Estimating hydraulic conductivity of fractured rocks from high-pressure packer tests with an Izbash's law-based empirical model

High‐pressure packer test (HPPT) is an enhanced constant head packer test for characterizing the permeability of fractured rocks under high‐pressure groundwater flow conditions. The interpretation of the HPPT data, however, remains difficult due to the transition of flow conditions in the conducting...

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Bibliographic Details
Published in:Water resources research 2015-04, Vol.51 (4), p.2096-2118
Main Authors: Chen, Yi-Feng, Hu, Shao-Hua, Hu, Ran, Zhou, Chuang-Bing
Format: Article
Language:English
Subjects:
Boreholes
Computational fluid dynamics
Conductivity
Confining
Depth
Empirical analysis
Empirical models
Fluid flow
Fluid pressure
fractured rocks
Fractures
Groundwater
Groundwater flow
Heterogeneity
High pressure
high-pressure packer tests
Hydraulic conductivity
Hydraulic fracturing
Injection
Intervals
Laminar flow
Linearity
non-Darcy flow
Permeability
Phases
Pressure
Reynolds number
Rock
Rocks
Structures
Tests
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Summary:High‐pressure packer test (HPPT) is an enhanced constant head packer test for characterizing the permeability of fractured rocks under high‐pressure groundwater flow conditions. The interpretation of the HPPT data, however, remains difficult due to the transition of flow conditions in the conducting structures and the hydraulic fracturing‐induced permeability enhancement in the tested rocks. In this study, a number of HPPTs were performed in the sedimentary and intrusive rocks located at 450 m depth in central Hainan Island. The obtained Q‐P curves were divided into a laminar flow phase (I), a non‐Darcy flow phase (II), and a hydraulic fracturing phase (III). The critical Reynolds number for the deviation of flow from linearity into phase II was 25−66. The flow of phase III occurred in sparsely to moderately fractured rocks, and was absent at the test intervals of perfect or poor intactness. The threshold fluid pressure between phases II and III was correlated with RQD and the confining stress. An Izbash's law‐based analytical model was employed to calculate the hydraulic conductivity of the tested rocks in different flow conditions. It was demonstrated that the estimated hydraulic conductivity values in phases I and II are basically the same, and are weakly dependent on the injection fluid pressure, but it becomes strongly pressure dependent as a result of hydraulic fracturing in phase III. The hydraulic conductivity at different test intervals of a borehole is remarkably enhanced at highly fractured zone or contact zone, but within a rock unit of weak heterogeneity, it decreases with the increase of depth. Key Points: The Q‐P curves by HPPTs were divided into Darcy, non‐Darcy, and fracking phases The characteristics of Q‐P curves were correlated with the intactness of rocks The permeability in different phases was evaluated with an analytical model
ISSN:0043-1397
1944-7973
DOI:10.1002/2014WR016458