BN洼陷岩性油气藏成藏主控要素分析

B盆地勘探风险大程度低,一直以寻找构造油气藏为主。2010年在其北部斜坡带首次发现Baobab N岩性油藏,拓展了盆地勘探新领域;其成藏具典型代表性,可为盆地其他凹陷岩性勘探提供指导。通过成藏要素分析,结合油藏和砂体展布特征,探讨了BN岩性油藏的成藏主控要素。研究表明:BN岩性油藏受构造和岩性双重因素控制。洼陷发育优质烃源岩,且与砂体直接接触,具较好的生储盖组合。控制油气沿其周缘分布,具构造背景的砂体利于油气充注,而扇中辨状水道微相控制油气富集,具良好封堵能力的断层与反转构造有机配置为BN洼陷岩性成藏最重要的控制因素。对于强反转裂谷盆地来说,保存条件要求相对苛刻,上覆M组厚层泥岩质纯厚度大;且不同程度地发育超压,为油气藏保存提供优越的条件,控制岩性体最终成藏。

Analysis for main controlling factors of the lithologic oil reservoir accumulation in the BN Sag

The B Basin, which had been exploring structural reservoirs all of these days, has a high exploration risk and a low exploration level. In 2010, Baobab N lithologic reservoir with conspicuous reserves was firstly found in the northeastern slope of The B Basin, which opened the new exploration field. Its reservoir accumulation has a typical representativeness for other sags of the B Basin. By analyzing main factors of reservoir accumulation, and combining the reservoir characteristics with sandstone body distribution, we discuss main controlling factors of reservoir accumulation in the BN lithologic reservoir. The research shows that the BN lithologic reservoir is controlled by double factors of lithology and structure. BN sag develops high-quality hydrocarbon source rocks, and these source rocks directly contact with sandstone bodies, which control the distribution of oil and gas along their periphery. Sandstone bodies with good structural settings are beneficial to hydrocarbon filling, and mid-fan braided channels control the rich accumulation of oil and gas. The organic configuration of faults with a good sealing ability and inversion structures is the most important controlling factor in the BN lithologic reservoir accumulation. For strong inversive rift basins, preserve conditions are relatively harsh. In the B Basin, overlying pure and thick-bedded group M mudstones, which develops different degrees of excess pressure, provide superior preserve conditions and control final hydrocarbon accumulation of lithologic reservoir.