准噶尔盆地玛湖凹陷下三叠统百口泉组源外“连续型”油藏成藏机理与富集规律

Accumulation mechanism and enrichment rules of the continuous hydrocarbon plays in the Lower Triassic Baikouquan Formation of the Mahu Sag,Junggar Basin

准噶尔盆地玛湖凹陷下三叠统百口泉组最近发现了该盆地首个源外"连续型"大型砂砾岩油气藏,展示出重要的典范研究意义。为及时丰富成藏理论与勘探实践,分析了成藏机理与富集规律。结果表明:百口泉组"连续型"油气成藏具有三大有利条件:资源基础好、储层和顶底板条件佳、油气充注和成藏演化配置好,这是油气能够源外大规模"连续型"成藏的机理。其富集规律与特色有三:优质湖相烃源岩提供了资源基础、沟通烃源和储集岩系的走滑断裂使得油气能够源外成藏、扇三角洲沉积体系提供了优越的储层与油气"连续型"分布条件。油气富集表现为"三元"控制:扇三角洲前缘沉积相带、构造鼻凸、断裂;此外,异常高压和裂缝对油气高产具有重要影响;这些多因素叠合之处为油气下步勘探的有利目标。

Hydrocarbon exploration in the Mahu Sag of the northwestern Junggar Basin has recently gained a significant discovery-continuous oil plays in the Lower Triassic Baikouquan Formation glutenite reservoir with a proven oil reserve of hundreds of millions tons,which is characterized by an extensive hydrocarbon accumulation far from source sequences.This displays significance of fundamental and practical studies.Here,to improve the theory and practice of the accumulation of this discovery,we address the accumulation mechanisms and enrichment rules of the hydrocarbon accumulations.Results show that there are three favorable conditions for the hydrocarbon accumulation in general：Large hydrocarbon resource base,good reservoir and overlying and underlying preservation conditions,and well matched hydrocarbon charge and evolution.The hydrocarbon accumulation has three special characteristics.High quality lacustrine source rocks provide a good resource base.Large-scale transverse faults communicating with source and reservoir sequences make the long-distance migration possible.Fan-delta sedimentary system provides good conditions for reservoir and continuous hydrocarbon occurrence.The enrichment of hydrocarbon accumulation is controlled by three elements：prodelta sedimentary facies,structural high points and faults.Abnormal reservoir overpressure and fractures have important impacts on hydrocarbon production.The combination of these controls decides the future favorable exploration targets.