Publications

A deterministic seismic inversion study was done in 2011 on the Sisi-Nubi fields, the results of which were used for 3D reservoir modeling and for guiding the location of gas development wells targeting the observed channel features. Unfortunately, this deterministic seismic inversion did not have the resolution needed to map thin sand objects, representing considerable stakes in these fields. To remedy this apparent lack of resolution a geostatistical seismic inversion based on a Bayesian framework was performed on the 3D 2011 PSDM processing. The goal of the geostatistical inversion was to invert the seismic angle stacks data into P-impedance and Poisson’s ratio volumes with a considerably better vertical resolution which could help thin sand objects interpretation, and to get a more quantitative assessment of the uncertainties on the inverted data . The geostatistical inversion uses a fine layered stratigraphic grid framework and combines the seismic data, well log data and the geological knowledge over the field to produce fine scale inversion results that honors each input data to a certain user defined limit. Sand probability cubes were generated from the Impedance and Poisson’s Ratio cubes after classification of all the realizations and will be used for mapping the sand objects. The result of the geostatistical seismic inversion has largely improved the vertical resolution of the seismic. Some thin sand objects not visible before in the deterministic seismic inversion result could be mapped with the geostatistical inversion. Some limitations on the results were noticed. The high vertical resolution observed around the wells tends to disappear beyond a certain distance away from the wells and becomes more or less similar to the deterministic inversion resolution. In addition, it seems that the geostatistical inversion smears the sand of some previously identified channels outside the interpreted limits. These limitations seem to be linked to the horizontal variogram used for the inversion. This particular parameter has to be carefully set up.