合肥盆地寒武系底部烃源岩沉积环境和地球化学特征

合肥盆地海相油气的勘探逐渐受到重视。盆地西部发现的寒武系底部海相泥质烃源岩具有重要的现实意义,对其沉积环境和地球化学特征的研究是进一步油气勘探的基础。层序地层学及有机地球化学研究表明,其沉积构造环境为拉张裂陷向移离扩张的过渡阶段,盆地性质属于内裂谷盆地向被动大陆边缘盆地的过渡类型,对于烃源岩的形成和保存极其有利。该套烃源岩有机碳平均含量为6.46%,有机质类型为I型,R_o(2%～3.5%)与T_max(500～600℃)反映的成熟度已进入过成熟早期乃至晚期阶段。生物标志物反映该套烃源岩在强还原高盐度的环境中形成,生源为菌藻类低等生物,其演化程度处于生油阶段。两类有机地化指标反映的成熟度差异,可能是各自代表的有机质不同。R_o和T_max主要反映烃源岩主体的成熟度,而生物标志物可能主要反映岩石包体有机质的成熟度。综合研究认为,该套烃源岩不仅处于生气高峰期,并具有生油的可能。该套烃源岩沉积环境和地球化学的研究,为合肥盆地勘探下古生界天然气藏提供了理论依据。 

SEDIMENTARY ENVIRONMENT AND GEOCHEMICAL CHARACTERISTICS OF HYDROCARBON SOURCE ROCKS IN THE CAMBRIAN BASE OF THE HEFEI BASIN

More and more attention is being paid to the marine hydrocarbon exploration in the Hefei Basin. The marime argillaceous source rock found in the Lower Cambrian base of the West Hefei Basin has important practical significance, and the stuey on its sedimentary environment and geochemical characteristics is the basis for the further hydrocarbon exploration. Sequence stratigraphical and orgnic geochemical study shows that its sedimentary tectonic environment is at the transitional stage of extensional depressing to shifting spreading, and the basin belongs to the transitional type of internal rift basins to passive continental marginal basins. The is very much advantageous to the formation and preservation of hydrocarbon source rocks. This set of source rocks has the average organic carbon content of 6.46% and I-typed organic matter, and its maturity characterized by R_o(2%-3.5%) and T_max (500-600℃) reflects its entering into the overmatured early or late stage, The biomarkers reveal that this set of source rocks was formed in the strong-reduction and high-salinity environment, and it originated from bacteria and algae these kinds of low-grade organism, and is in the evolutionary degree of the oil-generating stage. The maturity difference reflected from the two kinds of organic geochemical indexes may result from different organic matter they represent respectively, R_o and T_max mainly reflect the host rock maturity of source rocks, while biomarkers may mainly reflect the organic matter maturity of rock enclusure. The comprehensive study suggests that this set of source rocks not only is in the peak period of gas generation but also has the potential to form oil. The sedimentary environmental and geochemical research of this set of source rocks provides theoretical basis for the Lower Paleozoic natural gas pool prospecting in the Hefei Basin.