Favorable conditions for deep dissolution reservoirs in warm basins with stable source-to-sink systems: example from the eastern Pearl River Mouth Basin

Exploration results demonstrate the development of high-quality reservoirs with superior physical properties (porosity up to 22%, permeability up to 4 D) in the deep Paleogene strata of the eastern Pearl River Mouth Basin, despite burial depths greater than 3,500 m and formation temperatures exceeding 120 °C. Their formation is closely linked to dissolution by fluids. By integrating petrographic, geochemical, and basin analysis methods, this study identifies three principal types of dissolution fluids in the study area: meteoric water, organic acids, and hydrothermal fluids. Accordingly, three categories of dissolution reservoirs are delineated. The favorable geological conditions for each reservoir type are elucidated as follows: 1. Meteoric water dissolution reservoirs require prolonged shallow burial due to early tectonic uplift, early active faults serving as infiltration pathways, and sealing preservation provided by overlying thick mudstones. 2. Organic acid dissolution reservoirs are governed by a strong supply of organic acid sourced from hydrocarbon-rich sags, effective transport through late-stage active faults, and a close source-reservoir configuration. 3. Hydrothermal dissolution reservoirs are primarily associated with deep-seated faults (especially for NNW-trending concealed faults) penetrating the Moho, which act as conduits for hydrothermal fluid migration. This study clarifies that, within the context of a stable source-to-sink system and a warm basin setting, the differential distribution of deep high-quality reservoirs is predominantly controlled by the types of dissolution fluids and their specific geological conditions. Three conditions are the favorable geological conditions for their formation: 1. A stable source-sink system provides the material basis and dissolution channels for reservoirs; 2. Multi-source fluids are driving forces for the formation of reservoir improvement; 3. Tectonic activities provide channels and open environments for dissolution. These findings contribute to a deeper understanding of the genesis of deep reservoir and provide guidance for exploration in analogous basins.