Rock Physics Modeling Research Papers (original) (raw)

Shear velocity log is not measured at all wells in oil and gas fields, thus rock physics modeling plays an important role to predict this type of log. Therefore, seismic pre stack inversion is performed and elastic properties are estimated more accurately. Subsequently, a robust Petro-Elastic relationship arising from rock physics model leads to far more precise prediction of petrophysical properties. The more accurate rock physics modeling results in less uncertainty of reservoir modeling. Therefore, a valid rock physics model is intended to be built. For a better understanding of reservoir properties prediction, first of all rock physics modeling for each identified litho-facies classes should be performed separately through well log analysis.

- by Amir Abbas Babasafari
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- Rock Physics Modeling, Reservoir Geophysics

Partially saturated reservoirs are one of the major sources of seismic wave attenuation, modulus defect and velocity dispersion in real seismic data. The main attenuation and dispersion phenomenon is wave induced fluid flow due to the heterogeneity in pore fluids or porous rock. The identification of pore fluid type, saturation and distribution pattern within the pore space is of great significance as several seismic and petrophysical properties of porous rocks are largely affected by fluid type, saturation and fluid distribution pattern. Based on Gassmann-Wood and Gassmann-Hill rock physics models modulus defect, velocity dispersion and attenuation in Jurassic siliclastic partially-saturated rocks are studied. For this purpose two saturation patterns-uniform and patchy-are considered within the pore spaces in two frequency regimes i.e., lower frequency and higher frequency. The results reveal that at low enough frequency where saturation of liquid and gas is uniform, the seismic velocity and bulk modulus are lower than at higher frequency where saturation of fluid mixture is in the form of patches. The velocity dispersion and attenuation is also modeled at different levels of gas saturation. It is found that the maximum attenuation and velocity dispersion is at low gas saturation. Therefore, the dispersion and attenuation can provide a potential way to predict gas saturation and can be used as a property to differentiate low from high gas saturation. K e y w o r d s : fluid substitution; homogeneous and patchy saturation; wave induced fluid flow; velocity dispersion; modulus defect

- by Nisar Ahmed
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- Rock Physics Modeling, Seismic attenuation
- by Sonny Winardhi
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- Rock Physics Modeling

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.

- by Alexander Rozhko
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- Geophysics, Petrophysics, Seismology, Rock Physics Modeling

Rock physics model building and geological stochastic modeling as a route to increasing of the reliability of the seismic reservoir properties prediction of complex terrigenous deposits of Vendean age. Application of the methods proposed in this paper allowed to choose the optimal approach to the interpretation of seismic inversion results, as well as to estimate the uncertainty factors of the obtained model, related to the effect of complex geological and geophysical conditions in the area.

A simple rock model is presented which reproduces the measured hydraulic and electric transport properties of sedimentary rocks and connects these properties with each other, as well as with the acoustic propagation velocities and elastic moduli. The model has four geometric parameters (average coordination number Z of the pores, average pore radius r, average distance between nearest pores d, and average throat radius δ) which can be directly determined from the measured porosity Φ, hydraulic perme-ability k, and cementation exponent m of the rock via simple analytic expressions. Inversion examples are presented for published sandstone data, and for cores taken from Saudi Arabian, Upper Jurassic and Permian carbonate reservoirs. For sandstone, the inversion works perfectly; for carbonates, the derived rock model shows order-of-magnitude agreement with the structure seen in thin sections. Inverting the equations, we express the transfer properties Φ, k, and m as functions of r, d, δ, and Z. Formulae are derived for the bulk density D b , formation factor F, and P-wave velocity in terms of the proposed geometrical parameters.

- by Gabor Korvin
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- Rock Physics Modeling
- by Sonny Winardhi
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- Rock Physics Modeling

Petrophysical experiments on two Icelandic geothermal rock samples at simulated in situ reservoir conditions are analysed to delineate the effect of temperature on seismic velocity and attenuation. A goal of the present work is to predict the effect of the saturating pore fluid on seismic velocity using the Gassman equation, which has been modified for this purpose. To include the

- by David Bruhn
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- Geology, Geophysics, Geothermal, Rock Physics Modeling

With the conventional stacked P-wave seismic reflection data only, the interpretation is limited to the structure and P-wave impedance. However, with the AVO analysis, additional information such as S-wave velocity and impedance and elastic rock parameters are available, which can provide more detailed information for estimating lithology and fluid content. In this chapter, the generalized fluid method is applied to P-wave seismic data in the Blackfoot area to image the areal extent of porous sandstone within a Glauconitic incised valley system and also to discriminate the fluid content of the channel system. For real seismic data, not only the selection of c value but also the quality of AVO inversion of the seismic data will affect the result of the generalized fluid method. The estimation of the c value using well logs, and based on Gassmann fluid substitution theory, will be discussed in this chapter. Pre-stack inversion is performed to extract P-wave and S-wave impedance using the AVO and STRATA packages from Hampson-Russell Software. Finally, the fluid indicator Ip 2-c * Is 2 will be extracted to better understand the capability of this method to indicate the presence of hydrocarbons within the Glauconitic incised valley system. 6.2 Seismic and well data In 1995, a 3C-3D survey was acquired over the Blackfoot Field, located 20 km southeast of Strathmore, Alberta, as shown in Figure 6.1. This figure shows the paleogeography of the Lower Cretaceous, at the time the incised valley system was formed. The objectives of the survey were to 1) delineate a Glauconitic incised valley system, 2) distinguish