Seismic attributes and instantaneous spectral analysis-based temperature-porosity simulations: An example of imaging shale gas-bearing basin floor fans of early-cCretaceous delta sequences, Southeast Asian Basin

Abstract

Basin floor fans (BFF) of deltaic depositional systems are important stratigraphic traps, which are sourced by the regionally developed meandering channel belts and associated deposits of point bar facies. The vertical and lateral changes in the tectonics and sea level adversely affect the temperature (θ) and porosity constraints of petroleum plays within BFF of the lowstand system tracts. These fluctuations impact the sedimentary controls on thickness, lithology-impedance contrast, phase, and frequency of BFF. As a result of the reliance on full-spectrum seismics, quantifying thin-bedded stratigraphic wet gas-bearing intervals (WGI) and light oil-bearing intervals of petroleum systems becomes extremely difficult. This study utilizes seismic attributes and instantaneous spectral analysis-based temperature-porosity reservoir simulations (TPRS) to quantify the BFF of the Early-Cretaceous delta of the Miano gas field, Central Pakistan. The 47-Hz peak-tuned frequency component of spectral decomposition [SpecDecomp] images a 154 km2 NEE-SWW traversed and regionally developed stratigraphic prospect. Linear regression of R2 > 0.80 between spectral decomposition-based tuning frequency of 47-Hz and gross reservoir thickness of BFF validates the presence of gas-bearing shales. The 47-Hz wavelet-based TPRS has resolved the phase reversals and seismic-doublet signatures for thin-bedded shale PETROS at θ of 170°F to 200°F and porosities of 22 % to 32 % of WGI within BFF. TPRS at 47-Hz SpecDecomp profile between the frequency bandwidth spectrums of 12–62-Hz has reappraised the exact morphology of the continental shelf, shelf-slope, and BFF. A 21 m thick aggradational parasequence of BFF was deposited at an angle of 2° during the onset of subsidence and rapid fall, followed by a subsequent standstill of sea-level at θ of 170 to 200°F, ∼26 to 35 % porosities, and laterally fractured subsidized regimes of WGI.. A 20 m thick retrogradational fluvial-dominated facies was deposited at an angle of 35° during a rising followed by a standstill of sea level at a θ of 140 to 165°F, ∼08 % to 18 % porosity, and poorly fractured uplifted compressional regimes of light oil-bearing intervals. The aggradational WGI of Lowstand System Tracts was completely embedded by retrogradational shales of transgressed system tracts from the top of the aggradational and laterally. The uncertainty analysis has prevailed with a moderate-to-good R2 > 0.75 for BFF and a very poor R2 < 0.1 for fluvial-dominated point bar traps. Our workflow has implications in terms of exploring the tectonics and stratigraphic frameworks within the petroleum systems for imaging the most productive zones in a single snapshot of 47-Hz tuning frequency.