松辽盆地榆东地区泉头组四段特低—超低渗储集层成岩作用与成岩相^*

Diagenesis and diagenetic facies of extra-low to ultra-low permeability reservoir in the Member 4 of Quantou Formation in Yudong area,Songliao Basin

摘要

为明确松辽盆地北部榆东地区白垩系泉头组四段优质储集层成因及分布,综合薄片、X射线衍射、扫描电镜、核磁共振和微米CT等多种测试,系统分析泉四段特低—超低渗储集层孔隙结构和成岩作用特征,利用多种成岩强度指标开展特低—超低渗储集层成岩相定量划分。结果表明: (1)泉四段发育5种孔隙,孔喉半径细小、孔隙结构差,属亚微米—微米孔隙和纳米—亚微米喉道组合。(2)泉四段沉积时为碱性—酸性—碱性交替的成岩环境,在泉四段内形成2期方解石沉淀、伊利石、绿泥石和高岭石等黏土矿物胶结及长石、岩屑溶蚀。(3)压实作用是破坏泉四段原生孔隙结构和物性的主要原因,造成0.8%~35.6%的孔隙损失。1500~1600 m处石英加大、伊利石胶结和1800~2000 m处方解石胶结形成的2个异常减孔带,造成0.2%~32.1%的孔隙度损失,是储集层致密化的关键; 1400~1500 m和1600~1700 m由长石和火山岩岩屑溶蚀形成0.1%~6.5%的次生溶蚀,对于储集层物性的改善具有重要意义。(4)泉四段可分为5种成岩相,中压实强溶蚀长石溶孔相和弱压实中胶结残余粒间孔相物性最好,是研究区有利储集层类型;中压实中胶结残余粒间孔相次之;强压实弱胶结杂基晶间孔相和弱压实强胶结晶间微孔相基本无储集性能。

Abstract

To clarify the genesis and distribution of favorable reservoir in the Member 4 of Cretaceous Quantou Formation,we integrates thin-section petrography,X-ray diffraction(XRD),scanning electron microscopy(SEM),nuclear magnetic resonance(NMR),and micro-CT analyses to characterize pore structures and diagenetic processes. We also use multiple diagenetic intensity indices to classify the diagenetic facies. Key findings include: the reservoirs of the Member 4 of Quantou Formation exhibit five pore types with submicron-to-micron pores and nano-to-submicron throats,indicating poor pore structure. Alternating alkaline-acidic-alkaline diagenetic environments led to two phases of calcite cementation,clay mineral cementation(illite,chlorite,kaolinite),and dissolution of feldspar/lithic fragments. Compaction caused 0.8%~35.6% porosity loss,dominating reservoir degradation at depths <1600 m. Two porosity reduction zones were identified: quartz overgrowth and illite cementation at 1500~1600 m reduced porosity by 0.2%~32.1%,while calcite cementation at 1800~2000 m caused similar porosity destruction. In contrast,dissolution processes between 1400 m and 1700 m increased porosity by 0.1%~6.5% through leaching of feldspar and volcanic lithic fragments. We classify five diagenetic facies, with the moderate compaction-strong dissolution and weak compaction-moderate cementation types demonstrating the highest reservoir quality. The moderate compaction-moderate cementation type shows intermediate properties, whereas the strong compaction-weak cementation and weak compaction-strong cementation types are non-reservoirs.

关键词

成岩作用 / 成岩相 / 特低—超低渗储集层 / 泉四段 / 白垩系 / 松辽盆地

Key words

diagenesis / diagenetic facies / extra-low and ultra-low permeability reservoir / Member 4 of Quantou Formation / Cretaceous / Songliao Basin

基金资助

*国家科技重大专项(编号: 2017ZX05071)资助