Prediction of Diagenetic Facies via Well Logs and Petrophysical Properties in Tight Sandstone from Zhu-III Sag: Pearl River Mouth Basin, South China Sea

Abstract

The Zhu-III sag is a key area of resource exploration with great potential of resources in the Pearl River Mouth Basin. The reservoir in the Zhuhai Formation is a typical tight sandstone reservoir. Tight sandstone has the characteristics of low porosity, low permeability, complex pore structure, and diagenesis. However, past studies in the Zhu-III sag have mainly focused on sedimentology, and there has been little research on diagenesis and diagenetic facies. Diagenetic facies are a significant tool for determining the key parameters of tight sandstone reservoir properties. In this work, diagenesis of the tight sandstone reservoir in the Zhuhai Formation in the Zhu-III sag was investigated by multiple experiments using borehole core, thin sections observation, scanning electron microscope, energy dispersive spectrometry, X-ray diffraction, conventional rock analysis, and pore quantitative analysis to determine the influence of the main diagenesis and minerals. Based on these experiments, the diagenetic sequence was clarified. Four diagenetic facies were identified: strong-compaction facies, medium-compaction facies, carbonate-cemented facies, and clay mineral filling facies. The strong compaction and carbonate cements were the primary reasons for the development of low-quality reservoirs. The medium-compaction facies and clay mineral filling facies commonly corresponded to the high-quality reservoirs. The facies prediction system was established, and the favorable reservoir via well logs could be predicted. The findings showed that the reservoir quality or oil-bearing properties are dominated by diagenetic facies. This study provides guidance to distinguish the productive zones and evaluate the pore-throat systems and reservoir quality in the Zhu-III sag and the Pearl River Mouth Basin.