Abstract:
Sawan gas field area is located near the Khairpur district, Sindh, Pakistan. This
gas field is discovered in 1998 and have a very high gas potential. Lower Goru
Formation is the possible reservoir in Sawan gas field and in other associated gas fields.
It is studied by the aid of available wireline logs data. Lower Goru formation lies in the
Central Indus Basin, Pakistan and divided in different sand units on the basis of their
variegated behavior. Lithology of Lower Goru Formation includes majorly sand
deposits with interbedded shaley content while calcareous deposits are rarely found.
Hydrocarbon productive reservoir is the C-sand unit of Lower Goru Formation in
Sawan gas field and encountered at the depth of 3272 m to 3397 m. Here the possible
petroleum source rock is Sembar Formation and seal is Upper Goru Formation and form
a good trapping mechanism. Petrophysical evaluation is done on the C-sand reservoir
at Sawan field and estimated the volume of shale, effective porosity and water
saturation to elaborate net pay thickness of the reservoir rock. Net pay thickness
averages from 27.1 m to 35 m. Gamma ray logs are used for depositional facies analysis
of the reservoir unit and marks the progradational and retrogradational phenomena of
deposition while environment of deposition varies from deep marine to shallow marine.
Startigraphic correlation shows a northeast to southwest trend and the formation is
thinning towards north direction. Structural correlation reveals that the formation has a
northeast dipping trend. Isopach maps indicate a change in thickness from northeast to
southwest. Increase and decrease in thickness character indicates a change in
depositional environment from shallow to deep marine.