Improved understanding nanocomposite gel working mechanisms: From laboratory investigation to wellbore plugging application

Fluid loss is serious in low-pressure fractured reservoir. In this paper, the technique of wellbore isolation for temporary plugging is proposed to reduce the loss of workover fluid. Based on radical polymerization, the high-strength nanocomposite gel plugging agent was prepared by introducing nano-silica. Firstly, the strength properties of gel plug were studied through stress and strain evaluation, viscosity modulus test and wellbore sealing pressure evaluation, respectively. The working mechanism was revealed by infrared spectroscopy (FTIR), environmental scanning electron microscopy (ESEM) and differential scanning calorimetry (DSC) analysis. The study shows that under 50% compression strain, the compression capacity of the nanocomposite gel with 5% nano-silica is nearly three times higher than that of without adding nano-silica, and the thermal stability is improved by 38%, which has the potential to buffer the pressure of the liquid column in the bottom hole and perform good thermostability. Secondly, the actual wellbore simulation system confirmed its ability to seal the perforation zone. Result shows that the pressure-bearing gradient is 20 MPa/100m in the oil tube, and gel plug length can be designed according to the positive pressure demand. The addition of nano-silica makes the network of nanocomposite gel becoming denser, in favor to store more energy. The hydrogen bond generated in the nanocomposite gel increases its mechanical strength. Finally, the successful application of the nanocomposite gel for wellbore temporary plugging in a low-pressure carbonate gas well was summarized. This study provides an avenue to develop various nanocomposite gels for downhole jobs.