Core-scale characterization of hydraulic and poroelastic properties
using oscillating pore pressure method
Abstract
Accurate characterization of hydraulic and poroelastic rock properties
is crucial for successful management of groundwater, petroleum resources
and subsurface contaminant remediation. The oscillating pore pressure
method is a popular laboratory technique for permeability and specic
storage measurements of rock samples. We present an improvement of the
oscillating pore pressure method by simultaneously measuring hydraulic
and poroelastic properties of rocks. Measurements were carried out for
four conventional reservoir rock quality samples at oscillation
frequencies of 0.025–1 Hz and effective pressures of 3.5–62 MPa.
Interpreted permeability values decreased with increasing effective
pressure and increased sharply above a frequency range of 0.3–0.4 Hz.
We established that hydraulically measured storage capacities are
overestimated by an order of magnitude when compared to elastically
derived ones. Biot coecient was estimated both from pore pressure and
strain measurements, and comparison of two data sets reveals high
uncertainty of the hydraulic specic storage measurements. We documented
grain crushing and pore collapse in a dolostone sample, observed as a
permanent and drastic decrease of permeability and bulk modulus. We
validated our method by detecting irreversible microstructural changes
independently by hydraulic, elastic, X-ray microtomography ( CT) and
nuclear magnetic resonance (NMR) measurements. We further developed a
novel data processing approach that utilizes a broad, multifrequency
range of data which are inverted for permeability. We re- process
published data and demonstrate that our methodology outperforms
traditional data reduction techniques, as our inversion results show a
better t to pressure trends. To better understand the effect of
frequency on phase and amplitude data and to verify our inversion
approach we numerically simulate oscillating pore pressure experiments.
We document a strong deviation of experimentally obtained phase data
starting at 0.3 Hz oscillation frequency. Our method can be used for
robust determination of permeability and rapid prediction of
experimental results using numerical simulation, ultimately improving
experimental permeability measurements.