(398bt) Novel Environmentally Benign Hydrogel: Nano-Silica Hybrid Hydrolyzed Polyacrylamide/ Polyethyleneimine Gel System for Conformance Improvement in High Temperature High Salinity Reservoir

Reservoir heterogeneity in form of fractures or thief zones significantly impaired the sweep efficiency and reservoir conformance in oil recovery process. Among various remediation aiming at conformance improvement, gel treatment has been proven one of utmost cost-effective technologies. The hydrogels for conformance control, are usually prepared with polyacrylamide(PAM) and metallic crosskinker such as Chromium(III) or organic crosskinker for instance, phenol-formaldehyde. Whereas, the short gelation time and environmental toxicity impeded their applications in harsh oil reservoirs.

In order to address the conformance problem in high temperature(85 ℃) and high salinity(70,000 mg/L TDS) reservoir, an environmentally benign hydrogel was developed based on hydrolyzed polyacrylamide(HPAM) and polyethyleneimine(PEI). Moreover, silica nanoparticle(SNP) was embedded to reinforce the performance of HPAM/PEI gel. To achieve the optimum formulation of HPAM/PEI-SNP gel, a comprehensive investigation was first conducted with the respect of gelation time, gel strength, and thermal stability. Afterwards, the particle size of SNP was determined by Dynamic Light Scatter(DLS) and the microstructure of HPAM/PEI-SNP gel was characterized via Scanning Electron Microscopy(SEM).

The optimum formulation was obtained, containing a polymer/crosslinker ratio of 10,000 ppm to 2,000 ppm in which HPAM possessed high molecular weight (10-15 million Dalton) and low hydrolysis degree (3-7%). In accordance to the comparability between SNP and formation water, Ludox colloidal silica with an SNP concentration of 30 wt% was selected as hybrid resource. The results indicated that the gelation time of novel gel system was prolonged to 40-72 hours attributed to the introducing of nanomaterial. Taking advantage of nano-composite, the strength of HPAM/PEI-SNP gel can be improved to Grade F as a deformable nonflowing gel. Furthermore, the HPAM/PEI-SNP gel exhibited an excellent thermal stability at 85 ℃ for 20 days without any syneresis. Subsequently, SEM images confirmed the successful incorporation SNP in the 3-dimentional network of hydrogel, supporting an effective surface modification.

This work suggested that the novel environmentally benign hydrogel, HPAM/PEI-SNP gel system can be used as a potential plugging agent for the conformance improvement of high temperature high salinity reservoir.