AVD Technology

EAP pioneered the use of seismic anisotropy for characterization of natural fractured reservoirs. Since Phase 5, we have extended the expertise to go beyond what the conventional anisotropy concept for fracture imaging can offer by developing innovative methods to evaluate the dominant scale length from 3D VSP, 3D surface and 3D 4C-OBC seismic data.

AVD effect from Fracture model time interval varied with direction
Amplitude vs.azimuth and offset

The theories and methods allow the seismic response across a broad band of seismic frequencies to be computed, making it possible to observe and analyse the directional spectral/dispersion/attenuation variation and frequency-dependent anisotropy in seismic data and then to invert these variations for the properties of the fracture distribution. This will require advanced techniques for extracting spectral/dispersion and attenuation characteristics from seismic data using, for example, multi-instantaneous attribute analysis and modern spectral decomposition techniques.

Frequency dependent anisotropy Spectra of S1 wave Spectra of S2 wave

During Phase 7, a technique for inversion of fracture properties has been developed from azimuthal AVO analysis. The method is based on the decomposition and reconstructin of the amplitude changes with azimuth in terms of principal components, which are calculated via singualr value decomposition(SVD).

Inversion of fracture density using azimuthal AVO

In phase 8, advanced numerical methods (DFM, RTM, FWI) was also studied to simulate wave propagation in media with discrete fracture systems using the discrete dynamic rock physics model, which allows us to develop inversion techniques to obtain information about discrete formation or meso-scale fractures.

Numerical modelling using DFM
 
Fracture induced anisotropy

Areas of interest and deliverables:

o Characteristics of directional dispersion/spectral/attenuation variations in P- and converted-wave data and their applications for determining fracture properties such as the dominant scale length, and fluid saturation;

o Generation of realistic fracture networks and patterns at the meso-scale for seismic modelling, and computation of 3D synthetic VSP and reflection dataset using realistic reservoir models with discrete fracture distributions;

o Analysis and inversion procedure to quantify fracture size and fracture porosity (storability) from 3D VSP, 3D surface and 3D-4C OBC data including both synthetic and real data;

o Multi-Attribute Analysis, including coherency analysis, multi-component instantaneous polarization analysis, and spectral decomposition of seismic data to reveal anomalies that are related subsurface fracture distributions;

o Comprehensive software packages for fracture modelling and seismic imaging including enhanced 3D modelling capability to simulate seismic wave propagation in fractured media and software to extract information on fracture properties (size/storability, density, orientations, and fluid properties).

Datasets available:

o Emilio 3D 4C seismic dataset

o The Clair field OBC data and associated VSPs

o Physical modeling 3D datasets (CNPC Key Labs)

o Wind River 3D surface data.