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Probabilistic Estimation of Fracture Transmissivity from Wellbore Hydraulic Data Accounting for Depth-Dependent Anisotropic Rock Stress
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science. (Hydrologi)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science. (Hydrologi)
2005 (English)In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, Vol. 42, no 5-6, 793-804 p.Article in journal (Refereed) Published
Abstract [en]

A new method is introduced that incorporates the use of hydrological and rock mechanical data in assigning transmissivities for fracture-network models. The hydrological data comes from fixed-interval packer tests carried out in a borehole and the rock-mechanical data are the prevailing in situ depth-dependent stress-field and the stress-closure relationship of fractures.

In the model, the fracture transmissivity distribution is considered to be constituted of two components, one deterministic stress-induced component and the other a stochastic component that describes the intrinsic variability of fractures in a network. The outcome is a tensorial description of fracture transmissivities in an anisotropic stress-regime, where the transmissivity for an arbitrarily oriented fracture in the network is determined by its orientation in relation to the ambient stress-field. These transmissivities are conditioned such that the overall results satisfy the hydraulic packer test data. The suggested procedure is applied to an example data set from a site at Sellafield, England.

The results show that the probabilistic approach, relying on hydraulic data alone, may underestimate the true variability in fracture transmissivities, since the typically vertical boreholes entail a sampling bias towards horizontal fractures that are predominantly subject to vertical stress. The suggested method helps to account for the true underlying three-dimensional variability that is incompletely resolved by using the hydraulic borehole data alone. This method is likely to have the largest impact at low stress-levels, in strongly anisotropic stress-fields, for borehole directions parallel to one principal stress, and for fracture network geometries characterized by sets orthogonal to the three principal stresses.

Place, publisher, year, edition, pages
2005. Vol. 42, no 5-6, 793-804 p.
National Category
Oceanography, Hydrology, Water Resources
URN: urn:nbn:se:uu:diva-92873DOI: 10.1016/j.ijrmms.2005.03.016OAI: oai:DiVA.org:uu-92873DiVA: diva2:166182
Available from: 2005-03-31 Created: 2005-03-31 Last updated: 2013-03-22Bibliographically approved
In thesis
1. Upscaling of Flow, Transport, and Stress-effects in Fractured Rock
Open this publication in new window or tab >>Upscaling of Flow, Transport, and Stress-effects in Fractured Rock
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Uppskalning av flöde och ämnestransport i sprickigt berg samt bergspänningens inverkan
Abstract [en]

One of many applications of geohydraulic modelling is assessing the suitability of a site to host a nuclear waste repository. This modelling task is complicated by scale-dependent heterogeneity and coupled thermo-hydro-mechanical (THM) processes. The objective here was to develop methods for (i) upscaling flow and transport in fractured media from detailed-scale data and (ii) accounting for THM-induced effects on regional-scale transport. An example field data set was used for demonstration.

A systematic framework was developed where equivalent properties of flow, transport, and stress-effects were estimated with discrete fracture network (DFN) modelling, at some block scale, and then transferred to a regional-scale stochastic continuum (SC) model. The selected block scale allowed a continuum approximation of flow, but not of transport. Instead, block-scale transport was quantified by transit time distributions and modelled with a particle random walk method at the regional scale.

An enhanced SC-upscaling approach was developed to reproduce the DFN flow results more simply. This required: (i) weighting of the input well-test data by their conductivity-dependent test volumes and (ii) conductivity-dependent correlation structure. Interestingly, the best-fitting correlation structure resembled the density function of DFN transmissivities.

Channelized transport, over distances exceeding the block scale, was modelled with a transport persistence length. A linear relationship was found between this persistence length and the macroscale dispersion coefficient, with a slope equal to a representative mean block-scale dispersion coefficient.

A method was also developed to combine well-test data and rock-mechanical data in estimating fracture transmissivities, and its application was demonstrated.

Finally, an overall sequential THM analysis was introduced allowing the estimation of the significance of waste-related thermo-mechanical (TM) effects on regional transport; here TM effects are calculated separately and their impact on fracture transmissivities were incorporated into the hybrid framework. For the particular case, their effects on regional-scale transport were small.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. 71 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 35
Hydrology, Upscaling, fractured media, flow, solute transport, thermo-hydro-mechanical processes, hybrid approach, continuum approximation, discrete fracture network, stochastic continuum, Hydrologi
National Category
Oceanography, Hydrology, Water Resources
urn:nbn:se:uu:diva-5739 (URN)91-554-6208-1 (ISBN)
Public defence
2005-04-29, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
Available from: 2005-03-31 Created: 2005-03-31Bibliographically approved

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