Environmental and strength‐enhanced nanosilica‐based composite gel for well temporary plugging in high‐temperature reservoirs

Polymer gel is widely used for well temporary plugging in petroleum engineering. This paper researched on a novel environmental and strength-enhanced composite gel plug prepared by the nanosilica, the polymer hydrolyzed polyacrylamide and environmental friendly crosslinker polyethyleneimine, and the effect of strength enhancement and thermal stability mechanism of the nanosilica in this system was investigated. The experiments results showed that with the increase of the nanosilica concentration, the elastic modulus and viscous modulus, the stress under the same strain and the gel decompose temperature both increased. For the system containing 8% nanosilica, the elastic modulus is about 14 times than the one without it, whereas the viscous modulus is only 70.98 Pa, which is favorable for lowering the absorption damage to the formation. The strain-stress experiment results showed that to reach 45% strain, the stress of 44.6 KPa needed to be loaded (for composite gel with 8 wt% nanosilica) and during the compress process, the gel deformed with no break and after the stress was released, it got back to the original shape soon, indicating its good mechanical and elasticity performance. The differential scanning calorimetry (DSC) results revealed that the after adding nanosilica, more free water can be kept so that the system's thermal stability was effectively improved. The scanning electron microscopic images displayed that the nanosilica particles closely adhere to the polymer network; thus, the 3D structure of the composite gel became more compact and the gel's strength was improved. In the last section, some recommendations for well temporary plugging are proposed.