基准面旋回对冲积扇沉积演化及储层质量的控制作用——以百口泉油田百21井区百口泉组为例

Effects of base-level cycles on alluvial fan evolution and reservoir quality:A case study of the Baikouquan Formation in Bai21 Block,Baikouquan Oilfield

通过单井和多井层序地层及沉积特征分析,结合储层岩石学、成岩作用和储层质量研究成果,建立百口泉油田百21井区百口泉组高分辨率层序地层格架,阐明不同级次基准面旋回内部的沉积特征差异,进而探讨造成储层质量差异的控制因素。研究结果表明,研究区百口泉组发育多级次基准面上升半旋回,整体为长期基准面旋回,内部可细分为3个中期基准面旋回及9个短期基准面旋回,分别对应3个砂组和9个小层。长期基准面旋回控制研究区百口泉组冲积扇整体呈退积样式展布,中期基准面旋回控制百口泉组内部的砂体分布。由B3砂组扇根亚相块状砂砾岩逐渐演化为B2砂组块状砂砾岩与厚层细砾岩间互沉积,最终演变为B1砂组孤立状辫流水道微相。研究区百口泉组以岩屑砂砾岩为主,成分及结构成熟度均较低,塑性矿物含量较高,压实作用是导致其储层质量变差的主要控制因素,中、长期基准面旋回的中部水动力较强且趋于稳定,多以辫流水道微相发育为主,杂基含量较低,抗压实能力强,为较优质储层。

Based on the data of abundant wells and core analysis,combined with the characteristics of petrology,diagenesis and reservoir quality,the high-resolution sequence stratigraphic framework of the Baikouquan Formation in Bai21Block of Baikouquan Oilfield was built through the analysis of single well sequence and sedimentary characteristics.Moreover,the sedimentary characteristics and mechanism of reservoir quality in different orders of base-level cycle were clarified.And then control factors that cause the difference of reservoir quality were discussed.The research results show that:①The hier-archy base-level ascending hemicycles are well developed in the Baikouquan Formation which belongs to a long-term cy-cle.3middle-term cycles and9short-term cycles were divided respectively corresponding to3sandbeds and9layers with-in the formation;②The long-term base-level cycles control the alluvial fan distributed in retrogradational stacking pattern.The middle-term base-level cycles control the distribution of sandbodies in the Baikouquan Formation.Fan root subfacies,named B3member,characterized with massive sandy conglomerated evolves into B2member characterized with alternative deposition of massive sandy conglomerate and thick-layer fine conglomerate,and finally evolves into isolated braided chan-nel subfacies named B1member;③The Baikouquan Formation mainly consists of debris conglomerate with high content of plastic minerals and low textural-compositional maturity.Compaction is the main factor caused the loss of porosity.Hydro-dynamic forces in the middle of long-term and middle-term base-level cycle tend to be stable and strong,and there are braided channels with low matrix content and strong anti-compaction ability.Therefore,the braided channels in the longterm and middle-term base-level cycle are the best reservoir.