bruges.rockphysics.fluidsub module

copyright:2015 Agile Geoscience
license:Apache 2.0

fluidsub.py

Calculates various parameters for fluid substitution from Vp, Vs, and rho

Matt Hall, Evan Bianco, July 2014

Using http://www.subsurfwiki.org/wiki/Gassmann_equation

The algorithm is from Avseth et al (2006), per the wiki page.

Informed by Smith et al, Geophysics 68(2), 2003.

At some point we should do Biot too, per Russell… http://cseg.ca/symposium/archives/2012/presentations/Biot_Gassmann_and_me.pdf

bruges.rockphysics.fluidsub.avseth_fluidsub(vp, vs, rho, phi, rhof1, rhof2, kmin, kf1, kf2)[source]

Naive fluid substitution from Avseth et al, section 1.3.1. Bulk modulus of fluid 1 and fluid 2 are already known, and the bulk modulus of the dry frame, Kmin, is known. Use SI units.

Parameters:
  • vp (float) – P-wave velocity
  • vs (float) – S-wave velocity
  • rho (float) – bulk density
  • phi (float) – porosity (volume fraction, e.g. 0.20)
  • rhof1 (float) – bulk density of original fluid (base case)
  • rhof2 (float) – bulk density of substitute fluid (subbed case)
  • kmin (float) – bulk modulus of solid mineral (s)
  • kf1 (float) – bulk modulus of original fluid
  • kf2 (float) – bulk modulus of substitute fluid
Returns:

Vp, Vs, and rho for the substituted case

Return type:

Tuple

bruges.rockphysics.fluidsub.avseth_gassmann(ksat1, kf1, kf2, k0, phi)[source]

Applies the inverse Gassmann’s equation to calculate the rock bulk modulus saturated with fluid with bulk modulus. Requires as inputs the insitu fluid bulk modulus, the insitu saturated rock bulk modulus, the mineral matrix bulk modulus and the porosity.

Parameters:
  • ksat1 (float) – initial saturated rock bulk modulus.
  • kf1 (float) – initial fluid bulk modulus.
  • kf2 (float) – final fluid bulk modulus.
  • k0 (float) – mineral bulk modulus.
  • phi (float) – porosity.
Returns:

final saturated rock bulk modulus.

Return type:

ksat2 (float)

bruges.rockphysics.fluidsub.rhogas(gravity, temp, pressure)[source]

From http://www.spgindia.org/geohorizon/jan_2006/dhananjay_paper.pdf

bruges.rockphysics.fluidsub.rhosat(phi, sw, rhomin, rhow, rhohc)[source]

Density of partially saturated rock.

bruges.rockphysics.fluidsub.smith_fluidsub(vp, vs, rho, phi, rhow, rhohc, sw, swnew, kw, khc, kclay, kqtz, vclay, rhownew=None, rhohcnew=None, kwnew=None, khcnew=None)[source]

Naive fluid substitution from Smith et al. 2003. No pressure/temperature correction. Only works for SI units right now.

Parameters:
  • vp (float) – P-wave velocity
  • vs (float) – S-wave velocity
  • rho (float) – bulk density
  • phi (float) – porosity (v/v, fraction)
  • rhow (float) – density of water
  • rhohc (float) – density of HC
  • sw (float) – water saturation in base case
  • swnew (float) – water saturation in subbed case
  • kw (float) – bulk modulus of water
  • khc (float) – bulk modulus of hydrocarbon
  • kclay (float) – bulk modulus of clay
  • kqtz (float) – bulk modulus of quartz
  • vclay (float) – Vclay, v/v
  • rhownew (float) – density of water in subbed case (optional)
  • rhohcnew (float) – density of HC in subbed case (optional)
  • kwnew (float) – bulk modulus of water in subbed case (optional)
  • khcnew (float) – bulk modulus of hydrocarbon in subbed case (optional)
Returns:

Vp, Vs, and rho for the substituted case.

Return type:

Tuple

bruges.rockphysics.fluidsub.smith_gassmann(kdry, k0, kf, phi)[source]

Applies the direct Gassmann’s equation to calculate the saturated rock bulk modulus from porosity and the dry-rock, mineral and fluid bulk moduli.

Parameters:
  • kdry (float) – dry-rock bulk modulus.
  • k0 (float) – mineral bulk modulus.
  • kf (float) – fluid bulk modulus.
  • phi (float) – Porosity.
Returns:

saturated rock bulk modulus.

Return type:

ksat (float)

bruges.rockphysics.fluidsub.vels(Kdry, Gdry, K0, D0, Kf, Df, phi)[source]

Calculate velocities and densities of saturated rock via Gassmann equation. Provide all quantities in SI units.

Parameters:
  • Gdry (Kdry,) – Dry rock bulk & shear modulus in Pa.
  • G0 (K0,) – Mineral bulk & shear modulus in Pa.
  • Df (Kf,) – Fluid bulk modulus in Pa and density in kg/m^3.
  • phi (float or array_like) – Porosity, v/v.
Returns:

  • vp, vs (float or array_like) – Saturated rock P- and S-wave velocities in m/s.
  • rho (float or array_like) – Saturated rock density in kg/m^3.
  • K (float or array_like) – Saturated rock bulk modulus in Pa.

bruges.rockphysics.fluidsub.vrh(kclay, kqtz, vclay)[source]

Voigt-Reuss-Hill average to find Kmatrix from clay and qtz components. Works for any two components, they don’t have to be clay and quartz.

From Smith et al, Geophysics 68(2), 2003.

Parameters:
  • kclay (float) – K_clay.
  • kqtz (float) – K_quartz.
  • vclay (float) – V_clay.
Returns:

Kvrh, also known as Kmatrix.