Differential Permeability Reduction of CO2 and Water by Polymer Gel in Sandstone Rocks during WAG Process

Abstract

Polymer gels have been widely applied to control reservoir conformance and improve sweep efficiency for CO2 flooding reservoirs. The plugging performance of polymer gels on water and CO2 have been reported separately; however, few researches have been carried out about how the cycles of CO2 and water affect the plugging efficiency of gels on CO2 during a WAG (water alternated with CO2) process. The objective of this study is to investigate whether a polymer gel has a different effect on water and CO2 flow and how the cycles of water and CO2 affect the plugging performance during the WAG process. Core flooding experiments were carried out using four sandstone cores with different permeability varied from 100 to 1200 md. After determining the permeability of a core using brine and CO2, the Cr(III)-acetate-HPAM gelant was injected into the core until injection pressure reached stable and the cores were shut in for 24 hours to allow gelation. After that, two cycles of water and CO2 were injected to determine the effect of gel on the plugging efficiency of water and CO2 at different injection rates. Results showed that the polymer gel is a selective plugging material that can reduce the permeability to water much more than that to CO2 during the first flooding cycle. The resistance to CO2 was only 5% of that to brine. The selective plugging in low permeability cores was more prominent than that in high permeability cores. The cycles had a significant effect to polymer gel plugging performance. With increased cycles, the resistance to both CO2 and brine significantly decreased. The resistance of the polymer gel to CO2 became negligible only after two cycles of water and CO2 was injected for low permeability cores. This paper will be the first time to report that a polymer gel has much less plugging efficiency to CO2 than that to water. The WAG cycles could significantly decrease the plugging efficiency of a polymer gel to both water and CO2. The results will help the field engineers to understand why most polymer gel treatments are not very effective or the effective term is very limited.

Department(s)

Geosciences and Geological and Petroleum Engineering

Second Department

Chemical and Biochemical Engineering

Comments

U.S. Department of Energy, Grant DE-FE0024558

International Standard Book Number (ISBN)

978-151085814-5

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2024 Curran Associates Inc., All rights reserved.

Publication Date

01 Jan 2017

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