# Geochemical Analysis of a Multi-Layer Hydrocarbon Reservoir in the Wuerhe Area, Junggar Basin
## 2 Geological Setting and Petroleum Background
### Petroleum Background  
In the center of nose uplift, normal oil reservoirs in the 11 blocks of the Wuerhe oilfield have been found to have Permian-Triassic strata, with reserves of approximately 230 million tons of oil having a density of 0.863-0.904 t/m\({}^{3}\) (API gravity values is 25.0-32.5). The reservoir types are mainly structural or lithologic with a structural background (Table 1). Heavy oil reservoirs in six blocks of Fengcheng oilfield have been found to have Jurassic strata in the northwest wing of nose uplift, with reserves of approximately 372 million tons and density of 0.958 t/m\({}^{3}\). Through conventional thermal recovery, superheated steam huff and puff and Steam Assisted Gravity Drainage (SAGD) development tests [11], it has been determined that the Fengcheng heavy oil has entered the stage of large-scale development, with an annual production of more than 2 million tons.  
Compared with other areas, in the north of the Fengcheng oilfield, the depth of buried strata is shallower, and the physical properties of its Jurassic and Cretaceous reservoirs are better. After the migration of deep oil and gas, oil sand may be formed through oxidation, water washing, and light component volatilization. Some oil sands are exposed on the surface, forming the largest oil sandhill and residual hill in China [2].  
In the main part of the nose uplift, the fault system connects with a deep reservoir; oil and gas migrate to the surface via the fault system and forms bitumen through secondary action. The distribution of veins is controlled by the fault system, and it reflects the spatial distribution characteristics of faults (Figure 4). Eighteen main faults can be seen in the outcrop, forming a broom-like fault zone spreading in the southwest and converging in the northwest. The width of the bitumen vein (horizontal fault distance) generally ranges from  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Name**} & \multirow{2}{*}{**Block**} & \multirow{2}{*}{**Horizon**} & **Middle** & \multirow{2}{*}{**Reservoir**} & \multirow{2}{*}{**Reservoir Type**} & **Crude Oil** & **Gas Oil** & **Geological** \\  & & & **Buried** & **Lithology** & & **Density** & **Ratio** & **Reserves** \\  & & & **Depth (m)** & & **(f/m\({}^{3}\))** & & **(m\({}^{3}\)/m\({}^{3}\))** & **(10\({}^{4}\) t)** \\ \hline \multirow{8}{*}{
\begin{tabular}{c} Wuerhe \\ Oilfield \\ well blocks \\ \end{tabular} } & Feng 3, Feng 5, Feng & \multirow{2}{*}{4100} & P\({}_{1}\)\(f\) & \multirow{2}{*}{4600} & Dolomite & Structure. & \multirow{2}{*}{0.898} & \multirow{2}{*}{116} & \multirow{2}{*}{4682} \\  & 1 well blocks & P\({}_{1}\)\(f\) & \multirow{2}{*}{4600} & Dolomite & & Structure. & \multirow{2}{*}{0.904} & \multirow{2}{*}{75} & \multirow{2}{*}{3346} \\  & 1 well blocks & P\({}_{1}\)\(f\) & \multirow{2}{*}{4600} & & & structure-lithology & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic date for the discovered reservoirs in the Wuerhe area.  
0.05 m to 0.5 m, the maximum being about 1.2 m. The sandstone on both sides of the vein is black owing to bitumen impregnation; it has a width of 0.5-1.5 m, forming black oil sand deposit. The mine is the only natural bitumen mine for large-scale mining in China. The proven mineral reserves are about 120,000-150,000 tons. Bitumen production began in 1958, and the maximum annual production of bitumen can reach 8000 tons. After more than 60 years of mining, only 110 m of the upper part of the ore vein has been excavated, and the lower part of the bitumen vein, that is nearly 250 m deep, is yet to be mined. The bitumen produced by the ore vein is rare, high-quality, and hard bitumen which is an important raw material for special paint and ink.