准噶尔盆地玛湖凹陷东斜坡中二叠统扇三角洲储层特征与成因

Characteristics and Origin of the Middle Permian Fan-Delta Reservoir in the Eastern Slope Area of the Mahu Sag,Junggar Basin

准噶尔盆地玛湖凹陷东斜坡区中二叠统下乌尔禾组是区域油气勘探的重要领域,但勘探程度总体较低,成藏规律不明。以单井岩心、镜下薄片、扫描电镜等分析为基础,储层物性分析为辅,结合地震地球物理分析,对下乌尔禾组储层特征与成因进行分析。结果表明,研究区发育扇三角洲沉积体系,进一步可划分出扇三角洲平原、扇三角洲平原-前缘过渡、扇三角洲前缘等亚相。由于近物源区具有多级坡折古地貌形态,沉积相平面展布具较窄的平原亚相及较宽的三角洲前缘亚相,构成了纵向上由SW向NE方向长轴缓坡到短轴陡坡扇三角洲的潜在油气富集区带。扇三角洲前缘是油气富集的主要有利相带,其水下分流河道微相和水下分流河道间湾微相控制了主要的优质储层,加之多种成岩作用的共同影响及优越的鼻状构造圈闭条件,形成多个潜在油气藏富集区,是下步勘探的重点目标。

The middle Permian Lower Wuerhe Formation in the eastern slope area of the Mahu sag of the Junggar Basin has hydrocarbon exploration prospects and obtained exploration advances recently.However,the exploration degree in the region is still markedly low and thus the reservoir forming mechanism is not clear.To improve the understanding of this issue and provide reference for exploration,we address the reservoir characteristics and origin in this study,based on core observation,thin section and SEM analyses,combined with reservoir property and geophysics analyses.Results show that the study area developed a fan delta system,and can be further divided to subfacies of fan delta plain,transitional fan delta front-plain and fan delta front.Because the ancient landform is located near to the provenance and had several levels of slope breaks,the sedimentary facies is characterized by an narrow fan delta plain and a wide fan delta front.This formed a potential hydrocarbon enrichment area of fan delta which had a gentle slope with minor axis and a steep slope with long axis from southwest to northeast.Fan delta front is the favorable facies belt for hydrocarbon accumulation.The most high-quality reservoir was controlled by underwater distributary channel microfacies and bay between distributary channels microfacies,which,together with various diagenesis and excellent structural trap such as nose structure,form several potential hydrocarbon enrichment areas.They are the key targets of exploration in the future.The results and understanding here can also provide reference for hydrocarbon exploration with similar geological setting of fan delta sedimentary environments.