Abstract
The diagenetic environment is vital in controlling reservoir quality by influencing diagenetic processes, especially porosity evolution. The Zhuhai Formation is a critical exploration target in the Huizhou Sag. However, there are considerable differences between the reservoirs in the west (Huixi) and east (Huidong) Huizhou Sag with only a 400 m difference in burial depth. To investigate causes of these differences, scanning electron microscopy (SEM), cathodoluminescence analysis, fluorescence analysis, and fluid inclusion analysis are employed for the petrological and diagenetic characterization of the target formation. Moreover, image analysis software is used to qualitatively evaluate the impacts of diagenesis on porosity. The results show that the digenetic environments in Huixi and Huidong are different. Huixi is characterized by a high content of feldspar with a stronger dissolution phenomenon than that observed in Huidong. The main cement types in Huixi are siliceous cement and kaolinite. Moreover, Huixi had a low palaeo-temperature, low palaeo-salinity, and low palaeo-pH diagenetic environment. In contrast, Huidong is accessible via deep faults and rich in lithic fragments which show visible deformation. Moreover, cements in this area include carbonate, gypsum, quartz overgrowth, kaolinite, and chlorite. This evidence confirms that the diagenetic environment in Huidong was a high palaeo-temperature and high palaeo-salinity environment with high palaeo-pH. Additionally, the palaeo-pH evolved following the sequence of weakly alkaline, acidic, alkaline and acidic. Microscopy evidence indicates that the Dongsha Uplift was a likely source of Huixi sediments during the deposition of the Zhuhai Formation. The determination of the porosity evolution shows that compaction and lithic fragment content are the main controlling factors on the reservoir quality of the Zhuhai Formation.
Highlights
Porosity and permeability are the critical parameters that represent reservoir quality [1,2], and both are mainly controlled by the initial sedimentary structure and later diagenesis
The diagenetic process of sandstone can usually be divided into the eogenesis stage, mesogenesis stage and telodiagenesis stage based on depth, temperature, and later tectonic uplift
The present work established a model to to quantitively reconstruct for the Formation in the Huizhou sag based on. This model can mainly use data the Zhuhai Formation in the Huizhou sag based on PIBS
Summary
Porosity and permeability are the critical parameters that represent reservoir quality [1,2], and both are mainly controlled by the initial sedimentary structure and later diagenesis. High porosity and high permeability are the results of comprehensive interactions among primary sedimentary composition, texture, and diagenetic processes such as compaction, cementation, and dissolution [3]. During a long burial history, diagenesis is significantly influenced by the diagenetic environment. Diagenesis will affect reservoir quality through various physical and chemical means, and will determine the pore volume, pore geometry and filling state of the pore space [4]. Understanding the coupling between the diagenetic environment and porosity evolution is of significant importance in oil and gas exploration
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