Low-Salinity Chase Waterfloods Improve Performance of Cr(III)-Acetate Hydrolyzed Polyacrylamide Gel in Fractured Cores

Abstract

Polymer gels are frequently applied for conformance improvement in fractured reservoirs, where fluid channeling through fractures limits the success of waterflooding. Placement of polymer gel in fractures reduces fracture conductivity, thus increasing pressure gradients across matrix blocks during chase floods. A gel-filled fracture is reopened to fluid flow if the injection pressure during chase floods exceeds the gel-rupture pressure; thus, channeling through the fractures resumes. The success of a polymergel treatment, therefore, depends on the rupture pressure.Salinity differences between the gel network and surrounding water phase are known causes of gel swelling (e.g., observed in recent work on preformed particle gels). Gel swelling and its effect on fluid flow have, however, been less studied in conjunction with conventional polymer gels. By use of corefloods, this work demonstrates that low-salinity water can swell conventional Cr(III)-acetate hydrolyzed polyacrylamide (HPAM) gels, thereby significantly improving gel-blocking performance after gel rupture.Formed polymer gel was placed in fractured core plugs, and chase waterfloods were performed using four different brine compositions, of which three were low-salinity brines. The fluid flow rates through the matrix and differential pressures across the matrix and fracture were measured and shown to increase with decreasing salinity in the injected water phase. In some cores, the fractures were reblocked during low-salinity waterfloods, and gelblocking capacity was increased above the initial level. Low-salinity water subsequently flooded the matrix during chase floods, which provided additional benefits to the waterflood. The improved blocking capacity of the gel was caused by a difference in salinity between the gel and injected water phase, which induced gel swelling. The results were reproducible through several experiments, and stable for long periods of time in both sandstone and carbonate outcrop core materials. Combining polymer gel placement in fractures with low-salinity chase floods is a promising approach in integrated enhanced oil recovery (IEOR).

Quantitative Evaluation of the Plugging Effect of the Gel Particle System Flooding Agent Using NMR Technique

“…The plugging effect under low salinity was the best. This is mainly because gel particles with low salinity can generate a higher residual resistance coefficient, reduce interfacial tension, promote particles to easily enter matrix pores, expand sweep range, and complete effective plugging of matrix pore space. , …”

Water shutoff and conformance improvement: an introduction

“…Formulating gels based on higher-salinity water may therefore be an advantage. Recent laboratory studies have shown that injection of low-salinity water may repair a ruptured gel treatment (Brattekås et al 2016;Seright 2020, 2018). This favorable effect occurs when the salinity of the injected water is lower than that of the gel solvent, which cause the fracture-filling gel to swell.…”

Hidrogéis Compósitos Poliméricos Com Possível Aplicação No Controle De Permeabilidade Em Reservatórios De Petróleo: Uma Revisão.

“…Por exemplo, os compostos à base de cromo (III) costumavam ser utilizados pelo mecanismo de complexação deste metal com os grupos carboxilatos (RCOO -) presentes em cadeias poliméricas de poliacrilamidas hidrolisadas e derivados (SYDANSK, 1988;REDDY et al, 2003;VARGAS-VASQUES;ROMERO-ZERÓN, 2008;KARIMI et al, 2014;BRATTEKAS et al, 2016;SUN et al, 2016). No entanto, as adversidades que apresentavam incluíam, principalmente, a instabilidade térmica, questões ambientais associadas à sua forma oxidada, Cr (VI), e o tempo de gelificação imprevisível destes materiais que dependia do contra-íon associado ao cromo (III) (REDDY et al, 2003).…”