# Diagenesis of Deep Low Permeability Reservoir in Huizhou Sag and Its Influence on Reservoirs
## 1 Introduction  
The diagenesis of clastic rock reservoirs and its impact on reservoirs' physical properties has always been a research hotspot and a challenging topic, which is of great significance for deep oil and gas exploration and development [1; 2; 3; 4]. The continuous advancement in oil and gas exploration technology has led to the discovery of an increasing number of deep and ultra-deep oil and gas resources. These newly discovered areas are poised to become significant contributors to the global reserves and production of oil and gas [5; 6; 7; 8; 9]. Compared with conventional reservoirs, deep clastic rock reservoirs have undergone a more complex diagenetic process and are often characterized by \"low porosity, low permeability, strong heterogeneity\" [10; 11]. Although destructive diagenesis can cause the physical properties of deep reservoirs to deteriorate, they can still become high-quality reservoirs under specific conditions [12; 13; 14; 15; 16]. Therefore, studying the diagenesis of deep elastic rock reservoirs and its impact on reservoirs' physical properties can help effectively predict the distribution of favorable reservoir zones so as to provide a reliable geological basis for deep oil and gas exploration. Currently, it is generally suggested that factors such as particle size, sorting degree, and compositional components affect the initial properties of tight sandstones [17; 18]. Diagenesis, however, plays a pivotal role in determining their final characteristics, exerting significant control over the heterogeneity and reservoir properties of deep elastic rock reservoirs [18; 19]. The relationship between diagenesis and reservoir quality is mainly reflected in the impact of different types of diagenetic processes on pore development and pore evolution in the reservoirs [20; 21]. Generally speaking, deep sandstone reservoirs are controlled by compaction and cementation, leading to reduced porosity and permeability, and resulting in the reservoirs having poor physical properties overall [22; 23; 24; 25]. However, many scholars have found that there are a large number of primary pores and secondary dissolution pores in deep sandstone reservoirs, effectively improving the performance of the reservoirs [26; 27]. For instance, grain coatings composed of authigenic clay minerals (chlorite and microcrystalline quartz) often prevent contact between the grain surface and diagenetic fluids, inhibiting the occurrence of cementation, thereby playing a crucial role in preserving primary pores [28; 29; 30]. [PERSON] et al. conducted experiments on the mechanical properties of offshore loose sandstone reservoirs [31]. Their research suggests that the abnormally high pressure that developed in the deep layers effectively slowed down the occurrence of cementation, resulting in distinct zones of high-quality reservoir development [31]. [PERSON] et al. studied the Cachiri Group's tight sandstone reservoirs and found that the dissolution of carbonates and feldspars produced secondary pores, enhancing the reservoir quality in the region [32]. Although a large number of primary and secondary pores are found in deep sandstones, their diagenesis is still subjected to comprehensive control by various factors such as basin properties, tectonic evolution, sedimentary types, burial processes, fluid properties, and diagenetic physical and chemical environments in different regions [33; 34; 35; 36]. Therefore, more detailed research should be conducted on the types of diagenesis in different regions and their impact on reservoir performance so as to effectively guide the exploration and development of deep oil and gas resources. The Huizhou Sag, located in the Pearl River Mouth Basin, has demonstrated significant potential for oil and gas exploration and development (Figure 1C), having achieved notable results since the initiation of its production.