Abstract
A delayed crosslinked polymer gel was developed for in-depth water control in mature oilfields. The thermal gelation behavior of nonionic polyacrylamide (NPAM) and PEI was investigated, and sodium citrate (NaCit) was selected as a new retarder to prolong the gelation time. The gelation performance of NPAM/PEI gel system can be adjusted by varying NPAM or PEI concentration, and a quadratic model is developed by statistical analysis, which predicts the gelation time of NPAM/PEI gel system. The obtained model shows high significance and good reliability, as suggested by the F-ratio of 175.16 and high adjusted R-square value (0.9732). The addition of NaCit exhibits a good delayed gelation effect on the NPAM/PEI gel system, better than that of NaCl. The decrease of the initial pH value of the gelling solution leads to the weaker gel viscosity and longer gelation time due to the protonation of amine groups on the PEI chains. Increasing temperature results in higher gel viscosity but shorter gelation time. The gel system in the presence of NaCit exhibits good compatibility with injection and formation water. A dense three-dimensional structure was observed in matured NPAM/PEI/NaCit gel, and it could keep stable below 160 °C. The gel system could effectively reduce the permeability (>95%) and restricted the flow of water after matured in natural cores.
Highlights
Due to long-term water flooding for enhancing oil recovery, many high permeability channels are formed in the reservoir
The results indicate that nonionic polyacrylamide (NPAM)/PEI gel system has a good plugging capacity
The gel system composed of NPAM, PEI, and NaCit shows low initial viscosity (
Summary
Due to long-term water flooding for enhancing oil recovery, many high permeability channels are formed in the reservoir. It results in an increase in water productivity and the reduction of swept volume [1]. The hydrolyzed polyacrylamide contains many amide groups (-CONH2 ) and carboxyl groups (-COO− ) in its molecular chain. It could crosslink with different types of crosslinkers, such as Cr3+ [6,7], Al3+ [8], Zr4+ [9], phenolic resin [10,11], etc. Multivalent metal ions and phenolic resin are Materials 2020, 13, 4142; doi:10.3390/ma13184142 www.mdpi.com/journal/materials
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