# Analysis of Hydrocarbon Enrichment in Tight Sandstone Reservoirs in the Eastern Baiyun Depression
## 2 Geological Settings
### Baiyun Depression Sedimentary Strata  
Controlled by regional tectonic evolution, the Baiyun Depression in the Pearl River Estuary Basin is filled with sediments from the lake before the sea and is a continental deposit from Paleocene to early Oligocene, including the Shenhu Formation (Tg-T90), Wenchang Formation (T9-T80) and Enping Formation (T80-T70) [21; 22]. Since the Late Oligocene, there have been Marine and continental transition facies and Marine sediments, including Zhuhai Formation (T70-T60), Zhujiang Formation (T60-T40), Hanjiang Formation (T40-T20), Yuehai Formation (T20-T10), Pliocene Wanshan Formation and the Fourth Series (T10-T0) (Figure 2).  
Figure 2: Comprehensive column diagram of stratigraphic and structural evolution in Baiyun depression.  
The Shenhu Formation was deposited in the Shenhu Movement period of the Paleocene. It is an intermontane basin deposit at the early stage of the rift, with river and alluvial fan deposits at the early stage in the basin, mid-deep lacustrine facies deposits at the late stage, and fan delta and alluvial fan at the basin margin. The stratigraphic distribution of the Shenhu Formation is limited.  
The Wenchang Formation, deposited after the Zhuqiong movement, is widely distributed in the basin, mainly developing semi-deep lake-to-deep lake mudstone with a thickness ranging from 1000 m to 2000 m, and is the main source rock formation in the Pearl River Estuary Basin. Because the basin continued to settle after the second act of the Zhuqiong Movement, the Enping Formation has a wider development range than the Wenchang Formation [23; 24; 25]. It is mostly lacustrine and swamp facies deposits, a coal-bearing system, and one of the main source rock systems in the Pearl River Estuary Basin.  
The top and bottom boundaries of the Zhuhai Formation are T70 and T60, respectively, which correspond to the South China Sea movement and Baiyun movement. After the South China Sea Movement, the Pearl River Estuary basin entered the depression period from the fault depression period, the basin had a large area of subsidence, seawater began to invade, and most of the basin changed into the coastal shallow sea and delta environment of the transition phase, which is one of the main reservoir systems in the basin.  
The Zhujiang Formation was deposited after the Baiyun movement, when the basin entered the depression stage, the second-order sea level continued to rise, and the shelf slope break migration caused the Baiyun depression to enter the deep-water environment. The Zhuhai-I Depression and the central uplift zone are shallow Marine environments, the old Pearl River Delta develops, and the Dongsha uplift develops a carbonate platform, which is also one of the main reservoirs in the basin.  
During the sedimentary period of the Hanjiang Formation, it was mainly composed of delta and Guanghai shelf deposits, during which many large-scale transgressive regressions occurred. The Dongsha Movement had a profound influence on the sedimentary system, and the lithology was mainly sandstone, mudstone and siltstone.  
During the sedimentary period of the Yuehai Formation, Wanshan Formation and the Fourth Series, the sea level continued to rise, and the environment of the delta, shallow sea shelf and Guanghai mainly developed.