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Titel |
Single-well and inter-well dual-tracer test design for quantifying phase volumes and interface areas in subsurface flow and transport systems |
VerfasserIn |
I. Ghergut, H. Behrens, T. Licha, F. Maier, M. Nottebohm, M. Schaffer, M. Sauter |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250070965
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Zusammenfassung |
Technology-relevant georeservoirs in the realm of energy production (such as: spent-radionuclide
repositories, gas-storage, geothermal, as well as CCS candidate reservoirs) contain mobile
and immobile fluid regions, and often also different fluid and solid phases. The lifetime of a
particular reservoir (from a hydraulic, thermal, geomechanical and/or hydrogeochemical
point of view) depends on the volumes and/or interface areas of some of these regions and/or
phases. Mostly, their lifetime-effective values cannot be measured by geophysical and
hydraulic methods. Since they essentially relate to fluid-based transport processes, attempting
to measure them by tracer tests is a sensible endeavour. However, in designing and
dimensioning such tracer tests, one should keep in mind that not every tracer test is sensitive
w. r. to every fluid transport parameter. A certain complementarity exists, w. r. to parameter
sensitivity,
between single-well and inter-well methods,
between equilibrium and kinetic exchange processes,
between volume and area parameters.
Mobile-fluid volumes can be measured from inter-well conservative-tracer tests, whereas
single-well push-pull tests are generally insensitive w. r. to mobile-fluid volumes.
Immobile-fluid volumes, in single-phase systems, are rather difficult to measure, by either
kind of test. Different-phase volumes can be determined from inter-well tests using
partitioning tracers at equilibrium exchange between phases; whereas single-well
tracer push-pull tests are rather insensitive w. r. to tracer exchange processes at
equilibrium.
Im-/mobile fluid, or inter-phase interface areas can be determined from single-well tracer
push-pull tests relying on kinetic exchange processes between compartments or phases.
Single-well tests are often believed to be more sensitive w. r. to such processes than w. r. to
advective-dispersive processes, and than inter-well tests.
Inter-well tests are not physically insensitive w. r. to kinetic exchange processes,
but they are strongly affected by ambiguity between dispersion and non-advective
non-equilibrium processes. (Actually, this ambiguity also impedes upon single-well
tests.)
An interesting compromise between the advective- or equilibrium-dominated parameter
sensitivity regimes, and the advection- or equilibrium-insensitive regimes is obtained when
using in-situ tracer creation in a time-dependent manner (from another initially-injected
tracer with different phase-partitioning properties), as had been originally proposed by [1] for
determining residual-oil saturations.
The poster presents a model set-up enabling to directly compare the sensitivities of the
different tracer-test methods w. r. to the different parameters for a given system, and to
reshape the concept of [1], from its originally intended oilfield application, to a possible new
application for CCS site characterization.
We illustrate the latter by simulating such dual-tracer tests for the pilot site
of a CCS-related ‘MMV Experiment’ (Measuring, Monitoring, Verification) at
Heletz in Israel. The target storage formation at Heletz is assumed to consist of a
number (3–6) of permeable sandstone layers (with porosities ~12–17%) separated by
shale layers (with porosities ~3–5%), whose permeabilities contrast by factors
~103–104. While single-well tracer tests are rather insensitive w. r. to porosity
and permeability stratification details, they can yield information about gas-phase
saturations and gas-brine interface densities within selected layers; using the in-situ
creation of a dual tracer in the sense of [1], the sensitivity of single-well tests in the
low-saturation (residual-saturation) range can be enhanced significantly. A inter-well
conservative-tracer test, with depth-resolved monitoring at the ‘arrival’ well (as
intended at the Heletz site), can additionally yield the effective-porosity profile,
which can be used to better constrain the single-well test inversion. With bulk (not
depth-resolved) tracer monitoring, a inter-well conservative-tracer test still yields
very valuable information, which can be poured into the shape of a flow-storage
repartition[2],[3]. Furthermore, considering a CO2 plume with the radius–thickness
relationship derived by [4], and ‘integrating’ it ‘over’ the particular-site stratigraphy, with the
‘weighting’ defined by the flow-storage repartition (cumulative distribution function for
q against BÏ) that was derived from the inter-well, conservative-tracer test, we
get:
      A ( t ,Â Î¸Ë )   -   (t/Ï)1-2 Ã [ μ(Î¸Ë ) + 1/μ(Î¸Ë ) ] Ã Σi (qiBi/Ïi)1-2  ,       Â
from which the evolution of CO2–brine interface areas (A) during early injection regimes
(immiscible displacement) can roughly be estimated as a function of time t and temperature
Î¸Ë , with μ(Î¸Ë ) denoting the mobility ratio between CO2 and brine (mobilities being taken at
each one’s saturation).
The comparison of CO2 plume volumes and CO2–brine interface areas predicted for the
Heletz MMV experiment under different stratigraphy assumptions demonstrates the
importance of brine-phase (single-phase!), conservative-tracer tests for characterizing the
‘transport-effective hydrogeology’ of a candidate CCS site, prior to initiating any experiments
involving a CO2 phase.
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References:
[1]Â TOMICHÂ JÂ F, DALTONÂ RÂ LÂ JR, DEANSÂ HÂ A, SHALLENBERGERÂ LÂ K (1973):
Single-Well Tracer Method to Measure Residual Oil Saturation. J Petrol Technol / Transact,
255, 211-218Â
[2]Â SHOOKÂ GÂ M (2003): A Simple, Fast Method of Estimating Fractured Reservoir
Geometry from Tracer Tests. Geotherm Resour Council Transact, 27Â
[3]Â http://www.geothermal-energy.org/pdf/IGAstandard/SGW/2010/behrens.pdf
[4]Â NORDBOTTENÂ JÂ M, CELIAÂ MÂ A, BACHUÂ S (2005): Transp Porous Med, 58,
DOI 10.1007/s11242-004-0670-9 – page 348, rel.(8)
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Acknowledgement: Field and laboratory work for implementing the tracer
methods at the Heletz site are funded by the EU Seventh Framework Programme
FP7 / 2007–2013, within the MUSTANG project (grant agreement no. 227286). The
authors express their gratitude to Jac Bensabat (EWRE, Haifa) and Auli Niemi
(University of Uppsala), for fruitful discussions during their visit in Göttingen. |
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