Bulk moduli and seismic attenuation in partially saturated rocks: hysteresis of liquid bridges effect

Rozhko, Alexander Y.

doi:10.1111/1365-2478.12782

Cited by 10 publications

(28 citation statements)

References 62 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…According to our model, this effect is highly sensitive to the wettability of the rock. Effects of wettability on seismic wave velocities were observed more than 60 years ago, after Wyllie et al (), who were the first (to our knowledge) to report this effect (see also Waite et al, ; Wang et al, ; Rozhko, , ); however, the wettability effects are not mentioned in the literature review by Kazantsev (). If the rock is mixed wet (when contact angles are close to 90°), then equation would predict very high value of the critical wave amplitude ( ∆σ c ), required for the contact line slippage.…”

Section: Discussionmentioning

confidence: 86%

“…In this paper we extend both approaches of Gassmann () and Rozhko (, ) by coupling of the interfacial energy to Gassmann's theory. Interfacial energy effects on seismic wave velocity dispersion have been reported in many publications (Knight et al, ; Knight & Nolen‐Hoeksema, ; Moerig et al, ; Murphy, ; Murphy et al, ; Papageorgiou et al, ; Rozhko & Bauer, ; Vo‐Thanh, ; Waite et al, ; Wang et al, ; Wyllie et al, ); see Rozhko () for detailed literature review. The coupling is done by three extra parameters, which can be obtained from standard laboratory tests: pore‐size distribution and interfacial tension between immiscible fluids and rock wettability (advancing and receding contact angles).…”

Section: Introductionmentioning

confidence: 96%

See 1 more Smart Citation

Effective Fluid Bulk Modulus in the Partially Saturated Rock and the Amplitude Dispersion Effects

Rozhko

2020

JGR Solid Earth

Self Cite

View full text Add to dashboard Cite

Frequency dispersion is a well‐known effect in geophysics, which means that waves of different wavelengths propagate at different velocities. Amplitude dispersion is a less‐known effect, which means that waves of different amplitudes propagate at different velocities. Herewith, we consider the alteration of the interfacial energy during wave‐induced two‐phase fluid flow in a partially saturated rock and demonstrate that this leads to a nonlinear amplitude dispersion effect. When the wave amplitude is small, seismic waves cause bending of the interface menisci between immiscible fluids at the pore scale. However, when the wave amplitude is sufficiently large, the interface menisci will slip at the pore scale, causing attenuation of the elastic energy by the contact line friction mechanism. At the zero frequency limit, all viscous dissipation models predict zero attenuation of the elastic wave energy, while this approach predicts a nonzero attenuation due to a static contact angle hysteresis effect. Herein, we extend the Gassmann's theory with three extra terms, which can be obtained from standard laboratory tests: pore‐size distribution and interfacial tension between immiscible fluids and rock wettability (advancing and receding contact angles). We derive closed‐form analytical expressions predicting the effective fluid modulus in partially saturated rock, which falls between Voigt and Reuss averages. Next, we demonstrate that the nonlinear amplitude dispersion effect leads to energy transfer between different frequencies. This may explain the low‐frequency microtremor anomalies, frequently observed above hydrocarbon reservoirs, when the low‐frequency energy of ocean waves (0.1–1 Hz) is converted to higher frequencies (2–6 Hz) by partially saturated reservoirs.

show abstract

Section: Discussionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 96%

Effective Fluid Bulk Modulus in the Partially Saturated Rock and the Amplitude Dispersion Effects

Rozhko

2020

JGR Solid Earth

Self Cite

View full text Add to dashboard Cite

show abstract

“…Because the initial far‐field normal stress, the initial fluid pressure and initial contact angles are identical in two identical cracks, the initial saturation degree is also identical in two cracks. Rozhko (), Rozhko and Bauer () and Rozhko () derived equations, describing the initial equilibrium saturation and the capillary pressure of partially saturated crack. The capillary pressure inside the equilibrium crack is calculated as follows (Rozhko ):

\begin{matrix} true \\ right p_{normalcap} & = & left \frac{π}{4} ((), p_{c l} + σ_{n} + p_{we}) \\ left \times \frac{1 - \sqrt{1 - 8 p_{c l} \frac{γ \cos ((), θ)}{π b} \frac{(β + \cot (β) \ln [\cos (β)] - π / 2)}{{(p_{c l} + σ_{n} + p_{we})}^{2} \sin ((), β)}}}{β + \cot ((), β) \ln ([], \cos ((), β)) - π / 2}, \end{matrix}

where

p_{c l}

is the crack closure pressure, calculated as (Rozhko ):

p_{c l} = \frac{b μ}{a (1 - v)},

where μ and v are the Shear modulus and Poisson's ratio of the rock mineral.…”

