Rock Physics Investigations Using Pressure Oscillations

• Main Author: Hasanov, Azar K
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Geophysical engineering; Geophysics
• ISBN: 9781392245132; 1392245133

Knowledge of hydraulic and poroelastic properties is essential for simulating fluid flow in porous media. Accurate constraints on these properties have impacts on production forecasts and economics. Traditionally, transport and poroelastic properties are measured separately using, for example, the pulse-decay method to measure hydraulic transport properties, static strain measurements for elastic properties, and pore volumometry for storage capacity. In addition to time, the separate set of measurements require either multiple samples or subjecting the same sample to multiple tests. I modified the oscillating pore pressure method to allow for an experiment that is capable of measuring permeability, storage capacity and pseudo-bulk modulus of rocks simultaneously. I present the method, calibration measurements (capillary tube) and sample measurements (sandstone) of permeability and storage capacity at reservoir conditions. A concurrent measurement of elastic properties during the hydraulic experiment provides an independent constraint on specific storage.In this dissertation I document the utility of the modified oscillating pore pressure experiment for simultaneously determining hydraulic and poroelastic properties of reservoir rocks. Measurements were carried out on four conventional reservoir rock quality samples at oscillation frequencies of 0.025 -- 1 Hz and effective pressures of 3.5 -- 62 MPa. Estimated permeability values decreased with increasing effective pressure and increased sharply after at frequencies higher than about 0.3 Hz. I establish that hydraulically measured storage capacities are overestimated by almost an order of magnitude when compared to elastically derived ones. The Biot coefficient was estimated from hydraulic and strain measurements and comparison of the two datasets reveals high uncertainty of the hydraulic specific storage. I interpret grain crushing and pore collapse in a dolostone sample, observed as a permanent and drastic decrease of permeability and bulk modulus. I prove the validity of the method by detecting irreversible microstructural changes independently by hydraulic, elastic, μCT and NMR measurements. This approach can be used to constrain and to improve the estimation of storage capacity, and thus leads to better fluid flow model inputs and forecasts.Additionally, I present a novel data processing approach that utilizes a broad multifrequency range of data and inverts it for permeability. I re-process published data and demonstrate that our methodology outperforms the traditional data reduction techniques, as our inversion results show a better fit to the pressure data. I numerically simulate oscillating pore pressure experiments for four rock samples. I document a strong deviation of experimentally-obtained phase data, starting at 0.3 Hz oscillation frequency. A possible explanation for this deviation is an inertial fluid-solid coupling during the pressure diffusion. My method can be used for robust determination of permeability, rapid prediction of experimental results using numerical simulation and ultimately improving experimental permeability measurements.Throughout this dissertation I demonstrate the usefulness and applicability of pressure oscillations in experimental rock physics. Yet another application of pressure oscillations are valuable laboratory measurements of bulk modulus dispersion and attenuation. A common method to measure attenuation and dispersion of seismic waves in the laboratory is the stress-strain method. I present bulk modulus attenuation and dispersion data collected on two heavy oil-saturated rock samples using the oscillating confining pressure method. Data were acquired at 0.001-1 Hz frequencies and compared to existing quasi-static axial stress-strain measurements. I show that bulk viscosity can be a dominant factor in acoustic dispersion and attenuation of rocks containing a highly viscous fluid. I demonstrate that bulk losses are significant even at ultra-low frequencies.