Abstract
The Sembar Shale formation in the Lower Indus Basin, Pakistan, is thought to contain significant potential for unconventional resources; however, no detailed study has been carried out yet to quantify its potential. In conventional oil and gas exploration, reservoir rocks have been the main focus; therefore, a limited number of wells target the Sembar Formation. To explore its regional view, the seismic characterization of these shales is required. Generally, a poor correlation is observed between the compressional wave (P-wave) impedance and the reservoir and geomechanical properties of rocks, making it challenging to characterize them using seismic data. We have developed a workflow for characterizing the seismic-derived unconventional prospect of the Sembar Shale using prestack seismic data along with well logs. The logging results of the two wells show that the organic matter richness of well A has high to very high values, whereas well B has low to very low values. Considering the mineral composition and brittleness index evaluation, the Sembar Shale in well A is brittle to less brittle in nature. The organic content, porosity, and brittleness index result in well A make the Lower Cretaceous Sembar Formation favorable to be considered as a potential organic shale reservoir. Four sensitive attributes, derived through integration of the rock petrophysical, geochemical, and geomechanical parameters, are correlated with the P-wave impedance. The correlation of each sensitive attribute has been applied to characterize the Sembar Shale potential. These attributes are first-order indicators to depict organic matter, porosity, and geomechanical properties. This attribute approach is further validated through rock-physics modeling. The workflow presented in this study can be used to assess the unconventional reservoir potential of the Sembar Formation in other parts of the basin.
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