POROSITY DISTRIBUTION AND DIFFERENTIATION OF DIFFERENT TYPES OF FLUIDS IN RESERVOIR OF NANDPUR FIELD, CENTRAL INDUS BASIN, PAKISTAN

Abstract

The objectives of this research were porosity distribution and differentiation of different types of fluids in reservoirs. From well log data of Nandpur-02, potential reservoir formations were identified. The formations of interest were Ranikot Formation, Lumshiwal Formation, and Samana Suk Formation. These target formations were then identified and marked on the 2D seismic data of Nandpur area through synthetic seismogram of Nandpur-02 for delineation of subsurface structure. There was a normal fault disturbing the area and is trending north-east to south-west and strata is dipping towards north-west. Petrophysical analysis was performed on the target formations to identify their reservoir properties. The hydrocarbon saturation was about 57 % in Nandpur-02 well for Lumshiwal Formation also having the porosity 9.6 %. Then seismic inversion was performed, which develops a linkage between the seismic data and the interpreted reservoir properties from well logs. Post-stack seismic inversion (model-based inversion) was used to estimate reservoir characteristics from seismic data such as acoustic impedance. The reservoir parameters, as well as fundamental variables such as impedance of the target Formations, were delineated using post-stack seismic data and well log data of the study area. Inversion model showed low to moderate impedance values for Lumshiwal and Ranikot Formations. The rock physics develops a relationship between the elastic properties from seismic data (impedance) and the elastic properties calculated from well logs such as vp\vs ratio. These elastic properties were then calculated and plotted using the Gassmann equation. Cross plots of vp\vs ratio vs impedance, impedance vs porosity and vp\vs vs porosity were made for the differentiation of fluid types in the reservoir zones. All these cross-plots shows the presence of gas at certain reservoir level by showing low velocity and impedance values along with good porosity. Results showed that Lumshiwal Formation in Nandpur area has significant reservoir characteristics.