沾化凹陷孤北油田古近系沙三段扇三角洲沉积特征及油气储层意义

SEDIMENTARY CHARACTERISTICS AND RESERVOIR SIGNIFICANCE OF EOGENE Es_3 FAN DELTA IN GUBEI OILFIELD,ZHANHUA DEPRESSION

不同类型的扇三角洲沉积可发育在断陷盆地演化的不同阶段。由于受沉积物供给速率、可容空间增长速率及湖盆边界断层性质等因素的影响 ,孤北油田沙三段发育 4种扇三角洲沉积类型。在沙三段沉积早、中期 ,伴随湖侵发育退积型扇三角洲 ,而在沙三段沉积晚期 ,伴随湖退发育进积型扇三角洲。陡坡型和缓坡型扇三角洲在沉积特征、储层分布、储层物性等方面有明显差异 ,缓坡型扇三角洲前缘储层由于埋藏较浅 ,成岩作用较弱 ,平均孔隙度 18 2 %,平均渗透率约 2 93× 10 -3 μm2 ,因此其储集物性优于陡坡型扇三角洲前缘。另外 ,沉积微相对储层储集物性也具有明显的控制作用 ,扇三角洲前缘水下分流河道砂砾岩体物性最好 ,平均孔隙度2 0 5 %,渗透率 35 0× 10 -3 μm2 ,可成为优质储集层。深湖相暗色泥岩为主要的烃源岩和盖层 ,扇三角洲前缘的砂砾岩体是较好的储集层 ,生、储、盖发育齐全 ,有着良好的勘探开发前景。

Various types of fan delta systems have been developed in different evolution stages of faulted basin. Being controlled by the supply rate of sediments, expansion rate of available space and nature of lake basin's boundary fault, four types of fan deltas have been deposited in the 3rd member of Shahejie Fm(Es 3) in Gubei oilfield. Retrograding fan delta has been deposited along with the transgression of the lake in the early and middle Es 3 ;and the prograding fan delta has been deposited during the regression of the lake in late Es 3.There are obviously different sedimentary characteristics, reservoir distribution and reservoir quality between the steep fan delta and the gentle one, the latter has better reservoir quality with an average porosity of 18.2% and average permeability of 293×10 -3 μm 2, because it has relatively shallow burial depth and weak diagenesis.In addition, the microfacies of sediments would also control the reservoir quality.The glutenites deposited in subaqueous distributary channels in front of the fan delta have the best reservoir quality with an average porosity and permeability of 20.5% and 350×10 -3 μm 2,respectively.The deep lacustrine dark-colored mudstones constitutes the major hydrocarbon source and cap rocks, and the glutenites deposited in front of the fan delta are relatively good reservoirs,which would constitute a good combination of source,reservoir and cap rocks. The Es 3 would,therefore,be the target of further exploration.