乌尔逊—贝尔凹陷优质烃源岩发育特征及成因机制

DEVELOPED CHARACTERISTICS AND GENETIC MECHANISM OF HIGH-QUALITY SOURCE ROCKS IN WUERXUN-BEIER SAGS

乌尔逊—贝尔凹陷是海拉尔盆地的两大主力富油凹陷,其中南一段下部“特殊岩性段”中发育的暗色泥岩、泥灰岩、油页岩和含钙泥岩是优质烃源岩,但此前一直被忽视.借鉴贝尔凹陷勘探发现,重新对“特殊岩性段”中源岩进行了有机地球化学分析.结果表明：乌尔逊—贝尔凹陷南屯组,特别是南一段下部“特殊岩性段”发育高丰度的优质烃源岩,有机碳质量分数高达2％,平均生烃潜量为13.74 mg/g;有机质类型以I一Ⅱ1型母质为主;镜质体反射率0.7％ ～ 1.5％;无定形体和藻质体是烃源岩中有机质的重要来源,有效烃源岩厚度为30～70 m,该套烃源岩不仅类型好、丰度高,而且排烃效率高,具有巨大的生烃潜力.研究认为,微生物化石以藻类为主且含量丰富,表征优质烃源岩中有机质富集与藻类勃发事件有关;构造沉降与沉积充填、火山喷发活动等对优质烃源岩的形成发育具有重要促进作用.优质烃源岩对油藏有明显的源控作用,已发现的油藏纵向上多位于优质烃源岩层上下,平面上位于其内部或者边缘。

Wuerxun-Beier Sags are two important oil-enriched sags in Hailer Basin,among them,well-developed dark mudstone,marl,shale and calcareous mudstone in the ＂special lithology interval＂ of Lower Member Nan-1 are high-quality source rocks,but they have been ignored all the time before.Based on the exploration experience of Beier Sag,the geochemical analyses of the high-quality source rocks in the special section are renewed.The results show that in Nantun Formation of the sags,especially in the above interval,the high-quality/abundance source rocks are well developed,the mass fraction of the organic carbon content （TOC） is over 2％,the averaged hydrocarbon-generating potential is 13.74 mg/g; the main organic matter type is Type I-I1 ; the vitrinite reflectance is up to 0.7％-1.5％ ; the amorphous solid and algal body are the important sources of the organic matters in the source rocks,the thickness of the effective hydrocarbon source rock ranges from 30 m to 70 m,this set of the source rocks are not only good in the type and high in abundance,but also high in hydrocarbon expulsion rate,so they possess huge hydrocarbon generating potentials.The studies prove that the algal type is the main form and moreover its abundance is pretty higher,these characteristics show that the enrichment of the high-quality organic matters is related with the eruption events in the high-quality source rocks; Tectonic subsidence,depositional filling and volcanic eruptive activities play the important promoting roles in the high-quality source rocks＇ sedimentation and development.The high-quality source rocks possess the obvious controlling action on the hydrocarbon accumulation,the found reservoirs are often vertically distributed up and down the high-quality hydrocarbon source rocks and interior or the edge of the rocks on plane.