鄂尔多斯盆地新安边地区长7致密油特征及控制因素

鄂尔多斯盆地在新安边地区首次探明了致密油储量超亿吨级的新安边大油田。为了弄清致密油富集规律, 在前人对沉积相、烃源岩、储层特征及致密化原因研究的基础上, 利用铸体薄片、高压压汞、扫描电镜、岩芯物性、微米CT等分析手段, 通过对烃源岩特征、储集砂体规模及其连通性、储层物性和源储接触关系等因素的研究, 明确了新安边地区致密油的主要特征以及大面积展布的主要控制因素。延长组长7₂储集砂体发育, 储层渗透率差, 储集空间以微米级孔隙为主, 微米孔隙及纳米喉道构成了由多个独立连通孔喉体构成的复杂孔喉网络, 相对较好的孔喉连通性为石油在微观储集空间内流动提供了保障。原油性质好, 具有低密度、低黏度、低凝固点、不含硫、可流动性强的特点。致密储层紧邻优质烃源岩, 厚层烃源岩与较厚砂层共生形成了近源聚集的有利配置关系, 生烃增压为石油运聚提供了充足动力, 连片叠置发育的砂体和裂缝是油气运移的主要通道, 原油充注程度高, 多因素叠合形成了大面积展布的致密油区。

Characteristics & Controlling Factors of Chang 7 Tight Oil in Xin'anbian Area,Orods Basin

As a first proven big oil field in Xin'anbian area, Ordos Basin, the proved reserves of Xin'anbian oilfield tight oil is over hundred million tons. Based on previous study on sedimentary facies, source rock, reservoir feature and densification mechanism, by using thin sections, MICP, SEM, porosity & permeability, Micro-CT and other analysis methods, and through study on source rock characters, sand distribution, contact between source rock and reservoir, the geological characteristics and controlling factors on large-scale distribution of tight oil in Xin'anbian area were summarized to clarify the mechanism of tight oil accumulation and enrichment. Chang 7₂ tight sandstones are widely distributed and micrometer-scaled pores are the main reservoir space. The complex pore system consists of micrometer scaled pores and nanometer scaled throats, and the better pore-throat connectivity provide guarantee for oil flowing in micro-reservoir space. The oil quality is relatively good with characters of low density, low viscosity, low freezing point, no sulfur-containing and high mobility. Tight sandstones are close to high quality source rocks, which is favorable for near-sourced accumulation. Pressure increase during hydrocarbon generation process can provide sufficient power, and sandstones with high connectivity & fractures are migration pathway for hydrocarbon accumulation, resulting in high hydrocarbon charging percentage and large scaled tight oil play in Xin'anbian area.