Multiscale Analysis of Depositional Architecture and Diagenetic Evolution in the Cretaceous Shoreface‐to‐Shelf Sandstones, Lower Indus Basin, Pakistan

Abstract

ABSTRACT Understanding reservoir heterogeneity in siliciclastic systems requires integrated analysis across multiple scales. This study investigates the Early Cretaceous Lower Goru Formation in the Lower Indus Basin using a multiscale integrated approach that combines seismic stratigraphy with pore‐scale characterisation to constrain depositional environments, sequence architecture, pore system, mineralogy and diagenetic evolution. This study provides the first integrated framework linking seismic‐scale stratigraphy to pore‐scale diagenesis in the Lower Goru Formation, enhancing reservoir quality prediction in mature exploration settings. An integrated workflow of core description, petrophysical analysis, petrography, SEM, and 2D seismic data is employed to delineate stratigraphic architecture and depositional trends. Reservoir heterogeneity is assessed through an evaluation of depositional and diagenetic controls, while machine learning‐based classification enhances facies prediction and strengthens interpretive reliability. Based on core analysis, four facies associations were identified within the reservoir succession, including shoreface, mouth bar, and shelf delta lobe facies associations. The Lower Goru Formation comprises one second‐order sequence and nine third‐order sequences within the studied reservoir interval. Petrographic analysis reveals that the sandstones are fine to medium grained and moderate to well‐sorted reflecting a relatively uniform grain size distribution. Their mineralogical composition is diverse comprising litharenite, feldspathic arenite and quartz arenite. SEM observations reveal a complex pore system comprising primary intergranular macroporosity, secondary intragranular macropores, and intercrystalline micropores, which collectively exert a strong influence on reservoir storage capacity. Diagenesis led to the formation of chamosite and ooids that developed chlorite coatings which inhibited extensive quartz overgrowths while subsequent matrix recrystallisation produced microporous chlorite that further influenced reservoir properties. These integrated findings provide critical insights into the sequence stratigraphy and facies distribution of the Cretaceous sedimentary system and offer valuable guidance for hydrocarbon exploration in the Indus Basin.