COMPARISON OF SEISMIC INVERSION TECHNIQUES, MEHAR BLOCK, LOWER INDUS BASIN, PAKISTAN

Abstract

Mehar is present along the eastern front of Kirthar Fold belt, in the lower part of the Central Indus Basin, onshore Pakistan. Mehar is one of various gas producing from Late Paleocene and Cretaceous clastic reservoirs in Lower Indus Basin, Pakistan. Seismic data available for Maher Block shows the presence of a large anticline in the subsurface of Mehar block which is bounded by a large reverse fault in the East. In west, all the reflectors are highly dipping. A large north-south trending reverse fault disturbed the strata from Eocene age to the basement rocks in this area. This reverse fault may be generated due to the disturbance caused at the end or after Eocene time. Petrophysical analysis is done for Mehar-02 well to estimate the hydrocarbon saturation of potential zones for Pab Sandstone. Only two small potential zones were marked within Pab Sandstone and Ranikot formation having hydrocarbon saturation around 70% and porosity ranging in between 6-7%. Seismic inversion analysis was done over the 3D seismic cube of Mehar Block. Model based inversion makes the very model having 99% correlation and only 0.08% error. The colored inversion analysis shows the correlation of 80% over the provided seismic data of Maher Block. The correlation for sparse-spike inversion was also 99% which is very good. Colored inversion shows the change in lithology down the strata and shows the low to moderate values for both Pab and Ranikot Formations. Similarly, sparse spike inversion is also done and shows the change in lithology at every interaction of two different Formations. All these inversion techniques help to generate and analyze the impedance model for Maher Block where the model-based inversion and sparse-spike inversion shows the best results. Inversion methods help to identify the low to moderate character of the Pab Sandstone and Ranikot Formation.