Print this pageApplication of Stratigraphic Simulation to AVO Analysis
BOWMAN, SCOTT A
Analysis of AVO anomalies in seismic data is a valuable tool for locating gas reservoirs. However, to establish the importance of the anomalies, it is necessary to calibrate to known data or make an educated estimate of rock properties in the seismic profile. Stratigraphic simulation provides a technology for predicting the lithofacies and the presence of hydrocarbons from a limited dataset. Required input includes two-way travel time horizon data from workstation interpretations, horizon ages and depths from well logs and check shot surveys, and estimated paleobathymetric profiles for each horizon. This information is automatically "inverted" by adjusting the depositional and tectonic process inputs, to determine a best-fit model for the given observations.
Predicted rock properties including density, porosity, fluid type, pressure,
and temperature are used to describe the physical state in a synthetic seismic
profile that calculates the response of both the P- and S-waves. A distribution
of Vp and Vs can be calculated from the stratigraphic model using the
White-Boltzman equation. Values of the bulk modulus of the matrix and framework
material (which vary as a function of lithology, age, depth, and porosity), and
pore filling fluid are adapted to account for porosity-depth, and velocity
observations. Porosity is modeled as a function of depth or overburden stress.
Density is calculated as a function of mineral type and porosity. An
impedance/reflectivity model can be determined from the distribution of
velocities
. The fluid content, as calculated by the fluid-flow model, can also
determine the interval
velocity.