蒸发环境烃源岩生烃能力探讨——以川西坳陷雷口坡组为例

Discussion on hydrocarbon generation ability of evaporation environment:a case study of Leikoupo Formation in West Sichuan Depression

近年来,雷口坡组勘探屡屡突破,已成为川西坳陷海相天然气勘探的热点层系,搞清雷口坡组烃源岩的生烃能力,对后续的勘探开发具有重要意义。古盐度的定量化指标和高伽马蜡烷特征反映了雷口坡组沉积期发育高盐度、水体分层的咸化蒸发环境,Ba质量分数高、δ13C正偏移特征反映沉积环境具备较高的生物生产力,可以形成优质烃源岩;咸化蒸发环境有利于烃源岩有机质的保存和转化。川西地区雷口坡组烃源岩TOC整体较低,但含膏碳酸盐岩样品TOC相对较高,蒸发台地相发育较多的膏云坪和含膏潟湖,膏岩与碳酸盐岩交互沉积,是优质烃源岩发育的有利沉积相带及岩性组合。

In recent years, the Leikoupo Formation is a hot spot of marine natural gas exploration in the West Sichuan Depression. It is of great significance for the subsequent exploration and development to figure out the hydrocarbon generating ability of the source rocks of the Leikoupo Formation. The characteristics of Palaeosalinity quantitative index and high content of gammacerane reflects the salty environment development in high salinity and water stratification in the Leikoupo Formation sedimentary period; the high content of Ba and the positive shift of δ^13C reflects the characteristics of the sedimentary environment with high productivity, and high quality source rocks can be formed here; the salty environment is beneficial to the preservation and transformation of the organic matter of the source rocks. The TOC of the source rocks of the Leikoupo Formation in the West Sichuan area is low, but relatively high in the gypsum containing carbonate rocks. In the evaporative platform, there are more dolostone of tidal flat with gypsum and gypsum lagoon, and interactive deposition of gypsum rock and carbonate rock developed here, which is a favorable sedimentary facies belt and lithologic assemblage for the development of high quality source rocks.