Understanding the Plugging Performance of HPAM-Cr(III) Polymer Gel For CO2 Conformance Control

Abstract

Abstract With the demand for conformance control in CO2 flooding fields, the traditional HPAM-Cr(III) polymer gel has been applied to reduce excess CO2 production. However, the field application results are mixed. In order to understand the HPAM-Cr(III) polymer gel plugging performance in reservoirs, a numerical reservoir analysis is used to interpret the laboratory results and analyze how the laboratory results are connected to the field application results. The HPAM-Cr(III) polymer gel plugging performance was evaluated in the laboratory with sandstone core plugs. CO2 and water effective permeability was measured. Gelant was injected into the cores until the injection pressure stabilized. Breakthrough pressure was tested and followed by two WAG cycles injection. The injection pressure was monitored. Different permeability cores (100- 1200 md) were used to mimic different reservoir conditions. Residual resistance factor was calculated using the stabilized water/CO2 injection pressure before and after gel treatment. HPAM-Cr(III) polymer gel has higher breakthrough pressure in the low permeability cores. The polymer gel behavior is discussed using three scenarios: no breakthrough, partial breakthrough, and breakthrough. If no breakthrough, the numerical reservoir analysis reveals that the polymer gel can successfully divert the CO2 and water flow to the low permeability layers before breakthrough. The damage to polymer gel is caused by CO2 diffusion from the low permeability layers. The gel damage rate depends on the diffusion rate. This is the reason that polymer gel treatment can last for a longer time in some fields. In the breakthrough scenario, CO2 totally breaks through the gel-treated zone, polymer gel has a larger contact area with CO2 and the gel damage rate will be faster. Therefore, the polymer gel has almost no blocking to CO2 flow.