Rockphysic Template RPT the practical workflow
Mohamed Shihata
A Consultant and International Instructor in Seismic QI and Seismic Attributes
What is the practical workflow of The ?degaard and Avseth RPT involves computing the VP/VS ratio and P-Impedance of various rock types based on their mineralogy, porosity, fluid type, pressure and grain contacts?
?This involves four steps:
???????Computing the moduli of the dry rock frame for a given porosity/pressure using the Hertz-Mindlin theory.
????????Computing the moduli of the dry rock frame over a range of porosities using the lower Hashin-Shtrikman bound.
????????Performing fluid substitution with the Gassmann equations.
????????Computing the density, P-wave velocity, S-wave velocity for each scenario and cross-plotting VP/VS ratio versus P-impedance
RPT workflow involves computing the VP/VS ratio and P-Impedance
What The Modified Gregory-Pickett Method is for estimated for a range of porosities?
The Gregory-Pickett method is a simpler method for the moduli,
???????????????????????????????????proposed by Hilterman (1983).
·?????????In this method, the dry rock bulk modulus is estimated at a known
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??????????????????????????????????????????????Porosity by assuming a dry rock Poisson’s ratio.
·????????Next, the pore space stiffness is computed from:
??????????????????????????????????????????????????????????????????????
Where K dry = dry rock bulk modulus, φ = porosity, K m = mineral bulk modulus and K φ = pore space stiffness.
From the pore space stiffness, the dry rock bulk modulus can be estimated for a range of porosities, and gives the correct value in the mineral case.
This method was modified by Russell (2013) to perform the same computation for the shear modulus.
Rock physics templates for unconsolidated sands (top) and cemented sandstone
(bottom). Data from the same basin and same stratigraphic level, but with different burial depths are superimposed on the templates. The fluid effects are completely different in the two different situations because the deeper sands have been cemented, unlike the shallower sands. (Color codes:blue = shale, green = shaly sand, cyan = brine sand, red = oil sand, yellow = gas sand.) after Avthes 2007
Acoustic impedance (AI) and VP/VS logs (left) and VP/VS vs. AI cross-plot (right). The logs are color-coded based on the populations defined in the cross-plot domain, and the cross-plot points arecolor-coded using the gamma-ray log (not shown). The interpretation is based on all available log data.
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