Coreflooding Experiments on PAM/PEI Polymer Gel for Water Control in High-Temperature and High-Pressure Conditions: With and Without Crossflow Effect

Abstract

This study presents the coreflooding experiments to evaluate the performance of PAM/PEI polymer gels as conformance control agent in porous media. The experiments were designed to investigate the effectiveness of PAM/PEI polymer gels to block a high permeability zone and to divert water to low permeability zone. The work is based on four relevant elements that determine the suitability of a gel to mitigate excessive water production in a high temperature and high pressure conditions. They are adequate gelation time to achieve the target zone, reducing permeability to water, applicable injectivity, and long-term thermal stability. Two different coreflooding schemes were performed, which are coreflooding without crossflow using native sandstone, and coreflooding with crossflow using composite core that has permeability contrast. Native and composite cores represent homogeneous and heterogeneous reservoirs, respectively. Four different set of gelants, which are; 1) pure PAM/PEI polymer gelant; 2) PAM/PEI polymer gelant with NH4O; 3) PAM/PEI polymer gelant with NH4O at high salinity; and 4) Polymer gelant in high salinity and NH4Cl reinforced with SiO2 nanoparticles (NP), were prepared and injected into the cores. The selected mixture of gelants are sufficient to represent the effect of salinity, NH4Cl as retarder and solid nanoparticles on the gel in porous media. The pressure drop is an indication of the gel strength. Higher pressure drop signifies good gel strength. The highest pressure drop can be observed in the core treated with silica NP reinforced polymer gel. Compared to the gel without silica NP, the pressure drop during waterflooding post gel treatment can rise up to 1500 psi. On the oil recovery, highest recovery is established for core treated with reinforced polymer gel. Additional 24% of the trapped oil was recovered after treatment. It signifies the effectiveness of polymer gel with silica NP to divert the flow of water into where trapped oil is located. Good gel performance can be visualized through the dye stain on the surface of the core cut. When brine is injected, the dye stain will be left at the water flow path. For the core treated with reinforced gel, the dye stain is only spotted at the inlet of the core. It can be assumed that rigid gel is able to divert water to low permeability zone before water reaches further surface. The different mixture of PAM/PEI polymer gels were assessed in native and composite sandstone cores at high temperature and pressure. Results showed that PAM/PEI polymer gel reinforced with solid silica NP has proved to provide satisfactory gel strength to divert water flow, thus effective to recover more oil. Strengthening gel by addition of solid particles could be the remedy for the weakened polymer gel.