Polyacrylamide hydrogel used in conformance control is subjected to poor stability at an elevated temperature. In this paper, nanosilica has been found to be a very effective stabilizing agent for the polyacrylamide/polyethylenimine hydrogel, and the reinforcing performance of nanosilica on the hydrogel was investigated in detail. The result showed that the strength of hydrogel is enhanced obviously by the nanosilica, and the hydrogel syneresis is also significantly inhibited by the nanosilica, which can increase the hydrogel stability time from 18 to 180 days at 130 °C. Besides, nanosilica can increase the shear viscosity and hydrodynamic radius of polyacrylamide, and the bound water in the hydrogel is also grown in the presence of nanosilica. In comparison to the micromorphology of common hydrogel, the dense and strong mesh structure is formed as a result of the reinforcing behavior of nanosilica. According to the above results, it is inferred that the silanol group of nanosilica cross-links with the amidogen of polyacrylamide via the hydrogen bond, which is considered as the primary cause of the reinforcing performance of nanosilica for the hydrogel. In addition, as a result of the improving strength and stability and increasing absorption of the polymer to rock surface, the hydrogel enhanced by nanosilica has a higher water shutoff ratio and residual resistance factor and a longer period of validity.

Traditional foam hydraulic fracturing fluids used guar crosslinking technology. However, major production problems, such as high friction and difficulty to accurately control the cross-linking time, have influenced the large-scale application of cross-linked guar foam fracturing fluids. In this study, we developed a novel non-cross-linked foam fracturing fluid using a series of polymers synthesized with acrylamide and hexadecyl trimethylallyl ammonium chloride as monomers and improved the stability of foam by forming structures in solution through association. The results showed that the hydrophobic groups were the key factors that affect the foam stability, and the hydrolysis degree had a significant effect on the elasticity of the polymer solution. The model association polymer with 0.75% hydrophobic group content and 56% hydrolytic degree was optimal. The stability of our proposed foam was comparable to that of the cross-linked guar gum foam. The adsorption of associating polymers on the gas and water interface resulted in a high-stability foam. Our study demonstrates a new avenue to develop high-stability foams to satisfy the current hydraulic fracturing scheme.

Abstract The fundamental cause of the proppant suspension behavior in hydraulic fracturing fluids lies in its internal microcosmic network structure and structural strength. In addition to chemical crosslinking, another method to form a network structure is established in this paper. Hydrophobically associating polyacrylamide and an anionic surfactant self-assembly process was applied to form a network structure. Compared with crosslinked hydroxypropyl guar gel, the new fracturing fluid even has better proppant suspending properties in static conditions. The capability does not result from crosslinkage but from reinforced physical associations between chains. The performance of this new fracturing fluid was tested and the results showed that it can fully satisfy the requirement of fracturing fluid. Field test shows excellent stimulation effects during its applications in 400 wells in eight oilfields in China.

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A kind of JDL-1 thickener for betaine hydrophobic association polymer was prepared by aqueous solution polymerization of mixed micelles, AM, AA, AMPS and DM16 were used as raw materials, which was synthesized by redox initiator system. Friction tester and high-temperature rheometer were used to evaluate the resistance reduction and temperature and shear resistance of the thickener. The results show that the viscosity average molecular weight of the polymer prepared with AM, AA, AMPS and DM16 mass ratio of 70∶20∶5∶5 was higher than 12 million, and the dissolution time of the polymer was less than 3 min. When the surfactant is used for physical cross-linking, the apparent viscosity of the cross-linked fracturing fluid is larger than that of 60 mPa·s at 90 °C, 170 s-1 sheared 1 h; when metal cross-linking agent is used for coordination cross-linking, the apparent viscosity is larger than that of 80 mPa·s at 120 °C, 170 s-1 sheared 1 h. The drag reduction rate was 73%, the anti-swelling rate was higher than70%, and the damage rate was less than10%. The field trial was successful and confirmed the multifunctional effect of betaine-type hydrophobic associating polymer.