Affiliation:
1. University of Oslo (UiO), Department of Geosciences, Oslo, Norway..
2. Norwegian Geotechnical Institute (NGI), Oslo, Norway..
3. University of Oslo (UiO), Department of Geosciences, Oslo, Norway and Norwegian Geotechnical Institute (NGI), Oslo, Norway..
Abstract
Fracture networks inside geologic [Formula: see text] storage reservoirs can serve as the primary fluid flow conduit, particularly in low-permeability formations. Although some experiments focus on the geophysical properties of brine- and [Formula: see text]-saturated rocks during matrix flow, geophysical monitoring of fracture flow when [Formula: see text] displaces brine inside the fracture seems to be overlooked. We have conducted laboratory geophysical monitoring of fluid flow in a naturally fractured tight sandstone during brine and liquid [Formula: see text] injection. For the experiment, the low-porosity, low-permeability, naturally fractured core sample from the Triassic De Geerdalen Formation was acquired from the Longyearbyen [Formula: see text] storage pilot at Svalbard, Norway. Stress dependence, hysteresis, and the influence of fluid-rock interactions on fracture permeability were investigated. The results suggest that in addition to stress level and pore pressure, mobility and fluid type can affect fracture permeability during loading and unloading cycles. Moreover, the fluid-rock interaction may impact volumetric strain and consequently fracture permeability through swelling and dry out during water and [Formula: see text] injection, respectively. Acoustic velocity and electrical resistivity were measured continuously in the axial direction and three radial levels. Geophysical monitoring of fracture flow revealed that the axial P-wave velocity and axial electrical resistivity are more sensitive to saturation change than the axial S-wave, radial P-wave, and radial resistivity measurements when [Formula: see text] was displacing brine, and the matrix flow was negligible. The marginal decreases of acoustic velocity (maximum 1.6% for axial [Formula: see text]) compared with the 11% increase in axial electrical resistivity suggest that in the case of dominant fracture flow within the fractured tight reservoirs, the use of electrical resistivity methods have a clear advantage compared with seismic methods to monitor [Formula: see text] plume. The knowledge learned from such experiments can be useful for monitoring geologic [Formula: see text] storage in which the primary fluid flow conduit is the fracture network.
Publisher
Society of Exploration Geophysicists
Subject
Geochemistry and Petrology,Geophysics
Cited by
17 articles.
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