鄂尔多斯盆地富县地区三叠系延长组长7_(3)亚段页岩油储层特征与勘探前景

Characteristics of shale oil reservoir and exploration prospects in the third sub-member of the seventh member of the Triassic Yanchang Formation in Fuxian area,Ordos Basin

鄂尔多斯盆地富县地区三叠系延长组长73亚段沉积期位于湖盆东部沉积中心,蕴藏着丰富的页岩油资源,具有较好的勘探前景,但对于页岩油储层特征研究较少,缺乏储集特征和含油性研究,制约了页岩油勘探部署实践。以富县地区长73亚段为研究对象,利用岩心观察、全岩矿物X-射线衍射分析、氯仿抽提、核磁共振、有机碳及孔隙度测试等多种手段,从岩石矿物学特征、储集空间、孔隙结构、含油气性等方面开展分析,明确了长73亚段发育泥页岩类、粉—细砂岩类、凝灰岩类三大岩石类型,泥页岩类根据纹层发育程度又可细分为4种岩石类型。泥页岩段矿物组成主要为石英、长石、碳酸盐矿物和黏土矿物,还有少量的黄铁矿。储层主要发育粒间孔、粒内孔、有机质孔及微裂缝4种储集空间类型。粉—细砂岩中、大孔比较发育,核磁共振T2谱以多峰型和左偏单峰型为主;黑色页岩微孔相对较发育,大孔相对较少,核磁共振T2谱以多峰型、右偏单峰型为主。含油气性好、油饱和度指数高的粉—细砂岩是长73亚段最优的页岩油储层,其次是纹层状泥页岩。综合分析认为,粉—细砂岩类和泥页岩类目标均具备一定的勘探潜力,也是未来增储上产的潜在领域。

During the deposition period of the third sub-member of the seventh member of the Triassic Yanchang Formation(Chang 73 sub-member),Fuxian area was located in the depo-center of the eastern lake basin,showing abundant shale oil resources and good exploration prospects.However,few studies have been conducted on shale oil reservoir characteristics,and there is a lack of the study on reservoir space characteristics and oil-bearing property,which restrict shale oil exploration and deployment practice.By using core observation,whole rock mineral XRD analysis,chloroform extraction,NMR,organic carbon abundance and porosity test data,the petrological and mineralogical characteristics,reservoir space,pore structure and oil and gas bearing property are analyzed in Fuxian area,which indicates that three rock categories are observed in Chang 73 sub-member,such as shale,silty-fine sandstone and tuff.Based on the development degree of lamina,the shale category is subdivided into four rock types.The main mineral composition of shale section includes quartz,feldspar,carbonate and clay minerals,as well as a small amount of pyrite.The reservoir is dominated by four types of pores,i.e.,intergranular pore,intragranular pore,organic pore and microfracture.The meso-macropores are relatively developed in silty-fine sandstone,and the NMR T2 spectrum is characterized by multi-peak and left-biased single-peak types.The micropores are relatively developed in black shale,with relatively few macropores,and the NMR T2 spectrum is mainly multi-peak and right-biased single-peak types.The silty-fine sandstone with good oil-bearing property and high oil saturation index is the optimal shale oil reservoir in Chang 73 sub-member,followed by the laminated shale.The comprehensive study indicates that both silty-fine sandstone and shale targets have certain exploration potential,which are potential fields for increasing reserves and production in the future.