准噶尔盆地西北缘及玛湖凹陷沉积储集层研究进展

Advances in sedimentological reservoir research in Mahu sag and northwest margin of Junggar Basin

准噶尔盆地西北缘玛湖凹陷中心区10×108 t级砾岩大油区的发现,带动了该区沉积储集层研究的不断深入。作者梳理了准噶尔盆地西北缘及玛湖凹陷的沉积储集层研究现状和进展,认为准噶尔盆地西北缘及玛湖凹陷的沉积储集层研究的进展主要表现为:(1)提出了新的砂砾岩储集层岩石相和岩石学分析方法;(2)探索形成了新的沉积储集层地球物理测井和地震描述技术;(3)针对不同层系,在沉积物源、沉积相、沉积环境、沉积体系和沉积模式等方面取得大量新认识,建立了大型退覆式浅水缓坡扇三角洲沉积模式,指导油气勘探不断获得新突破;(4)在成岩作用理论指导下,所发现的储集层埋藏深度不断增加。研究表明,玛湖凹陷的沉积体系具有继承性:从二叠纪到新近纪,发育了火山—碎屑岩沉积体系、细粒—蒸发盐沉积体系以及粗粒冲积扇、扇三角洲、辫状河三角洲等沉积体系,气候、构造和湖平面变化控制了沉积体系的形成和演化。沉积储集层研究为玛湖砾岩大油田的发现提供了有力的理论支持。未来应当加强针对古老层系和深部地层的沉积储集层研究工作,重视新理论新技术在西北缘和玛湖沉积储集层研究中的应用,已经形成的理论技术需要在勘探实践中接受进一步检验和完善。

The discovery of a billion-ton conglomerate oil reservoir at central Mahu sag,northwestern margin of Junggar Basin,has driven the research progresses on sedimentary geology and reservoir characterization.This paper reviewed the advances of sedimentology and reservoirs research in the Mahu sag and northwest margin of the Junggar Basin and summarized the following significant advances:(1)new methods in petrological and lithofacies analysis have been proposed for conglomerate reservoirs description;(2)a series of techniques in logging and seismic have been adapted for geophysical reservoir description;(3)obtain new knowledge of the provenance,sedimentary environment,facies and depositional system and models.The retrogradation model of large-scale shallow water fan delta on a gentle slope has been established,which led to the breakthroughs in oil and gas exploration;(4)diagenesis theory guided to find new reservoirs in deeper strata.Depositional system in Mahu sag is consistent since Permian to Neogene.Depositional systems include volcanic and volcano-clastic system,fine-grained and evaporite system,coarse-grained alluvial fan,fan delta,braided river delta and others.Climate variation,structure configuration,and lake level fluctuation controlled the formation and evolution of the depositional system.This research provides strong theoretical support for the discovery of Mahu conglomerate oil field.In turn,oil and gas exploration promotes the continuous development of sedimentology and reservoir research.There are at least three petroleum systems in Mahu sag,which were associated with different depositional systems and reservoirs.However,the studies for different petroleum systems,different kinds of reservoirs,and explorational discoveries are not in the same stage.The authors suggested to pay more attention to the older and deeper strata and to use more new theory and technology in sedimentological and reservoir research of this area.The presented theories and technologies need to be further tested in future exploration activity.