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.

You do not currently have access to this article.