Gas injection into saturated porous media has a high practical relevance. It is applied in
groundwater remediation (air sparging), in CO2 sequestration into saline aquifers, and
in enhanced oil recovery of petroleum reservoirs. This wide range of application
necessitates a comprehensive understanding of gas flow patterns that may develop
within the porous media and required modeling of multi-phase flow. There is an
ongoing controversy in literature, if continuum models are able to describe the complex
flow pattern observed in heterogeneous porous media, especially the channelized
stochastic flow pattern. Based on Selker’s stochastic hypothesis, a gas channel is
caused by a Brownian-motion process during gas injection. Therefore, the pore-scale
heterogeneity will determine the shape of the single stochastic gas channels. On the
other hand there are many studies on air sparging, which are based on continuum
modeling. Up to date it is not clear under which conditions a continuum model can
describe the essential features of the complex gas flow pattern. The aim of this study is
to investigate the gas flow pattern on bench-scale and field scale using the continuum
model TOUGH2. Based on a comprehensive data set of bench-scale experiments and
field-scale experiments, we conduct for the first time a systematic study and evaluate
the prediction ability of the continuum model.
A second focus of this study is the development of a “real world”-continuum model,
since on all scales – pore-scale, bench scale, field scale – heterogeneity is a key driver
for the stochastic gas flow pattern. Therefore, we use different geostatistical programs
to include stochastic conditioned and unconditioned parameter fields.
Our main conclusion from bench-scale experiments is that a continuum model, which is
calibrated by different independent measurements, has excellent prediction ability for
the average flow behavior (e.g. the gas volume-injection rate relation). Moreover, we
investigate the impact of both weak and strong heterogeneous parameter fields
(permeability and capillary pressure) on gas flow pattern. The results show that a
continuum model with weak stochastic heterogeneity cannot represent the essential
features of the experimental gas flow pattern (e.g., the single stochastic gas channels).
Contrary, applying a strong heterogeneity the continuum model can represent the
channelized flow. This observation supports Stauffer’s statement that a so-called subscale
continuum model with strong heterogeneity is able to describe the channelized
flow behavior. On the other hand, we compare the theoretical integral gas volumes with
our experiments and found that strong heterogeneity always yields too large gas
volumes.
At field-scale the 3D continuum model is used to design and optimize the direct gas
injection technology. The field-scale study is based on the working hypotheses that the
key parameters are the same as at bench-scale. Therefore, we assume that grain size and
injection rate will determine whether coherent channelized flow or incoherent bubbly
flow will develop at field-scale. The results of four different injection regimes were
compared with the data of the corresponding field experiments. The main conclusion is
that because of the buoyancy driven gas flow the vertical permeability has a crucial
impact. Hence, the vertical and horizontal permeability should be implemented
independently in numerical modeling by conditioned parameter fields.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:22800 |
| Date | 02 August 2012 |
| Creators | Samani, Shirin |
| Contributors | Geistlinger, Helmut, Merkel, Broder, TU Bergakademie Freiberg |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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