Foam generation in flow across a sharp permeability transition: Effect of velocity and fractional flow

Swej Shah, Herru As Syukri, Karl Heinz Wolf, Rashidah Mohd Pilus, William R. Rossen

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

3 Citations (Scopus)

Abstract

Foam reduces gas mobility and can help improve sweep efficiency in an enhanced-oil-recovery (EOR) process. For the latter, long-distance foam propagation is crucial. In porous media, strong foam generation requires that the local pressure gradient exceed a critical value (!P min). Normally, this happens only in the near-well region. Away from wells, these requirements might not be met, and foam propagation is uncertain. It has been shown theoretically that foam can be generated, independent of pressure gradient, during flow across an abrupt increase in permeability (Rossen 1999). The objective of this study is to validate theoretical explanations through experimental evidence and to quantify the effect of fractional flow on this process. This article is an extension of a recent study (Shah et al. 2018) investigating the effect of permeability contrast on this process. In this study, the effects of fractional flow and total superficial velocity are described. Coreflood experiments were performed in a cylindrical sintered-glass porous medium with two homogeneous layers and a sharp permeability jump in between, representing a lamination or cross lamination. Unlike previous studies of this foam-generation mechanism, in this study, gas and surfactant solution were coinjected at field-like velocities into a medium that was first flooded to steady state with gas/brine coinjection. The pressure gradient is measured across several sections of the core. X-ray computed tomography (CT) is used to generate dynamic phase-saturation maps as foam generates and propagates through the core. We investigate the effects of velocity and injected-gas fractional flow on foam generation and mobilization by systematically changing these variables through multiple experiments. The core is thoroughly cleaned after each experiment to remove any trapped gas and to ensure no hysteresis. Local pressure measurements and CT-based saturation maps confirm that foam is generated at the permeability transition, and it then propagates downstream to the outlet of the core. A significant reduction in gas mobility is observed, even at low superficial velocities. Foam was generated in all cases, at all the injected conditions tested; however, at the lowest velocity tested, strong foam did not propagate all the way to the outlet of the core. Although foam generation was triggered across the permeability boundary at this velocity, it appeared that, for our system, the limit of foam propagation, in terms of a minimum-driving-force requirement, was reached at this low rate. CT images were used to quantify the accumulation of liquid near the permeability jump, causing local capillary pressure to fall below the critical capillary pressure required for snap-off. This leads to foam generation by snap-off. At the tested fractional flows, no clear trend was observed between foam strength and f g. For a given permeability contrast, foam generation was observed at higher gas fractions than predicted by previous work (Rossen 1999). Significant fluctuations in pressure gradient accompanied the process of foam generation, indicating a degree of intermittency in the generation rate—probably reflecting cycles of foam generation, dryout, imbibition, and then generation. The intermittency of foam generation was found to increase with decreasing injection velocities and increasing fractional flow. Within the range of conditions tested, the onset of foam generation (identified by the rise in !P and S g) occurs after roughly the same amount of surfactant injection, independent of fractional flow or injection rate.

Original languageEnglish
Title of host publicationSociety of Petroleum Engineers - SPE Europec Featured at 81st EAGE Conference and Exhibition 2019
PublisherSociety of Petroleum Engineers
Pages451-464
Number of pages14
Volume25 (2020)
Edition1
ISBN (Electronic)9781613996614
DOIs
Publication statusPublished - 2019
Event81st EAGE Conference and Exhibition 2019 - ExCeL Centre, London, United Kingdom
Duration: 3 Jun 20196 Jun 2019
https://eage.eventsair.com/81st-eage-annual-conference-and-exhibtion/

Publication series

NameSPE Journal
PublisherSociety of Petroleum Engineers (SPE)
ISSN (Print)1086-055X

Conference

Conference81st EAGE Conference and Exhibition 2019
CountryUnited Kingdom
CityLondon
Period3/06/196/06/19
Internet address

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