Gelation Kinetics and Performance Evaluation of an Organically Crosslinked Gel at High Temperature and Pressure

Abstract

Organically crosslinked gels have been used to control water production in high temperature applications. These chemical systems are based on the crosslinking of a polyacrylamide-based polymer/ copolymer with an organic crosslinker. Polyethyleneimine (PEI) has been used as an organic crosslinker for polyacrylamide-based copolymers to provide thermally stable gels.Literature reported that PEI can form aqueous gels with polyacrylamide (PAM) at room temperature. In this paper, we show for the first time the possibility of crosslinking polyacrylamide with PEI at temperatures up to 140°C (285°F) and pressures up to 30 bars (435 psi). This paper reports data both in bulk and in porous media.The gelation time of the PAM crosslinked with PEI at high temperatures up to 140°C (285°F) and pressures up to 435 psi (30 bars) was measured. The effects of polymer concentration, crosslinker concentration, temperature, salinity, initial pH value, and the initial degree of hydrolysis of the polymer on the gelation time were examined in detail. All measurements were conducted in the steady shear mode. 13 C Nuclear Magnetic Resonance Spectroscopy ( 13 C NMR) was used to relate the gelation time to changes in the structure of the polymer and hence explain the variation in the gelation time in terms of the gelling system chemistry.In bulk, thermally stable gels were obtained by crosslinking PAM with PEI at 130°C (266°F) for at least 8 weeks. The performance of the PAM/PEI system in sandstone cores at a temperature of 90°C (194°F) and pressure drops of 68.95 bars (1,000 psi) was examined. The system was found to be stable for 3 weeks, where the permeability was reduced by a factor of 100%.

Modelling Gelation Time of Organically Cross-linked Water-shutoff Systems for Oil Wells

“…Irrespective of the cross-linker and brine concentration, an increase in temperature drastically decreased the gelation time with the greatest impact occurring at lower crosslinker concentrations. This is predictive of gel systems indicating endothermic reaction as increase in temperature decreases gelation time [14]. An increase in temperature is a good platform for viscosity of gel systems to build-up as crosslinking density is increased resulting in increased rate of reaction and thereby shortening the gelation time.…”

“…Researchers [1,6,[13][14][15][16] have identified polymer gels for near wellbore area (organically or inorganically crosslinked) and microgels for deep profile modification (Bright water and Methylene bisacrylamide Aggregates) as the broad categories of chemicals for water sealants in wells producing excessive and unwanted water. According to Watters, Kabir, Sydansk, these broad categories include; inorganic gels, resins or elastomers, monomer based systems, polymer gels, viscous systems, bio-polymers and foam gel among others [1,13,17,18].…”

“…There is a gradual rise in viscosity followed by an asymptotic increase to infinity as the gel point is approached Marfo [19]. Al-Muntasheri [14] developed correlation for gelation time as a function of temperature for watershutoff systems. These equations showed that increasing the temperature shortened the gelation time of organically crosslinked gels.…”

“…It was concluded that increasing degree of salinity increased the gelation time of organically crosslinked water-shutoff systems. El-Karsani, Reddy BR, Al-Muntasheri and Das concluded that increasing the polymer and cross-linker concentrations resulted in a decrease in the gelation time of water-shutoff systems [4,6,9,14,20].…”

Flow of a Cross-Linking Polymer in Porous Media

“…One of the commonly Fig. 1 Diversion of the injected water in the reservoir after it was treated with the XL polymer: IW-injection well; PW-production well applied cross-linking systems is a mixture of a hydrolysed polyacrylamide (HPAM) and polyethylenimine (PEI) (Al-Muntasheri et al 2008;Crespo et al 2013). Despite its frequent application, there is a lack of knowledge about the in situ dynamic cross-linking of such systems and hence the efficiency of the XL polymer cannot be predicted from reservoir to reservoir.…”