Synthesis of a preformed hydrogel based on polyacrylamide and related gel-breakers with potential application for conformance control

In oil recovery processes, fluids injected to increase oil production may find preferential paths or fractured rocks that offer less resistance to passage through the reservoir, leaving many areas of the reservoir without being swept and consequently reducing the oil recovery efficiency, increasing water production compared to oil production. Conformance control technique can be applied to avoid these problems and then redirect the injected fluids to the segments that were previously not being reached. The preformed particle gels (PPG) have been evaluated for this application, which were obtained from precursor hydrogels and injected into oil reservoirs in the form of brine suspensions. In this study, an evaluation was conducted on the thermal, rheological, morphological, stability, and swelling properties of partially hydrolyzed polyacrylamide (PHPA) crosslinked with polyethyleneimine (PEI) PPG. Another study of this work was the evaluation of gel-breaker systems based on ammonium persulfate and sodium hypochlorite, which can be used to solve eventual operational problems arising from obstructions in the PPG application. The results indicated that the optimal chemical composition of the precursors consisted of 1.0% partially hydrolyzed polyacrylamide (PHPA) crosslinked with 3.0% polyethyleneimine (PEI). This combination exhibited higher material strength and swelling capacity, exceeding 20 times its initial mass. The ammonium persulphate proved to be a powerful gel-breaker, causing reductions in elastic modulus by as much as 97%, alongside causing structural damage that was confirmed by scanning electron microscopy (SEM).

Graphical abstract