三塘湖盆地芦草沟组页岩油储层形成机理及分布特征

Formation mechanism and distribution characteristics of Lucaogou shale oil reservoir in Sangtanghu Basin

三塘湖盆地芦草沟组受印支运动影响,发育一套火山碎屑岩、云质岩及泥质岩混杂沉积的特殊湖相沉积建造。该区页岩油储集层以(中酸性)晶屑凝灰岩为主,晶屑成分主要是长英质,为熔浆中早期结晶的斑晶或火山通道围岩中的矿物在火山喷发过程中破碎形成。主要储集空间为火山尘粒间微孔、晶屑溶蚀微孔、岩屑溶蚀微孔及微裂缝。综合分析表明,芦草沟组主要发育上、中、下3套甜点段,厚度主要为5~40m,其形成主要受细粒凝灰岩的矿物组分、有机质丰度、构造运动影响,其中间歇性火山喷发是形成优质页岩油储集层的关键,溶蚀作用是储集层微储集空间形成的主要因素,微缝、微断裂是储层改造的关键。优质页岩油甜点有利区主要分布在马朗凹陷腹部及条湖凹陷南缘,埋深基本在2 500~3 500m之间,具有形成较大规模致密油藏的趋势,目前已发现的凝灰岩油藏主要位于该溶蚀区,油气显示活跃,具有较大的勘探潜力。

The Lucaogou Formation in the Santanghu Basin is affected by Indosinian movement and develops a special lacustrine deposit of volcanic clastic rocks,cloud rocks and argillaceous mixed sediments.The shale oil reservoir in this area is dominated by(medium-acidic)crystal tuff.Crystal chips are mainly composed of felsic which is the phenocryst crystallized early in the volcanic eruption process or the minerals in volcanic channel surrounding rocks.The main reservoir space is the micropores between volcanic dust particles,the micropores of chip corrosion,the cuttings dissolution microporous and micro-cracks.The comprehensive analysis shows that the Lucaogou Formation mainly developed three sets of"sweet sections"in the longitudinal direction,and the thickness was mainly between 5-40 meters.The formation of"sweet sections"is mainly affected by the mineral composition,organic matter abundance of fine-grained tuff and tectonic movement.The interstitial volcanic eruption is key to the formation of high-quality shale oil reservoirs.Dissolution is a main factor for the formation of reservoir micro-reservoir space.The micro-seam and microfracture are keys to the reservoir reconstruction.The favorable sweet area of high-quality shale oil is mainly distributed in the abdomen of Malang Sag and the southern margin of Tiaohu Sag.The burial depth is basically 2 500-3 500 meters.These areas have the tendency to form large scale reservoirs.The tuff reservoirs that have been discovered so far are mainly located in the dissolution zone.The oil-gas show is active,and exploration potential is great.