256 / 2019-06-30 21:35:02

Petrological characteristics and their geological significance of Zhuhai Formation in Huihzou Sag, Pearl River Mouth Basin, the South China Sea

Petrological Characteristics,Diagenetic Evionment,,Provenance,Zhuhai Formation,Huizhou Sag

Abstract The Zhuhai Formation sandstone reservoir in Huizhou sag is the critical exploration target in recent years. However, due to the lack of research about petrological characteristics, reservoir characteristics and provenance, its exploration has been severely hindered. Therefore, In this paper, based on thin sections mainly, the petrological characteristics and its geological significance of Zhuhai Formation will be researched by means like scanning electron microscopy(SEM), cathodoluminescence, fluorescence analysis and fluid inclusion.
The results show that there are obvious differences in petrological characteristics between Huixi and Huidong. Both areas are rich in quartz (70% on average), Huixi area is characterized by high content of feldspar (15.2% on average), and low content of lithics (9.1% on average) which are mainly brittle grains like quartiza. The contact relationship between grains is mainly point to long contact. On the contray, Huidong area is characterized by high content of lithics (21.9% on average) which are mainly plastic debris like mudstone with obvious deformation, and the content of feldspar content is relatively low (7.1% on average). And the main contact relactionship in Huidong is long contact and concave-convex contact. Compaction and compression deformation of plastic grains are the main reasons for resevoir quality differences between Huixi and Huidong.
Petrological characteristics also indicat that the diagenetic evionment is diaparate in these two areas. In Huixi, cementation is mainly composed of quartz overgrowth and kaolinite. In addition to a few depths, calcareous cement is not visible, the inclusion temperature is low (117 ℃ on average), and there is a strong feldspar dissolution phenomenon. Therefore, Huixi is a low-temperature, low salinity and acidic diagenetic environment. In contrast, Huidong possesses many types of cement, such as carbonate, sulfate, potassium salt and pyrite, illite and chlorite are the main clay minerals. The dissolution of silicon is visible, and the inclusion temperature is high (140 ℃ on average). Therefore, Huidong is a high-temperature, high salinity, alkaline diagenetic environment.
At the same time, the comparing of lithic types and stratigraphic correlation show that the Zhuhai Formation gradually overlaps from Huixi area to the Dongsha uplift, and the main lithic type in this two areas is granite. The analysis of sand body thickness shows that the sand body thickness gradually decreases from Dongsha uplift to Huixi area. Thes two evidences confirm that the Dongsha uplift is possible to provide provenance during the sedimentary of Zhuhai Formation.