# A New Method of Geological Modeling for the Hydrocarbon Secondary Migration Research
## 4 Reservoir Modeling of the Sangonghe Formation in the Central Junggar Basin
### Petroleum Geological Setting  
The study area, located in the MXZ area in the central part of the Junggar Basin, is southeast of the Well Pen-1 Western Sag (Figure 7). The dominant structural feature in the study area is a dipping monoclonal structure, with the burial depth gradually increasing from the northeast to the southwest. The target reservoir is generally found at depths ranging from 4000 m to 4500 m. In terms of trap types, the MXZ area does not exhibit typical structural traps, but, instead, a small number of intralayer faults are present in the main oil-bearing formations. The predominant types of oil reservoirs in this area are structural-lithological reservoirs [67].  
The central Junggar Basin primarily focuses on the Jurassic formations for oil and gas exploration and development. These formations include J\({}_{1}\)b, J\({}_{1}\)s, J\({}_{2}\)x, and J\({}_{1}\)t, from bottom to top (Figure 7C). After the Yanshan Movement, the region experienced uplift, leading to the erosion of the Upper Jurassic strata. Among the Jurassic formations, J\({}_{1}\)s is the primary oil-bearing reservoir and can be further subdivided into three members from bottom to top. The J\({}_{1}\)s\({}_{1}\) and J\({}_{1}\)s\({}_{3}\) consist mainly of semi-deep and deep lacustrine dark mudstone, with thin siltone and fine sandstone layers. The J\({}_{1}\)s\({}_{2}\) member, which belongs to the delta front deposit, serves as the main reservoir. It exhibits longitudinal superposition and transverse composite contiguous distribution of multi-stage sand bodies.  
The characteristics of the lower sub-member (J\({}_{1}\)s\({}_{2}\)1) and upper sub-member (J\({}_{1}\)s\({}_{2}\)2) of J\({}_{1}\)s\({}_{2}\) differ significantly. J\({}_{1}\)s\({}_{2}\)1 was deposited at the front of a braided river delta, showcasing highly developed distribution channel sand bodies and estuarine bar sand bodies. The multi-stage channel sand bodies vertically stack with a cumulative thickness of 60 to 80 m. Notably, the lower part of J\({}_{1}\)s\({}_{2}\)1 exhibits pan-connected massive thick sand bodies, accompanied by an increase in the mudstone content and enhanced heterogeneity. On the other hand, J\({}_{1}\)s\({}_{2}\)2 was deposited at the front of the meander delta, featuring isolated or laterally overlapping sand bodies. The section shows a lithological combination known as \"mud-coated sand\". Distribution channel sand bodies are found at the base of J\({}_{1}\)s\({}_{2}\)2, generally with a thickness of less than 15 m, and they exhibit poor horizontal connectivity.  
The main reservoir within J\({}_{1}\)s\({}_{2}\) consists of feldspathic lithic sandstone and lithic sandstone with low compositional maturity. The reservoir is characterized by a significant burial depth, strong diagenesis, a wide range of sandstone physical properties, and porosity ranging from 1.9% to 18% (with an average of 8.3%). The permeability varies from 0.01 \(\times\) 10\({}^{-3}\) to 78 \(\times\) 10\({}^{-3}\) um\({}^{2}\) (with a mean of 0.92 \(\times\) 10\({}^{-3}\) um\({}^{2}\)) [68]. Due to the influence of the original rock composition and differential diagenesis, the diagenetic evolution within the reservoir shows significant variations. The sandstone can be classified into different rock facies types, including rich plastic grain sandstone, strong carbonate cement sandstone, and poor plastic grain sandstone. The rich plastic grain sandstone and the strong carbonate cement sandstone undergo densification during early diagenesis. The poor plastic grain sandstone, however, experiences multi-stage cementation and dissolution during deep burial, reflecting a complex interaction between organic and inorganic fluids [69; 70].