Sedimentological and diagenetic effects on petrophysical characteristics and hydraulic flow units of Zhujiang sandstones in the Pearl River Mouth Basin, south China Sea

The Zhu-Ⅲ sag is a key oil and gas rich basin. The Zhujiang Formation is characterized by strong heterogeneity, a changeable sedimentary environment and complex diagenesis, which presents great challenges in the identification of the reservoir sweet spot. Previous researchers have almost no study on it. Therefore, finding high-quality reservoir units is the top priority. In this study, we focus on classifying and evaluating the reservoir units, finding high-quality units and providing exploration recommendations. We carried out core observations and description, X-ray diffraction, cast thin-section observations, electron microscopy observations and mercury intrusion experiments. We used the normal probability distribution model to divide the hydraulic flow unit into six types and determined their hydraulic flow capacity. We summarized the depositional model of the study area through core observations and well analysis. By combining the data on the hydraulic flow units, pore throat radius, sedimentary background, diagenesis and reservoir physical properties, we classified six rock facies (RFs). We found that there is good correspondence between rock facies, hydraulic flow units and sedimentary environments. The results indicate that the quality of the RF-1, RF-2 and RF-3 reservoirs are good, while the quality of the reservoir in RF-4, RF-5 and RF-6 are poor. We conclude that RF-2 mainly corresponds to oil layers and oil-water layers, which are favourable target layers for exploration. This research is the first time to study the sedimentation and diagenesis and combine them to evaluate the reservoir physical properties and flow units in the South China Sea comprehensively.