Orderly variations in the spatial and geological characteristics of carbonate reservoirs in the northern Tarim Basin, China

Deep marine carbonate rocks in the Tarim Basin, Northwest China, have significant burial depths, ancient ages, and complex diagenetic evolution. Multi-stage tectonic activities and periodic sea-level changes create unconformities that expose carbonate rocks, resulting in interlayer, syn-sedimentary, and epigenetic karst systems. These processes, along with host rock composition and faulting, shape carbonate reservoir distribution and properties. Dissolution is most intense in shallow water grainstones and packstones, where fracturing enhances fluid flow, serving as both reservoirs and migration pathways. Consequently, carbonate reservoir characteristics in the northern Tarim Basin vary systematically from north to south, shaped by variations in unconformity size, diagenetic patterns and fault activity intensity, reflecting the basin’s evolution from deposition to deep burial. In the Yakela area, the northernmost region, significant uplift and erosion have exposed Cambrian, sometimes even Sinian bedrocks beneath Cretaceous layers, forming buried hill dolomite reservoirs. Moving south to the Tahe area, a paleokarstic erosion zone has developed large-scale dissolved fracture-cavity reservoirs due to the combined effects of faulting, surface karstification, and river system development near the base Carboniferous erosion surface. Further south, in the Tahe slope zone, reservoirs are shaped by a combination of dissolution and faulting, with bedding-parallel dissolution pores and enlarged fractures becoming more prominent as proximity to the paleoerosion surface decreases. This reflects a decrease in karstification intensity and an increase in fault-induced fluid pathways. In the Shunbei area where marine carbonates are deeply buried, structural features such as fault slip surfaces and open fractures dominate reservoir formation, with tectonic activity and fluid flow through fractures driving diagenetic alterations. The spatial variations in diagenetic pathways—from initial deposition and uplift in the north to deep burial in the south—highlight the interplay of dissolution, tectonics, and fluid migration across varying depths and time scales, providing insights into the mechanisms that control carbonate reservoir formation and evolution globally.