松辽盆地徐西北部地区沙河子组细分层序格架下的沉积特征

Sedimentary characteristics of subdivided sequence framework of Shahezi Formation in northwest Xujiaweizi area of Songliao Basin

为了指导松辽盆地徐西北部地区沙河子组致密储层下一步精细勘探,针对沙河子组岩性复杂多样、相带变化快,不同期次有利储层发育规模及展布规律难预测的问题,利用层序地层学及沉积学理论,在细分四级层序地层格架基础上,结合地震预测技术,对目的层开展沉积微相类型及砂体展布特征研究。结果表明:沙河子组纵向发育4个三级层序及9个四级层序,整体发育扇三角洲、辫状河三角洲及湖泊3种沉积相类型,进一步细分为6种亚相及8种微相,不同沉积类型的分布位置及对应砂体发育规模差异较大;控陷断裂附近发育扇三角洲沉积体系,构造落差大,近物源,砂体厚度大,但孤立分布,平面连续性较差;断陷缓坡发育辫状河三角洲沉积,平面延伸远,砂体连续性好;断陷中部凹陷内主要发育湖泊相,暗色泥岩发育且规模较大;扇三角洲及辫状河三角洲砂砾岩储层发育,厚度大,粒度粗,抗压实能力强,深埋条件下仍保留部分原生孔隙,物性条件好。研究成果可为松辽盆地北部深层致密储层有利区预测及勘探部署提供基础。

In order to guide further fine exploration of tight reservoirs of Shahezi Formation in northwest Xujiaweizi area of Songliao Basin,meeting challenge of complicate and diversified lithology,rapid facies belt change and difficulty in predicting development scale and extension law of favorable reservoirs in different stages,sequence stratigraphy theory and sedimentology theory are used to study sedimentary microfacies types and sandbody distribution of target layers based on subdividing fourth-order sequence stratigraphic framework and combined with seismic prediction technique.The results show that 4 third-order sequences and 9 fourth-order sequences developed vertically in Shahezi Formation,and 3 major sedimentary facies types developed including fan delta,braided river delta and lake,subdivided into 6 subfacies and 8 microfacies.Distribution locations of different sedimentary types and developed scales of corresponding sandbodies are quite different.Fan-delta deposit system developed near depressioncontrolling fault is characterized by large topographic elevation difference,proximal,thick sandbodies,isolated distribution and poor areal continuity.Braided-river delta deposit system well-developed on gentle slope of the rift is characterized by farther areal extension and better sandbody continuity.Lacustrine facies mainly well-developed in middle part of the rift is characterized by well-developed dark mudstone with large scale.Fan delta and braided river delta glutenite reservoirs are characterized by better development,large thickness,coarse particle size and strong anti-compaction capacity,and part of primary pores still preserved in the condition of deep burial and thus with favorable physical property.The research provides basis for prediction of favorable area and exploration deployment of deep tight reservoirs in north Songliao Basin.