New Insights into the Gelation Behavior of Polyethyleneimine Cross-Linking Partially Hydrolyzed Polyacrylamide Gels

Abstract

Using polymer gel is still the mainstream technique of the chemical method for water shut-off in mature oilfield development. The gelation performance of polyethyleneimine (PEI) cross-linking partially hydrolyzed polyacrylamide (HPAM) gel was systematically investigated in this paper by using three types of molecular weight (M w ) HPAM. Results show that the gelant solution (the fluid solution of cross-linker and polymer that exists before gelation) can slightly gel even at room temperature and form a rudimentary 3D network structure for protecting the subsequent gelling. The main factors, including HPAM, PEI concentrations, HPAM M w , and total dissolved solids (TDS) to affect the gelation performance are also discussed. The gelation time is around 18−72 h at 65 °C, which is much longer than the commonly used chromium(III)-acetate crosslinking HPAM gel system. The gelation performance of the PEI/HPAM gel system is improved after flowing through porous media and shows the adverse law for a porous media sheared chromium(III)-acetate or phenol-formaldehyde cross-linking HPAM gel system. Atomic force microscopy (AFM) scanning results show that the microstructure of PEI/HPAM gel distributes a lot of cavities. Compared to the original premature gel (code B), the cavities are more uniform and regular after flowing through porous media. In addition, this study revealed that the presence of free oxygen in the uniform cavities of the weak crosslinked gel after flowing through porous media can accelerate the oxidation reaction to produce a darker brown gel. It also discusses how these new findings will affect the application of the gel system in the oil field.

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

“…Furthermore, we concluded from the study involving the effect of the polymer concentration that the gelation time was reduced with increasing polymer concentration. When the polymer concentration increased, it brought more crosslinking sites, and the crosslinking reaction chance increased . Thus, the gel formation rate increased, and this led to a decrease in the gelation time.…”

“…The gelation time is defined as the time needed to reach the inflection point on the viscosity versus time curve. This method has been widely used . Before gel formation, the viscosity of the gelant solutions is relatively low, so it can be measured accurately.…”

“…The lifting and separation of large amounts of water also greatly increases the operating costs. It may also induce other problems, such as a higher pipeline corrosion rate, reservoir emulsion blockage, or scaling …”

“…Recently, the PEI crosslinking of copolymers of acrylamide and tert ‐butyl acrylate (PAtBA) as water shutoff gels has been widely reported. PEI‐based gel systems can be used for either high‐temperature reservoirs or low‐temperature reservoirs . However, the dosages of the polymer and crosslinker are still large, and the initial viscosity is high; this cannot guarantee good injectivity.…”

Study of the polymer concentration and polymer/crosslinker ratio effect on gelation time of a novel grafted polymer gel for water shutoff using a central composite design method

“…[4][5][6] The gel polymer treatment is one of the most efficient chemical methods to control of excess water production in chemically enhanced oil recovery. [7][8][9] The most widely used gelant system is the aqueous solution of partially hydrolyzed polyacrylamide as polymer and Cr(III) acetate as crosslinker. That system, firstly, was proposed for reducing water permeability and consequently increasing oil sweep efficiency in enhanced oil operations.…”