深层—超深层古老烃源岩滞留烃及其裂解气资源评价

我国高-过成熟海相天然气主要成因类型为原油裂解气,滞留烃是原油裂解气的重要来源,对其进行定量研究意义重大。为此,结合正演(实验模拟)和反演(地质剖面解剖)两种方法,求取了我国重点盆地不同类型、不同丰度、不同演化阶段的滞留烃量,建立了5种类型烃源岩(腐泥型、偏腐泥混合型、偏腐殖混合型、腐殖型、煤型)的滞留烃演化模型。结果表明:腐泥型、偏腐泥混合型优质烃源岩在低成熟阶段的排烃效率低于20%,在主生油阶段的排烃效率介于20%~50%,在高成熟阶段的排烃效率介于50%~80%,而相应阶段偏腐殖混合型和腐殖型烃源岩的排烃效率则要低约10%。基于该演化模型,初步计算了四川盆地海相烃源岩中高成熟阶段-现今滞留烃资源分布和裂解排气量:该盆地下寒武统筇竹寺组滞留烃在高演化阶段裂解排出的气态烃总量达230.4×10~(12)m~3,震旦系陡山沱组烃源岩滞留烃裂解气的排出量为12.3×10~(12)m~3,均显示出很好的天然气成藏潜力;进而指出,四川盆地筇竹寺组烃源岩滞留烃裂解气的有利区主要包括高石梯-磨溪、资阳、威远地区,有利分布面积达4.3×10~4 km~2。

Evaluation on occluded hydrocarbon in deep-ultra deep ancient source rocks and its cracked gas resources

Oil-cracked gas, as the main type of high-over mature marine natural gas in China, is mainly derived from occluded hydrocarbon. So it is significant to carry out quantitative study on occluded hydrocarbon. In this paper, the occluded hydrocarbon volume of the main basins in China was calculated depending on their types, abundances and evolution stages by means of the forward method (experimental simulation) and the inversion method (geologic profile dissection). And then, occluded hydrocarbon evolution models were established for five types of source rocks (sapropelic, sapropelic prone hybrid, humic prone hybrid, humic and coal). It is shown that the hydrocarbon expulsion efficiency of sapropelic and sapropelic prone hybrid excellent source rocks is lower than 20% at low-maturity stage, 20%-50% at the principal oil generation stage, and 50%-80% at high-maturity stage, which are all about 10% higher than that of humic prone hybrid and humic source rocks at the corresponding stages. The resource distribution and cracked gas expulsion of occluded hydrocarbon since high maturity stage of marine source rocks in the Sichuan Basin were preliminarily calculated on the basis of the evolution models. The cracked gas expulsion is 230.4×10¹² m³ at the high evolution stage of occluded hydrocarbon of Qiongzhusi Formation, Lower Cambrian in this basin, and 12.3×10¹² m³ from the source rocks of Doushantuo Formation, Sinian, presenting good potential of natural gas reservoir accumulation. It is indicated that the favorable areas of occluded hydrocarbon cracked gas in Qiongzhusi Formation source rocks in the Sichuan Basin include Gaoshiti-Moxi, Ziyang and Weiyuan, covering a favorable area of 4.3×10⁴ km².