Effect of metal ions on the rheology and thermal properties of polymeric lost circulation material

Drilling oil wells is burdened with a large number of technical and economical problems that makes it unprofitable or difficult to further develop some of the fields. One of the most commonly occurring problems during drilling an oil well is Lost Circulation. Lost circulation is the continuous loss of drilling fluid when it encounters fractures, high permeable zones or pore spaces, during drilling. Lost circulation can lead to blowout endangering the life, and causing serious damages to the drilling rig. Polymeric materials such as Polyacrylamide can be used as Lost Circulation Materials (LCMs) to seal the fractures and prevent the drilling fluid from entering into them. Metal ions such as Magnesium, Manganese and Calcium can be injected with the drilling fluid to increase the viscosity or to increase flexiblity of polymer and form a gel that seals the loss zone. This paper will demonstrate the influence of these counterions on viscosity, thermal stability, and elastic modulus of the Polyacrylamide (PAM) polymer which is used as a main component in LCM. It has been observed that the concentration of counterions has noticeable effect on the rheological properties of PAM solution. On comparison of the results of viscosity between pure 1% wt concentration of PAM and that for a mixture consisting of PAM with 0.95 wt% and counterions with 0.05 wt%, there was a huge viscosity loss. For solutions with Counterions Ca, Mg and Mn²⁺ at 0.05 wt% concentration the viscosity decreased by 42.02%, 39.28%, 31.06% and 10.79%, respectively as compared with viscosity of pure 1 wt% PAM. This paper explained the chemistry behind such precipitation. Additionally this paper also presents the research findings of the effect of these counterions on the thermal stability of the PAM. The thermal stability of pure PAM considered was 70°C, but in the presence of the Ca, Mn and Mg ions, the thermal stability reduced.