New insights into phenol–formaldehyde‐based gel systems with ammonium salt for low‐temperature reservoirs

Abstract

Polymer gels are effective tools that are still widely used in mature oilfield development to stop unwanted fluid production from oil and gas wells, but conventional gelant formulations have become increasingly difficult to apply at low and ultralow temperatures. Because of this situation, the gelation performance of phenol-formaldehyde-based gel systems at a low temperature of 25 C is discussed in this article. The results show that the gelation time and strength of the gel systems can be perfectly controlled by the adjustment of the polymer concentration, the molecular weight, the crosslinking agent concentration, the ammonium salt concentration, and the composition. The polymer concentration and molecular weight can affect not only the gelation time and the gel strength but also its stability. The ammonium salt concentration affected not only the gelation time but also its viscosity before a detectable gel formed. Among them, the polymer concentration was the most important factor affecting the gel stability. For lowtemperature reservoirs, the phenol-formaldehyde-based gel system achieved a much longer gelation time. Polymer gels formulated with a combination of 0.2-0.4 wt % polymer, 0.5-1.0 wt % formaldehyde or phenol-formaldehyde, and 0.1-0.6 wt % ammonium salt, and we added 0.02-0.03 wt % resorcinol to provide a gelation time between 2 h and 2 days. The maximum gel strength reached code I. The results of this study suggest that the formaldehyde-based gel system could be used effectively in low-temperature reservoirs.

In situ organically cross‐linked polymer gel for high‐temperature reservoir conformance control: A review

“…In comparison, NaCl delayed the gelation time to about 40 minutes only, whereas NH 4 Cl delayed the gelation time of PAM/PEI gel system to more than 3 hours at same temperature and concentration . From the study by Ren et al, the high amount of ammonium salt concentrations will prolong the gelation time for the phenol‐formaldehyde‐based gel systems . However, degradation of gel strength and also dehydration synthesis might happen if too much of NH 4 Cl or NH 4 HCO 3 is added.…”

“…41 From the study by Ren et al, the high amount of ammonium salt concentrations will prolong the gelation time for the phenol-formaldehyde-based gel systems. 104 However, degradation of gel strength and also dehydration synthesis might happen if too much of NH 4 Cl or NH 4 HCO 3 is added.…”

“…This is due to there is a possible of overcross‐linking resulted from excessive concentration of cross‐linker and cause the gel syneresis consequently. The water expulse out of the gel by osmosis and polymer gel dehydrate …”

An Optimization Study of Polyacrylamide-Polyethylenimine-Based Polymer Gel for High Temperature Reservoir Conformance Control

“…Syneresis is caused by overcrosslinking from excessive concentration of crosslinker. Consequently, the water will expulse out of the gel by osmosis and polymer gel dehydrate [45]. Because of this, gel volume reduces, and new flow paths are created, eventually affecting the performances of gel treatment.…”

Study on ammonium-promoted phenol-formaldehyde-based gel for enhanced oil recovery and its seepage characteristics in porous media

“…Polymer gel is one of the most commonly used profile control agents in oilfield, mainly obtained by cross-linking reaction between polyacrylamide and cross-linking agent. The cross-linking agent controls the gel-forming performance and application temperature range of the polymer gel [1][2][3]. At present, the commonly used crosslinking agents are mainly divided into organic crosslinking agents and inorganic crosslinking agents.…”