Probabilistic Estimation of Fracture Transmissivity from Wellbore Hydraulic Data Accounting for Depth-Dependent Anisotropic Rock Stress
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
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.
Oceanography, Hydrology, Water Resources
IdentifiersURN: urn:nbn:se:uu:diva-92873DOI: 10.1016/j.ijrmms.2005.03.016OAI: oai:DiVA.org:uu-92873DiVA: diva2:166182