## 4 Gas Generation Potential
### Hydrocarbon Generation Simulation  
To reveal the gas generation potential of the Fengcheng Formation source rocks, hydrocarbon generation simulation experiments were carried out to evaluate their gas generation potential. The hydrocarbon generation simulation experiment is the most intuitive method to evaluate the gas potential of source rocks. Currently, the commonly used hydrocarbon generation simulation methods mainly include Rock-Eval pyrolysis hydrocarbon generation, autoclave confined space hydrocarbon generation and gold tube hydrocarbon generation simulation [20; 21]. Rock-Eval pyrolysis hydrocarbon generation is carried out in an open system under atmospheric pressure. It is easy to operate and can analyze various hydrocarbon components online with a single injection. However, this experimental system does not consider the influence of formation water and pressure on hydrocarbon generation process, so it differs significantly from the natural geological background. The autoclave confined space hydrocarbon generation simulation is carried out in an ample hydrocarbon generation space with low fluid pressure and no hydrostatic pressure, and the influence of formation water and pressure on hydrocarbon generation process is not considered enough [22]. The gold tube hydrocarbon generation simulation experiment is more suitable for hydrocarbon simulation of pure kerogen because the space of the gold tube is small, and the sample used is of milligram level. The error of quantitative analysis of hydrocarbon products is more significant, but the hydrocarbon simulation of kerogen ignores the influence of inorganic minerals on hydrocarbon formation. In addition, the pressure inside the gold tube can be changed by adjusting the water pressure of the autoclave outside the gold tube. Still, due to the deformation of the gold tube and the uncertainty of the number of products generated, it is doubtful whether the fluid pressure inside the gold tube is equal to the external pressure [23]. Considering different hydrocarbon generation simulation methods, the DK-II type of formation pore thermal pressure hydrocarbon generation and discharge simulation instrument developed by the Wuxi Institute of Petroleum Geology of Sinopec Petroleum Exploration and Development Research Institute was selected. We consider the limited space, overlying formation pressure, the internal fluid pressure of source rock and temperature of the hydrocarbon generation process thoroughly, to restore the hydrocarbon generation process of source rock under geological conditions to the greatest extent. Since the Fengcheng Formation source rocks were only drilled in the Mahu Sag, were selected for hydrocarbon generation simulation experiments in this study. And the information on sample parameters is shown in Table 1.  
The oil and gas production rate at different evolutionary stages of each sample was obtained by conducting a hydrocarbon generation simulation experiment. [PERSON] et al. ([24] made statistics on the gas generation intensity of the large and medium-sized gas fields discovered in China, and found that the gas generation intensity was all greater than \(20\times 10^{8}\) m\({}^{3}\)/km\({}^{2}\). The latter authors concluded that the gas generation intensity greater than \(20\times 10^{8}\) m\({}^{3}\)/km\({}^{2}\) was \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Samples** & **Lithology** & **TOC (\%)** & **I\({}_{\mathbf{H}}\) (mg/g TOC)** & **T\({}_{\mathbf{max}}\) (\({}^{\circ}\)C)** \\ \hline S1 & Dolomitic mudstone & 3.05 & 608 & 436 \\ S2 & Dolomitic mudstone & 2.37 & 604 & 446 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Geochemical parameters of simulated hydrocarbon generation samples. one of essential conditions for forming large and medium-sized gas fields [24].