Integrated interpretation with Gassmann fluid substitution for optimum field development of Sanghar area, Pakistan: a case study

The optimum field development of area under exploration for hydrocarbons requires an integrated analysis of seismic and well log data. Fluid substitution is a process which provides a tool for fluid identification and quantification in a reservoir during the development phase. In the present study, an integrated approach of seismic, petrophysics, and Gassmann fluid substitution has been applied on Goru sands of Sanghar area, Pakistan, for optimum field development. The results of seismic indicate probable prospect zones of hydrocarbons in eastern and western part of the study area. These prospect zones have vertical closures of 20 to 50 ms and 20 to 30 ms at Goru sands and Chiltan levels, respectively. Four hydrocarbon-bearing zones (zones 1, 2, 3, and 4 with thicknesses of 28, 9, 24, and 8 m respectively) were identified on the basis of petrophysical interpretation of well log data at Goru sand level. Fluid substitution results at Goru sand level show maximum variation of P-wave velocity and density when hydrocarbon phase was substituted completely with water. This represents the maximum change in the acoustic impedance after complete extraction of hydrocarbon phase which can be modeled using synthetic seismograms.