Tight sandstone reservoir quality in the Lower Cretaceous Quantou Formation, Songliao Basin, NE China: Prospects from differential diagenesis and hydrocarbon-water-rock interactions

Tight sandstones constitute important oil and gas reservoirs worldwide. However, tight sandstone reservoirs generally exhibit varying porosities and permeabilities due to the occurrence of differential diagenesis combined with nonhomogeneous distributions of sedimentary facies. To evaluate the influences of sedimentary facies, diagenesis and hydrocarbon-water-rock interactions on the quality of tight sandstone reservoirs in this research, the Lower Cretaceous Quantou Formation, northern Songliao Basin, China, was studied via core and thin section observation, scanning electron microscopy (SEM), X-ray diffraction (XRD), cathodoluminescence, fluid inclusion, electron probe microanalysis, and stable carbon and oxygen isotope analysis methods. The results demonstrated that the sandstones occurring in underwater distributary channels in the terrace region constituted high-quality reservoirs, whereas the sandstone reservoirs located in the sag region were distributed primarily within distributary channels. The sandstones in the terrace and sag regions experienced differential diagenesis. Affected by hydrocarbon charging and the initial mineral compositions of the reservoir rocks, the calcite and pyrite cements exhibited different characteristics. The sandstones in the terrace developed mainly Mn-rich (average = 3.40 wt%) calcites with negative δ 13 C values (−19.9‰ to −4.1‰) and framboidal pyrites, whereas the sandstones in the sag developed Mn-poor (average = 0.95 wt%) calcites with even more negative δ 13 C values (−32.9‰ to −12.2‰) and euhedral pyrite cements. These phenomena indicate the possible occurrence of hydrocarbon oxidation, organic matter decarboxylation, and sulfate reduction during diagenesis in the reservoir. However, hydrocarbon charging also led to the extensive dissolution of feldspar minerals, especially K-feldspars, thereby generating secondary pores to improve the reservoir quality. This study highlights that sedimentary facies and differential compaction determine the quality of tight sandstone reservoirs and that hydrocarbon-water-rock interactions locally improve reservoir quality. • A set of shallow-water delta tight sandstone reservoirs in China was studied. • The sandstone strata exhibit differential diagenetic features. • The reservoir rocks underwent complex hydrocarbon-water-rock interactions. • Controlling factors of the tight sandstone reservoir quality were clarified.