A method is presented that integrates a triple porosity model with sonic, density and resistivity logs for evaluation of tight gas formations. The interpretation takes into account results from petrographic work in the Western Canada Sedimentary Basin (WCSB), which indicate that tight rocks are comprised of different pores types including (i) intergranular, (ii) slot + microfractures, and (iii) isolated non-effective porosities.
Seismic data are powerful in the exploration and production domains but a method that integrates seismic velocities and the observed triple porosity petrographic characteristics of tight gas formations is not available. This work provides the theoretical foundation and development of equations for this integration along with examples using real data from tight gas formations in the WCSB.
As part of integration of seismic data and well log formation evaluation, a previously developed methodology is used for calculating a fracture index from conventional well logs. The well log attribute computations are carried out on those wells that have a minimum amount of conventional logs such as caliper, gamma ray, density, neutron, deep and shallow resistivity, micro-resistivity, compressional (P) and shear (S) sonic, and photoelectric potential (PEF) logs.
Finally, a post stack seismic inversion is applied on the 2D and 3D seismic data in order to obtain quantitative rock-property description of the reservoir including density and porosity. This inversion has the potential of estimating inter-well formation resistivity, porosity and water saturation to obtain estimates of original gas in place. Under favorable conditions, the partition between effective and non-effective porosity might be estimated.