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Previous HitEffectiveTop sandstone reservoir determination and its lower limit in Chuanxi Depression of Sichuan Basin, China

Abstract

The petroleum exploration in Chuanxi Depression of Sichuan Basin has moved toward deep layers since 2013. The drilling results show that sandstone reservoirs ineffective in shallow layers (<3,500 m) can be effective in deep layers (≥3,500 m). Some reservoirs whose porosity less than 4% are good gas layers and some are dry layers. Determination of effective sandstone reservoir and its lower limit avoiding costly drilling mistakes are the goals pursued by oil explorers and companies. Capillary force plays an important role in the deep hydrocarbon migration process. The study identifies the effective sandstone reservoirs and its lower limit based on the index of ratio of capillary force between the surrounding rock and the sandstone. First, acquiring the parameter pore throat radius of sandstone and mudstone by sampling the cores and processing the conventional mercury intrusion experiment. Second, the ratio of capillary force between the surrounding rock (i.e., mudstone) and sandstone samples at the same depth is calculated. The evolution profile of capillary force ratio and the depth is established. Finally, the effective sandstone reservoirs and its lower limit are determined based on the profile. There will be a clear boundary line between the effective and ineffective reservoirs on the evolution profile. The effective reservoirs are on the right side. The ratio on the boundary line is the lower limit of effective reservoirs changing with the depth. The workflow is crucial for deep petroleum resources evaluation and exploration in Chuanxi Depression and may have a broad applications in other basins.