A Device for Quantitatively Evaluating the Hydration of Cement in Impacting Stability of Hydrate Layers and a Case Evaluation
A new device is developed aimed at evaluating the effect of the hydration heat of the cement on the amount of the dissociated hydrate during well cementing operation.In developing this device,the contact manners of the cement slurries with the hydrate are fully considered.Using this device,hydrates at low temperature and high pressure can be generated,the cement slurry can be pumped under pressure into the wellbore while in contact with the hydrate layers,and the effect of the hydration heat of the cement slurry which is directly in contact with the hydrate layers on the formation temperature and pressure is directly measured.By calculating the gas saturation of hydrates and the amount of gas released from the dissociation of hydrates,a method of developing simulated hydrate formation is established taking into account the properties of the device,and a method is formulated for evaluating the effect of the hydration of cement on the stability of hydrate layers.In laboratory experiments,a simulated hydrate formation is constructed based on the geology of the shallower formations in south China Sea,three different cement slurries(a blank class G oil well cement slurry,a low-density cement slurry and a low-heat cement slurry)are pumped into the simulated hydrate formation.The experiment results show that in the setting process of the cement slurries,the quantities of the gas released from the hydrate by the heat from the hydration of the three kinds of cement are 0.7356,0.1091 and 0.0649 mol/L,respectively.These results show that the low-heat cement slurry can greatly shorten the time required for the cement slurry to set.This study has provided a method of directly testing the effect of cement hydration on the hydrates in the shallower formations,and it also shows that low-heat cement should be used in cementing the hydrate formations in deep water drilling.
Simulated formationDissociation of hydratePumping in of fluid under pressureEvaluation methodCement slurry system
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