Seismic attributes and spectral decomposition-based inverted porosity-constrained simulations for appraisal of shallow-marine lower-Cretaceous sequences of Miano gas field, Southern Pakistan.

Seismic attributes can play an important role in the exploration of hydrocarbon-bearing stratigraphic systems. Incised valley systems are developed during the falling sea, which causes the deposition of coarse-grained sandstone facies inside the low-standing tracts (LST). These regional phenomena constrain the quantitative attributes of ultra-thin-bedded stratigraphic petroleum traps, e.g., vertical and lateral variations in the thickness, accommodation space, lithology, and porosity. This study deals with the application of the continuous wavelet transform (CWT) of a spectral decomposition (SD) tool on a 3D post-stack seismic volume of the Miano gas Field, Lower Indus basin, Pakistan. The results show that the CWT accurately detected the regionally faulted/fractured system and distinguished the frequency-dependent amplitude anomalies. The wedge model resolved a 24-meter-thick gas-bearing resource. Quality control analysis was carried out using CWT-based broadband processing between the designed amplitude spectrum of 17 Hz and 70 Hz. The reservoirs with over 25% porosity that were located within the shale-dominated facies with less than 8% porosity were imaged through the processing of the instantaneous spectral porosity model at the 48-Hz tuning block. Moreover, 190 to 165-m-thick thin-bedded sandstone reservoirs at a 25% porosity zone were resolved using 22-Hz and 28-Hz, which implicates the sea standstill and medium-to-coarse-grained depositional reservoir facies. The ultra-thin-bedded traps inside the laterally continuous stratigraphic lens of 121 m and the prograding clinoform lens of 101-m within the incised valley petroleum system were resolved using 48-Hz, which implicates the falling sea and fine-scaled transgressed erosional facies. These implications suggest that the identified regional stratigraphic traps have development potential for this gas field. The treatment of the inverted model at the highest frequencies can be utilized to investigate the porous stratigraphically trapped facies of LST and can serve as an important analogue for the leading gas field of the Indus Basin and similar basins.