鄂尔多斯盆地湖盆中部长73亚段深水砂质沉积特征及勘探前景

Characteristics and Exploration Prospects of Deep-Water Sandstone Reservoir of Chang 73 Sub-Member,Ordos Basin

鄂尔多斯盆地延长组长73亚段发育大套厚层的富有机质泥页岩夹薄层粉细砂岩,深水环境的砂质岩类受到优质烃源岩的高强度源内充注,局部具有一定规模,是盆地深水勘探的重要目标.基于湖盆中部长73亚段的岩心、测录井、分析测试资料,结合岭页、池页水平井风险勘探实践,对长73亚段深水砂质岩类的沉积储层特征进行分析.结果表明:长73沉积期水体较深,优质烃源岩发育,湖盆西南祁秦造山带地震火山活动频发,物源供给充足,降雨量大、湖平面上升,滑塌成因与洪水成因的重力流沉积在湖盆中部广泛发育;环绕湖盆的一级坡折带控制着深水重力流的发育范围,沉积物入湖后受古地貌与沉积微相的控制,发育滑动-滑塌、砂质碎屑流、混合事件层、浊流、异重流等沉积类型,坡折带的坡脚、古沟道相对富砂,砂质碎屑流、浊流沉积是有利的储层类型;单砂体较薄,平均厚度1 m,孤立或叠置发育,空间上厚度、长度、宽度较小,较厚的块状单砂体和紧密连续叠置的薄层单砂体组合是期待钻遇的储层;高R_(o)、高TOC的泥页岩是砂质岩类充注油气的物质基础,高剩余压差下,储集性能较优的紧密叠置细砂岩薄储层与优质烃源岩互层的源储配置关系最易出现优质砂岩“甜点”.长73亚段深水砂质沉积勘探潜力较好,需持续攻关薄储层地球物理探测技术及砂泥一体压裂改造工艺.

Thick organic-rich shale with thin silty sandstones is developed in Chang 73Sub-member of Yanchang Formation in Ordos Basin.The sandstones in deep water environment are charged high intensity by source rocks and have a certain scale,which is an important target of deep water exploration in the basin.Based on the core,logging and test data of Chang 73Submember,combined with the risk exploration practice of Lingye and Chiye horizontal wells,this paper discusses and analyzes the sedimentary and reservoir characteristics of deep-water sandy rocks in Chang 73Sub-member.The results show that during the Chang 73sedimentary period,the water body was deep,organic-rich shale was developed,the Qiqin orogenic belt in the southwest of the basin had frequent seismic and volcanic activities,and the source supply was sufficient,the rainfall was large and the lake level was rising.The gravity flow deposits of slump origin and flood origin were widely developed in the middle of the basin.Slope break belt controlled the development of deep-water gravity flow,the characteristics of deep-water gravity flow were controlled by the ancient landform and sedimentary microfacies,developing sliding-slump,sandy debris flow,hybrid event bed,turbidity current and density flow,such as slope break zone of slope toe,relatively rich ancient channel sand,sandy debris flow and turbidity current deposits are favorable reservoir types.The single sand body is thin,with an average thickness of 1 m,and is isolated or superimposed.In terms of spatial thickness,length and width,the combination of thick block single sand body and tightly continuous superimposed thin single sand body is the reservoir expected to be drilled.Shale with high R_(o) and high TOC is the material basis for sandy rock.Under high residual pressure difference,high-quality sandy“sweet spot”is most likely to appear in the source-reservoir configuration relationship between tightly stacked thin sandstone reservoir with better reservoir performance and interbedded high-quality source rock.The exploration potential of deep-water sandy rocks in Chang 73Sub-member is good,so it is necessary to continuously explore the geophysical exploration technology of thin reservoir and the matched fracturing technology.