Comparing the pyrolysis parameters of the Fengcheng and Carboniferous source rocks, it is evident that the Fengcheng source rocks have higher chloroform bitumen “A” and free hydrocarbon content (
S1), indicating better retention of liquid hydrocarbons (
Fig. 4). While the Fengcheng source rocks thermally cracks into natural gas, the retained oil will also undergo secondary cracking, making a significant contribution to gas generation. On the other hand, the Carboniferous source rocks are gas-prone. With lower chloroform bitumen “A” and
S1, their gas generation almost depends on the cracking of kerogen. Taking into account the contribution of secondary cracking of the retained oil in the Fengcheng source rocks and the similarity in hydrocarbon generation and evolution processes in different systems for the Carboniferous source rocks, gold tube pyrolysis experiments in a closed-system were conducted to compare the gas-generating capabilities and processes of these two sets of source rocks. The samples of the Fengcheng source rocks were taken from Well Fengnan 2, characterized by silicified dolomitic shale with a TOC value of 1.56% and a measured
Ro value of 0.60%. The samples of the Carboniferous source rock were taken from Well Shaqiu 12, consisting of siliceous mudstone with a TOC value of 2.17% and a measured
Ro value of 0.54%. The results show that the maximum gas (C
1-5) yield from the Fengcheng source rocks can be 651 mL/g, while that from the Carboniferous source rock is only 381 mL/g, which is significantly lower than the former (
Fig. 5). Some scholars have pointed out that there is a significant difference in the gas-generating potential of different types of source rocks in a closed system, mainly influenced by the quantity of liquid hydrocarbons generated from the source rocks
[31]. The Fengcheng source rocks, dominated by types I-II
1 kerogen (
Fig. 2), have a high potential for oil generation. In addition to being expelled from the source rock through primary migration, the liquid hydrocarbons generated also remain to a considerable extent within the source rock, which may crack into gas later, making a significant contribution to gas generation from the source rock
[31]. The hydrogen index (HI) of the samples of the Fengcheng source rocks used in the hydrocarbon-generating simulation experiment is 683 mg/g, with a maximum oil-generating potential of 725 mg/g. In a closed system, the liquid hydrocarbons initially generated can crack again into natural gas, significantly enhancing the late-stage gas-generating potential of the Fengcheng source rocks. In contrast, the Carboniferous source rocks, dominated by types II
2-III kerogen (
Fig. 2), have a hydrogen index of 274 mg/g according to the samples used in the simulation experiment, so their oil generation potential (only 186 mg/g at most) is low, and accordingly, their gas-generating potential is significantly lower than the Fengcheng source rocks (
Fig. 5).