Various types of organic and inorganic crosslinkers have been used to crosslink polyacrylamide (PAM) polymer in oil and gas reservoir conditions. The in-situ gel developed by crosslinking PAM with polyethyleneimine (PEI) was reinforced by adding nanosilica at different sizes for high temperature (130^oC) applications. Functionalized silica (Triamine silica (TAS) mixed with nanosilica was tested as an alternative to PEI. Furthermore, inorganic crosslinkers such as aluminum acetate and cobalt acetate have been investigated as potential crosslinkers for low and high temperatures and a wide range of pH. All these developed formulations were mixed with drilling fluids to investigate their applicability in actual field practice as lost circulation materials.
The obtained results showed that nanosilica with different sizes reinforced the PAM/PEI solution, which resulted in a stronger gel compared to the base solution. The small size was better with high molecular weight PAM, whereas the big size nanosilica was more convenient with low molecular weight. 50 nm nonfunctionalized silica was able to stabilize PAM/TAS system and reinforce the produced gel.
On the other hand, 4 wt.% cobalt acetate successfully crosslinked 9 wt. %PAM at high temperatures (130–150 °C), providing a strong and stable gel at pH higher than 7. Aluminum-based crosslinkers were found to have a wider range of tolerance toward high acidity. Therefore, increasing the pH decreased the gelation time of aluminum acetate-based gels. PAM/aluminum acetate gels were stable at temperatures between 25 and 100°C and pH range of 3.5 to 8.5. Reducing the size of AlAc particles significantly improved the stability of the PAM/AlAc system. Furthermore, PAM/PEI-based drilling formulation revealed an 80% reduction in lost circulation compared to conventional materials. All the formulations were found to be compatible with saline water.

Figure 1. Reinforcement of high molecular weight PAM/TAS gel by nanosilica

Mustafa Nasser

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