The Thermal Gelation Behavior and Performance Evaluation of High Molecular Weight Nonionic Polyacrylamide and Polyethyleneimine Mixtures for In-Depth Water Control in Mature Oilfields

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.

Progress and Prospects of In Situ Polymer Gels for Sealing Operation in Wellbore and Near-Well Zone

“…Citric acid is also a retarder (Table 2). Qin et al 74 compared the retardation effects of NaCl, sodium citrate (NaCit), and NH 4 Cl on PAM/PEI gel. The retardation effect of NaCit was better than that of NaCl, and the addition of NH 4 Cl resulted in the longest gelation time, but also a significant reduction in the viscosity of the gel.…”

Plugging Performance of a New Sulfonated Tannin Gel System Applied in Tight Oil Reservoir

“…The dispersed gel is easy to inject because it has low viscosity and controllable particle size; it can be elastically deformed, spontaneously aggregate in the pore throat, and migrate to the deep part of the reservoir [20][21][22][23][24][25], which can avoid the dilution of formation water during pumping and formation shearing and migration. Compared with other granular plugging control agents, dispersed gel has better stratum adaptability [26,27].…”