鄂尔多斯盆地中奥陶统乌拉力克组页岩油气富集条件及勘探方向

Enrichment characteristics and exploration direction of shale oil and gas in Wulalike Formation of Middle Ordovician in the Ordos Basin

鄂尔多斯盆地油气资源丰富,常规油气与非常规油气并存,是中国油气重点勘探开发的含油气盆地之一。近年来,盆地中奥陶统乌拉力克组先后有多口探井获得工业油气流,展现出该盆地海相页岩油气良好的勘探开发新局面,研究其油气富集规律对于客观认识地质特征和指导下一步油气勘探具有重要意义。为此,基于岩心观察、铸体薄片、扫描电镜、核磁共振和有机地球化学分析等资料,系统分析了页岩烃源条件、储层特征及控藏因素,探讨了乌拉力克组海相页岩油气富集条件及勘探方向。研究结果表明:(1)与四川盆地下志留统龙马溪组页岩气藏相比,海相乌拉力克组页岩气藏具有“低丰度、低含气量、深埋藏、常压”的不足和“高硅质含量、高脆性指数”的优势;(2)乌拉力克组页岩总有机碳含量平均值为0.86%,含气量一般介于0.94~2.21 mL/g,埋深一般介于3 700~4 500 m,地层压力系数介于0.96~1.00,硅质矿物含量平均值为54.0%,脆性指数平均值为75.0%;(3)乌拉力克组页岩大面积含气、局部富集,具有“三元控藏”的特征,硅质页岩大规模发育是物质基础,良好的顶底板是必要条件,稳定的构造条件是页岩气富集的关键。结论认为,鄂尔多斯盆地海相乌拉力克组页岩油气发育4个勘探有利区,有利勘探面积为5 500 km^(2),其中马家滩、棋盘井地区为目前现实的页岩气勘探目标区。

The Ordos Basin is one of the important petroliferous basins of oil and gas exploration and development in China,where oil and gas resources are abundant and conventional and unconventional oil and gas coexist.In recent years,many exploration wells in the Ordos Basin have produced industrial oil and gas flow from the Wulalike Formation of Middle Ordovician,which unveils a exploration and development of marine shale oil and gas.Therefore,researching its oil and gas enrichment laws is of great significance to objectively understanding the geological characteristics and guiding the next oil and gas exploration.Based on core observation,cast thin section,SEM,NMR and organic geochemical analysis data,this paper systematically analyzes shale source conditions,reservoir characteristics and reservoir-controlling factors,and discusses the enrichment characteristics and exploration direction of Wulalike Formation Marine shale oil and gas.And the following research results are obtained.First,compared with the shale gas reservoir of Longmaxi Formation of Lower Silurian in the Sichuan Basin,the marine shale gas reservoir of Wulalike Formation has the disadvantages of"low abundance,low gas content,great burial depth and normal pressure"and"high siliceous content and high brittleness index".Second,the average TOC of the Wulalike Formation shale is 0.86%,the gas content is generally 0.94-2.21 ml/g,the burial depth is generally 3700-4500 m,the formation pressure coefficient is 0.96-1.0,the average siliceous content is 54%and the average brittleness index is 75%.Third,the Wulalike Formation shale reservoir is characterized by a large gas bearing area,local enrichment and"three elements controlling reservoir".The large-scale development of siliceous shale is the material basis,good roof and floor are the requisite conditions,and stable tectonics is the key to shale gas enrichment.In conclusion,there are four favorable exploration areas of Wulalike Formation marine shale oil and gas in the Ordos Basin,covering an area of 5500 km^(2),among which,Majiatan and Qipanjing areas are practical shale gas exploration target areas at present.