鄂尔多斯盆地富县—甘泉地区三叠系延长组7油层组致密油富集主控因素

Main factors controlling the tight oil enrichment in the 7^(th) oil layer group of the Triassic Yanchang Formation in Fuxian-Ganquan area,Ordos Basin

根据野外露头、岩心、测井、录井与分析化验等资料,结合试油、试采等动态数据,多角度深入探讨了鄂尔多斯盆地富县-甘泉地区三叠系延长组第7油层组(简称长7油层组)致密油富集成藏的主控因素。结果显示,广泛发育的长7油层组优质烃源岩厚度大,有机质丰富,类型优越,成熟度适宜,为致密油提供了丰富的油源,控制了长7油层组致密油含油边界。长71与长72亚油组与下部烃源岩构成下源上储、源储紧邻的成藏组合。储层优质成岩相控制着致密油富集的区带。致密储层内存在多期原油充注,早期原油充注使储层岩石颗粒润湿性由亲水变为混合润湿,形成原油运移聚集的优势通道,控制了主力成藏期原油运聚的路径和范围,一定程度上限制了长7致密油成藏范围。不同尺度隔夹层将储层分隔为"网状"结构,结构非均质性强,导致了砂岩中差异化的流体流动以及复杂的油水关系。同时,致密层遮挡也对致密油富集成藏起到了一定控制作用。上述因素共同造成了致密油成藏范围局限,油藏内油水关系复杂,油井与水井共存。

The major factors controlling the enrichment of tight oil in the 7th oil layer group of the Triassic Yanchang Formation(Chang 7 oil layer group)in Fuxian-Ganquan area,Ordos Basin,were investigated from multiple perspectives of outcrop,core,logging and laboratory testing,combined with such dynamic data as production tests.The results show that the high-quality source rocks of Chang 7 oil layer group are developed well and widely and are characterized by large thickness,high organic richness,favorable type of kerogen and moderate maturity,thus provide an abundant oil source for tight oil enrichment and control the oil-water contact of the Chang 7 tight oil reservoirs.The Chang 7 1 and Chang 7 2 sub-layer groups in the Chang 7 oil layer group together with the underlying source rocks make up a source-reservoir assemblage characteristic of closeness between the underlying source rock and overlying reservoir.The analysis of diagenetic facies shows that quality diagenetic facies of reservoir controls the zones of tight oil enrichment.There is multi-phase oil charging in the tight oil reservoirs.During the early charging stages,the wettability of the reservoir rock was turned from water wet to mixed wettability with oil charging,leading to the formation of preferential channels for oil migration and accumulation,which determines the pathway and scope of oil migration and accumulation in the major pool-forming period,and to a certain extent constrains the distribution of the Chang 7 tight oil reservoirs.Baffles and barriers of various sizes compartmentalize the reservoirs into a network structure with intense heterogeneity,leading to differential fluid flow and complex oil-water contact in the sandstone.Meanwhile,the shelter of tight layers can also play a role in controlling the accumulation of Chang 7 tight oil.All the factors mentioned above collectively determine the limited distribution of tight oil,the complexity of water-oil contact and the coexistence of oil wells and water wells.