Seismic Inversion Techniques as Aids in Basin Modeling

R. Jonk and R. Saltzer
ExxonMobil Upstream Research Company, P.O Box 2189, Houston TX 77008

The challenge for generating a basin model is the estimation of rock properties at a regional scale for the full range of lithologies. To date, the application of seismic data obtained through 2D and 3D surveys are the primary means for developing the spatial and temporal distribution of rock properties required for modeling thermal and pressure evolution of basins. Firstly, mapping of seismic reflections and establishment of age-control provide a framework for the stratigraphic and structural evolution of a basin, seismic facies of intervals provides a first-order approximation of the bulk rock properties (e.g. sand-prone versus shale-prone intervals). Secondly, seismic surveys provide spatial coverage of basins at resolutions appropriate for basin modeling applications that cannot be obtained by other means.

There are however, gaps in the conventional use of seismic data to populate model properties. Detailed mapping of seismic reflections and inferred environments of deposition from seismic facies is itself complex and as a result seismic interpreters generally restrict such detailed efforts to reservoir-prone intervals where well-penetrations aid in increasing confidence in the interpretation. Away from reservoir-prone intervals, detailed interpretation in fine-grained strata is often lacking and confidence diminishes due to fewer well-penetrations and the non-unique character of seismic facies. To further add to the difficulty, the fluid flow properties of shales and mudstones are more poorly understood than their coarser-grained counterparts, and it is the distribution and properties of these that largely control the thermal and pressure evolution and petroleum accumulation in the subsurface.

We propose that inversion of seismic data (angle stacks) provides a relatively rapid method for generating basin-scale volumes of relevant rock properties such as clay content and porosity. This presentation will review the rock physics relationships between these properties and the elastic (seismic) parameters focusing on the sedimentary rocks that are dominated by clay mineral grains (i.e. shales and mudstones).

In addition, rock property prediction methods that are suited for different data density and quality will be discussed. As a conclusion, the workflow of generating seismically-derived basin-scale volumes of flow properties (permeability and capillary entry pressure) from porosities and clay contents (calibrated to well log data and sample measurements) is explained. These are the parameters ultimately used as inputs in modeling a basin's thermal, pressure and fluid flow evolution.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands