# Analysis of Hydrocarbon Enrichment in Tight Sandstone Reservoirs in the Eastern Baiyun Depression
## 2 Geological Settings  
### Baiyun Depression Structure  
The Pearl River Estuary Basin is located on the vast continental shelf and continental slope margin in the north of the South China Sea, with Taiwan and the Hainan Islands as the borders in the east and west, respectively. It covers an area of about 17.5 \(\times\) 10\({}^{4}\) km\({}^{2}\) and is one of the largest oil-bearing basins in offshore China with a NE-SW distribution. Located in the southern margin of the South China continent, the Pearl River Estuary Basin is a Cenozoic oil-bearing basin formed on the base of complex folds in Paleozoic and Mesozoic under the complex continental dynamic background under the influence of the intersection of the Pacific plate, Indian plate and Eurasian plate [7; 8; 9].  
The Pearl River Estuary Basin is dominated by the NE-trending fault system, which, together with the NWW-trending fault, controls the uplift and depression pattern of the basin. It has a north-south zoning and east-west zoning structure and is mainly divided into five tectonic units (Figure 1): the northern uplift belt, the northern depression belt, the central uplift belt, the southern depression belt and the southern uplift belt [10; 11; 12]. The northern depression zone is composed of the Zhu-I Depression and Zhu-III Depression, and the Zhu-II Depression is in the southern part of the Pearl River Estuary Basin.  
The Baiyun Depression is in the second basin of two oil-bearing belts in offshore China, in the northeast of Zhu II Depression in the Pearl River Estuary Basin, and is a transitional gas-rich depression basin located in the continental slope area of the northern continental margin of the South China Sea, is a long-term stable sinking negative tectonic unit [11; 13; 14; 15; 16]. The Baiyun depression has an area of more than 20,000 km\({}^{2}\) and a water depth of 200-3000 m. About 70% of the depression has a water depth of more than 500 m. The maximum sedimentary thickness of the Cenozoic exceeds 11 km, making it the largest depression in the Pearl River Estuary Basin and the sedimentation and sedimentation center of the basin [17; 18; 19].  
The Baiyun depression is generally a compound graben structure separated by low protrusions, with an NEE strike, and the Panyu low uplift and slope belt on its north side. The west side is a Yunkai low bulge and steep slope zone; the southern part is a Yunkai low bulge, the southern uplift zone and the fault step zone. The east side is the Dongsha uplift, and a low uplift is developed in the depression (Figure 1). Overall, it can be divided into the Baiyun main depression (about 4800 km\({}^{2}\)), Baiyun East depression (about 512 km\({}^{2}\)) and Baiyun West depression (about 900 km\({}^{2}\)), in which the north side of the main depression of the Baiyun depression is a gentle slope zone, the south side is a steep slope fault step zone, and the fault structure is not completely controlled by the fault center overall [14; 20].  
During the sedimentary period of the Enping Formation, the Baiyun Depression was in the late stage of rift evolution, and the fault features were obvious, with a wide \"half graben\" feature of \"steep in the south and gentle in the north and faulting in the south and overrunning in the north\". Under the joint action of fault retention and deep thermal attenuation, the Baiyun Sag settled as a whole, and the sedimentary range expanded continuously. It related to the Liwan Sag to the southeast, and the sedimentary background was  
Figure 1: Position of Baiyun depression in the Pearl River Mouth basin. **(A)** Structural division of Pearl River Mouth basin; **(B)** Structural division of Baiyun depression.  
shoreline shallow sea and limited sea, which ended the sedimentary pattern of \"depression separation\" during the sedimentary period of the Wenchang Formation.