bruges

Bruges: reflection and rock physics

Use Bruges for interface reflectivity, elastic properties, fluid substitution, and analytic wavelets. Use a wave-equation solver for propagation modelling; use a log reader for LAS input. Companion skills are optional.

Inputs and conventions

• Convert velocity to m/s, density to kg/m³, and moduli to Pa for the examples below. Divide Pa by 1e9 only when reporting GPa.
• Reflection functions take incidence angles in degrees. Supply finite layer properties; positive density and shear modulus alone are insufficient: an isotropic solid also needs vp**2 > (4/3) * vs**2 for positive bulk modulus.
• Keep missing log intervals marked. Do not turn NaNs into zero-valued rock properties or convolve through missing intervals as if they were observed.
• A synthetic seismic trace requires regularly sampled two-way time. Convert and resample depth logs first, retaining the velocity/datum choices.

AVO at one interface

Runnable example with illustrative upper/lower properties:

import numpy as np
from bruges.reflection import zoeppritz, shuey, akirichards

vp1, vs1, rho1 = 3000.0, 1700.0, 2300.0  # m/s, m/s, kg/m³
vp2, vs2, rho2 = 3200.0, 1800.0, 2350.0
theta_deg = np.arange(0.0, 31.0)
r_exact = zoeppritz(vp1, vs1, rho1, vp2, vs2, rho2, theta_deg)
r_shuey = shuey(vp1, vs1, rho1, vp2, vs2, rho2, theta_deg)
r_aki = akirichards(vp1, vs1, rho1, vp2, vs2, rho2, theta_deg)
intercept, gradient = shuey(vp1, vs1, rho1, vp2, vs2, rho2,
                            return_gradient=True)

return_gradient belongs to shuey, not akirichards; it returns the intercept/gradient pair, not reflectivity plus gradient. Shuey's intercept is an approximation to the exact normal-incidence impedance contrast. Verify the exact result against (rho2*vp2 - rho1*vp1) / (rho2*vp2 + rho1*vp1).

At or beyond critical angles, Zoeppritz responses can be complex. Retain their phase or explicitly define the amplitude being plotted. An approximate angle limit alone does not establish accuracy for every elastic contrast. Interpret AVO classes using polarity convention, angle coverage and lithology; an intercept/gradient sign pair is not a unique fluid diagnosis.