Application

Cement

 Introduction

Cement is used in many domains, such as building materials, petroleum field, road
making where it is used to consolidate the oil wells and to maintain zonal isolation
for the lifetime of the wells, not only for primary cementing, but also after well
abandonment. Because their injection is performed via pumping, it is necessary to
control their rheology, and their workability time.

 There are many interests in using a non-invasive technique such as microrheology for this study:
working without shear, thus simulating the behaviour of the cement once it has been introduced in
its final environment, and determining the workability of the mixtures without disturbing the kinetics
by applying a stress to the structure : simulate real life.

Moreover, chemical reactions taking place during the setting of cements are very
complex and still under investigation, so it is useful to study new and powerful data.
In this example, the purpose is to monitor the effect of various polymers on cement
rheological properties and on the cement workability time.

 Objective

Adjust the mechanical properties and setting time of cement by introducing polymer in theformulation.

Device

Rheolaser Master

Basics on the cement setting kinetics
Setting of cement is described in the literature as a 3 stages process. Just after the
mixing of water and cement:
- Step 1 : sulphate and gypsum dissolve in the water. This phase is called
“dormant” or induction and happens during few hours, the cement paste
does not evolve anymore and is still workable.
- Step 2 : the aluminate phase then reacts with the water to form a gel, in just
few minutes, in a reaction which is strongly exothermic.
- Step 3 : at the end of the previous period, the other phases of the cement
(alite and belite) start to react at a slower pace, until the system reaches its
final state after weeks of evolution.

Raw data: Particles Mean Square Displacement (MSD)
In microrheology, particles probe the viscoelastic behaviour of the sample. Thus,
particle Mean Square Displacement curve is the signature of the product rheology
(microrheology concept).

   
The observation of the MSD enables to monitor the viscoelastic evolution of the cement during its setting without any interaction with the sample and therefor monitor the three phases.

It is noticeable that the MSD curves are getting lower and lower (elasticity increases) and are getting longer (viscosity increases) (step 1) then shorter (viscosity decreases) (step 2) then longer again (new increase of viscosity) (step 3).

These changes can be quantified thanks to the following microrheological parameters: Elasticity Index (EI) and Macroscopic Viscosity Index (MVI) as shown below.

The elasticity and viscosity enable to monitor the stages of the cement setting described in the previous paragraph.
- Step 1 : The first increase corresponds to the dormant phase, the cement forms a paste,
- Step 2 : The elasticity and viscosity decrease after few hours. This is due to the exothermicity of stage 2 which increases the brownian motion by increasing temperature providing more energy to the particles.
- Step 3 : The decrease of the parameters is followed by a second increase, the cement is setting. The cement goes on evolving for a long time.

Quantitative comparison of cement/polymer mixtures
Three formulations of cement, cement with polymer have been analyzed and compared

Polymer addition in cement to form composite modifies the setting characteristic times and the rheological properties.
- The time to reach the end of step 1 is delayed by 8 or 13 hours depending on the polymer nature. HEC increases more the workability time than PAM.
- Polymer addition decreases the elasticity. Indeed the cement particles are substituted by polymer and interactions between cement particles is greater than interaction between cement and polymer, leading to a weaker network.

Rheolaser Master offers:
- 1-click experiment & results ;
- Measurement at rest ;
- Non intrusive measurement ;
- Ageing analysis on the very 
  same sample ;

Summary

Monitoring the setting time of cement(with or without polymer) without any external force or drying phenomenon is one of the challenge of adjuvant industry. The use of Rheolaser will allow the user to adjust its formulation and easily monitor the effect on the workability time.
Rheolaser® is a powerful tool, which can fully and easily characterize, in real time the viscoelasticity of cements during the setting process. Measurement is done thanks a non-contact method which enables to analyse the sample without any external stress, on the very same sample versus ageing time in a glass disposable cell.

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