Section: Mathematical Formulationmentioning

confidence: 99%

“…Although the volume of the wetting fluid phase inside the partially saturated crack

(V_{we})

is calculated as (Rozhko and Bauer ; Rozhko ):

V_{we} = {\overset{V}{true}}_{we} + δ V_{we}

where

\begin{matrix} true \\ right \frac{{\tilde{V}}_{we}}{π a b} & = & left (1 + \frac{σ_{n} + p_{we} + p_{normalcap} (1 + \frac{4}{π} [\frac{β \sin ((), 2 β) - β^{2} + 2 \cos^{2} ((), β) \ln ([], \cos ((), β))}{2 β - \sin ((), 2 β)}])}{p_{c l}}) \\ left \times \frac{(2 β - \sin (2 β))}{π} . \end{matrix}

And

\begin{matrix} true \\ right \frac{δ V_{we}}{b^{2}} & = & left - \frac{(π - 2 θ - \sin (2 θ))}{\cos^{2} ((), θ)} \sin^{2} ((), β) \\ left \times {(1 + \frac{σ_{n} + p_{we} + (\frac{π - 2 β - 2 \cot ((), β) \ln ([], \cos ((), β))}{π}) p_{normalcap}}{p_{c l}})}^{2} . \end{matrix}

…”

Section: Mathematical Formulationmentioning

confidence: 99%

See 1 more Smart Citation

Effects of pore fluids on quasi‐static shear modulus caused by pore‐scale interfacial phenomena

Rozhko

2019

Geophysical Prospecting

Self Cite

View full text Add to dashboard Cite

It is evident from the laboratory experiments that shear moduli of different porous isotropic rocks may show softening behaviour upon saturation. The shear softening means that the shear modulus of dry samples is higher than of saturated samples. Shear softening was observed both at low (seismic) frequencies and high (ultrasonic) frequencies. Shear softening is stronger at seismic frequencies than at ultrasonic frequencies, where the softening is compensated by hardening due to unrelaxed squirt flow. It contradicts to Gassmann's theory suggesting that the relaxed shear modulus of isotropic rock should not depend upon fluid saturation, provided that no chemical reaction between the solid frame and the pore fluid. Several researchers demonstrated that the shear softening effect is reversible during re‐saturation of rock samples, suggesting no permanent chemical reaction between the solid frame and the pore fluid. Therefore, it is extremely difficult to explain this fluid–rock interaction mechanism theoretically, because it does not contradict to the assumptions of Gassmann's theory, but contradicts to its conclusions. We argue that the observed shear softening of partially saturated rocks by different pore fluids is related to pore‐scale interfacial phenomena effects, typically neglected by the rock physics models. These interface phenomena effects are dependent on surface tension between immiscible fluids, rock wettability, aperture distribution of microcracks, compressibility of microcracks, porosity of microcracks, elastic properties of rock mineral, fluid saturation, effective stress and wave amplitude. Derived equations allow to estimate effects of pore fluids and saturation on the shear modulus and mechanical strength of rocks.

show abstract

Stimulating relative permeability changes by low-frequency elastic waves: Theory and lab experiments

Rozhko

Lozovyi

Naumann

et al. 2022

Journal of Petroleum Science and Engineering

View full text Add to dashboard Cite

Bulk moduli and seismic attenuation in partially saturated rocks: hysteresis of liquid bridges effect

Cited by 10 publications

References 62 publications

Effective Fluid Bulk Modulus in the Partially Saturated Rock and the Amplitude Dispersion Effects

Effective Fluid Bulk Modulus in the Partially Saturated Rock and the Amplitude Dispersion Effects

Effects of pore fluids on quasi‐static shear modulus caused by pore‐scale interfacial phenomena

Stimulating relative permeability changes by low-frequency elastic waves: Theory and lab experiments

Contact Info

Product

Resources

About