components of oil well cement slurry.The change of pressure and temperature with the formation depth has a significant impact on the initial fluidity,fluidity maintaining ability and hydration process of oil well cement slurry.In this paper,polycarboxylate superplasticizer with different side chain lengths and functional groups were designed,and two temperatures were selected to study the influence of superplasticizers on two rheological properties of oil well cement slurry,starting with initial rheological properties and aging rheological properties.At the same time,the influence mechanism of superplasticizers was revealed through the analysis of adsorption properties and hydration process.At 25℃,PCE2400-8 will break up the flocculation structure in cement paste,greatly reducing the yield stress and plastic viscosity of the system.The fluidity maintaining ability increases with the increase of superplasticizer content,which is because superplasticizer obviously hinders the early hydration of slurry.When the mass ratio of acid and ether is the same,when the dosage of superplasticizer is low,the superplasticizer with shorter side chains reduces the yield stress of slurry more obviously,and the number of side chains plays a main role in dispersion.When the dosage is high,the steric hindrance between particles provided by superplasticizer plays a major role in dispersing.The shorter the side chain length of dispersant,the stronger the delay effect on cement hydration.This may be because for polycarboxylate superplasticizer,superplasticizer free in liquid phase plays a more critical role in inhibiting cement hydration,and it can be considered that the formation of hydration products is the key to the beginning of cement hydration acceleration period.The dispersion effect of superplasticizer modified by sulfonic acid group becomes worse,but the effect of delaying hydration decreases.This effect is more obvious in superplasticizer modified by SSS than that of superplasticizer modified by AMPS.PCE2400-AA4-HEA4 has a similar effect to PCE2400-8 in delaying the hydration of cement due to the particularity that ester groups are hydrolyzed with time to generate carboxyl groups,and the fluidity maintaining ability is good.At 80℃,the change of side chain length has little effect on the plastic viscosity of the system.With the increase of temperature,the thermal movement of cement particles intensifies,which will reduce the force between particles.At the same time,the viscosity of free water also decreases with the increase of temperature,which will weaken the influence of superplasticizer itself on the plastic viscosity of slurry.Except for two kinds of dispersants modified by sulfonic acid groups,when the dosage of superplasticizer reaches 0.5%,the phenomenon that the exothermic peak of cement hydration is delayed due to the increase of temperature appears.This may be because the nano-scale hydration product particles no longer exist at this temperature,and the free superplasticizer molecules in the liquid phase increase,thus delaying the hydration of cement is more serious.It is further proved that the free superplasticizer in the liquid phase inhibits the nucleation growth of the hydration product by complexing calcium ions with carboxyl groups and adsorbing on the surface of the hydration product,which plays a key role in delaying the hydration of cement.Increasing the temperature is beneficial to the hydrolysis of ester groups in PCE2400-AA4-HEA4 molecular structure,which makes it show good fluidity maintaining ability.It has important guiding significance for the development of superplasticizer with good fluidity maintaining ability at high temperature.