Structural and reservoir interpretation of cretaceous lower Goru Formation, Sanghar area, lower Indus Basin, Pakistan
Keywords:
Synthetic seismogram; Horst and graben; Saturated rocks; Reflection coefficient; Hydrophobic effect.Abstract
The present study incorporates structural and reservoir interpretation using seismic and well log data. The primary formation of focus is Lower Goru of Cretaceous age in Sanghar Block, Southern Pakistan. The area is characterized by extensional regime and normal faulting is indicated by time contour map which further represent closures towards center portion as we move from East to West (Hydrocarbon leads). Comparison of Geophysical parameters estimated from seismic and well log data indicates that the study area is less complex (as compared to collisional belt resulting in folding and faulting) with horizontal reflectors. Two wells (Fateh-01 and Panairi-01) are studied through well logs for identification of reservoir zone. The reservoir zone identified in both the well ranges from depth of 2700 m to 3100 m. An average value of volume of shale (43% and 28 %), Water saturation (73% and 60%) and hydrocarbon saturation (36% and 33%) were evaluated in Fateh-01 and Panairi-01 wells respectively. The average percentage of water saturation (63.45%) from both wells classifies these wells as water saturated. A strong correlation results in reflection coefficient values between seismic data and Fateh-01 (R=0.62) and Panairi-01 (R=0.43) wells. The absences of useful quantities of hydrocarbons are associated with “Hydrophobic Effect” caused due to excessive water. This effect might have prevented the hydrocarbons to penetrate in the rock at the time of migration and they have probably moved to other distant location which can later on be confirmed by presence of hydrocarbons in adjacent blocks.
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