Delayed HPAM Gelation via Transient Sequestration of Chromium in Polyelectrolyte Complex Nanoparticles

Abstract

Heterogeneity of oil reservoirs often leads to unproductive cycling of injected oil recovery chemicals, resulting in the loss of significant quantities of reserves. To maximize recovery efficiency, a blocking agent may be placed deep into high-permeability channels so that the subsequently injected chemicals can be redirected into previously unswept regions. Cr(III)−polyacrylamide gels have been used extensively in field applications as blocking agents for sweep improvement; however, the gelation time of the current state-of-the-art is too short to achieve in-depth placement. This paper describes a novel approach of using polyelectrolyte complex nanoparticles to entrap and control the release Cr(III) to effectively extend gelation time. Self-assembly of polyethylenimine (PEI) and dextran sulfate (DS) resulted in the formation of ∼100−200 nm particles that efficiently entrapped chromium while maintaining colloidal stability in water or gelant. Although the addition of chromium chloride to HPAM typically produced gels in minutes, chromium was efficiently sequestered in nanosuspensions of polyelectrolyte complexes, resulting in a significant delay in gel formation that was dependent on pH, ionic strength, and temperature. The gel formation kinetics of PEI, polyelectrolyte complexes (PECs) of PEI and DS, and PECs loaded with chromium were compared. PEI, a known cross-linker of HPAM, produced a steady increase in gelant viscosity over time. PECs without chromium demonstrated a delayed gel formation compared to PEI but possessed a similar creeping increase in viscosity. In contrast, PECs loaded with chromium typically showed minimal viscosity increase over time followed by an abrupt viscosity increase, resulting in gel formation. This study suggests that PECs offer a flexible nanotechnology platform that may enable novel chemical delivery schemes in the oil and gas industry.

Fracturing fluid cleanup by controlled release of enzymes from polyelectrolyte complex nanoparticles

“…[10][11][12][13][14] Combining this technology with knowledge of breakers for fracturing fluids provides the impetus for the following research.…”

“…Cordova et al [14] modified the system presented by Tiyaboonchai [10] to delay hydrolyzed polyacrylamide (HPAM) gelation by sequestering the chromium (III) crosslinker in PEC nanopartciles. Cordova et al [14] hampered the rapid release of Cr (III) by generating transient electrostatic binding events.…”

“…Cordova et al [14] hampered the rapid release of Cr (III) by generating transient electrostatic binding events. Cordova et al [14] formed < 200 nm PEC nanoparticles by adjusting the concentration of PEI and DS and also PEI:DS ratio. They mentioned that mixing ratios above 1:1 v/v are needed to generate positively charged nanoparticles.…”

“…Cordova et al [14] showed that the Cr-loaded nanoparticles were capable of delaying the gelation time for about 4.5 days at 40 °C while the controlled system with no PECs showed gelation time of around 30 minutes. They also reported that increasing the temperature reduces the gelation time significantly.…”

“…[10][11][12] Polyelectrolyte complex (PEC) nanoparticles have been also used successfully to entrap and release Cr(III) in a controlled manner for water control applications. [13,14] It was hypothesized that such nanoparticles will be capable of releasing enzymes in a controlled manner with the potential for application in breaking fracturing fluids. Use of such a carrier for breakers in fracturing fluids would require high entrapment efficiency of the breaker, homogeneous distribution and flexible release time.…”