# Analysis of Hydrocarbon Enrichment in Tight Sandstone Reservoirs in the Eastern Baiyun Depression
## 2 Geological Settings
### Reservoir-Cap Combination Characteristics and Trap Types in Baiyun Depression  
Four sets of favorable reservoir-cover assemblages developed vertically in the Baiyun Depression, namely, the lacustrine delta assemblage of the Wenchang Formation, the Marine and continental transitional delta assemblage of the Enping Formation, the continental shelf delta assemblage of the Zhuhai Formation and Zhujiang deep-water fan assemblage of the Zhujiang Formation. The sand-mudstone association in the lacustrine delta of the Wenchang Formation and the sand-mudstone association in the Marine and continental transitional delta of the Enping Formation have lower reservoir physical properties due to their deep burial depth and high compaction degree. Through comprehensive reservoir analysis of multiple exploration Wells on the north slope, it is found that the sandstone porosity is obviously affected by the compaction of buried depth. The greater the buried depth, the smaller the porosity, and if the depth is greater than 3700 m, and the porosity drops below 10%. However, the delta sand body, the middle-deep lacustrine mudstone and the shallow Marine mudstone are finger-like interactions, which can form effective reservoir-cap assemblages. Source rocks in the Niger Delta of Nigeria, the large shallow water braided river delta of North Kanafon of Australia, the Daqing Changyuan delta and the Huagang Formation delta of Xihu Depression are in direct contact with reservoir rocks, all of which have the characteristics of self-generated and self-stored reservoirs [29; 30; 31; 32]. Judging from the breakthrough of deep natural gas exploration in China in recent years, such as Kuqa depression and Xihu Depression, deep traps have a high degree of charging [19; 33; 34; 35], the development of sweet reservoir, large reserves and other characteristics, from the perspective of reservoir formation, the large delta of the Enping Formation-Zhuhai Formation is large in scale and has superior reservoir conditions. Therefore, the deep structure-lithology trap in the Baiyun Depression is of great value not only as a potential strategic exploration direction but also as a potential exploration target. The Zhuhai Formation is a shallow Marine shelf environment, a large shelf delta developed in the Baiyun Depression during this period and the delta advanced southward to the south side of the Baiyun depression, where a slope turbidite fan reservoir formed by front collapse may also have developed [13]. The sand body of the shelf delta has the characteristics of large area distribution. Drilling data show that the average porosity of the delta sandstone of the Zhuhai Formation is 15%-20% [36], with high porosity and good reservoir physical properties. In the highly constructive delta, the pre-delta mudstones with rapid sand-mudstone interlayer accumulation and thick layer development during the advancing process easily form mud mounds, diapirs, etc., forming good reservoir-cap assemblages and lithologic traps. Moreover, a large-scale transgression occurred in the middle of the Zhuhai Formation, forming widely distributed mudstones, which can be used as regional cap beds. During the Zhujiang Formation and Hanjiang Formation period, the Baiyun depression was strongly settled, forming a deep-water environment on the continental slope, and the slope break zone moved northward. The Pearl River deep-water fan system developed in the continental slope area, the deep-water fan developed in the low area inside the sequence and the vertical superposition was multi-stage. Because the Pearl River Delta is dominated by sandstone, the deep-water fan caused by gravity flow at the front of the delta is also mostly a sandy reservoir. The deep-water fan sand body revealed by well LGH-2 has a porosity of up to 27%, which is a high-quality reservoir. Moreover, the deep-water fan is surrounded by extremely thick deepwater mudstone, making it a good reservoir cap combination [5,27].